Renin exists in human adrenal tissue

Vascular and hormonal interactions in the adrenal gland

Primary aldosteronism is the most common form of secondary arterial hypertension, due to excessive aldosterone production from the adrenal gland. Although somatic mutations have been identified in aldosterone producing adenoma, the exact mechanisms leading to increased cell proliferation and nodule formation remain to be established. One hypothesis is that changes in vascular supply to the adrenal cortex, due to phenomena of atherosclerosis or high blood pressure, may influence the morphology of the adrenal cortex, resulting in a compensatory growth and nodule formation in response to local hypoxia. In this review, we will summarize our knowledge on the mechanisms regulating adrenal cortex development and function, describe adrenal vascularization in normal and pathological conditions and address the mechanisms allowing the cross-talk between the hormonal and vascular components to allow the extreme tissue plasticity of the adrenal cortex in response to endogenous and exogenous stimuli. We will then address recent evidence suggesting a role for alterations in the vascular compartment that could eventually be involved in nodule formation and the development of primary aldosteronism.

Angiotensin peptides in the regulation of adrenal cortical function

The adrenal cortex plays a key role in the regulation of metabolism, salt and water homeostasis and sex differentiation by synthesizing glucocorticoid, mineralocorticoid and androgen hormones. Evidence exists that angiotensin II regulates adrenocortical function and it has been contended that angiotensin peptides of the non-canonical branch of the renin angiotensin system (RAS) might also modulate steroidogenesis in adrenals. Thus, the aim of this review is to examine the role of the RAS, and particularly of the angiotensin peptides and their receptors, in the regulation of adrenocortical hormones with particular focus on aldosterone production.

Increased expression of (pro)renin receptor in aldosterone-producing adenomas

(Pro)renin receptor ((P)RR) is a specific receptor for renin and prorenin. The aim of the present study is to clarify expression and possible pathophysiological roles of (P)RR in aldosterone-producing adenomas (APAs) and other adrenal tumors. Expression of (P)RR was studied by immunocytochemistry, western blot analysis and real-time RT-PCR in adrenal tumor tissues obtained at surgery. Immunocytochemistry showed that (P)RR was expressed in normal adrenal glands and tumor tissues of adrenocortical tumors including APAs. In the normal adrenal glands, positive (P)RR immunostaining was observed in both adrenal cortex and medulla, with higher (P)RR immunostaining observed in zona glomerulosa and zona reticularis. Positive (P)RR immunostaining was also observed in the adrenocortical tumors, with elevated (P)RR immunostaining found in APAs, particularly in compact cells. By contrast, no apparent (P)RR immunostaining was observed in pheochromocytomas. Western blot analysis showed a band of (P)RR protein in normal adrenal glands and adrenocortical tumors at the position of 35 kDa. The relative expression levels of (P)RR protein were higher in tumor tissues of APAs than in attached non-neoplastic adrenal tissues of APAs. Real-time RT-PCR showed that expression levels of (P)RR mRNA were significantly increased in tumor tissues of APAs compared with other adrenal tumor tissues and attached non-neoplastic adrenal tissues of APAs. The present study has shown for the first time that expression of (P)RR is elevated in tumor tissues of APAs, raising the possibility that (P)RR may play pathophysiological roles in APAs, such as aldosterone secretion and cell proliferation.

Severe hyperaldosteronism in neonatal Task3 potassium channel knockout mice is associated with activation of the intraadrenal renin-angiotensin system

Task3 K(+) channels are highly expressed in the adrenal cortex and contribute to the angiotensin II and K(+) sensitivity of aldosterone-producing glomerulosa cells. Adult Task3(-/-) mice display a partially autonomous aldosterone secretion, subclinical hyperaldosteronism, and salt-sensitive hypertension. Here, we investigated the age dependence of the adrenal phenotype of Task3(-/-) mice. Compared with adults, newborn Task3(-/-) mice displayed a severe adrenal phenotype with strongly increased plasma levels of aldosterone, corticosterone, and progesterone. This adrenocortical dysfunction was accompanied by a modified gene expression profile. The most strongly up-regulated gene was the protease renin. Real-time PCR corroborated the strong increase in adrenal renin expression, and immunofluorescence revealed renin-expressing cells in the zona fasciculata. Together with additional factors, activation of the local adrenal renin system is probably causative for the severely disturbed steroid hormone secretion of neonatal Task3(-/-) mice. The changes in gene expression patterns of neonatal Task3(-/-) mice could also be relevant for other forms of hyperaldosteronism.

Local renin-angiotensin systems in the adrenal gland

In the adrenal gland all components of the renin-angiotensin system (RAS) are expressed in both the adrenal cortex and the adrenal medulla. In this review evidence shall be presented that a local secretory RAS exists in the adrenal cortex that stimulates aldosterone production and serves as an amplification system for circulating angiotensin (ANG) II. The regulation of the secretory adrenal RAS clearly differs from the regulation of the circulatory RAS in terms of renin expression as well as of renin secretion. For example under potassium load the activity of the renal and circulatory RAS is suppressed whereas the activity of the adrenal RAS is stimulated. Thus the activity of the adrenal RAS but not of the circulating RAS correlates well with the regulation of aldosterone production by potassium. The present review also summarizes the knowledge about the expression and functions of an additional renin transcript that has recently been discovered. This transcript encodes for a non-secretory cytosolic renin isoform. The cytosolic renin may be a basis for the existence of an intracellular renin system in the adrenal gland that has long been proposed. The present state of knowledge shall be discussed indicating that such an intracellular system modulates cell survival and cell death such as apoptosis and necrosis or cell functions such as aldosterone production.

Presence of cellular renin-angiotensin system in chromaffin cells of bovine adrenal medulla

The presence of a local renin-angiotensin system has been established in organs that serve as angiotensin targets. In this study, the expression of angiotensinogen mRNA and subcellular localization of renin, angiotensin-converting enzyme, and angiotensin II were investigated in bovine adrenal medullary cells in primary culture. By light microscopy, expression of angiotensinogen mRNA, immunoreactive renin, angiotensin-converting enzyme, and angiotensin II were readily detectable only in the chromaffin cells. The density distribution of renin and angiotensin II in sucrose gradients suggested a concentration in chromaffin granules, a localization directly confirmed by immunoelectron microscopy. Reverse transcriptase-polymerase chain reaction and sequencing confirmed the expression of angiotensinogen in bovine chromaffin cells and the adrenal medulla. In addition, in vitro autoradiography indicated that both angiotensin-converting enzyme and angiotensin type 1 receptors were present in the adrenal medulla. These results provide the first direct evidence that chromaffin cells in the adrenal medulla are not only the target for angiotensin but should also be considered as potential local angiotensin-generating and -storing cells.

Nephrectomy and peritoneal dialysis eliminates circulating renin and controls uraemia in the rat

OBJECTIVE

The aim of the present study was to develop a rat model for in vivo studies of the local effects of the renin-angiotensin system (RAS) following elimination of circulating renin.

METHODS

Sprague Dawley rats were bilaterally nephrectomised and had a peritoneal dialysis catheter implanted. The rats were maintained on dialysis continuously for 48 hours, using Dianeal PD4 3.86% glucose dialysis solution. The peritoneal catheter and an automated system for dialysate exchange were made in our laboratory. A sham nephrectomised control group of rats was also dialysed.

RESULTS

Nephrectomised and sham-operated rats remained active and in good general condition during peritoneal dialysis. At 48 hours, in nephrectomised, dialysed rats, peritoneal urea clearance was 4.14+/-0.52 ml/hour, plasma urea was 40.0+/-7.7 mmol/L, plasma creatinine was 0.423+/- 0.070 mmol/L and plasma renin was below the limit of detection.

CONCLUSIONS

In conclusion, it was possible to sustain bilaterally-nephrectomised rats on continuous peritoneal dialysis for 48 hours, pending elimination of renin from the circulation. The nephrectomised dialysed rat model should be useful for investigation of the physiological effects of the circulating versus the local RAS.

Adrenaline cells of the rat adrenal cortex and medulla contain renin and prorenin

The distribution and content of renin in Sprague-Dawley (SD) and transgenic (mREN-2)27 rats (TG) were compared to further define the cellular basis and function of the adrenal renin-angiotensin system. Antibody binding (to rat and mouse renin protein and prosequence) was visualised in serial paraffin sections using an avidin-biotin peroxidase technique. Chromaffin and adrenaline cells were identified by tyrosine hydroxylase (TH) and phenylethanolamine N-methyltransferase immunoreactivity, respectively. In SD zona glomerulosa (ZG), renin and its prosequence localised to small steroid cells while in homozygous (receiving lisinopril) and heterozygous (untreated) TG, steroid cells labelled in all cortical zones. In addition, throughout the cortex of each strain, large polyhedral adrenaline chromaffin cells occurring singly or in small groups and occasionally in rays labelled for renin and prosequence. Similar large adrenaline cells immunolabelled for all antisera in medulla while other cells were only TH-positive. Total adrenal renin content was 53 times higher in heterozygous transgenics than SD rats and was mainly (74%) prorenin. In SD, 37% of cortical renin was prorenin but in adrenal medulla only active renin was detected. Thus, from present and previous work both renin and prorenin occur not only in mitochondrial dense bodies of the ZG, but also in secretory granules of adrenaline chromaffin cells in both cortex and medulla implying in situ synthesis and paracrine functions.

Tissue angiotensin generation and regulation of vascular tone

The renin-angiotensin system is intimately involved in the control of sodium and water balance, the activity of the sympathetic nervous system, mitogenesis and the regulation of vascular tone. There is evidence that many of these effects may be controlled at a local level by independent tissue renin-angiotensin systems. Drugs that are specific inhibitors of the cascade have proved powerful tools for dissecting the physiology of the renin-angiotensin system, and are of major benefit in the treatment of hypertension and chronic heart failure. Recent evidence suggests that variations in the genes coding for components of the system may affect the risk of developing hypertension and ischaemic heart disease.

Angiotensin II receptor subtypes and phosphoinositide hydrolysis in rat adrenal medulla

Angiotensin II (ANG) receptor subtypes were characterized by quantitative autoradiography after incubation with the ANG agonist [124I]Sar1-ANG in rat adrenal medulla. ANG receptors are highly localized in adrenal medulla. Specific binding was displaced by 4% and by 95% with the AT, receptor blocker losartan and the AT2 receptor competitor CGP 42112A, respectively. Analysis of competition curves indicated relative binding potencies for the AT2 population of CGP 42112A>PD 123319> PD 123177. ANG stimulated +-nositol phosphate formation in a dose-dependent manner in rat adrenal medulla. Losartan at concentrations of 10(-9) to 10(-5) M antagonized the effect of ANG, whereas PD 123177 or PD 123319 had no antagonistic action. However, at a higher concentration (10(-5) M) PD 123177 or PD 123319 potentiated the effect of ANG on InsP1-accumulation. In the presence of PD 123319 (10(-5) M) ANG dose-response curve was shifted to the left with no change in the maximal effect. This affect was blocked by the addition of losartan (10(-5) M). On the contrary, the addition of CGP 42112A (10(-6) M) inhibited ANG-induced increase in InsP1-accumulation. On the other hand, ANG and CGP 42112A reduced basal cyclic GMP formation, this effect was partially reverted by sodium orthovanadate, a phosphotyrosine phosphatase inhibitor. Our results further demonstrate the presence of two ANG receptor subtypes in adrenal medulla: ANG binding to AT, receptor stimulates inositol phospholipid metabolism, whereas ANG binding to AT2 receptors decreases both inositol phosphate production and cGMP formation.

The renin gene and aldosterone-producing adenomas

Approximately one half of the aldosterone-producing adenomas (APA) removed from patients with primary aldosteronism in the Hypertension Unit at Greenslopes Hospital belong to a subgroup in which aldosterone levels are responsive to the renin-angiotensin system (angiotensin-responsive APA; AII-R-APA), unlike classical APAs in which aldosterone is unresponsive (AII-U-APA). Renin mRNA levels in AII-R-APA were elevated when compared with those in AII-U-APA or normal adrenal cortices. Renin mRNA levels in some adrenal cortices surrounding AII-R-APA (but never in AII-U-APA) were raised, suggesting that a genetic defect is not confined to the tumor. Renin gene RFLP analysis in peripheral blood DNA revealed a significant difference in allelic frequencies between patients with AII-R-APA and AII-U-APA, suggesting an association between an alteration in the renin gene and aldosterone responsiveness to the renin-angiotensin system in patients with APAs.

Enhanced adrenal renin and aldosterone biosynthesis during sodium restriction in TGR (mREN2)27

The aim of the study was to investigate the relationships between tissue renin and the steroid production in the adrenal cortex during dietary sodium restriction in the transgenic rat (TGR) (mREN2)27. Thus the effects of a 1-wk low-sodium intake (0.04% NaCl) were studied in 5-wk-old male TGR (n = 33, systolic blood pressure = 151 +/- 3 mmHg) and in 24 age- and sex-matched outbred normotensive Sprague-Dawley (SD) rats. Measurements of plasma and tissue hormones were obtained at 0, 4, and 7 days of a low-sodium diet. Sodium restriction caused sustained increases of adrenal renin activity (from 28.5 +/- 3.5 to 87.5 +/- 4.5 ng.mg protein-1.h-1 on day 7) and of adrenal renin mRNA (+63 +/- 13 and +43 +/- 7% on days 4 and 7, respectively), whereas plasma renin activity (from 3.3 +/- 0.3 to 4.4 +/- 0.6 ng.ml-1.h-1) and renal renin activity (from 0.85 +/- 0.25 to 0.7 +/- 0.4 microgram.mg protein-1.h-1) did not change. The stimulation of the adrenal renin-angiotensin system was associated with a large increase of the aldosterone synthase cytochrome P-450 mRNA (+165 +/- 35 and +184 +/- 44%, on days 4 and 7) and of plasma aldosterone levels (from 125 +/- 32 to 338 +/- 59 pg/ml, P < 0.01). In SD rats, in spite of a more consistent increase in renal and circulating renin, mineralocorticoid production did not increase significantly. These results demonstrate that the exaggerated biosynthesis of aldosterone in TGR during sodium restriction is associated with an activation of renin in the adrenal cortex but not in the kidney.

Renin is not synthesized by cardiac and extrarenal vascular tissues. A review of experimental evidence

A comprehensive review of physiological and molecular biological evidence refutes claims for synthesis of renin by cardiac and vascular tissues. Cardiovascular tissue renin completely disappears after binephrectomy. Residual putative reninlike activity, where investigated, has had the characteristics of lysosomal acid proteases. Occasional reports of renin or renin mRNA in vascular and cardiac tissues can be ascribed to failure to remove the kidneys 24 hours beforehand, overloading of detection systems, problems with stringency in identification, and illegitimate transcripts after more than 25 cycles of polymerase chain reaction. Others, using more stringent criteria, have failed to detect cardiac and vascular renin mRNA. Accordingly, a growing number of investigators have concluded that the kidneys are the only source of cardiovascular tissue renin. Although prorenin is secreted from extrarenal tissues as well as from the kidneys, there is no evidence that it is ever converted to renin in the circulation. The kidney is the only tissue with known capacity to convert prorenin to renin and to secrete active renin into the circulation. Accordingly, renin of renal origin determines plasma and hence, extracellular fluid renin levels. In these loci, angiotensin (Ang) I, formed by renin cleavage of circulating and interstitial fluid angiotensinogen, is in turn cleaved by angiotensin converting enzyme, located in plasma and extracellular fluids and on the luminal surface of pulmonary and systemic vascular endothelial cells, to Ang II, which perfuses and bathes the heart and vasculature. Consistent with this model, plasma renin and angiotensin and the antihypertensive action of renin inhibitors, converting enzyme inhibitor, or Ang II antagonists all disappear after binephrectomy. Thus, the plasma renin level, via Ang II formation, determines renin system vasoconstrictor activity, the antihypertensive potential of anti-renin system drugs, and the risk of heart attack in hypertensive patients. This analysis redirects renin research to renal mechanisms that create the plasma renin level, to renal prorenin biosynthesis and its processing to renin, and to their regulated secretion, extracellular distribution, and possible binding to by target tissues. In this context, it is still possible that changes in circulating and interstitial renin substrate or available converting enzyme might exert subtle modulating influences on Ang II formation. However, this analysis redefines the importance of plasma renin measurements to assess clinical situations, because plasma renin is the only known initiator driving the cardiovascular renin-angiotensin system, and its strength can be measured.

Angiotensin II suppresses Na+ currents in bovine adrenal chromaffin cells

We investigated the effects of angiotensin II (ANG II) on the voltage-dependent Na+ channel currents (INa) recorded from bovine adrenal medullary chromaffin cells (BCCs) under whole-cell voltage clamp. Angiotensin II reversibly reduced the peak INa in a dose-dependent fashion. Inhibition was observed at a concentration of 1 nM (6.3 +/- 1.4%, mean +/- SEM) and reached a maximum at 1 microM (35 +/- 3.8%), with a half-maximal effect at 11.6 nM. The ANG II-induced inhibition resulted from a reduction in peak conductance (control, 7.2 +/- 0.7 nS; ANG II 4.3 +/- 0.5 nS; p < 0.01). Angiotensin II had no effect on the reversal potential or the decay time of INa. In addition, the V1/2 and k values, two parameters that describe the voltage dependence of INa for both steady-state activation and inactivation, were not affected by ANG II. The response to ANG II (1 microM) had a delay and attained maximum inhibition in 0.9 +/- 0.2 min (n = 10). Recovery from the effect was slow and took 3.5 +/- 0.8 min (n = 10) after the application of ANG II had been terminated. The inhibitory effects of ANG II were effectively blocked by a specific ANG II receptor antagonist. [Sar1, Val5, Ala8]ANG II. The present study demonstrates that ANG II inhibits voltage-dependent INa+ channel currents in BCCs via a specific receptor-coupled mechanism. The prolonged time course of the ANG II response indicates a possible involvement of second messenger(s) mediating this inhibition.

Endothelial production of C-type natriuretic peptide and its marked augmentation by transforming growth factor-beta. Possible existence of "vascular natriuretic peptide system"

C-type natriuretic peptide (CNP), the third member of the natriuretic peptide family, is thus far known to be distributed mainly in the central nervous system and is considered to act as a neuropeptide, in contrast to atrial natriuretic peptide (ANP) and brain natriuretic peptide (BNP), which act as cardiac hormones. Recently, we and others have demonstrated that the ANP-B receptor, which is selectively activated by CNP, is localized not only in the central nervous system but in peripheral tissues, including blood vessels. This finding has made us speculate regarding the peripheral production of CNP. In the present study, cultured endothelial cells were examined for CNP production by RIA and Northern blot analysis. CNP-like immunoreactivity was detected in the conditioned media of endothelial cells. Northern blot analysis detected CNPmRNA with a size of 1.2 kb. In addition, transforming growth factor (TGF)-beta, one of the key growth factors for vascular remodeling, markedly stimulated the expression of CNPmRNA and induced a tremendous increase in CNP secretion. We could also detect CNP transcript in the bovine thoracic aorta using the reverse transcription-polymerase chain reaction method. The present study demonstrates the endothelial production of CNP and suggests that a member of the natriuretic peptide family may act as a local regulator in vascular walls. Since evidence for the pathophysiological importance of the vascular renin-angiotensin system has been accumulating and the natriuretic peptide system is known to be antagonistic to the renin-angiotensin system, the possible existence of "vascular natriuretic peptide system" may prove to be of physiological and clinical relevance.

Lewis K. Dahl Memorial Lecture. The renin system and four lines fo hypertension research. Nephron heterogeneity, the calcium connection, the prorenin vasodilator limb, and plasma renin and heart attack

As the major regulator of arterial blood pressure and sodium balance, the renin axis supports normotension or hypertension via angiotensin-mediated vasoconstriction and angiotensin plus aldosterone-induced renal sodium retention. In this endocrine servo control, renal renin is released by hypotension or salt depletion; conversely, with hypertension or volume excess, plasma renin activity falls to zero. Accordingly, any renal renin secretion is abnormal in the face of arterial hypertension. Human hypertensive disorders comprise a spectrum of abnormal vasoconstriction-volume products (renin-sodium profiles). Excess plasma renin activity for the sodium balance is created by nephron heterogeneity in which a subpopulation of ischemic nephrons hypersecretes renin and retains sodium. This excess renin impairs adaptive natriuresis of neighboring normal nephrons. Research defining the pivotal role of vascular cytosolic calcium for transducing sodium or renin-mediated vasoconstriction explains the selective value of calcium antagonists for correcting the sodium-volume-mediated, and beta-blockers or angiotensin converting enzyme inhibitors for correcting renin-mediated, arteriolar vasoconstriction. The renin precursor prorenin appears to be physiologically active, causing selective vasodilation that offsets renin-mediated vasoconstriction. Overactivity of prorenin may be involved in the hyperperfusion vascular injuries of diabetes mellitus and toxemias. Prorenin underactivity may facilitate renin-mediated ischemic vascular injury. In essential hypertension, undue plasma renin activity is powerfully and independently associated with heart attack risk. Conversely, patients with low renin activity are protected from heart attack despite higher blood pressures and greater age. Also, renin or angiotensin administration consistently causes vascular injury in the heart, brain, and kidneys of animals. These data suggest new potentials for the prevention of cardiovascular sequelae (heart attack and stroke) by using explicit strategies to curtail plasma renin activity.

Local renin-angiotensin system in human adrenals and aldosteronomas

The local renin-angiotensin system may regulate adrenal cell growth and function. Angiotensinogen, renin, and angiotensin converting enzyme gene expression were studied in four normal adrenal glands (removed from patients with renal carcinomas) and five aldosterone-secreting adenomas. Northern blot analysis showed expression of angiotensinogen messenger RNA (mRNA) in normal adrenals at levels approximately 35-fold lower than liver and sixfold lower than kidney. Similar angiotensinogen mRNA levels were present in two aldosteronomas, whereas a third had levels approximately 50% of those found in kidney. Renin mRNA was detectable in most normal adrenals and in three adenomas, one of which had relatively high renin mRNA levels. Angiotensin converting enzyme gene was expressed in adrenal tissue and in three adenomas. Portions from these normal adrenals and two of these aldosteronomas, as well as samples from two other adrenals and three aldosteronomas, were also studied in an in vitro superfusion system coupled with active renin radioimmunometric assay, angiotensin II/III, and aldosterone radioimmunoassay. Total amounts of active renin and angiotensin II/III released from normal adrenals during 270 minutes of superfusion were higher than the amounts released from aldosteronomas (312 +/- 35 versus 187 +/- 43 and 823 +/- 100 versus 436 +/- 55 pg/100 mg tissue, respectively; mean +/- SEM, p less than 0.05), whereas aldosterone release from the adenomatous tissue was approximately threefold higher (320 +/- 21 versus 115 +/- 18 ng/100 mg tissue; mean +/- SEM, p less than 0.01). Total amounts of active renin and angiotensin II/III released by normal or adenomatous adrenal samples exceeded threefold to fourfold the amounts extracted from similar samples of the same surgical specimen.(ABSTRACT TRUNCATED AT 250 WORDS)

Regulated tissue- and cell-specific expression of the human renin gene in transgenic mice

Transgenic mice containing the human renin gene were constructed with the aim of examining the tissue- and cell-specific expression of human renin. The human renin transgene used consisted of a genomic sequence extending approximately 900 bp upstream and 400 bp downstream of the coding region and included all exon and intron sequences. Two assays were developed to differentiate human renin transcripts from endogenous mouse renin transcripts at the whole-tissue level. High level human renin expression was evident in the kidney, adrenal gland, ovary, testis, lung, and adipose tissue of all four transgenic lines examined. Human renin mRNA could also be detected at lower levels in the submandibular gland and heart of two different individual lines. No expression was evident in the liver or brain of any line tested. In situ hybridization revealed the human renin mRNA to be localized and exquisitely restricted to renal juxtaglomerular cells. Treatment of transgenic mice with captopril resulted in an increase in the accumulation of renal renin mRNAs derived from both the mouse and human renin genes. Plasma renin activity assays using synthetic human renin substrate clearly demonstrated the elaboration of active human renin into the systemic circulation of transgenic mice. These data strongly suggest that the human renin transgene exhibits both tissue- and cell-specific expression in transgenic mice. Its expression is entrained to the same regulatory signals as the endogenous renin gene in kidney, and active human renin is released into the plasma of the transgenic mice.(ABSTRACT TRUNCATED AT 250 WORDS)

High blood pressure: Hunting the genes

High blood pressure is a disease of unknown cause. Family history of the disease indicates higher risk, but it is not known which genes are involved or how they interact with environmental influences to produce the disorder. Molecular biology offers an approach to problems that have not so far been solved by classical physiology or biochemistry. By analysing polymorphic variation in chromosome markers such as minisatellite sequences, or by restriction fragment polymorphism analysis of candidate genes, attempts are being made to link genetic variations with hypertension. In genetically hypertensive rats, hypertension is associated with a polymorphism of the renin gene and with other loci on chromosomes 10 and 18. The role of these loci in human hypertension remains to be determined. Other genes such as sodium-lithium countertransport may be involved. Environmental factors such as stress or salt intake could influence the rate or timing of expression of certain genes and thus result in hypertension.

Structure, expression, and regulation of the murine renin genes

It has long been known that the renin-angiotensin system plays an integral role in the regulation of blood pressure and electrolyte and fluid balance in mammals. The advent of molecular biologic techniques has afforded new insights into the genes regulating blood pressure. Laboratory mice and rats have been used as experimental models to examine the structural organization and expression of the renin gene. It is now well established that some mice, unlike rats and humans, contain a duplicated copy of the renin locus, which accounts for the high level of renin activity long known to be found in the submandibular gland of some mice. Indeed it is this fortuitous observation that facilitated the isolation of the first complementary DNA clones for renin and ultimately the many species-specific probes now available to analyze mammalian tissues for evidence of primary renin expression. The use of complementary DNAs as probes for primary renin expression helped confirm and further clarify earlier studies demonstrating the presence of renin activity in a number of extrarenal tissues. Although expression in some of these tissues is evolutionarily conserved, their significance has still been elusive. In this report we review the impact of molecular biology on our current understanding of renin gene structure and organization, tissue- and cell-specific expression and regulation, and the changes in renin expression throughout ontogeny. In addition, we describe how new developments in gene transfer technology have added important tools to our arsenal for examining renin gene regulation and how these technologies can be used to develop new tools for renin and hypertension research.

Role of the adrenal renin-angiotensin system on adrenocorticotropic hormone- and potassium-stimulated aldosterone production by rat adrenal glomerulosa cells in monolayer culture

The rat zona glomerulosa has a renin-angiotensin system that appears to function as an autocrine or paracrine system in the regulation of aldosterone production. To further investigate dynamic changes of production of renin and aldosterone in vitro we developed a primary monolayer culture of rat adrenal glomerulosa cells in serum-free medium. Collagenase-dispersed glomerulosa cells were incubated in PFMR-4 medium containing 10% fetal calf serum for 48 hours; the medium was then replaced with serum-free PFMR-4 medium. The cell viability and the aldosterone secretion were stable over the additional 48 hours in the serum-free control medium. After incubation for 24 hours in the serum-free medium, the cells were exposed to high K+ or adrenocorticotropic hormone (ACTH) for another 24 hours. ACTH stimulated aldosterone secretion, and this increased secretion was associated with an increase in renin activity (cell active renin, from 15.56 +/- 0.71 to 45.75 +/- 5.69; cell inactive renin, from 0.67 +/- 0.54 to 8.75 +/- 3.40; medium inactive renin, from 5.58 +/- 1.16 to 106.20 +/- 14.01 pg angiotensin I (Ang I)/micrograms protein/3 hr). Aldosterone was also stimulated by high K+. This increase was also associated with an increase in active renin in the cells (from 15.08 +/- 1.80 to 23.26 +/- 2.15 pg Ang I/micrograms protein/3 hr) and an increase in inactive renin in the medium (from 10.87 +/- 1.62 to 21.37 +/- 3.20 pg Ang I/micrograms protein/3 hr). Addition of the angiotensin converting enzyme inhibitor lisinopril attenuated both ACTH- and high K(+)-stimulated aldosterone secretion significantly.(ABSTRACT TRUNCATED AT 250 WORDS)

Expression of murine renin genes in subcutaneous connective tissue

A renin promoter-large tumor antigen (T antigen) fusion gene was constructed to provide a reporter function for renin expression in transgenic mice. These transgenic mice gave rise to tumors in subcutaneous soft tissue, which was attributed to transgene expression at this site. An immunohistochemical analysis of transgenic fetuses from several independent lines revealed scattered T-antigen-containing mesenchymal cells and fibroblasts in the subcutaneous layer of the skin between the panniculus carnosus muscle of the skin and the skeletal muscle of the body wall. This localization is consistent with the location of overt tumorigenesis in adult mice. This pattern was specific for the renin-T antigen fusion gene as no immunohistochemical staining was observed in transgenic fetuses containing a heterologous promoter-T antigen fusion gene. Northern blot analysis of tumor RNA indicated that most of the tumors expressed both T antigen and the endogenous renin gene Ren-1c. In addition, when multiple renin genes were introduced by crossing transgenic mice with nontransgenic DBA/2J mice, which contain another allele of the Ren-1 locus as well as the duplicated locus Ren-2, the resultant tumors expressed the Ren-2 gene. Northern blots were then used to analyze renin expression in the subcutaneous tissue of normal mice. Fully processed renin mRNA was detected in eviscerated 15.5-day postcoitus fetal and newborn carcasses and in newborn skin. Our data indicate that there is a renin-expressing cell population in fetal and newborn subcutaneous tissue.

Angiotensin II stimulates the expression of proenkephalin A mRNA in cultured bovine adrenal chromaffin cells

The effects of angiotensin II on the expression of proenkephalin A (ProEnk A) mRNA and enkephalin release were examined in cultured bovine adrenal chromaffin cells. Exposure of chromaffin cells for 24h to 10 nM angiotensin II produced a more than 2-fold increase in cellular ProEnk A mRNA levels with a concomitant elevation in the levels of high molecular weight Met5-enkephalin-Arg6-Gly7-Leu8-like immunoreactivity in the culture medium. These stimulatory effects of angiotensin II on enkephalin release and mRNA expression were fully antagonized by the angiotensin II antagonist [Sar1, Ala8]-angiotensin II. The angiotensin II-induced increase in ProEnk A mRNA levels was also abolished by the RNA synthesis inhibitor actinomycin D. These results indicate that specific angiotensin II receptor activation is responsible for stimulating transcription of ProEnk A mRNA and enkephalin. Angiotensin II may therefore be involved in the long-term regulation of ProEnk A gene expression in the adrenal medulla.

Renin immunohistochemistry in the adrenal gland of the mouse fetus and neonate

The development of renin-containing cells in fetal and neonatal adrenal glands of the mouse was studied using immunohistochemistry. On days 13-14 of gestation, immunoreactivity for renin was first observed in a few cortical cells of the gland, appearing as small patchy or granular reaction products in the perikaryon. The mitotic configurations of the cells demonstrating immunoreactivity were noted. On day 16 of gestation, a number of intensively immunoreactive cells were distributed in the aortal side of the cortical zone. On day 18 of gestation, and day 1 postparturition, a small number of potent immunoreactive cells were still found in the cortical area. Immunoreactivity of the cytoplasm was observed in the cells, some showing an intensive reaction and others possessing numerous tiny granules just below the cell membrane. On days 3, 5, and 7 after birth, no renin-containing cells were found in the adrenal gland. The ratio of the numbers of renin-positive cells in certain areas to the numbers in the entire cortical area was significantly increased on day 16 of gestation, but there was no sexual difference in the ratios. The ratios were decreased subsequently until day 1 after birth. The possible significance of renin synthesis in specific adrenal cells in fetal life is discussed with respect to an important involvement of angiotensin II in the morphogenesis of the adrenal gland of the mouse.

Effects of angiotensin II on cultured, bovine adrenal medullary cells

Primary cultures of bovine adrenal medullary cells have been used to study the effects of angiotensin II on catecholamine secretion and inositol phosphate accumulation. Angiotensin II induced a weak secretion of both adrenaline and noradrenaline, with a threshold of 10-100 pM and a shallow concentration-dependence up to 10 microM. The response was fully dependent on extracellular Ca++, was partially inhibited by 100 nM nifedipine, was completely blocked by [Sar1, Ala8]-angiotensin II (IC50 5-10 nM) and was unaffected by 0.1 mM hexamethonium. Angiotensin II also increased inositol phosphate accumulation over the range 1 pM-10 microM. Inositol trisphosphate levels increased in a biphasic manner after 15 sec and 1 min exposure to 10 nM angiotensin II, but were not significantly increased at 30 sec or 5, 15 or 30 min stimulation. Inositol bisphosphate was significantly increased after 1 min. Inositol monophosphate levels only increased after 1 min stimulation, but continued to rise during 30 min stimulation. Removal of extracellular Ca++ or addition of EGTA reduced basal inositol phosphate accumulation but not the ability of angiotensin II to stimulate inositol phosphate accumulation relative to basal. Nifedipine (100 nM) had no effect on basal or angiotensin II-induced inositol phosphate accumulation. The inositol phosphate response to angiotensin II was abolished by 1 microM [Sar1, Ala8]-angiotensin II. The results suggest that secretion of adrenal medullary catecholamines can be evoked by angiotensin II, at concentrations that are compatible with a role for circulating angiotensin II or for angiotensin II generated locally within the adrenal medulla. They do not support the suggestion that the secretory actions of angiotensin II on chromaffin cells are mediated by mobilization of intracellular Ca++ stores.

Localization of angiotensin II binding sites in the bovine adrenal medulla using a labelled specific antagonist

Angiotensin II binding sites have been localized in sections of bovine adrenal glands and on living cultured bovine adrenal medullary cells using [125I]-[Sar1,Ile8]-angiotensin II and autoradiographic techniques. Binding sites were observed over both adrenaline and noradrenaline chromaffin cells. However, they were present in higher density over adrenaline cells, as determined by the distribution of phenylethanolamine N-methyltransferase mRNA by in situ hybridization histochemistry and of glyoxylic acid-induced fluorescence of noradrenaline. Binding sites were also observed in low density over nerve tracts within the bovine adrenal gland. Living cultured bovine adrenal medullary cells possessed angiotensin II binding sites. Not all cells were labelled. At least 73% of identified dispersed chromaffin cells in these cultures were labelled. Some chromaffin cells were not labelled with the ligand, and at least some non-chromaffin cells in the cultures did possess angiotensin II binding sites. The results provide direct anatomical support for the known ability of angiotensin II to elicit catecholamine secretion from perfused adrenal glands and from cultured adrenal chromaffin cells. They also suggest that some of the effects of angiotensin II on calcium fluxes and second messenger levels measured in cultured adrenal medullary cell preparations may be due to angiotensin II acting on non-chromaffin cells present in these cultures.

Adrenal renin: a possible local hormonal regulator of aldosterone production

The complete renin-angiotensin system is present in the adrenal cortex: prorenin, renin, angiotensinogen, angiotensin I and II, and converting enzyme. Most of the renin found is probably synthesized there since the renin concentration increases after nephrectomy, and the mRNA for renin is present. The renin-angiotensin system has the highest activity in the zona glomerulosa cells, the site of aldosterone formation. A low-sodium diet or a high-potassium diet, or nephrectomy markedly increases the adrenal renin concentration in the zona glomerulosa cells without any effect on the fasciculata-medullary cells. There is a close correlation between adrenal renin and aldosterone production. The adrenal renin angiotensin system may be a local regulator of aldosterone production.

Presence of renin secretory granules in rat adrenal gland and stimulation of renin secretion by angiotensin II but not by adrenocorticotropin

Renin has been identified biochemically and immunohistochemically in the adrenal gland. We examined the subcellular distribution and behavior of adrenal renin. By differential centrifugation of adrenal capsules, we found renin mainly in mitochondrial fractions. By Percoll density gradient centrifugation of this fraction, dense granules were separated from mitochondria and microsomes. The renin activity in the dense granules from the capsules of nephrectomized rats was 15 times greater than that of the intact rat. Immunohistochemical studies revealed that the dense granules increased in number after bilateral nephrectomy. Immunogold staining of these granules showed unequivocally the presence of renin in these granules. Adrenal capsules in organ culture were found to release renin at a steady rate. Renin release from bilaterally nephrectomized rat adrenals was 46 times faster than from the organs of intact animals. The mechanism of the control of renin secretion from the adrenal gland was different from the kidney in that the secretion was stimulated by potassium chloride (10 mM) or angiotensin II (10(-9)-10(-7) M) but not by ACTH (10(-9)-10(-7) M), suggesting stimulation by intracellular calcium. These results provide evidence that the adrenal synthesizes renin, stores it in specific secretory granules and secretes it in a regulated manner.

Lack of effect of opioid compounds on angiotensin II responses of bovine adrenal medullary cells

Angiotensin II (10 nM) increased basal adrenaline and noradrenaline secretion from cultured bovine adrenal chromaffin cells by 2.5- to 3-fold and 4- to 6-fold, respectively, and stimulated basal accumulation of inositol phosphates more than 2-fold. Etorphine and diprenorphine in the range 10(-9) to 10(-5) M had no effect on the catecholamine secretion induced by angiotensin II, and, at 10(-8) and 10(-5) M, had no effect on angiotensin II-induced inositol phosphate accumulation. The functions of adrenal medullary opioid receptors remain to be determined.

Endothelial renin-angiotensin pathway: evidence for intracellular synthesis and secretion of angiotensins

Cultured bovine aortic endothelial cells (BAEC) contain renin and angiotensinogen. To examine whether angiotensins are synthesized intracellularly and secreted by these cells, we assayed cell extracts as well as serum-free media of intact confluent BAEC. Angiotensins were identified by their retention time on reverse phase high performance liquid chromatography and direct radioimmunoassay. BAEC and their media contain angiotensin II and angiotensin III. The rate of angiotensin accumulation in the media was a nonlinear function of time; the highest rate occurred in the first 15 minutes. The amount of angiotensin II accumulated in 30 minutes exceeded 200% of the intracellular concentration and that of angiotensin III exceeded 500% of the initial intracellular content. Neither renin nor angiotensinogen could be detected in the media. The viability of these cells was supported by low lactic dehydrogenase activity in the media (less than 0.5% of cellular level). These data suggest that BAEC is capable of synthesizing and secreting angiotensins. We postulate that this endothelial-derived angiotensin system may play an important paracrine or autocrine role in influencing local vascular tone.

Mechanisms by which nephrectomy stimulates adrenal renin

Renin has been identified in the adrenal gland by several investigators. Nephrectomy is the most potent stimulator of adrenal renin, and in the present study we investigated the mechanism by which nephrectomy stimulates adrenal renin. The pituitary plays a permissive role since hypophysectomy abolished the response of adrenal renin to nephrectomy (from 117.3 +/- 14.55 to 10.37 +/- 1.63 ng angiotensin I/mg protein/hr) and adrenocorticotropic hormone (ACTH) treatment restored the response to nephrectomy in hypophysectomized rats to 120 +/- 20.62 ng angiotensin I/mg protein/hr. However, large doses of ACTH given to intact rats did not increase adrenal renin to the high level observed after nephrectomy. Potassium also plays an important role, since prevention of hyperkalemia after nephrectomy by treatment with a cation exchange resin, sodium polystyrene sulfonate (Kayexalate), significantly reduced the adrenal renin response to nephrectomy. A third factor involved is the lack of negative feedback by plasma angiotensin II. Infusion of angiotensin II intraperitoneally prevented the rise in adrenal renin after nephrectomy (from 65.25 +/- 7.60 to 9.27 +/- 0.99 ng angiotensin I/mg protein/hr) despite an increase in plasma potassium and corticosterone. In conclusion, three factors influence the response of adrenal renin to nephrectomy: 1) the pituitary through the release of ACTH, 2) a direct stimulation by high plasma potassium levels, 3) the lack of angiotensin II feedback inhibition. Whether the high adrenal renin contributes to the high aldosterone observed in rats after nephrectomy remains to be established.

A case of adrenal tumor producing renin, aldosterone, and sex steroid hormones

A 27-year-old woman with an adrenal tumor that produced renin and aldosterone, associated with hypertension and adrenogenital syndrome, is described. Severe hypertension, cardiomegaly, a low serum potassium level, clinical symptoms of adrenogenital syndrome, and a left upper abdominal tumor also were found. Endocrinological studies showed that plasma and urinary levels of sex steroid hormones such as dehydroepiandrosterone, androsterone, and testosterone were markedly increased. Plasma renin activity, plasma angiotensin II, and plasma aldosterone levels also were increased markedly, although deoxycorticosterone levels remained within the normal range. The possibility of renovascular hypertension was excluded by angiography of the renal artery and by venous sampling of plasma renin activity. Abnormal elevations in plasma aldosterone levels persisted despite normalization of plasma angiotensin II by converting enzyme inhibitor administration. It was suspected that this patient had an adrenal tumor producing renin as well as sex steroids and aldosterone. Microscopy of the resected tumor revealed that the tumor was composed mostly of cells with large nuclei and light cytoplasm. The tumor contained dehydroepiandrosterone, dehydroepiandrosterone sulfate, testosterone, aldosterone, and renin. Immunohistochemical study showed that some of the tumor cells produced renin. Biopsy of the left renal tissue showed evident atrophy of the juxtaglomerular cells and pronounced arteriosclerosis. After resection of the tumor, all blood and urinary levels of the abnormally increased hormones returned to a normal range and an apparent fall of blood pressure was noted. To our knowledge, this is the first report of a renin and aldosterone-producing adrenal tumor associated with hypertension and adrenogenital syndrome.

Analysis by immunocytochemistry and in situ hybridization of renin and its mRNA in kidney, testis, adrenal, and pituitary of the rat

Renin gene expression in cells and tissues of the rat was examined by in situ hybridization histochemistry and immunocytochemistry. By using a mouse cDNA probe, hybridization histochemistry revealed renin mRNA in the renal juxtaglomerular cells, testicular Leydig cells, adrenal zona glomerulosa cells, the intermediate lobe of the pituitary, and scattered cells of the anterior lobe of the pituitary. With four separate antisera to mouse submaxillary renin, there was immunoreactivity in the renal juxtaglomerular cells. However, only one of the antisera stained the Leydig cells, a second stained the adrenal zona glomerulosa, a third stained the intermediate lobe of the pituitary, and a fourth stained scattered cells of the anterior lobe of the pituitary that were identified as gonadotrophs. The variations with the different antisera in detecting extrarenal renin are unexplained but could imply that posttranslational proteolysis or glycosylation of preprorenin varies in different tissues with consequent variations in immunoreactivity. The finding of renin mRNA and renin-like immunoreactivity in these tissues supports the notion that these tissues are sites for production of renin.

Multiple forms of immunoreactive renin in human pituitary tissue

Immunoreactive renin was demonstrated in pituitary tissues of postmortem human subjects with different diseases. The specific immunoreactive renin activity comprised the majority of the tissue renin-like activity (mean, 83%), indicating the absence of nonspecific actions of proteases such as cathepsin D. We used three pituitary specimens with high levels of the specific renin activity for further biochemical characterization of the enzyme. Small differences were found in the molecular mass (45 K, 42 K and 37 K), binding to concanavalin A-Sepharose, and isoelectric points (pI) (4.72, 4.78, 4.86, 5.06, 5.28 and 5.44). These results seem to be interpreted as evidence for the presence of specific renin in the human pituitary with microheterogeneity.

Effect of indomethacin on the adrenal renin response to nephrectomy in the rat

The role of prostaglandins in the control of adrenal renin in vivo was evaluated in nephrectomized rats. Nephrectomy increased adrenal renin from 13.2 +/- 1.37 ng angiotensin I/mg protein/hr to 166.5 +/- 17.3 ng angiotensin I/mg protein/hr. Indomethacin treatment significantly suppressed the adrenal renin response to nephrectomy. (47.8 +/- 5.22 ng angiotensin I/mg protein/hr). Adrenal aldosterone was also suppressed by indomethacin. Adrenal prostaglandin E2 increased after nephrectomy and decreased after indomethacin. Plasma corticosterone and serum potassium did not change after indomethacin. These data indicate that inhibition of prostaglandin synthesis by indomethacin partially blocks the adrenal renin response to nephrectomy, suggesting that prostaglandins may play a role in the adrenal response to nephrectomy.

Renin and angiotensin-converting enzyme in human neuroblastoma tissue

High activity of renin was demonstrated in human neuroblastoma tissue. This activity was inhibited by specific antibody raised against human renal renin, indicating that it was not due to the nonspecific action of proteases. The specific activity of renin was 122.8 ng of angiotensin I generated mg of protein-1 h-1. It shared some biochemical features with well-known kidney renin, such as molecular weight, optimum pH, the presence of trypsin-activatable inactive renin, and glycoprotein nature. Furthermore, angiotensin-converting enzyme (ACE) activity (2.64 nmol mg of protein-1 min-1) was found in the tissue. This activity was inhibited by captopril, a specific ACE inhibitor, or by omission of chloride ion. These results suggest that true renin in addition to ACE exists in human neuroblastoma tissue.

Are the renin-containing granules of juxtaglomerular epithelioid cells modified lysosomes?

Mature secretory granules of epithelioid cells--the so-called renin granules--exhibit certain properties, which in this particular combination are expressed only by lysosomes: Renin granules have autophagic capabilities; they react to the application of lipidosis-inducing, lysosomotropic substances by the gradual accumulation of polar lipids; all secretory granules of epithelioid cells contain acid phosphatase until maturity; and exogenous tracers reach renin granules without labeling the Golgi complex. Several functional implications can therefore be considered. Hydrolytic enzymes, constitutive elements of the granule matrix, might either cleave inactive prorenin to yield active renin within the granules or, by unspecific hydrolysis of renin, participate in the regulation of the overall quantity of secretory product. Autophagic phenomena, the involvement of renin granules in the traffic of exogenous tracers, and the build-up of polar lipids following experimental interference with lipid catabolism indicate a large turnover of membrane material in renin granules. They also suggest that cytoplasmic and extracellular fluid gains access to the granule content and may thus be involved there in the regulation of biochemical reactions by changing the intragranular milieu or via signal molecules. In addition to the lysosome-like properties of epithelioid cell secretory granules, the secretory product, renin, as a carboxyl protease, is structurally related to other acidic proteases. In the case of cathepsin D, even functional similarities exist.

True renin in human pituitary tissue

Readily detectable levels of renin activity were demonstrated in human pituitary tissues. This activity was inhibited by specific antibody raised against human renal renin, indicating that it was not due to the nonspecific action of proteases. It shared some biochemical features with well-known kidney renin, such as molecular weight, optimum pH, and the presence of trypsin-activatable inactive renin. These results suggest that true renin exists in human pituitary tissue.

Production and release of inactive renin by human vascular smooth muscle cells

Human arterial smooth muscle cells were obtained from surgically excised tissues and cultured by the explant method. The cultured cells had both active and inactive forms of an angiotensin I forming enzyme. About a five-fold increase in the activity was obtained by trypsin treatment. This renin-like enzyme was also found in abundance in the culture media, mostly in an inactive form. Most of the enzyme activity, either before or after the activation, was suppressed by an antibody specific to human renin. The inactive enzyme was activated to some extent also by acidification and by cold exposure. The molecular weight of the inactive enzyme was estimated to be approximately 49,000 by gel filtration. These results suggest that human vascular smooth muscle cells can produce renin and release an inactive form of renin, and can be a potential source of plasma inactive renin under certain conditions such as the anephric state.

Androgen modulation of adrenal angiotensin receptors

Several polar androgens increased the binding of angiotensin and its stimulation of aldosteronogenesis in bovine adrenal glomerulosa cells. The effect was seen only if the steroids were applied to the cells and then washed away. This phenomenon and the technique for demonstrating it may have implications for studies of receptor modulation and for clinical states in which responsiveness to angiotensin is increased.

Generation of angiotensins in cultured pheochromocytoma cells

Cultured rat pheochromocytoma cells, PC-12, were found to contain renin-like activity. The activity which was inhibited by monospecific antibodies to rat renal renin showed a pH optimum between 6 and 7, indicating that it was a specific renin. The cells also contained angiotensin I and angiotensin I converting enzyme. Angiotensin II/III were also detected in lysate. These findings indicated an intrinsic pathway of angiotensin formation in pheochromocytoma. The formation of angiotensins in pheochromocytoma cells suggests modulating functions of angiotensin on neurotransmitter release from adrenal medulla.