The effect of sodium intake on angiotensin content of the rat adrenal gland

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.

Effects of sequential chemotherapy of FOLFIRI/FOLFOX on the endocrine axes of ACTH-cortisol and renin-angiotensin-aldosterone

The chemotherapies of FOLFOX (leucovorin + 5-fluorouracil + oxaliplatin) and FOLFIRI (folinic acid + 5-fluorouracil + irinotecan) are effective for a variety of malignant tumors. In particular, the sequential chemotherapy of FOLFOX/FOLFIRI has become the preferred post-operational treatment approach for gastrointestinal cancer and an important palliative care program for advanced cancer. However, the sequential chemotherapy of FOLFOX/FOLFIRI showed severe side effects due to the fact that the toxicity of the drugs can be enhanced by each other. Here, we report the dynamic changes in the activities of serum ACTH, cortisol, renin, angiotensin, and aldosterone in patients following multiple cycles of FOLFOX/FOLFIRI sequential chemotherapy. We found that the sequential chemotherapy might cause damage to the activities of the endocrine cells and/or the sympathetic nerve, and alter endocrine function, specifically the ACTH-cortisol and renin-angiotensin-aldosterone axes.

Gustatory terminal field organization and developmental plasticity in the nucleus of the solitary tract revealed through triple-fluorescence labeling

Early dietary sodium restriction has profound influences on the organization of the gustatory brainstem. However, the anatomical relationships among multiple gustatory nerve inputs have not been examined. Through the use of triple-fluorescence labeling and confocal laser microscopy, terminal fields of the greater superficial petrosal (GSP), chorda tympani (CT), and glossopharyngeal (IX) nerves were visualized concurrently in the nucleus of the solitary tract (NTS) of developmentally sodium-restricted and control rats. Dietary sodium restriction during pre- and postnatal development resulted in a twofold increase in the volume of both the CT and the IX nerve terminal fields but did not affect the volume of the GSP terminal field. In controls, these nerve terminal fields overlapped considerably. The dietary manipulation significantly increased the overlapping zones among terminal fields, resulting in an extension of CT and IX fields past their normal boundaries. The differences in terminal field volumes were exaggerated when expressed relative to the respective NTS volumes. Furthermore, increased terminal field volumes could not be attributed to an increase in the number of afferents because ganglion cell counts did not differ between groups. Taken together, selective increases in terminal field volume and ensuing overlap among terminal fields suggest an increased convergence of these gustatory nerve terminals onto neurons in the NTS. The genesis of such convergence is likely related to disruption of cellular and molecular mechanisms during the development of individual terminal fields, the consequences of which have implications for corresponding functional and behavioral alterations.

Aldosterone biosynthesis, regulation, and classical mechanism of action

Circulating aldosterone is principally made in the glomerulosa zone of the adrenal cortex by a series of enzyme steps leading to the conversion of cholesterol to aldosterone. Uniquely, aldosterone's production is regulated at two critical enzyme steps: (1) early in its biosynthetic pathway (the conversion of cholesterol to pregnenolone cholesterol side chain cleavage enzyme) and (2) late (the conversion of corticosterone to aldosterone by aldosterone synthase). A variety of factors modify aldosterone secretion--the most important are angiotensin II (AngII), the end-product of the renin-angiotensin system (RAS), and potassium. However ACTH, neural mediators and natriuretic factors also contribute at least over the short run. Aldosterone's classical epithelial effect is to increase the transport of sodium across the cell in exchange for potassium and hydrogen ions. Although still controversial, there is an increasing body of data that supports the hypothesis that aldosterone can be synthesized in tissues outside of the adrenal cortex, specifically in the heart and the vasculature. Aldosterone's biosynthesis appears to be regulated in these tissues similar to what occurs in the adrenal cortex. The role of this extra adrenal aldosterone production in health and disease is as of yet undetermined.

Tissue angiotensin II as a modulator of erectile function. I. Angiotensin peptide content, secretion and effects in the corpus cavernosum

PURPOSE

Although Angiotensin II (Ang II) is a major modulator of regional blood flow in the extracavernosal segments of the vascular bed, its role in erectile function is unknown. The corpus cavernosum penis is a modified vascular tissue that contains endothelial and smooth muscle cells. In other segments of the vascular bed, these cell types produce Ang II. Therefore, we explored the presence and function of an Ang II producing paracrine system in the corpus cavernosum.

METHODS

The angiotensin content of the human corpus cavernosum was measured by radioimmunoassay. The distribution pattern of Ang II containing cells within the corpus cavernosum was assessed by an immunohistochemical technique, and the rate of its secretion was determined by superfusion. The effects of Ang II and its antagonist, losartan, on intracavernosal pressure were determined under in vivo conditions, in anesthetized dogs.

RESULTS

Human corpus cavernosum contained 1178 +/- 223 (SEM) fmol Ang II, 528 +/- 171 fmol Ang I, 475 +/- 67 fmol des-asp-Ang I, and 1897 +/- 371 fmol des-asp-Ang II/gm. tissue (n = 4). Ang II was found mainly in endothelial cells lining blood vessels and smooth muscle bundles within the corpus cavernosum. Superfused cavernosal tissue secreted immuno-reactive Ang II (Ang II(ir)) at a rate of 57 +/- 36.5 fmol Ang II(ir)/gm. tissue/minute (n = 10). The amount of Ang II released per gram of tissue in an hour was 3-fold greater than the Ang II content/gm. tissue, suggesting a local production of Ang II. Papaverine and prostaglandin E1 suppressed Ang II secretion significantly (p <0.001, p = 0.013). The responsiveness to inhibition was a function of the initial rate of Ang II secretion. Tissue samples with a high rate of secretion were less responsive to the inhibitors than tissue that secreted small amounts of Ang II (n = 6). In anesthetized dogs, intra-cavernosal injection of Ang II terminated spontaneous erections, while losartan increased the intracavernosal pressure in a dose dependent manner up to the mean arterial pressure (n = 4).

CONCLUSIONS

The corpus cavernosum produces and secretes physiologically relevant amounts of Ang II. The rate of Ang II secretion can be modulated by pharmacologic agents that regulate cytosolic calcium levels and are used clinically to treat erectile dysfunction. Intracavernosal injection of Ang II causes contraction of cavernosal smooth muscle and terminates spontaneous erection in anesthetized dog, while administration of an Ang II receptor antagonist results in smooth muscle relaxation and thus erection.

Local upregulation of colonic angiotensin II receptors enhances potassium excretion in chronic renal failure

The role of angiotensin II (ANG II) in colonic secretion of K+ was examined in rats with chronic renal failure (CRF). The basal net secretory flux of 86Rb+ (as a tracer for K+) across the CRF distal colon (-0.20 +/- 0.04 mu eq.cm-2.h-1) was reversed to an absorptive flux (0.35 +/- 0.05 mu eq.cm-2.h-1) by injecting the rats with the AT1 receptor antagonist, losartan. A similar result was observed when losartan was added to the CRF colonic tissue in vitro. In contrast, an AT2 receptor antagonist, PD-123319, did not reverse the CRF-induced alterations in Rb+ transport across the short-circuited colonic tissue. Plasma concentrations of ANG II, aldosterone, and K+, as well as the ANG II content of colonic tissues from CRF and normal rats, were similar. However, specific 125I-labeled ANG II binding sites in rat distal colon increased twofold in CRF [maximal specific binding (Bmax) = 28.6 +/- 1.6 fmol/mg protein] compared with normal (Bmax = 15.2 +/- 0.4 fmol/mg protein). These studies suggest that CRF-induced secretion of K+ by the colon is mediated by an upregulation of AT1 receptors present in CRF.

Angiotensin-independent mechanism for aldosterone synthesis during chronic extracellular fluid volume depletion

Wild-type (Agt+/+) and homozygous angiotensinogen deletion mutant (Agt-/-) littermates were placed on normal (NS) or low Na diet (LS) for 2 weeks. Plasma aldosterone levels (P(aldo)) were comparable during NS, and similarly elevated during LS in Agt+/+ and Agt-/-. Moreover, in both, the elevation in P(aldo) was accompanied by marked increase in adrenal zona glomerulosa cells and adrenal P450aldo mRNA. Agt-/- mice were distinguished from Agt+/+ mice by their higher plasma K level, by approximately 1.5 and approximately 3.8 mEq/liter during NS and LS, respectively. Within the Agt-/- group, P(aldo) was directly proportional to plasma K. The importance of K for the hyperaldosteronism during dietary Na restriction was verified by the observation that superimposition of K restriction led to hypotension in Agt+/+ and uniform death in Agt-/- mice along with a reduction in P(aldo) by 75 and 90%, respectively. Thus, suppression of potassium, but not angiotensin, led to a marked attenuation of hyperaldosteronism during dietary Na restriction. Therefore, (a) a powerful angiotensin-independent mechanism exists for the hyperaldosteronism during LS; (b) high K is a central component of this mechanism; (c) contrary to current belief, the tonic effect of high K on aldosterone synthesis and release does not require an intact renin-angiotensin system; and (d) normally, intermediary feedback signals for hyperaldosteronism, i.e., both hypotension and high K, are effectively masked by aldosterone actions.

Presence of renin within intramitochondrial dense bodies of the rat adrenal cortex

It has been suggested that tissue-specific expression of the genes of the renin-angiotensin system (RAS) leads to local generation of angiotensin (ANG) II with specific physiological implications. We demonstrate here that an intracellular RAS exists in adrenal glomerulosa cells; 60 h after bilateral nephrectomy and hemodialysis, renin and prorenin were eliminated from the circulation, whereas intra-adrenal renin content increased (control rats: 2 +/- 0.5 ng ANG I.mg-1.h-1; anephric rats: 25 +/- 2). Thus renin is produced locally within adrenal cells. We obtained immunocytochemical and biochemical evidence for the presence of renin within intramitochondrial dense bodies of the zona glomerulosa. After nephrectomy, dense bodies increased in number, size, and renin content (control rats: 2.5 +/- 0.7 ngANGI.mg-1.h-1; anephric rats: 43 +/- 7). Angiotensin-converting enzyme (ACE) was also present within mitochondria and their dense bodies. In addition, in adrenal cortex of anephric rats, giant dense bodies were observed, which contain renin and strongly react with an anti-angiotensinogen antibody. The localization of renin, ACE, and angiotensinogen at these sites provides new evidence for the existence of an intracellular adrenal RAS.

Study of the rat adrenal renin-angiotensin system at a cellular level

To address the question as to how zona glomerulosa (ZG) cell angiotensin II (Ang II) secretion is regulated, we developed an immuno-cell blot assay to measure its secretion from single cells. We compared these results with those obtained from population studies using a superfusion system. Modulation of Ang II secretion was investigated acutely (by administrating potassium [K+] or captopril) and chronically (by feeding the animals low or high sodium diets). The area of secretory cells, halo areas, and halo intensities varied widely but were highly significantly correlated (P < 0.001) with each other. A disproportionate amount of Ang II was secreted by a small number of large cells. When K+ concentration was increased from 3.6 to 0 mM, superfused ZG cells increased their Ang II secretion 2.32 +/- 0.59-fold. Administration of captopril reduced the K(+)-stimulated Ang II secretion 1.24 +/- 0.07 fold. These findings were reflected in the cell blot assay as a change in the frequency distribution of halo area by K+ and captopril in the same direction as in the population study. In both conditions, the percentage of secretory cells did not change significantly from control. Superfused ZG cells from rats on a low sodium diet secreted 1.85 +/- 0.58-fold more Ang II than cells from sodium-loaded rats (p < 0.05, n = 6). The cell blot assay confirmed these findings with sodium restriction significantly increasing (P < 0.001) both the halo area and its frequency distribution to a larger portion of high secreting cells. However, in contrast to acute treatment with K+ or captopril, the number of secretory cells also doubled. Thus, the individual ZG cell uses two mechanisms to modify Ang II production. In response to acute stimulation and suppression, the amount of Ang II secreted per cell is modified without changing the number of secretary cells. With chronic stimulation, both the amount of Ang II secreted per cell and the number of secretary cells increase.

Morphology and function of the adrenal zona glomerulosa of transgenic rats TGR [mREN2] 27: effects of prolonged sodium restriction

Heterozygous female transgenic rats for the murine Ren-2 gene (TGR) display a high blood pressure, together with a low kidney and high adrenal renin content. The effects of prolonged sodium restriction on the morphology and secretory activity of adrenal zona glomerulosa (ZG) of TGR and their age- and sex-matched Sprague-Dawley control rats (SDR) were investigated. Under basal conditions, TGR had a moderately hypertrophic ZG, that showed a significantly higher secretion of 18-hydroxylated (18OH) steroids: 18-hydroxy-11-deoxycorticosterone (18OH-DOC), 18-hydroxycorticosterone (18OH-B) and aldosterone (ALDO); ZG cells of TGR showed angiotensin II (AII)-binding site concentrations and ALDO secretory responses to AII similar to those of SDR ZG cells. Prolonged sodium restriction increased plasma ALDO level in both SDR and TGR, and significantly raised the volume of ZG. ZG hypertrophy was due to the increase in both the number and average volume of its parenchymal cells. The secretion of 18OH-steroids was markedly enhanced in both groups of rats; however, in TGR this rise was exclusively due to increases of 18OH-DOC and 18OH-B, while in SDR also ALDO production was enhanced. The yield of non-18OH-steroids was not affected. 11-Dehydrocorticosterone production was not changed in SDR, but doubled in TGR. ZG cells of sodium-restricted SDR and TGR displayed similar increases in their AII-binding site concentration and ALDO secretory response to AII. In conclusion, our present findings confirm that TGR possess a hypertrophic ZG and an elevated secretory capacity o 18OH-steroids, but show only slight differences in ZG and ZG-cell responses to prolonged sodium deprivation.

The distribution of angiotensin II type 1 receptors, and the tissue renin-angiotensin systems

Since its discovery, the functions of the renin-angiotensin system (RAS) have attracted a great deal of attention, and the roles it plays under normal conditions, and in disease, acquire a deepening significance with every year. In general, the RAS has been considered largely in terms of its roles in sodium and potassium homeostasis and the regulation of blood pressure. The continued acquisition of information on the distribution of angiotensin receptors, however, emphasizes that our interpretation needs to be widened, and it is now clear that angiotensin II has an array of functions in the tissues, which are unrelated to its systemic roles. This paracrine function is brought about by the existence of complete, localized tissue RASs, which respond to physiological demand independently from the systemic system.

Neuropeptides in the adrenal gland: distribution, localization of receptors, and effects on steroid hormone synthesis

In this review we defined and classified the neuropeptides (NPs) related to the adrenal gland, according to Palkovits (Frontiers Neuroendocrinol 10:1 1988). The concentration (RIA) and distribution (immunohistochemistry) of NPs, as well as the localization of the receptors (radioligand studies) were summarized. Direct effects of NPs on aldosterone and corticosterone synthesis obtained by in vivo, in situ perfusion, and in vitro experimental approaches were reviewed. Data (from different rat strains and genders) for 35 NPs are presented.

The relationship between the adrenal tissue renin-angiotensin system, internalization of the type I angiotensin II receptor (AT1) and angiotensin II function in the rat adrenal zona glomerulosa cell

Many data suggest that the elements of the tissue renin-angiotensin system (RAS) in the adrenal cortex are mostly located in the zona glomerulosa. The relationship of this paracrine/autocrine system with the cellular localization of the angiotensin II (AII) receptor has not bee clarified. Using a specific monoclonal antibody (6313/G2) to the first extracellular domain of the type 1 receptor (AT1), we show here that most of the receptor is internalized in the rat glomerulosa cell. This may result from tonic stimulation by the tissue RAS, and consequent permanent receptor occupancy. When viable glomerulosa cells are incubated with 6313/G2, the receptor is transiently concentrated on the cell surface, and aldosterone output is stimulated. This stimulated output is enhanced by neither threshold nor maximal stimulatory concentrations of AII amide, although the antibody does not inhibit AII binding to the receptor. The antibody directly stimulates inositol trisphosphate (IP3) generation, but, while having no intrinsic action on protein kinase C (PKC) activation, significantly inhibits the PKC response to angiotensin II. The data suggest that although the receptor is mostly internalized, recycling to the plasma membrane is constitutive, or regulated by unknown factors. Retention of the AT1 receptor in the membrane is alone enough to allow sufficient G protein interaction to generate maximal steroidogenic effects, through IP3 generation. PKC activation induced by angiotensin II has no bearing on steroidogenesis in the dispersed glomerulosa cell system.

Converting enzyme inhibition and renal tissue angiotensin II in the rat

Multiple observations suggest local control of renal function via an intrarenal renin-angiotensin system, including evidence for local angiotensin (Ang) II production. Our first goal was to examine renal tissue Ang I:Ang II relations to ascertain whether Ang II formation differs in the circulation and in renal tissue. We have recently shown an authentic Ang II/Ang I ratio of 1.5:1 in renal lymph, the opposite of the Ang II:Ang I relation in plasma. Our second goal was to examine the influence of maximal angiotensin converting enzyme inhibition on these relations in plasma and in renal tissue. We used two converting enzyme inhibitors with differing lipid solubility, on the premise that tissue penetration and action might differ on that basis. We measured Ang I and Ang II in plasma and renal tissue of rats given an intravenous dose of either vehicle, enalapril, or ramipril, over a wide dose range, from 0.1 to 10.0 mg/kg i.v. Renal and plasma angiotensin concentrations were measured by high-performance liquid chromatography and radioimmunoassay. Whereas the Ang I concentration in normal rat plasma (273 +/- 84 fmol/mL) was over threefold the plasma Ang II concentration (83 +/- 12 fmol/mL), the ratio was reversed in the kidney (Ang II, 178 +/- 12 versus Ang I, 91 +/- 3 fmol/g; P < .001). Although ramipril and enalapril induced an indistinguishable dose-related acute fall in blood pressure and plasma Ang II concentration, lower enalapril doses were less effective in reducing renal tissue Ang I:Ang II conversion and Ang II concentration (P < .025).(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of an angiotensin II receptor antagonist, CV-11974, and its prodrug, TCV-116, on production of aldosterone

In dispersed rabbit adrenocortical glomerulosa cells, a non-peptide angiotensin II (AT1) receptor antagonist, CV-11974 (10(-10)-10(-5) M), competitively inhibited angiotensin II- or angiotensin III-stimulated aldosterone production, whereas PD123177, an angiotensin AT2 receptor antagonist, did not. CV-11974 inhibited aldosterone production induced by 4 mM K+ but not by 12 mM K+. CV-11974 had no effect on adrenocorticotropic hormone-stimulated aldosterone or corticosterone production, but inhibited angiotensin II-stimulated corticosterone production. In the rat, TCV-116, the prodrug of CV-11974, (0.1 and 1 mg/kg, p.o.) markedly reduced the elevation of both plasma aldosterone concentration and blood pressure induced by i.v. infusion of angiotensin II. In spontaneously hypertensive rats, TCV-116 at daily p.o. doses of 0.1, 1 and 10 mg/kg for 2 weeks caused a dose-dependent reduction of blood pressure and plasma aldosterone concentration without affecting plasma corticosterone. Thus, TCV-116 inhibited the induction of aldosterone production by not only exogenous but also endogenous angiotensin II.

Responses to converting enzyme and renin inhibition. Role of angiotensin II in humans

We compared the renal vascular responses to angiotensin converting enzyme inhibition and renin inhibition to assess the influence of angiotensin II (Ang II). We examined the renal and endocrine responses to the renin inhibitor enalkiren, to captopril, and to placebo in nine healthy and nine hypertensive men on a 10-mmol sodium diet. Ang II was infused to assess effects of the agents on renal and adrenal responsiveness to Ang II. Plasma Ang II concentration was suppressed similarly with enalkiren and captopril--an identical level of blockade was achieved. Although renal plasma flow was stable during placebo, a substantial rise was seen with both enalkiren (+133 +/- 26 mL/min per 1.73 m2) and captopril (+99.4 +/- 22.6). There was remarkable intrasubject concordance between the renal plasma flow responses to renin inhibition and converting enzyme inhibition (r = .90, P < .004). The vasodilator response to both agents correlated inversely with the fall in renal plasma flow induced by Ang II alone (r = -.66, P < .05). Both agents significantly enhanced the renal vascular response to Ang II (P = .01), and, furthermore, the renal vasodilator response to captopril predicted the potentiation of the renal plasma flow response to Ang II after either agent (enalkiren: r = .91, P < .001; captopril: r = .56, P < .05). Concordance of the maximal renal plasma flow response to the two agents appeared in the hypertensive men as well. Our results indicate that the acute renal response to captopril largely reflects a reduction in Ang II formation.(ABSTRACT TRUNCATED AT 250 WORDS)

Autocrine release of angiotensin II mediates stretch-induced hypertrophy of cardiac myocytes in vitro

Hypertrophy is a fundamental adaptive process employed by postmitotic cardiac and skeletal muscle in response to mechanical load. How muscle cells convert mechanical stimuli into growth signals has been a long-standing question. Using an in vitro model of load (stretch)-induced cardiac hypertrophy, we demonstrate that mechanical stretch causes release of angiotensin II (Ang II) from cardiac myocytes and that Ang II acts as an initial mediator of the stretch-induced hypertrophic response. The results not only provide direct evidence for the autocrine mechanism in load-induced growth of cardiac muscle cells, but also define the pathophysiological role of the local (cardiac) renin-angiotensin system.

In vivo regulation of gene expression of enzymes controlling aldosterone synthesis in rat adrenal

We studied the effect of alterations in the intake of sodium and potassium as well as changes in circulating adrenocorticotropin (ACTH) on the expression of the two rate-limiting systems of aldosterone formation in the rat. Low sodium and high potassium intake promoted time-dependent increases in the zona glomerulosa cytochrome P450scc (P450scc) and cytochrome P450c11 (P450c11) protein and mRNA levels, but no changes were found in the zona fasciculata-reticularis. In addition, these responses were associated with markedly elevated transcriptional activities. To further define the contribution of P450c11 and P450c18 (aldosterone synthase) in response to these differing intakes, we evaluated their mRNA levels using gene-specific oligonucleotide probes. P450c18 mRNA was restricted to the zona glomerulosa, whereas P450c11 mRNA was detected in both zona glomerulosa and zona fasciculata-reticularis. Furthermore, only P450c18 mRNA was induced by both low sodium or high potassium intake, as P450c11 mRNA levels remained unchanged. Captopril, an inhibitor of angiotensin-I converting enzyme, abolished the enhancing effects of the low sodium regimen on P450scc and P450c18 mRNA levels. Captopril also suppressed the augmentation of P450c18 mRNA observed with potassium supplementation but had no effect on P450scc mRNA levels. When the hypocholesterolemic drug 4-aminopyrazolopyrimidine (4-APP) was administered to rats for 3 consecurive days, both the level of plasma ACTH and the adrenal content of mRNA encoding P450scc increased 24 h post final injection. The coadministration of dexamethasone with 4-APP prevented these increases. In contrast, the mRNA content of P450c11 remained at control levels. In conclusion, this work demonstrates that variations in the intake of sodium and potassium act on the expression of the CYP11B2 gene, but not on that of the CYP11B1 gene. Moreover angiotensin-II (A-II) is an important factor in this mechanism of action. Both ions also enhance the expression of the CYP11A1 gene. A-II appears to participate in the mechanism of action of the low sodium intake at this level. Another mechanism is postulated for the action of potassium supplementation since captopril did not prevent the increased expression of the CYP11A1 gene. In addition, the fact that 4-APP enhanced the mRNA level of P450scc but not that of P450c, also demonstrates different regulation of the P450s involved at the early and final steps of aldosteroone formation in the rat adrenal zona glomerulosa in vivo.

Adrenal and circulating renin-angiotensin system in stroke-prone hypertensive rats

The plasma and adrenal renin-angiotensin system in stroke-prone spontaneously hypertensive rats (SHRSP) and Wistar-Kyoto (WKY) rats were examined in animals at 5, 11, 18, and 25 weeks of age. Plasma active renin was significantly increased in 18- and 25-week-old SHRSP with impaired renal function, whereas there was no difference in the plasma prorenin level or renal renin content between the two strains at all ages examined. Thus, the rate of activation of prorenin seems to be enhanced in the kidney of SHRSP with malignant hypertension. Adrenal renin contents were severalfold higher in SHRSP than WKY rats at all ages. However, adrenal angiotensin peptides were not increased in SHRSP aged 5 and 11 weeks. In 18-week-old SHRSP, adrenal angiotensin II (Ang II) and III (Ang III) levels were fourfold and 1.8-fold higher, respectively, than in WKY rats, accompanied by 1.5-fold higher plasma aldosterone. Increased adrenal angiotensin and plasma aldosterone were also found in 25-week-old SHRSP. Zonal distribution studies indicated that the elevated Ang II and III in SHRSP were derived mainly from the capsular tissue (the zona glomerulosa). To examine the contribution of circulating angiotensin to the adrenal angiotensin content, effects of bilateral nephrectomy on adrenal angiotensin and renin were examined in 18-week-old rats. At 24 hours after nephrectomy, plasma angiotensin, prorenin, and active renin were decreased to almost negligible concentrations. Conversely, in both adrenal capsular and decapsular tissues of SHRSP and WKY rats, neither angiotensin nor renin was significantly decreased after nephrectomy. These results suggest that the increase in adrenal capsular Ang II contents in SHRSP may be partly due to an enhanced local production of Ang II.

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)

Influence of captopril on adrenal cytochrome P-450s and adrenodoxin expression in high potassium or low sodium intake

To investigate the role of the renin-angiotensin system in steroidogenic enzyme expression, the angiotensin-I converting enzyme inhibitor captopril was administered in conjunction with high potassium (K+) or low (Na+) intake to rats for a 7-day period. Northern blot analysis of adrenocortical zona glomerulosa RNA revealed that sodium restriction markedly increased mRNA production of P-450scc (3.1-fold) and P-450(11 beta) (3.4-fold) as well as of the electron donor adrenodoxin (2.0-fold). Captopril combined to the low Na+ diet led to suppression of these effects and, as also seen with captopril alone, further diminished P-450(11 beta) mRNA levels below controls. These responses were accompanied by parallel changes in respective protein levels of the enzymes as indicated by Western blot analyses. Captopril was also shown to inhibit the K(+)-stimulated levels of P-450(11 beta) mRNA (3.3-fold) and protein (1.4-fold) beneath control values (0.6- and 0.8-fold, respectively). On the other hand, increased P-450scc mRNA and protein levels by K+ loading were not affected by captopril treatment. No response was observed in any steroidogenic enzyme expression in zona fasciculata-reticularis following either diet with or without captopril. Thus, the inhibitory effect of captopril on stimulated steroidogenesis seemed to be mediated in part through transcriptional regulation of P450s. In addition, it appeared that P-450(11 beta) expression might be under the control of the renin-angiotensin system in both high K+ and low Na+ diets as opposed to the K+ stimulation of P-450scc where other mechanisms seemed to be involved.

Dissociation in plasma renin and adrenal ANG II and aldosterone responses to sodium restriction in rats

In rats, plasma renin activity (PRA) increases sharply, reaching a plateau within hours of sodium restriction. Plasma aldosterone increases gradually, not reaching a plateau for 1-2 days. To determine whether this dissociation is secondary to the time needed to modify adrenal sensitivity to angiotensin II (ANG II) and to assess the role of locally produced ANG II in this process, rats were salt restricted for 0-120 h. Plasma hormone levels were assessed, adrenal ANG II was measured, and basal and ANG II (1 x 10(-8) M)-stimulated steroidogenesis were determined in vitro. Although PRA attained an elevated plateau within 8 h, plasma aldosterone did not peak until after 48 h of sodium depletion. The in vitro aldosterone sensitivity to exogenous ANG II was not apparent until rats had been salt restricted for 16 h. A plateau (4-fold increase above the ANG II response on high salt) was achieved between 24 and 48 h. Adrenal ANG II also exhibited a similar delayed response that correlates significantly with changes in aldosterone biosynthesis and late pathway activity. Thus the dissociation between PRA and plasma aldosterone may be secondary to a lag in the zona glomerulosa's (ZG) steroidogenic response to ANG II as well as a parallel lag in tissue ANG II production, suggesting that changes in tissue ANG II may mediate ZG sensitivity to ANG II during sodium deprivation.