Induction of 5-aminolevulinate synthase by activators of steroid biosynthesis

Different cytochromes P450 are involved in steroid biosynthesis. These cytochromes have heme as the prosthetic group. We previously reported that ACTH, an activator of glucocorticoid biosynthesis in adrenal, requires heme biosynthesis for a maximal response. In the present study, we investigated the effect of ACTH, and the effect of two activators of the adrenal mineralocorticoid synthesis, endothelin-1 and low sodium diet on 5-aminolevulinate-synthase (ALA-s) mRNA. ALA-s is the rate-limiting enzyme in heme biosynthesis. It was found that infusion of rats with ACTH for 1 h caused an increase of adrenal ALA-s mRNA and activity accompanied by an increase in plasma corticosterone. CYP21, a cytochrome involved in the synthesis of both corticosterone and aldosterone, was not modified at the RNA level in adrenal glands by 1 h of ACTH infusion. Consistently, infusion of endothelin-1 for 1 h increased ALA-s mRNA and aldosterone content in adrenal gland without modifying CYP21 mRNA levels. To study if ALA-s is also regulated by the main physiological stimuli that increase adrenal mineralocorticoid secretion, we fed rats with low salt diet for 2 or 15 days. Low salt diet treatment increased adrenal gland ALA-s mRNA levels. On the other hand, the rapid stimulation of ALA-s mRNA by ACTH which acts through cyclic AMP was confirmed in H295R human adrenocortical cells, the only human adrenal cell line that has a steroid secretion pattern and regulation similar to primary cultures of adrenal cells. Our findings suggest that the acute activation of adrenal steroidogenic cytochromes by trophic hormones involves an increase in heme biosynthesis which will favor the production of active cytochromes.     

Effect of atrial natriuretic factor on the plasma aldosterone response to potassium infusion in rats--in vivo study

Previous in vitro studies have shown that atrial natriuretic factor inhibits the secretion of aldosterone stimulated by AII, ACTH, and potassium in adrenal cell suspensions. The present study investigated the effects of atriopeptin II on the plasma aldosterone response to a potassium infusion in conscious unrestrained rats in vivo. The infusion of potassium chloride solution increased plasma aldosterone level from 20.4 +/- 3.7 to 168.4 +/- 27.3 ng/dl. The simultaneous administration of atriopeptin II reduced the increase in plasma aldosterone level (16.0 +/- 2.1 to 63.3 +/- 10.4 ng/dl). There was no significant difference in the plasma renin activity, corticosterone, or serum potassium levels between the two groups. These results suggest that atriopeptin II may be important in the regulation of aldosterone secretion.     

Metoclopramide fails to stimulate aldosterone secretion and inhibits serotonin-mediated aldosterone secretion in the rat

The acute and chronic effects of metoclopramide on aldosterone secretion in the rat model were examined. Metoclopramide 50 micrograms iv in dexamethasone-treated rats did not increase plasma aldosterone concentration. Chronic infusion of metoclopramide (72 micrograms/hr) over 5 days also did not show any increase in the plasma or urinary aldosterone concentration when compared with control rats. Metoclopramide in vitro showed no effect on aldosterone secretion from rat adrenal capsular cells but it inhibited serotonin-mediated aldosterone secretion from the same cells significantly.     

Effect of atrial natriuretic peptide on adrenal renin and aldosterone

The effect of atrial natriuretic peptide (ANP) on adrenal renin and aldosterone was investigated in anesthetized rats. Under pentobarbital anesthesia 40 mg/kg), intravenous infusion of ANP (0.25 micrograms/kg/min) for 45 min failed to alter the adrenal renin, adrenal aldosterone, and plasma aldosterone (PA). In this condition, intraperitoneal injection of ACTH (10 micrograms/kg) significantly increased the adrenal renin (from 2.4 +/- 0.1 to 5.0 +/- 0.08 ng/mg protein/h, P less than 0.05), adrenal aldosterone (from 13.6 +/- 1.3 to 22.7 +/- 2.3 ng/mg protein, P less than 0.01) and PA (from 59.8 +/- 5.8 to 75.5 +/- 7.4 ng/dl, P less than 0.05), respectively. Under ACTH stimulation, ANP infusion induced significant decreases in adrenal renin (from 5.0 +/- 0.08 to 2.8 +/- 0.2 ng/mg protein/h, P less than 0.05), adrenal aldosterone (from 22.7 +/- 2.3 to 16.2 +/- 1.8 ng/mg protein, P less than 0.05) and PA (from 75.5 +/- 7.4 to 61.6 +/- 4.9 ng/dl). These results suggest a possible role for adrenal renin in the mechanism underlying the inhibitory effect of ANP on aldosterone production in vivo.     

Angiotensin-II-directed glomerulosa cell function in fetal adrenal cells

These studies were undertaken to examine the role of angiotensin II (A-II) in the regulation of adrenal glomerulosa cell differentiation. We were interested particularly in the ability of A-II to support aldosterone production in fetal adrenal cells. Many in vitro studies on acute A-II stimulation of aldosterone synthesis in adrenocortical cells have been documented. However, it is the long-term modification of steroid-metabolizing enzyme expression that leads to the formation and release of specific adrenal steroids. Herein, we used primary cultures of fetal bovine adrenal (FBA) cells to examine the effects of A-II on aldosterone production and the expression of aldosterone synthase cytochrome P450 (P450c18). A-II treatment caused the primary cultures to maintain glomerulosa cell functions. Cells treated for 3 days with A-II increased aldosterone production by 10-fold. A-II stimulation of aldosterone production occurred rapidly (within 30 min) and in a dose-dependent manner. In addition, A-II enhanced the activity of P450c18, the enzyme responsible for conversion of corticosterone to aldosterone. A-II also suppressed ACTH-promoted cortisol production, while increasing ACTH-stimulated release of aldosterone. It appears that these effects of chronic treatment with A-II were mediated through an A-II type 1 (AT₁) receptor since the AT₁ receptor antagonist, Dup753, blocked aldosterone production and the increased P450c18 activity. Receptor binding studies suggest that FBA cells possess approx. 110,000 AT₁ binding sites/cell with K_d = 1.8 × 10⁻⁹ M. Via AT₁ receptors, A-II was able to stimulate both inositol phosphates and cAMP production. The stimulation of cAMP production, however, was much less than seen following ACTH treatment. These data give support to the hypothesis that A-II is involved in the differentiation of fetal adrenal cells into glomerulosa cells. This process appears to be mediated through regulation of steroid-metabolizing enzyme expression and the activation of steroid production.     

A new transgenic rat model overexpressing the angiotensin II type 2 receptor provides evidence for inhibition of cell proliferation in the outer adrenal cortex

This study aimed to elucidate the role of the AT(2) receptor (AT(2)R), which is expressed and upregulated in the adrenal zona glomerulosa (ZG) under conditions of increased aldosterone production. We developed a novel transgenic rat (TGR; TGRCXmAT(2)R) that overexpresses the AT(2)R in the adrenal gland, heart, kidney, brain, skeletal muscle, testes, lung, spleen, aorta, and vein. As a consequence the total angiotensin II (Ang II) binding sites increased 7.8-fold in the kidney, 25-fold in the heart, and twofold in the adrenals. The AT(2)R number amounted to 82-98% of total Ang II binding sites. In the ZG of TGRCXmAT(2)R, the AT(2)R density was elevated threefold relative to wild-type (WT) littermates, whereas AT(1)R density remained unchanged. TGRCXmAT(2)R rats were viable and exhibited normal reproduction, blood pressure, and kidney function. Notably, a slightly but significantly reduced body weight and a moderate increase in plasma urea were observed. With respect to adrenal function, 24-h urinary and plasma aldosterone concentrations were unaffected in TGRCXmAT(2)R at baseline. Three and 14 days of Ang II infusion (300 ng·min(-1)·kg(-1)) increased plasma aldosterone levels in WT and in TGR. These changes were completely abolished by the AT(1)R blocker losartan. Of note, glomerulosa cell proliferation, as indicated by the number of Ki-67-positive glomerulosa cells, was stimulated by Ang II in TGR and WT rats; however, this increase was significantly attenuated in TGR overexpressing the AT(2)R. In conclusion, AT(2)R in the adrenal ZG inhibits Ang II-induced cell proliferation but has no obvious lasting effect on the regulation of the aldosterone production at the investigated stages.     

Endothelin-1 stimulates mitotic activity in the zona glomerulosa of the rat adrenal cortex.

Subcutaneous infusion with endothelin-1 (ET-1; 30 pM min-1) for 24 h induced a 9-fold increase in the mitotic index (% of metaphase-arrested cells) of rat adrenal zona glomerulosa (ZG). Infusions with adrenocorticotrophic hormone (ACTH) angiotensin-II (ANG-II) or arginine vasopressin (AVP) (30 pM min-1/24 h) raised the ZG mitotic index 13-fold, 9-fold and 10-fold, respectively. Combined infusion with ET-1 and ACTH increased the ZG mitotic index 20-fold, while the effects of ET-1 and ANG-II or AVP were not additive. These findings suggest that ET-1 exerts a strong proliferogenic effect on the rat ZG, by a mechanism probably similar to that underlying the adrenoglomerulotrophic actions of ANG-II and AVP.     

Evidence for a paracrine role of adrenomedullin in the physiological resetting of aldosterone secretion by rat adrenal zona glomerulosa

Adrenomedullin (ADM) has been recently found to directly inhibit agonist-stimulated aldosterone secretion by dispersed zona glomerulosa (ZG) cells and to stimulate basal catecholamine release by adrenomedullary fragments. In light of the fact that catecholamines enhance aldosterone secretion acting in a paracrine manner, we have investigated whether these two effects of ADM may interact when the integrity of the adrenal gland is preserved. ADM increased basal aldosterone output by adrenal slices containing a core of adrenal medulla, and the effect was blocked by the beta-adrenoceptor antagonist l-alprenolol. In contrast, ADM evoked a moderate inhibition of K(+)-stimulated aldosterone production, and the blockade was complete in the presence of l-alprenolol. The in vivo bolus injection of ADM did not affect plasma aldosterone concentration (PAC) in rats under basal conditions. Conversely, when rat ZG secretory function was enhanced (by sodium restriction or infusion with angiotensin-II [ANG-II]) or depressed (by sodium loading or infusion with the angiotensin-converting enzyme inhibitor captopril), ADM evoked a sizeable decrease or increase in PAC, respectively. The prolonged infusion with the ADM receptor antagonist ADM(22-52) caused a further enhancement of PAC in sodium-restricted or ANG-II-treated rats, and a further moderate decrease of it in sodium-loaded or captopril-administered animals. RIA showed that ADM plasma concentration did not exceed a concentration of 10(-11) M in any group of animals. Under basal conditions, ADM adrenal content was 1.2-2.0 pmol/g, which may give rise to local concentrations higher than 10(-8) M (i.e. well above the minimal effective ones in vitro). ADM adrenal concentration was markedly increased (from two-fold to three-fold) by both ZG stimulatory and suppressive treatments. Collectively, our findings suggest that in vivo 1) ADM, in addition to directly inhibit aldosterone secretion, may enhance it indirectly by eliciting catecholamine release, the two actions annulling each other under basal conditions; 2) under conditions leading to enhanced aldosterone secretion, the direct inhibitory effect of ADM prevails over the indirect stimulatory one, and the reverse occurs when aldosterone secretion is decreased; and 3) the modulatory action of ADM on the aldosterone secretion has a physiological relevance, endogenous ADM being locally synthesized in adrenals.     

Mineralocorticoid receptor antagonism protects the aorta from vascular smooth muscle cell proliferation and collagen deposition in a rat model of adrenal aldosterone-producing adenoma

The number of patients with adrenal aldosterone-producing adenomas (APAs) has gradually increased. However, even after adenoma resection, some patients still suffer from high systolic blood pressure (SBP), which is possibly due to great arterial remodeling. Moreover, mineralocorticoid receptors (MRs) were found to be expressed in vascular smooth muscle cells (VSMCs). This study aims to determine whether MR antagonism protects the aorta from aldosterone-induced aortic remolding. Male rats were subcutaneously implanted with an osmotic minipumps and randomly divided into four groups: control; aldosterone (1 μg/h); aldosterone plus a specific MR antagonist, eplerenone (100 mg/kg/day); and aldosterone plus a vasodilator, hydralazine (25 mg/kg/day). After 8 weeks of infusion, aortic smooth muscle cell proliferation and collagen deposition, as well as the MDM2 and TGF-β1 expression levels in the aorta, were examined. Model rats with APAs were successfully constructed. Compared with the control rats, the model rats exhibited (1) marked SBP elevation, (2) no significant alteration in aortic morphology, (3) increased VSMC proliferation and MDM2 expression in the aorta, and (4) enhanced total collagen and collagen III depositions in the aorta, accompanied with up-regulated expression of TGF-β1. These effects were significantly inhibited by co-administration with eplerenone but not with hydralazine. These findings suggested that specific MR antagonism protects the aorta from aldosterone-induced VSMC proliferation and collagen deposition.     

Central infusion of aldosterone synthase inhibitor prevents sympathetic hyperactivity and hypertension by central Na+ in Wistar rats

In Wistar rats, increasing cerebrospinal fluid (CSF) Na+ concentration ([Na+]) by intracerebroventricular (ICV) infusion of hypertonic saline causes sympathetic hyperactivity and hypertension that can be prevented by blockade of brain mineralocorticoid receptors (MR). To assess the role of aldosterone produced locally in the brain in the activation of MR in the central nervous system (CNS), Wistar rats were infused ICV with artificial CSF (aCSF), Na+ -rich (800 mmol/l) aCSF, aCSF plus the aldosterone synthase inhibitor FAD286 (100 microg x kg(-1) x day(-1)), or Na+ -rich aCSF plus FAD286. After 2 wk of infusion, rats treated with Na+ -rich aCSF exhibited significant increases in aldosterone and corticosterone content in the hypothalamus but not in the hippocampus, as well as increases in resting blood pressure (BP) and sympathoexcitatory responses to air stress, and impairment of arterial baroreflex function. Concomitant ICV infusion of FAD286 prevented the Na+ -induced increase in hypothalamic aldosterone but not corticosterone and prevented most of the increases in resting BP and sympathoexcitatory and pressor responses to air stress and the baroreflex impairment. FAD286 had no effects in rats infused with ICV aCSF. In another set of rats, 24-h BP and heart rate were recorded via telemetry before and during a 14-day ICV infusion of Na+ -rich aCSF with or without FAD286. Na+ -rich aCSF without FAD286 caused sustained increases ( approximately 10 mmHg) in resting mean arterial pressure that were absent in the rats treated with FAD286. These data suggest that in Wistar rats, an increase in CSF [Na+] may increase the biosynthesis of corticosterone and aldosterone in the hypothalamus, and mainly aldosterone activates MR in the CNS leading to sympathetic hyperactivity and hypertension.     

Effects of prolonged infusion with endothelin-1 on the function and morphology of rat adrenal cortex

A week of SC infusion with endothelin-1 (ET-1) (0.2 microgram.kg-1.hr-1) lowered PRA and raised plasma aldosterone (A) concentration in rats. Kalaemia and the plasma levels of ACTH and corticosterone (B) were not affected. Prolonged ET-1 administration caused a notable hypertrophy of zona glomerulosa (ZG) and its parenchymal cells, without inducing any apparent change in zona fasciculata. Stereology showed that ZG cell hypertrophy was mainly due to the increase in the volume of the mitochondrial compartment and to the proliferation of smooth endoplasmic reticulum (i.e., the two organelles in which the enzymes of steroid synthesis are contained). Isolated ZG cells from ET-1-infused animals evidenced a notable enhancement in their basal production of A and B. The secretory responses of ZG cells to the maximal effective concentrations of their three main stimulators (ACTH, angiotensin-II and K+) displayed comparable increases. These findings indicate that ET-1, when chronically administered, is able to specifically enhance the growth and steroidogenic capacity of rat ZG, and suggest that the mechanism underlying this ET-1 effect involves stimulation of the de novo synthesis of both the steroidogenic enzymes and the membrane framework in which they are located.     

Atrial natriuretic factor is unlikely to be involved in the reduced aldosterone production in the Brattleboro rat

We have previously reported that basal and stimulated aldosterone production in Brattleboro rat (DI) lacking hypothalamic arginine vasopressin is lower than that observed in control Long-Evans rat (LE). In the present study, we investigated the secretion under various experimental conditions, adrenal binding sites, and the aldosterone-inhibiting effect of atrial natriuretic factor (ANF). In the conscious resting state, the plasma ANF concentration was similar between LE and DI rats. Pentobarbital anaesthesia (5 mg/100 g body wt.) reduced the plasma ANF concentration equally in both groups, with or without captopril pretreatment. Morphine (10 mg/100 g body wt.) increased ANF secretion dramatically and equally in the two groups of pentobarbital anaesthetized (2 mg/100 g body wt.) rats. In dexamethasone pretreated-pentobarbital anaesthetized rats, a concurrent i.v. ANF infusion (50 ng/min) did not change significantly the corticosterone response to ACTH (1-24) (1 mI.U./100 g body wt.) but steeply depressed ACTH-induced aldosterone production to a similar extent between DI and LE rats. A single class of adrenal ANF receptor sites was found with a similarity in high affinity and maximum binding capacity between the two groups of rats. Taken together, these results suggest that the reduced aldosterone production by Brattleboro rat adrenals is unlikely to be related to the inhibitory effect of ANF.     

Effect of Swimming on the Production of Aldosterone in Rats

It has been demonstrated that exercise is one of the stresses known to increase the aldosterone secretion. Both potassium and angiotensin II (Ang II) levels are shown to be correlated with aldosterone production during exercise, but the mechanism is still unclear. In an in vivo study, male rats were catheterized via right jugular vein (RJV), and divided into four groups namely water immersion, swimming, lactate infusion (13 mg/kg/min) and pyruvate infusion (13 mg/kg/min) groups. Each group was treated for 10 min. Blood samples were collected at 0, 10, 15, 30, 60 and 120 min from RJV after administration. In an in vitro study, rat zona glomerulosa (ZG) cells were challenged by lactate (1–10 mM) in the presence or absence of Ang II (10⁻⁸ M) for 60 min. The levels of aldosterone in plasma and medium were measured by radioimmunoassay. Cell lysates were analyzed by immunoblotting assay. After exercise and lactate infusion, plasma levels of aldosterone and lactate were significantly higher than those in the control group. Swimming for 10 min significantly increased the plasma Ang II levels in male rats. Administration of lactate plus Ang II significantly increased aldosterone production and enhanced protein expression of steroidogenic acute regulatory protein (StAR) in ZG cells. These results demonstrated that acute exercise led to the increase of both aldosterone and Ang II secretion, which is associated with lactate action on ZG cells and might be dependent on the activity of renin-angiotensin system.     

Evidence for direct inhibitory effects of dopamine on zona glomerulosa secretion of 18-hydroxycorticosterone in rhesus monkeys

This study was designed to more selectively investigate the dopaminergic regulation of 18-hydroxycorticosterone (18-OHB) and aldosterone production by the adrenal zona glomerulosa. Mature rhesus monkeys received either an infusion of dopamine (2 micrograms/kg/min) or 5% dextrose (0.2 ml/min) over a 60 min period (N=6). Dopamine had no effect on plasma levels of renin activity, cortisol, corticosterone, aldosterone or blood pressure. However, dopamine suppressed (p less than 0.05) plasma 18-OHB levels from a baseline of 31.6 +/- 3.5 ng/dl to 23.6 +/- 2.1 ng/dl at 60 min after onset of infusion. This observation is in agreement with some studies in humans but differs from others in which no depression in 18-OHB was observed following dopamine infusion. Dopamine infusion markedly (p less than 0.001) suppressed plasma PRL levels by 30 min after onset of infusion. Corticosteroid responses to metoclopramide (200 micrograms/kg) after dexamethasone 1 mg im every 6 h X 5 days or placebo treatment (vehicle im every 6 h X 5 days) was then evaluated. Dexamethasone significantly suppressed basal cortisol, corticosterone, 18-OHB and aldosterone. Although dexamethasone blunted the prolactin response, it did not inhibit the aldosterone response to metoclopramide. The 18-OHB response to metoclopramide was increased (p less than 0.01) following dexamethasone treatment. Following dexamethasone suppression, 18-OHB levels were still lowered (p less than 0.05) by dopamine infusion. These results suggest that dopamine selectively inhibits zona glomerulosa production of 18-OHB and aldosterone in rhesus monkeys.     

Norbormide enhances late steps of steroid-hormone synthesis in rat and mouse adrenal cortex

Norbormide (N) is a vasoconstrictor agent, which acts selectively on the peripheral arteries of the rat, through the activation of the phospholipase C (PLC) cascade and the stimulation of Ca(2+) entrance in the vascular myocytes. Several endogenous vasoconstrictor agent (e.g. angiotensin-II (ANG-II) and endothelin-1 (ET-1)), that stimulate PLC pathway, are also able to enhance aldosterone secretion by the adrenal gland. Hence, we examined the effects of norbormide ((0.5, 1.0 or 5) x 10(-5)M) on corticosteroid-hormone secretion from adrenal slices of rats and mice. Quantitative HPLC assay showed that under basal conditions rat and mouse adrenal quarters secreted progesterone (PROG), 11-deoxycorticosterone (DOC), 18-hydroxy-DOC (18OH-DOC), corticosterone (CORT), 18-hydroxy-corticosterone (18OH-CORT) and aldosterone (ALDO), as well as large amounts of pregnenolone (PREG) when its metabolism was blocked by 10(-5)M cyanoketone. Norbormide concentration-dependently raised the secretion of all post-DOC steroids assayed, decreased progesterone and DOC production, and did not affect pregnenolone release. In conclusion, norbormide is able to enhance late steps of steroid synthesis, i.e. those leading to the transformation of DOC to corticosterone and aldosterone, without affecting early steps. This is an interesting finding because the other main endogenous adrenal secretagogues are known to stimulate both early and late steps of steroid synthesis. The mechanism underlying the selective activating action of norbormide on 11beta- and 18-hydroxylation remains to be investigated.     

Proopiomelanocortin-derived peptides, phosphoinositides, cAMP, and aldosterone secretion

Since the intracellular messengers of various proopiomelanocortin-derived peptides remain ambiguous at best, we have investigated the possible involvement of phosphoinositide metabolism in aldosterone secretion evoked by alpha-MSH, beta-LPH, as well as ACTH in rat and calf adrenal glomerulosa cells. We have also examined the cAMP responses in the adrenal glomerulosa cells to alpha-MSH comparing it with those of ACTH. Our results showed that neither alpha-MSH, beta-LPH, nor ACTH increased inositol triphosphate (IP3) or other inositol phosphates in adrenal glomerulosa cells while increasing aldosterone secretion from the same cells. Angiotensin II, known to cause hydrolysis of the phosphoinositides, increased IP3 in these adrenal cells in a dose-dependent manner. Both ACTH and alpha-MSH raised the cAMP levels in the calf adrenal glomerulosa cells, although the magnitude of the increase of cAMP in response to ACTH was greater. These findings suggest that IP3 as a mediator of alpha-MSH- and beta-LPH-induced aldosterone secretion is not likely and other mediator(s) may be involved.     

An in vivo role of bone morphogenetic protein-6 in aldosterone production by rat adrenal gland

Aldosterone is synthesized in the zona glomerulosa of the adrenal cortex. We previously reported the presence of a functional BMP system including BMP-6 in human adrenocortical cells. BMP-6 contributes to Ang II-induced aldosterone production by activating Smad signaling, in which endogenous BMP-6 action is negatively controlled by Ang II in vitro. In the present study, we examined the in vivo role of BMP-6 in regulation of aldosterone by neutralizing endogenous BMP-6 in rats treated with immunization against BMP-6. Three-week-old male rats were actively immunized with rat mature BMP-6 antigen conjugated with keyhole limpet hemocyanin (KLH). The immunization treatment had no effect on bilateral adrenal weight or its ratio to body weight. Urinary aldosterone excretion was time-dependently increased during the 8-week observation period in the control group. Of note, the level of urinary aldosterone excretion in BMP-6-KLH-immunized rats was significantly reduced compared to that in the control group, suggesting that endogenous BMP-6 contributes to the induction of aldosterone production in vivo. Moreover, the level of urinary aldosterone/creatinine after 8-week treatment was significantly lowered by treatment with BMP-6-KLH. In contrast, with chronic Ang II treatment, urinary aldosterone and creatinine-corrected values at 8 weeks were not significantly different between the two groups, suggesting that the effects of BMP-6-KLH were impaired under the condition of chronic treatment with Ang II. The mRNA levels of Cyp11b2, but not those of Star, P450scc and 3βhsd2, were significantly decreased in adrenal tissues isolated from BMP-6-KLH-immunized rats after 8-week treatment. Furthermore, the ratio of plasma aldosterone level to corticosterone was significantly decreased by immunization with BMP-6-KLH. Collectively, the results indicate that endogenous BMP-6 is functionally linked to aldosterone synthesis by the zona glomerulosa in the adrenal cortex in vivo.     

Enalapril attenuates endothelin-1-induced hypertension via increased kinin survival

Recent studies have shown that angiotensin-converting enzyme (ACE) inhibitors attenuate endothelin-1 (ET-1)-induced hypertension, but the mechanisms for this effect have not been clarified. Initial experiments were conducted to contrast the effect of the ACE inhibitor enalapril, the combined ACE-neutral endopeptidase inhibitor omapatrilat, and the angiotensin II receptor antagonist candesartan on the hypertensive and renal response to ET-1 in anesthetized Sprague-Dawley rats. Acute intravenous infusion of ET-1 (10 pmol x kg(-1) x min(-1)) for 60 min significantly increased mean arterial pressure (MAP) from 125 +/- 8 to 145 +/- 8 mmHg (P < 0.05) and significantly decreased glomerular filtration rate (GFR) from 0.31 +/- 0.09 to 0.13 +/- 0.05 ml x min(-1) x 100 g kidney wt(-1). Pretreatment with enalapril (10 mg/kg iv) before ET-1 infusion inhibited the increase in MAP (121 +/- 4 vs. 126 +/- 4 mmHg) before and during ET-1 infusion, respectively (P < 0.05) without blocking the effect of ET-1 on GFR. In contrast, neither omapatrilat (30 mg/kg) nor candesartan (10 mg/kg) had any effect on ET-1-induced increases in MAP or decreases in GFR. To determine whether the effect of enalapril was due to the decrease in angiotensin II or increase in kinin formation, rats were given REF-000359 (1 mg/kg iv), a selective B(2) receptor antagonist, with or without enalapril before ET-1 infusion. REF-000359 completely blocked the effect of enalapril on ET-1 infusion (MAP was 117 +/- 5 vs. 135 +/- 5 mmHg before and during ET-1 infusion, respectively, P < 0.05). REF-000359 alone had no effect on the response to ET-1 infusion (MAP was 117 +/- 4 vs. 144 +/- 4 mmHg before and during ET-1 infusion, respectively, P < 0.05). REF-000359 with or without enalapril had no significant effect on the ability of ET-1 infusion to decrease GFR. These findings support the hypothesis that decreased catabolism of bradykinin and its subsequent vasodilator activity oppose the actions of ET-1 to increase MAP.     

Effects of prolonged sodium restriction on the morphology and function of rat adrenocortical autotransplants

Summary Regenerated adrenocortical nodules were obtained by implanting fragments of the capsular tissue of excised adrenal glands into the musculus gracilis of rats (Belloni et al. 1990). Five months after the operation, operated rats showed a normal basal blood level of corticosterone, but a very low concentration of circulating aldosterone associated with a slightly increased plasma renin activity (PRA). Regenerated nodules were well encapsulated and some septa extended into the parenchyma from the connective-tissue capsule. The majority of parenchymal cells were similar to those of the zonae fasciculata and reticularis of the normal adrenal gland, while zona glomerulosa-like cells were exclusively located around septa (juxta-septal zone; JZ). In vitro studies demonstrated that nodules were functioning as far as glucocorticoid production was concerned, while mineralocorticoid yield was very low. Prolonged sodium restriction significantly increased PRA and plasma aldosterone concentration, and provoked a marked hypertrophy of JZ, which was due to increases in both the number and average volume of JZ cells. Accordingly, the in vitro basal production of aldosterone and other 18-hydroxylated steroids was notably enhanced. The plasma level of corticosterone, as well as zona fasciculata/reticularis-like cells and in vitro production of glucocorticoids by regenerated nodules were not affected. These findings, indicating that autotransplanted adrenocortical nodules respond to a prolonged sodium restriction similar to the normal adrenal glands, suggest that the relative deficit in mineralocorticoid production is not due to an intrinsic defect of the zona glomerulosa-like JZ, but is probably caused by the impairment of its adequate stimulation under basal conditions. The hypothesis is advanced that the lack of splanchnic nerve supply and chromaffin medullary tissue in regenerated nodules may be the cause of such an impairment.     

Interrenal activity in the female lizard Lacerta vivipara J.: in vitro response to ACTH 1-39 and to [Sar1, Val5] angiotensin II (ANG II)

A perifusion system technique was developed in order to determine in vitro the respective roles of ACTH and ANG II in the regulation of adrenal steroidogenesis in the lizard Lacerta vivipara. Synthetic human ACTH 1-39, administered as 20-min pulses, stimulated corticosterone (B) and aldosterone (A) release in a dose-dependent manner. The increase in corticosterone output was higher than that in aldosterone output, leading to an enhancement of the B/A ratio. Iterative stimulations with 1 nM ACTH (20-min pulses every 120 min) led to reproducible increases in corticosterone and aldosterone release. Prolonged stimulation with 1 nM ACTH (up to 240 min) caused a sustained increase in corticosteroid release, suggesting that, in the lizard, ACTH does not induce any desensitization phenomenon. The angiotensin II analogue [Sar1, Val5] ANG II also stimulated corticosterone and aldosterone release in a dose-dependent manner; the stimulatory effects of ANG II on both steroids were very similar. These results indicate that, in lizards, ACTH plays a major role in the regulation of adrenal steroidogenesis. Since ANG II stimulates the production of gluco- and mineralocorticoids, our data raise the question of the existence of two cell types synthesizing corticosterone and aldosterone, respectively, in reptiles.