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Newly Recognized Components of the Renin-Angiotensin System: Potential Roles in Cardiovascular and Renal Regulation

Division of Endocrinology and Metabolism, Department of Medicine, University of Virginia Health System, Charlottesville, Virginia 22908

Correspondence: Address all correspondence and requests for reprints to: Robert M. Carey, M.D., M.A.C.P., University Professor and Professor of Medicine, Box 801414, University of Virginia Health System, Charlottesville, Virginia 22908-1414. E-mail: RMC4C{at}virginia.edu

	Abstract

Top Abstract I. Introduction II. The Classical Renin... III. Local Tissue Renin... IV. Renin Receptor V. Angiotensin-Converting Enzyme... VI. Angiotensin (1-7) VII. The AT2 Receptor VIII. Angiotensin Receptor... IX. Summary and Conclusions References

 
The renin-angiotensin system (RAS) is a coordinated hormonal cascade in the control of cardiovascular, renal, and adrenal function that governs body fluid and electrolyte balance, as well as arterial pressure. The classical RAS consists of a circulating endocrine system in which the principal effector hormone is angiotensin (ANG) II. ANG is produced by the action of renin on angiotensinogen to form ANG I and its subsequent conversion to the biologically active octapeptide by ANG-converting enzyme. ANG II actions are mediated via the ANG type 1 receptor.

Here, we discuss recent advances in our understanding of the components and actions of the RAS, including local tissue RASs, a renin receptor, ANG-converting enzyme-2, ANG (1–7), the function of the ANG type 2 receptor, and ANG receptor heterodimerization. The role of the RAS in the regulation of cardiovascular and renal function is reviewed and discussed in light of these newly recognized components.

I. Introduction

II. The Classical Renin-Angiotensin System

III. Local Tissue Renin-Angiotensin Systems

A. Intrarenal renin-angiotensin system

B. Cardiac renin-angiotensin system

C. Vascular renin-angiotensin system

D. Adrenal renin-angiotensin system

IV. Renin Receptor

V. Angiotensin-Converting Enzyme-2

VI. Angiotensin (1–7)

VII. The AT₂ Receptor

VIII. Angiotensin Receptor Heterodimerization

IX. Summary and Conclusions

	I. Introduction

Top Abstract I. Introduction II. The Classical Renin... III. Local Tissue Renin... IV. Renin Receptor V. Angiotensin-Converting Enzyme... VI. Angiotensin (1-7) VII. The AT2 Receptor VIII. Angiotensin Receptor... IX. Summary and Conclusions References

 
THE RENIN-ANGIOTENSIN SYSTEM (RAS) is a coordinated hormonal cascade in the control of cardiovascular, renal, and adrenal function that governs fluid and electrolyte balance and arterial pressure (1). Although the existence of the RAS has been known for over three decades, recent advances in cell and molecular biology, as well as cardiovascular and renal physiology, have introduced a greater understanding of the role of this system in normal and disease states. Exciting new concepts, such as the identification of new peptides, new enzymes that generate these peptides, novel receptors and new functions for those already known, receptor-receptor interactions, and the local tissue RAS not requiring hormone secretion into the systemic circulation, have been derived from recent studies. The discovery of single nucleotide polymorphisms in a number of different constituents of the RAS in man holds hope for enhanced comprehension of the pathophysiology of complex disease states of the cardiovascular and renal systems. This review will focus on the newly recognized components of the RAS and their functions, insofar as they are known.

	II. The Classical Renin-Angiotensin System

Top Abstract I. Introduction II. The Classical Renin... III. Local Tissue Renin... IV. Renin Receptor V. Angiotensin-Converting Enzyme... VI. Angiotensin (1-7) VII. The AT2 Receptor VIII. Angiotensin Receptor... IX. Summary and Conclusions References

 
The classical RAS (Fig. 1) begins with the biosynthesis of the glycoprotein enzyme, renin, in the juxtaglomerular (JG) cells of the renal afferent arterioles. Renin is encoded by a single gene, and renin mRNA is translated into the protein, preprorenin, consisting of 401 amino acid residues (1, 2). In the JG cell endoplasmic reticulum, a 20-amino-acid signal peptide is cleaved from preprorenin, which is packaged in secretory granules in the Golgi apparatus, where it is further processed to active renin by severance of a 46-amino-acid peptide from the N terminus of the molecule. Mature, active renin is a glycosylated carboxypeptidase with a molecular mass of approximately 44 kDa. Active renin is released from the JG cell by an exocytic process involving stimulus-secretion coupling. Inactive prorenin is released constitutively across the cell membrane. Prorenin is converted to active renin by a trypsin-like activating enzyme (3). In the classical RAS, renin has no biological activity but cleaves angiotensinogen (AGT), the only known precursor protein for angiotensin (ANG) peptides, to form the decapeptide, ANG I. AGT synthesized in the liver provides the majority of systemic circulating ANG peptides, but AGT is also synthesized and constitutively released in other tissues including the heart, vasculature, kidneys, and adipose tissue. ANG-converting enzyme (ACE), a glycoprotein with a molecular mass of 180 kDa and two active carboxy-terminal sites, hydrolyzes the inactive ANG I into biologically active ANG II (4). ACE exists in two forms, soluble and membrane-bound. Most of the ACE is membrane-bound and is localized on the plasma membranes of various cell types, including vascular endothelial cells, microvillar brush border epithelial cells (e.g., renal proximal tubule cells), and neuroepithelial cells. In addition to cleaving ANG I to ANG II, ACE metabolizes bradykinin (BK), an active vasodilator and natriuretic substance, to BK (1, 2, 3, 4, 5, 6, 7), an inactive metabolite (5). ACE, therefore, increases the production of a potent vasoconstrictor, ANG II, while simultaneously degrading a vasodilator, BK. Unlike renin and AGT, which have relatively long plasma half-lives, ANG II is degraded within seconds by peptidases, collectively termed angiotensinases, at different amino acid sites to form fragments, mainly des-aspartyl-ANG II (ANG III), ANG (1–7), and ANG (3, 4, 5, 6, 7, 8). The vast majority of the cardiovascular, renal, and adrenal actions of ANG II are mediated by the ANG type 1 (AT₁) receptor, a seven-transmembrane G protein-coupled receptor that is widely distributed in these tissues, is coupled positively to protein kinase C, and is negatively coupled to adenylyl cyclase (6). AT₁ receptors mediate vascular smooth muscle contraction, aldosterone secretion, dipsogenic responses, renal sodium reabsorption, pressor and tachycardiac responses. ANG II also binds to another cloned receptor, the ANG type 2 (AT₂) receptor, but until recently the cell signaling mechanisms and functions of the AT₂ receptor were unknown (6).

View larger version (24K): [in this window] [in a new window]   Figure 1. Schematic representation of the classical RAS.

	III. Local Tissue Renin-Angiotensin Systems

Top Abstract I. Introduction II. The Classical Renin... III. Local Tissue Renin... IV. Renin Receptor V. Angiotensin-Converting Enzyme... VI. Angiotensin (1-7) VII. The AT2 Receptor VIII. Angiotensin Receptor... IX. Summary and Conclusions References

AT₁ receptors are widely distributed throughout the kidney, including vascular smooth muscle cells of the afferent and efferent arterioles and mesangial cells as well as proximal tubule cell brush border and basolateral membranes, thick ascending limb epithelia, distal tubules, cortical collecting ducts, glomerular podocytes, and macula densa cells (35). The multiple direct intrarenal actions of ANG II include renal vasoconstriction, tubular sodium reabsorption, tubuloglomerular feedback sensitivity, and modulation of pressure-natriuresis (12, 36). The influence of ANG II on sodium reabsorption is amplified by its synergistic actions at renal vascular and tubular sites. ANG II constricts both afferent and efferent arterioles and stimulates mesangial cell contraction, leading to reduced renal blood flow, glomerular filtration rate, and filtered sodium load. Additionally, ANG II decreases medullary blood flow, thereby increasing passive sodium reabsorption in the loop of Henle. ANG II also has a major direct effect on tubular sodium transport, enhancing proximal tubule Na⁺/H⁺ exchanger and basolateral membrane Na⁺/HCO₃^- cotransporter and Na⁺/K⁺ ATPase activities (38, 39). In the distal nephron, ANG II modulates the activity of the Na⁺/H⁺ exchanger and the epithelial sodium channel (40). The net effect of these renal vascular and tubular actions of ANG II is to decrease sodium excretion.

The intrarenal RAS is a powerful physiological regulator of renal function. In the setting of sodium restriction/depletion, interruption of the local system causes a severalfold increase in renal plasma flow, glomerular filtration rate, and sodium and water excretion (41). On the other hand, during sodium repletion, renal tubule sodium reabsorption is highly sensitive to the intrarenal levels of ANG II (42). Recently, selective renal overexpression of AGT, leading to a high degree of intrarenal ANG II formation, was demonstrated to cause an increase in systemic blood pressure in the absence of a change in circulating ANG II (43). In light of the renal tubule sensitivity to ANG II, it is highly likely that the level of stimulation of intrarenal RAS plays an important role both in minute-to-minute regulation of sodium reabsorption and in the pathophysiology of sodium retention states such as hypertension and congestive heart failure.

B. Cardiac renin-angiotensin system
Renin and its mRNA were originally found in the heart in 1987 (44, 45). Conclusive evidence now exists that all of the components of the RAS necessary for biosynthesis of ANG II are present in the heart and that cardiac tissue formation of ANG II occurs (13, 46). Renin, AGT, ACE, and ANG II receptors are all present in the myocardium (46). There is substantial evidence that the majority of the ANG II found in cardiac tissue derives from the myocardial synthesis of ANG I and not from uptake into the heart from the systemic circulation (8, 48, 49). The necessary components for ANG II biosynthesis are distributed in both myocardial fibroblasts and cardiomyocytes, as well as the endothelium and vascular smooth muscle of the coronary arteries and veins (46). It is interesting that although the myocardial concentrations of renin and AGT are 1–4% of those in plasma, the cardiac interstitial fluid concentrations of ANG I and ANG II are over 100-fold those of plasma (49, 50). There is evidence that the cardiac interstitial fluid represents a separate compartment from the systemic circulation and that interstitial ANG II derives exclusively from de novo biosynthesis in the heart (8). AGT and ACE have a heterogeneous distribution in the heart. AGT is primarily distributed in atrial muscle and the neuronal fibers of the conduction system, with small amounts in the subendocardial region of the ventricle (51). ACE is primarily expressed by coronary endothelial cells and cardiac fibroblasts (52). ACE levels also are higher in the atria than the ventricles, and ACE is present in all four valves and the coronary vessels, aorta, pulmonary arteries, endocardium, and epicardium (53). The conduction system contains little ACE. The intracardiac conversion of ANG I to ANG II may occur via heart chymase, which (in contrast to ACE) does not degrade BK (54). In the human myocardial extracts, chymase converts approximately 90% of the ANG I to ANG II (55).

There is considerable evidence that ANG II biosynthesis and release from ventricular myocytes is regulated. Glucocorticoids, estrogen, and thyroid hormone increase AGT and mRNA levels in the heart (56). Both atrial natriuretic peptide and isoproterenol up-regulate renin and AGT gene expression (46). Because ANG II increases these transcripts in cardiac myocytes (57), it is likely that ANG II can autoamplify the activity of the cardiac RAS, similar to the kidney (30, 31). In addition, mechanical stretch of ventricular myocytes increases ANG II release (58), which may be responsible for increased local ANG II production in dilated cardiomyopathy. The Janus kinase and signal transducers and activators of transcription pathway as well as p53 signaling pathways are thought to be important in the regulation of the RAS in cardiac myocytes (46). Also, the RAS in dog ventricular myocytes can be up-regulated by ventricular pacing (59).

Although there is substantial evidence that all of the components of the RAS are present within the heart and that cardiac synthesis of ANG II occurs and is regulated, controversy remains as to whether ANG II synthesized in the heart acts as an autocrine/paracrine regulator of cardiac function. It has been difficult to distinguish growth and functional responses due to ANG II synthesized in the heart vs. that which is taken up from circulation. Analysis of the role of cardiac interstitial fluid ANG II in the regulation of cardiac function with microanalysis techniques in conscious animals would help resolve this issue in the future.

C. Vascular renin-angiotensin system
Vascular smooth muscle, endothelial, and endocardial cells have been recognized to generate ANG I and ANG II (60, 61, 62, 63, 64). However, the synthesis of renin in blood vessels remains controversial (65, 66). Recent studies have helped clarify the possibility of a vascular RAS. It appears that renin is probably not synthesized locally in the blood vessel wall, because renin mRNA was not detectable by RT-PCR using as much as 5 µg of vascular RNA (67). However, a renin signal in blood vessels was easily detectable with 5 ng of kidney RNA, indicating that renin is taken up by the endothelium. In the isolated, perfused rat hindquarters, the spontaneous generation of ANG I was recorded, and this was abolished by bilateral nephrectomy. ANG I formation was rescued by renin infusion and abolished by endothelial denudation (67). These studies strongly suggest that the endothelium mediates vascular ANG II formation via the cellular uptake of renin.

D. Adrenal renin-angiotensin system
ANG II is a major stimulator of aldosterone secretion, and until the mid-1980s this was thought to occur via the systemic endocrine RAS. However, adrenal renin and AGT mRNA were identified, and ANG II formation was demonstrated in isolated adrenal zona glomerulosa cell culture. Ninety percent of adrenal renin activity is localized to the zona glomerulosa, with very little in the fasciculata, reticularis, or adrenal medulla (68). Adrenal renin concentrations are increased by sodium restriction and a high-potassium diet, which increases aldosterone production in parallel (69). Nephrectomy decreased plasma renin to undetectable levels within 4–6 h, but adrenal renin increased to a peak at 24–36 h (69). Nephrectomy increased adrenal renin via increased serum potassium (70). In renin transgenic animals, sodium restriction increased adrenal renin and aldosterone without a change in plasma or kidney renin content (71). In zona glomerulosa cells, inhibition of ACE or the AT₁ receptor blocked the stimulation of aldosterone by potassium or ACTH (71, 72, 73), and ACE inhibition decreased ANG II and aldosterone production (74). At present, it is not known whether the adrenal RAS functions physiologically as an autocrine or paracrine system, whether it serves to up-regulate adrenal responses to systemic ANG II, or whether it plays any role in pathophysiology.

Although there is very little renin in the adrenal medulla, all of the components of the RAS are thought to be present in the adrenal medullary chromaffin cells, in which ANG II has been localized to secretory granules (75). Whether the ANG II produced in and exported from chromaffin cells stimulates epinephrine release awaits further study.

	IV. Renin Receptor

Top Abstract I. Introduction II. The Classical Renin... III. Local Tissue Renin... IV. Renin Receptor V. Angiotensin-Converting Enzyme... VI. Angiotensin (1-7) VII. The AT2 Receptor VIII. Angiotensin Receptor... IX. Summary and Conclusions References

 
As stated earlier, renin has been considered as an enzyme responsible for removing the decapeptide ANG I from the substrate AGT. Renin has been thought to have no direct biological action. Although several proteins, such as the mannose-6-phosohate receptor, have been shown to bind renin in various cell membranes, no functional effects as a result of such binding have been reported (76, 77, 78, 79, 80). Recently, it was shown for the first time that renin can bind to human mesangial cells in culture and that the binding causes cell hypertrophy and increased levels of plasminogen activator inhibitor-1 (81, 82). The bound renin was not internalized or degraded. A renin receptor has now been cloned from mesangial cells; its functional significance has only been partially clarified (83). The receptor is a 350-amino-acid protein with a single transmembrane domain that specifically binds both renin and prorenin. Binding induced the activation of the extracellular signal-related MAPKs (ERK1 and ERK2) associated with serine and tyrosine phosphorylation and a 4-fold increase in the catalytic conversion of AGT to ANG I. The receptor was localized in the glomerular mesangium and the subendothelial layer of both coronary and renal arteries, associated with vascular smooth muscle cells and colocalized with renin (83). The early data (83) support the possibility of a direct functional role for prorenin and renin. These proteins (renin and prorenin) may be not only aspartyl proteases but also hormones with specific cellular actions in their own right. A direct functional role of the renin/prorenin receptor might contribute to the generation of tissue ANGs in the heart, kidney, and/or peripheral blood vessels and may be relevant to the pathophysiology of increased tissue RAS activity in disease processes such as hypertension, preeclampsia, and diabetes mellitus.

It is worth noting that the majority of work on the renin receptor comes from one group (81, 82, 83), and this will require independent confirmation.

	V. Angiotensin-Converting Enzyme-2

Top Abstract I. Introduction II. The Classical Renin... III. Local Tissue Renin... IV. Renin Receptor V. Angiotensin-Converting Enzyme... VI. Angiotensin (1-7) VII. The AT2 Receptor VIII. Angiotensin Receptor... IX. Summary and Conclusions References

 
ACE inactivates two vasodilator peptides, BK and kallidin (84). BK dilates blood vessels via stimulation of nitric oxide (NO) and cGMP and also by release of the vasodilator prostanoids, prostaglandin E₂ and prostacyclin (84). NO and vasodilator eicosanoids are physiological antagonists of ANG II. Thus, when an ACE inhibitor (ACEI) is used, not only is the synthesis of ANG II inhibited, but also formation of BK, NO, and prostaglandins is facilitated. ACEI appears to induce cross-talk between the BK B₂ receptor and ACE on the plasma membrane, abrogating B₂ receptor desensitization, thereby potentiating not only the levels of BK but also the vasodilator action of BK at its receptor (85, 86). These actions of ACEI may serve to reinforce vasodilation and lower blood pressure.

In the year 2000, ACE 2 was discovered and was characterized as an enzyme similar to ACE (87). ACE 2 is a zinc metalloprotease consisting of 805 amino acids with significant homology to ACE. Unlike ACE, however, ACE 2 functions as a carboxypeptidase rather than a dipeptidyl carboxypeptidase. In contrast to ACE, ACE 2 hydrolyzes ANG I to ANG (1–9), ANG II to ANG (1–7), and BK to -[des-Arg⁹] BK (an inactive metabolite). In marked contrast to ACE, ACE 2 does not convert ANG I to ANG II, and its enzymatic activity is not inhibited by ACEI. Therefore, ACE 2 is effectively an inhibitor of the formation of ANG II by stimulating alternative pathways for ANG I degradation. ACE 2 has been localized to cell membranes of cardiac myocytes, renal endothelial and tubular cells, and the testis (88).

Insight to the functional significance of ACE 2 in the cardiac and intrarenal RAS has recently been provided using genetic approaches. The gene for ACE 2 has been mapped to the X chromosome in humans, to the region that has been previously shown to be a quantitative trait locus for several rat models of hypertension (89). Indeed, ACE mRNA and protein levels were down-regulated in the kidneys of these rat models, indicating that ACE 2 may be a candidate gene for the quantitative trait locus on the X chromosome. ACE gene ablation did not alter blood pressure, but severely impaired cardiac contractility and caused mild ventricular dilation and increased ANG II levels, suggesting that ACE 2 may nullify the physiological actions of ACE. The changes in cardiac function were associated with up-regulation of a set of hypoxia-induced genes. Ablation of both the ACE and ACE 2 genes completely prevented the cardiac abnormalities and the increase in ANG II production (89). These observations suggest a direct effect of ANG II on cardiac function and indicate that ACE 2 probably counterbalances the enzymatic actions of ACE. The recent biosynthesis of a potent, selective ACE 2 inhibitor will afford a means to determine the role of ACE 2 in cardiovascular and renal function and disease (90).

	VI. Angiotensin (1–7)

Top Abstract I. Introduction II. The Classical Renin... III. Local Tissue Renin... IV. Renin Receptor V. Angiotensin-Converting Enzyme... VI. Angiotensin (1-7) VII. The AT2 Receptor VIII. Angiotensin Receptor... IX. Summary and Conclusions References

 
The ANG (1–7) heptapeptide fragment of ANG II was first discovered to have biological activity in 1988 (91). Since that time, several studies have documented that ANG (1–7) is a major biologically active peptide product of the RAS (92). ANG (1–7) can be formed directly from ANG I by the action of several peptidases, including neutral-endopeptidase (NEP) 24.11 or prolyl-endopeptidase (PEP) or from ANG II via PEP or prolyl-carboxypeptidase. Current data suggest that NEP 24.11 plays a major role in both circulating and tissue ANG (1–7) formation (93). Once synthesized, ANG (1–7) can be cleaved to biologically inactive fragments by aminopeptidases or ACE. The ACE pathway appears to be an important mode of inactivation of circulating and possibly tissue ANG (1–7) (Ref. 94). Therefore, ACE inhibition increases plasma concentrations of ANG (1–7), due in part to the increase in ANG I and in part to reduced ANG (1–7) degradation by ACE (95). In contrast, the increase in circulating ANG (1–7) with AT₁ receptor blockade may be due to PEP-mediated ANG (1–7) formation from ANG II (96). New concepts of the formation and metabolism of ANG (1–7) by ACE and ACE 2 are depicted schematically in Fig. 2.

View larger version (19K): [in this window] [in a new window]   Figure 2. Schematic representation of the pathways of formation and metabolism of ANG (1–7) and the role of ACE and the newly discovered enzyme ACE-2. The inhibitory actions of ACEI are depicted in dashed lines with arrows and railroad tracks. ASES, Angiotensinases.

ANG (1–7) generally opposes the actions of ANG II by stimulation of NO and vasodilator prostaglandins, and there is evidence that ANG (1–7) can potentiate the action of BK at its B₂ receptor by binding to the active site (c-domain) of ACE (98, 99). In addition to BK potentiation, ANG (1–7) promotes release of prostaglandins from vascular endothelial and smooth muscle cells (100, 101), release of NO (102), vasodilation, inhibition of vascular cell growth, and attenuation of ANG II-induced vasoconstriction (103).

The kidney is a major target organ for ANG (1–7) (Ref. 104). The peptide can be formed in the kidney via the action of NEP and has complex renal actions that are dependent on the state of sodium and water balance, renal nerve activity, and the activation of the RAS (104). ANG (1–7) has only moderate effects on renal hemodynamic function. However, in isolated renal tubules, ANG (1–7) inhibits sodium absorption. Very low ANG (1–7) concentrations (10^-9 to 10^-12 M) can affect sodium and water flux at both proximal and distal tubule sites (104, 105). In addition to its effect to release arginine vasopressin (AVP) from central sites, ANG (1–7) engenders an AVP-independent antidiuretic action that is due to reduction in glomerular filtration (106).

The receptor site of action of ANG (1–7) is a matter of controversy. A specific ANG (1–7) receptor has not been cloned, although there is physiological evidence for its existence, and a recent report suggested that the peptide is an endogenous ligand for the G protein-coupled receptor Mas (107). ANG (1–7) also interacts with the AT₁ receptor, and some of its actions can be blocked with losartan. Also, some of the actions of ANG (1–7) can be inhibited with the AT₂ receptor antagonists. These observations suggest the possibility of interaction between ANG II and ANG (1–7) receptors (92). The intracellular signaling mechanisms of ANG (1–7) are largely unknown (92).

	VII. The AT2 Receptor

Top Abstract I. Introduction II. The Classical Renin... III. Local Tissue Renin... IV. Renin Receptor V. Angiotensin-Converting Enzyme... VI. Angiotensin (1-7) VII. The AT2 Receptor VIII. Angiotensin Receptor... IX. Summary and Conclusions References

 
As mentioned in Section I, the second major cloned ANG II receptor is the AT₂ receptor. The gene for this receptor resides as a single copy on the X chromosome (108). The AT₂ receptor is a seven-transmembrane-type G protein-coupled receptor containing 363 amino acids. It has a low amino acid sequence homology (34%) with AT₁ receptors (109).

The AT₂ receptor is highly expressed in fetal mesenchymal tissues from both rodents and man. However, within only a few days of birth, AT₂ receptor expression diminishes rapidly to low levels. Nevertheless, the receptor protein is clearly detectable by Western blot in the adult kidney, heart, and blood vessels. In the adult kidney, the AT₂ receptor is expressed in glomerular epithelial cells, cortical tubules, and interstitial cells (110). In the heart, the receptor can be localized to the atria and ventricular myocardium and the vascular smooth muscle cells of the coronary arteries (111). Although the receptor protein is easily detectable, the mRNA has been difficult to demonstrate, and receptor expression is poorly characterized in humans. However, the AT₂ receptor is clearly expressed in the human heart, where it predominates over the AT₁ receptor (112, 113). The regulation of the AT₂ receptor is poorly understood. Expression of the AT₂ receptor is up-regulated by sodium depletion and is inhibited by ANG II and growth factors such as platelet-derived growth factor and epidermal growth factor (110, 114). The AT₂ receptor also is up-regulated by insulin and IGF-I (115).

The cell signaling pathways involved in the activation of the AT₂ receptor are not fully clarified, but appear to involve G protein-dependent and -independent pathways (116). Recent evidence indicates that the receptor is G protein-coupled via G_i2 and G_i3 (117). Current evidence suggests that AT₂ receptor stimulation activates phosphotyrosine phosphatases, especially serine/threonine phosphatase 2A, protein kinase phosphatase, and SHP-1 tyrosine phosphatase, resulting in the inactivation of MAPKs, specifically p42 and p44 MAPKs or ERKs (118). There is also evidence that the AT₂ receptor opens the delayed rectifier K⁺ channel, activates phospholipase A₂ and prostaglandin generation, and stimulates ceramide production (6, 116). In contrast to the AT₁ receptor, the AT₂ receptor does not internalize in response to agonist binding, suggesting that the AT₂ receptor may remain available on the plasma membrane without desensitization for long-term biological responses (120).

A physiological role for the AT₂ receptor in the cardiovascular system was first suggested by the observations that mice lacking the AT₂ receptor have a slight but significant increase in baseline blood pressure (121, 122). The AT₂ receptor was subsequently shown to mediate vasodilation by stimulating the production of BK, NO, and cGMP (123, 124), and mice lacking the AT₂ receptor were demonstrated to have markedly decreased tissue levels of BK, NO, and cGMP associated with pressor and natriuretic hypersensitivity to ANG II (125, 126). These responses could have been mediated, at least in part, by up-regulation of the AT₁ receptor in mice lacking the AT₂ receptor (127). Overexpression of the AT₂ receptor in vascular smooth muscle cells extinguished pressor responses to ANG II, which were restored by blockade of NO synthase or the BK B₂ receptor (128). The AT₂ receptor caused cellular acidosis, probably by activating the amiloride-sensitive epithelial sodium channel, thus activating the kallikrein-kinin system to release BK, which triggered the formation of NO and cGMP (128).

The vascular actions of the AT₂ receptor can be enhanced by blockade of the AT₁ receptor, under which circumstances ANG II causes both an acute and a sustained hypotensive response in normal animals (129, 130). Activation of AT₂ receptors by endogenous ANG II promotes flow-induced dilation of rat mesenteric resistance arteries and induces hypotension in hypertensive rats fed a purified synthetic diet (131, 132). In addition, ANG II relaxes microvessels via the AT₂ receptor (133). Recently, it was conclusively demonstrated that the AT₂ receptor mediates vasodilation in rat mesenteric resistance vessels (134). Of special interest, there was preservation of AT₂ receptor function during long-term receptor stimulation without desensitization (134). In aggregate, these studies strongly suggest that the AT₂ receptor facilitates a vasodilator pathway that is counterregulatory to the actions of ANG II via the AT₁ receptor.

In the kidney, the AT₂ receptor appears to influence proximal tubule sodium reabsorption either directly via cell membrane receptors or indirectly via an interstitial NO-cGMP pathway (135, 136). The AT₂ receptor also appears to stimulate the conversion of renal prostaglandin E₂ to prostaglandin F₂, and the absence of a major increase in blood pressure in mice lacking the AT₂ receptor is attributable to the increased production of vasodilator prostanoids (137). Regarding the role of the AT₂ receptor in pressure natriuresis, the original observations suggested that the receptor was inhibitory (138). However, recent work suggests that the AT₂ receptor amplifies the natriuretic response to increased renal perfusion pressure (127, 139, 140). The absence of the AT₂ receptor, which counterregulates AT₁ receptor-mediated ANG II actions, aggravates the renal and blood pressure response to NO synthase inhibition (140).

In the heart, the AT₂ receptor inhibits growth and remodeling, induces vasodilation, and is up-regulated in pathological states (141, 142). Conflicting data on its antigrowth effects emerged from studies of mice lacking the AT₂ receptor (143, 144). However, recent studies have helped to clarify the role of the AT₂ receptor in cardiac remodeling post myocardial infarction (145) and in cardiac hypertrophy and fibrosis due to ANG II infusion (146) in mice overexpressing the AT₂ receptor selectively in the myocardium. After myocardial infarction, AT₂ receptor overexpression resulted in preservation of left ventricular global and regional function, indicating a beneficial role for the AT₂ receptor in volume-overload states, including post-myocardial infarction remodeling (145). Overexpression of the AT₂ receptor in cardiomyocytes was demonstrated to attenuate ANG II-induced cardiac interstitial fibrosis via a BK/NO/cGMP pathway without effect on cardiomyocyte hypertrophy (146).

In blood vessels, in addition to its vasodilatory actions, the AT₂ receptor exerts antiproliferative and apoptotic effects in vascular smooth muscle cells and decreases neointimal formation in response to injury by counteracting ANG II actions at the AT₁ receptor (147). Part of the actions of AT₂ receptors in blood vessels may be to down-regulate the expression of AT₁ receptors and also TGF-ß receptors via BK/NO pathway (148). Interestingly, the AT₂ receptor does not possess these actions in spontaneously hypertensive rats (148).

The AT₂ receptor appears to mediate, at least in part, some of the beneficial effects of the AT₁ receptor blockade on blood vessels, heart, and kidneys (149). For example, the hypotensive action of the AT₁ receptor blockade with losartan is completely blocked by AT₂ receptor inhibition with PD123319 in rats with renovascular hypertension (150). Also, the AT₂ receptor mediates the hypotensive response to AT₁ receptor blockade with valsartan in conscious sodium-restricted normal rats (151). AT₁ receptor blockade increases renal BK, NO, and cGMP, and these responses are abrogated when the AT₂ receptor is concurrently blocked (150, 151). The hypotensive response to AT₁ receptor blockade also is completely blocked by inhibition of either the BK B₂ receptor or NO synthase (150, 151). In the heart, the protective effects of AT₁ receptor antagonists during congestive heart failure or after myocardial infarction are at least partially mediated by the AT₂ receptor (152, 153). When the AT₁ receptor is blocked, the negative feedback loop by which the AT₁ receptor inhibits renin secretion from JG cells is inhibited, leading to increased renin secretion and ANG II levels. If the AT₁ receptor is blocked, ANG II can only bind to the unblocked AT₂ receptor. These characteristics of AT₁ receptor blockade may be responsible for the concomitant increase in AT₂ receptor stimulation and, therefore, the beneficial effects observed. Taken together, the available observations validate the concept that activation of the AT₂ receptor mediates at least some of the beneficial effects of AT₁ receptor blockade via a BK/NO/cGMP pathway. In many cases, the experimental evidence suggests that the AT₂ receptor exerts a protective action only when the AT₁ receptor is blocked. This paradigm opens the door for potential synergistic therapeutic effects of AT₂ receptor agonists in combination with AT₁ receptor blockers. The pursuit of a specific AT₂ receptor agonist is a potentially fruitful area for future research.

	VIII. Angiotensin Receptor Heterodimerization

Top Abstract I. Introduction II. The Classical Renin... III. Local Tissue Renin... IV. Renin Receptor V. Angiotensin-Converting Enzyme... VI. Angiotensin (1-7) VII. The AT2 Receptor VIII. Angiotensin Receptor... IX. Summary and Conclusions References

 
In addition to the interactions described earlier between the RAS and the kallikrein-kinin system, the AT₁ receptor and the BK B₂ receptor can communicate directly with each other. These two receptors can physically associate to form stable heterodimers in the cell membrane, resulting in the increased activation of G proteins G_q and G_i, the major signaling proteins mediating AT₁ receptor responses (154). Although heterodimer formation is common to many G protein-coupled receptors, this was the first demonstration of signal enhancement triggered by the physical association of two vasoactive hormone receptors. Interestingly, AT₁-B₂ receptor dimer formation was demonstrated in vivo and was shown to be potentially important in the mediation of increased ANG II responsiveness in preeclampsia (154). Preeclamptic women had significantly increased heterodimerization in platelets and omental vessels, which correlated with a 4- to 5-fold increase in B₂ receptor protein levels (154). Expression of the AT₁-B₂ receptor heterodimer increased cell signaling responses to ANG II and conferred resistance to inactivation of these processes by reactive oxygen species.

The AT₁ and AT₂ receptors also have been shown to heterodimerize (155). Thus, the AT₂ receptor binds directly to the AT₁ receptor, thereby antagonizing the signaling pathways and functions of the AT₁ receptor. The direct inhibition of the AT₁ receptor by the AT₂ receptor binding does not depend on AT₂ receptor-stimulated G protein activation. Furthermore, increased AT₁/AT₂ receptor heterodimerization in myometrial cells of pregnant women correlated with decreased ANG II responsiveness. The results of these studies were consistent with the concept that the AT₂ receptor stabilizes AT₁ receptor structurally so that it can no longer undergo the requisite conformational changes to activate G proteins (156). Thus, it appears that the AT₂ receptor can be a direct AT₁ receptor-specific antagonist.

It should be noted that all of the heterodimerization work reported thus far is from a single group and, thus, requires confirmation.

	IX. Summary and Conclusions

Top Abstract I. Introduction II. The Classical Renin... III. Local Tissue Renin... IV. Renin Receptor V. Angiotensin-Converting Enzyme... VI. Angiotensin (1-7) VII. The AT2 Receptor VIII. Angiotensin Receptor... IX. Summary and Conclusions References

 
The RAS is a major hormonal system in the control of cardiovascular and renal function. During the past several years, the RAS has come to be recognized as an important physiological regulator not only through endocrine pathways but also via a self-contained paracrine/autocrine system at the local tissue level. Although the circulating system governs responses to major total body disturbances such as sodium depletion or hypotension, the tissue system seems to be sensitive and responsive to relatively minor alterations within the local compartment. It is likely that these tissue systems are critical to both normal physiology and the pathophysiology of disease states such as hypertension, congestive heart failure, and postinfarction cardiac remodeling.

Recently, several new components of the RAS (Fig. 3) have been discovered, adding complexity, but also the potential to increase our understanding of the function of the RAS in health and disease. Renin, which previously was considered only as an enzyme, may be a direct cellular mediator via its own receptor. ACE 2 has emerged as a potential inhibitor of ACE and a supplier of active peptides such as ANG (1–7) at the tissue level. ANG (1–7) is a major biologically active product of the RAS, counterbalancing the actions of ANG II in the heart, blood vessels, and kidneys, probably via its own receptor that is yet to be identified. The AT₂ receptor also appears to be counterregulatory to the action of ANG II at the AT₁ receptor and to mediate at least some of the beneficial effects of AT₁ receptor blockade via AT₂ receptor-mediated generation of BK, NO, and cGMP. In addition, it is now apparent that the direct physical association of the AT₁ receptor with other receptors on the cell membrane can have major effects to activate or inhibit AT₁ receptor function. Thus, a biochemical or hormonal mediator may no longer be necessary to influence AT₁ receptor function.

View larger version (27K): [in this window] [in a new window]   Figure 3. Schematic representation of the newly recognized components of the RAS.

	Footnotes

 
Abbreviations: ACE, Angiotensin-converting enzyme; ACEI, ACE inhibitor; AGT, angiotensinogen; ANG, angiotensin; AT₁, ANG type 1; AT₂, ANG type 2; BK, bradykinin; ERK, extracellular signal-related MAPK; JG, juxtaglomerular; NO, nitric oxide; NEP, neutral endopeptidase; PEP, prolyl-endopeptidase; RAS, renin-angiotensin system.

	References

Top Abstract I. Introduction II. The Classical Renin... III. Local Tissue Renin... IV. Renin Receptor V. Angiotensin-Converting Enzyme... VI. Angiotensin (1-7) VII. The AT2 Receptor VIII. Angiotensin Receptor... IX. Summary and Conclusions References

 

1. Peach MJ 1977 Renin-angiotensin system: biochemistry and mechanisms of action. Physiol Rev 57:313–370[Free Full Text]
2. Griendling KK, Murphy TJ, Alexander RW 1993 Molecular biology of the renin-angiotensin system. Circulation 87:1816–1828[Free Full Text]
3. Hsueh WA, Baxter JD 1991 Human prorenin. Hypertension 17:469–477[Abstract/Free Full Text]
4. Soubrier F, Wei L, Hubert C, Clauser E, Alhenc-Gelas F, Corvol P 1993 Molecular biology of the angiotensin I-converting enzyme: II. Structure-function. Gene polymorphism and clinical implications. J Hypertens 11:599–604[CrossRef][Medline]
5. Erdos EG, Skidgel RA 1997 Metabolism of bradykinin by peptidases in health and disease. In: Farmer SG, ed. The kinin system: handbook of immunopharmacology. London: Academic Press; 112–141
6. De Gasparo M, Catt KJ, Inagami T, Wright JW, Unger TH 2000 International Union of Pharmacology. XXIII. The angiotensin receptors. Pharmacol Rev 52:415–472[Abstract/Free Full Text]
7. Muller DN, Bohlender J, Hilgers KF, Dragnun D, Costerousse O, Menard J, Luft FC 1997 Vascular angiotensin converting enzyme expression regulates local angiotensin II. Hypertension 29:98–104[Abstract/Free Full Text]
8. Dell’Italia LJ, Meng QC, Balcells E, Wei CC, Palmer R, Hageman GR, Durand J, Hankes GH, Oparil S 1997 Compartmentalization of angiotensin II generation in the dog heart. Evidence for independent mechanisms in intravascular and interstitial spaces. J Clin Invest 100:253–258[Medline]
9. Campbell DJ 1987 Circulating and tissue angiotensin systems. J Clin Invest 79:1–6
10. Engeli S, Negrel R, Sharma AM 2000 Physiology and pathophysiology of the adipose tissue renin-angiotensin system. Hypertension 35:1270–1277[Abstract/Free Full Text]
11. Johnston CI 1992 Renin-angiotensin system: a dual tissue and hormonal system for cardiovascular control. J Hypertens Suppl 10:513–526
12. Navar LG, Harrison-Bernard LM, Nishiyama A, Kobori H 2002 Regulation of intrarenal angiotensin II in hypertension. Hypertension 39:316–322[Abstract/Free Full Text]
13. Dostal DE 2000 The cardiac renin-angiotensin system: novel signaling mechanisms related to cardiac growth and function. Regul Pept 91:1–11[CrossRef][Medline]
14. Re RN 2003 Implications of intracrine hormone action for physiology and medicine. Am J Physiol Heart Circ Physiol 284:H751–H757
15. Ryan JW 1967 Renin-like enzyme in the adrenal gland. Science 158:1589–1590[Abstract/Free Full Text]
16. Ganten D, Minnich JL, Hayduk K, Brecht HM, Barbeau A, Boucher R, Genest J 1971 Angiotensin-forming enzyme in brain tissue. Science 173:64–65[Abstract/Free Full Text]
17. Kimbrough HM, Vaughan Jr ED, Carey RM, Ayers CR 1977 Effect of intrarenal angiotensin II on renal function in conscious dogs. Circ Res 40:174–178[Abstract/Free Full Text]
18. Levens NR, Freedlender AE, Peach MJ, Carey RM 1983 Control of renal function by intrarenal angiotensin II. Endocrinology 112:43–49[Abstract]
19. Levens NR, Peach MJ, Carey RM 1981 Role of the intrarenal renin-angiotensin system in the control of renal function. Circ Res 48:157–167[Free Full Text]
20. Gomez RA, Lynch KR, Chevalier RL, Wilfong N, Everett A, Carey RM, Peach MJ 1988 Renin and angiotensinogen gene expression in the maturing rat kidney. Am J Physiol 254:F582–F587
21. Ingelfinger J, Zuo WM, Fon EA, Ellison KE, Dzau VJ 1990 In situ hybridization evidence for angiotensinogen messenger RNA in the rat proximal tubule. J Clin Invest 85:417–423
22. Yanagawa N, Capparelli AW, Jo OD, Friedal A, Barrett JD, Eggena P 1991 Production of angiotensinogen and renin-like activity by rabbit proximal tubule cells in culture. Kidney Int 39:938–941[Medline]
23. Bruneval P, Hinglais N, Alhenc-Gelas F, Tricottet V, Corvol P, Menard J, Camilleri JP, Bariety J 1986 Angiotensin I converting enzyme in human intestine and kidney. Ultra-structural and immunohistochemical localization. Histochemistry 85:73–80[CrossRef][Medline]
24. Douglas JG 1987 Angiotensin receptor subtypes in the kidney cortex. Am J Physiol 253:F1–F7
25. Terada Y, Tomita K, Nonoguchi H, Marumo F 1983 PCR localization of angiotensin II receptor and angiotensinogen mRNA in rat kidney. Kidney Int 43:1251–1259
26. Hunt MK, Ramos SP, Geary KM, Norling LL, Peach MJ, Gomez RA, Carey RM 1992 Colocalization and release of angiotensin and renin in renocortical cells. Am J Physiol 263:F363–F373
27. Darby IA, Sernia C 1995 In situ hybridization and immunohistochemistry of renal angiotensinogen in neonatal and adult rat kidneys. Cell Tissue Res 281:197–206[Medline]
28. Robrwasser A, Morgan R, Dillon HF, Zhao L, Callaway CA, Hillas E, Zhang S, Cheng T, Inagami T, Ward K, Teveros DA, Lalouel JM 1999 Elements of a paracrine tubular renin-angiotensin system along the entire nephron. Hypertension 34:1265–1274[Abstract/Free Full Text]
29. Moe OW, Ujiie K, Star RA, Miller RT, Widell J, Alpern RJ, Henrich WL 1993 Renin expression in renal proximal tubule. J Clin Invest 91:774–779
30. Henrich WL, McAllister EA, Eskue A, Miller T, Moe OW 1996 Renin regulation in cultural proximal tubule cells. Hypertension 27:1337–1340[Abstract/Free Full Text]
31. Sibong M, Gase J-M, Soubrier F, Alhenc-Gelas F, Corovol P 1993 Gene expression and tissue localization of the two isoforms of angiotensin I converting enzyme. Hypertension 21:827–835[Abstract/Free Full Text]
32. Nishiyama A, Seth DM, Navar LG 2002 Renal interstitial fluid concentrations of angiotensins I and II in anesthetized rats. Hypertension 39:129–134[Abstract/Free Full Text]
33. Ingelfinger JR, Jung F, Diamont D, Havervan L, Lee E, Brem A, Tang S-S 1999 Rat proximal tubule cell line transformed with origin-defective SV40DNA: autocrine ANG II feedback. Am J Physiol 276:F218–F227
34. Kobari H, Harrison-Bernard LM, Navar LG 2001 Enhancement of angiotensinogen expression in angiotensin II-dependent hypertension. Hypertension 37:1329–1335[Abstract/Free Full Text]
35. Miyata N, Park F, Li XF, Cowley Jr AW 1999 Distribution of angiotensin AT₁ and AT₂ receptor subtypes in the rat kidney. Am J Physiol 277:F437–F446
36. Mitchell KD, Braam B, Navar LG 1992 Hypertension mechanisms mediated by the renal actions of the renin-angiotensin system. Hypertension 19(Suppl I):I-18–I-27
37. Deleted in proof
38. Garvin JL 1991 Angiotensin stimulates bicarbonate transport and Na⁺/K⁺ ATPase in rat proximal straight tubules. J Am Soc Nephrol 1:1146–1152[Abstract]
39. Quan A, Baum M 1996 Endogenous production of ANG II modulates rat proximal tubule transport. J Clin Invest 97:2878–2882[Medline]
40. Wang J, Giebisch G 1996 Effects of angiotensin II on electrolyte transport in the early and late distal tubule in the kidney. Am J Physiol 271:F143–F149
41. Siragy HM, Howell NL, Peach MJ, Carey RM 1990 Combined blockade of the intrarenal renin-angiotensin system in the conscious dog. Am J Physiol 27:F522–F529
42. Siragy HM, Lamb NE, Woodson JF, Ragsdale NV, Rose Jr CE, Peach MJ, Carey RM 1987 Renal sensitivity to angiotensin II in the conscious dog. Endocrinology 120:1272–1278[Abstract]
43. Davisson RL, Ding Y, Stec DE, Catterall JF, Sigmund CD 1999 Novel mechanism of hypertension revealed by cell-specific targeting of human angiotensinogen in transgenic mice. Physiol Genomics 1:3–9
44. Dzau VJ, Re R 1987 Evidence for the existence of renin in the heart. Circulation 75:I134–I136
45. Re R 1987 The myocardial intracellular renin-angiotensin system. Am J Cardiol 59:56A–58A
46. Dostal DE, Baker KM 1999 The cardiac renin-angiotensin system: conceptual, or a regulator of cardiac function? Circ Res 85:643–650[Abstract/Free Full Text]
47. Deleted in proof
48. Neri Serneri GG, Boddi M, Coppo M, Chechi T, Zarone N, Moira M, Poggesi L, Margheri M, Simonetti I 1996 Evidence for the existence of a functional cardiac renin-angiotensin system in humans. Circulation 94:1886–1893[Abstract/Free Full Text]
49. Danser AHJ, van Kesteren CAM, Bax WA, Tavenier M, Derkx FHM, Saxena PR, Schalekamp MADH 1997 Prorenin, renin, angiotensin, and angiotensin converting enzyme in normal and failing hearts: evidence for renin binding. Circulation 96:220–226[Abstract/Free Full Text]
50. Danser AHJ, van Kats JP, Admiraal PJ, Derkx FH, Lamers JM 1994 Cardiac renin and angiotensins: uptake from plasma versus in situ synthesis. Hypertension 24:37–48[Abstract/Free Full Text]
51. Sawa H, Tokuchi F, Mochizuki N, Endo Y, Furuta Y, Shinohara T, Takada A, Kawaguchi H, Yasuda H, Nagashima K 1992 Expression of the angiotensinogen gene and localization of its protein in the human heart. Circulation 86:138–146[Abstract/Free Full Text]
52. Zhou J, Allen AM, Yamada H, Sun Y, Mendelsohn FAO 1994 Localization and properties of angiotensin converting enzyme and angiotensin receptors in the heart. In: Lindpainter K, Ganten D, eds. The cardiac renin-angiotensin system. Armonk, NY: Futura Publishing Co., Inc.; 63–68
53. Falkenhahn M, Franke F, Bohle RM, Zhu Y-C, Stauss HM, Bachmann S, Danilov S, Unger T 1995 Cellular distribution of angiotensin-converting enzyme after myocardial infarction. Hypertension 25:219–226[Abstract/Free Full Text]
54. Urata H, Boehm KD, Philip A, Kinoshita A, Gabrovsek J, Bumpus FM 1993 Cellular localization and regional distribution of an angiotensin II-forming chymase in the heart. J Clin Invest 91:1269–1281
55. Balcells E, Meng QC, Johnson WH, Oparil S, Dell’Italia LJ 1997 Angiotensin II formation from ACE and chymase in human and animal hearts: methods and species considerations. Am J Physiol 273:H1769–H1774
56. Lindpainter K, Jin M, Niedermajer N, Wilhelm MJ, Ganten D 1990 Cardiac angiotensinogen and its local activation in the isolated perfused beating heart. Circ Res 67:564–573[Abstract/Free Full Text]
57. Sadoshima J, Izumo S 1993 Molecular characterization of angiotensin II-induced hypertrophy of cardiac myocytes and hyperplasia of cardiac fibroblasts. Circ Res 73:413–423[Abstract/Free Full Text]
58. Sadoshima J, Xu Y, Slater HS, Izumo S 1993 Autocrine release of angiotensin II mediates stretch-induced hypertrophy of cardiac myocytes in vitro. Cell 75:977–984[CrossRef][Medline]
59. Barlucchi L, Leri A, Dostal DE, Fiordaliso F, Tada H, Hintze TH, Kajstura J, Nadal-Ginard B, Anversa P 2001 Canine ventricular myocytes possess a renin-angiotensin system that is up-regulated with heart failure. Circ Res 88:298–304[Abstract/Free Full Text]
60. Re RN, Fallon JT, Dzau VJ, Quay S, Haber E 1982 Renin synthesis by canine aortic smooth muscle cells in culture. Life Sci 30:99–106[CrossRef][Medline]
61. Dzau VJ 1984 Vascular wall renin-angiotensin pathway in control of the circulation. A hypothesis. Am J Med 77:31–36[CrossRef][Medline]
62. Kifor I, Dzau VJ 1987 Endothelial renin-angiotensin pathway: evidence for intracellular synthesis and secretion of angiotensins. Circ Res 60:422–428[Abstract/Free Full Text]
63. Campbell DJ 1985 The site of angiotensin production. J Hypertens 3:199–207[CrossRef][Medline]
64. Danser AHJ, Koning MMG, Admiraal PJJ, Sassen LMA, Derkx FHM, Verdouw PD, Schalekamp MADH 1992 Production of angiotensins I and II at tissue sites in intact pigs. Am J Physiol 263:H429–H437
65. Von Lutterotti N, Catanzaro DF, Sealey JE, Laragh JH 1994 Renin is not synthesized by cardiac and extrarenal vascular tissues. Circulation 89:458–470[Abstract/Free Full Text]
66. Rosenthal J, Thurnreiter M, Plaschke M, Geyer M, Reiter W, Dahlheim H 1990 Reninlike enzymes in human vasculature. Hypertension 15:848–853[Abstract/Free Full Text]
67. Hilgers KF, Veelken R, Muller DN, Kohler H, Hartner A, Botkin S, Stumpf C, Schmieder RE, Gomez RA 2001 Renin uptake by the endothelium mediates vascular angiotensin formation. Hypertension 38:243–248[Abstract/Free Full Text]
68. Mulrow PJ, Franco-Saenz R 1996 The adrenal renin-angiotensin system: a local hormonal regulator of aldosterone production. J Hypertens 4:173–176
69. Doi Y, Atarashi K, Franco-Saenz R, Mulrow PJ 1984 Effects of changes in sodium or potassium balance, and nephrectomy, on adrenal renin and aldosterone concentrations. Hypertension 6:I124–I129
70. Baba K, Doi Y, Franco-Saenz R, Mulrow PJ 1986 Mechanisms by which nephrectomy stimulates adrenal renin. Hypertension 8:997–1002[Abstract/Free Full Text]
71. Rubattu S, Enea I, Ganten D, Salvatore D, Condorelli G, Russo R, Romano M, Gigante B, Trimarco B 1994 Enhanced adrenal renin and aldosterone biosynthesis during sodium restriction in TGR (mRen) 27. Am J Physiol 267:E515–E520
72. Horiba N, Nomura K, Shizume K 1990 Exogenous and locally synthesized angiotensin II and glomerulosa cell function. Hypertension 15:190–197[Abstract/Free Full Text]
73. Gupta P, Franco-Saenz R, Mulrow PJ 1995 Locally generated angiotensin II in the adrenal gland regulates basal, corticotropin- and potassium-stimulated aldosterone secretion. Hypertension 25: 443–448
74. Chiou Cy, Kifor I, Moore TJ, Williams GH 1994 The effect of losartan on potassium-stimulated aldosterone secretion in vitro. Endocrinology 134:2371–2375[Abstract]
75. Wang JM, Slembrouck D, Tan J, Archens L, Leenen FHH, Courtoy PJ, Depotter WP 2002 Presence of cellular renin-angiotensin system in chromaffin cells of bovine adrenal medulla. Am J Physiol 283:H1811–H1818
76. van Kesteren CAM, Danser AHJ, Derkx FHM, Dekkers DHW, Lamers JMJ, Saxena PR, Schalekamp MADH 1997 Mannose-6-phosplate receptor mediated internalization and activation of prorenin by cardiac cells. Hypertension 30:1389–1396[Abstract/Free Full Text]
77. Admiraal PJ, van Kesteren CA, Danser AH, Derkx FH, Sluiter W, Schalekamp MA 1999 Uptake and proteolytic activation of prorenin by cultured human endothelial cells. J Hypertens 17:621–629[CrossRef][Medline]
78. Mary I, Ohta Y, Muruta K, Tsukada Y 1966 Molecular cloning and identification of N-acyl-D-glucosamine 2-epimerase from paracrine kidney as renin-binding protein. J Biol Chem 271:16294–16299
79. Campbell DJ, Valentiin AJ 1994 Identification of vascular renin binding proteins by chemical cross-linking inhibition of binding of renin by renin inhibitors. J Hypertens 12:879–890[Medline]
80. Sealey JE, Catanzaro DF, Lavin TN, Gahnem F, Pitarresi T, Hu-LF, Laragh JH 1996 specific prorenin/renin binding (proBP). Identification and characterization of a novel membrane site. Am J Hypertens 9:491–502[CrossRef][Medline]
81. Nguyen G, Delarue F, Berrou J, Rondeau E, Sraer JD 1996 Specific receptor binding of renin on human mesangial cells in culture increases plasminogen activator inhibitor-1 antigen. Kidney Int 50:1897–1903[Medline]
82. Nguyen G, Bouzhir L, Delarue F, Rondeau E, Sraer JD 1998 Evidence of a renin receptor on human mesangial cells: effects on PAI1 and cGMP. Nephrologie 19:411–416[Medline]
83. Nguyen G, Delarue F, Burckle C, Bouzhir L, Giller T, Sraer JD 2002 Pivotal role of the renin/prorenin receptor in angiotensin II production and cellular responses to renin. J Clin Invest 109:1417–1427[CrossRef][Medline]