Estradiol attenuates angiotensin-induced aldosterone secretion in ovariectomized rats

Estrogen replacement therapy significantly reduces the risk of cardiovascular disease in postmenopausal women. Previous studies indicate that estradiol (E2) decreases angiotensin II (AT) receptor density in the adrenal and pituitary in NaCl-loaded rats. We used an in vivo model that eliminates the potentially confounding influence of ACTH to determine whether the E2-induced decrease in adrenal AT receptor expression affects aldosterone responses to angiotensin II (Ang II). Female rats were ovariectomized, treated with oil (OVX) or E2 (OVX+E2; 10 microg, s.c.) for 14 days, and fed a NaCl-deficient diet for the last 7 days to maximize adrenal AT receptor expression and responsiveness. On days 12-14 rats were treated with dexamethasone (DEX; 25 microg, i.p., every 12 h) to suppress plasma ACTH. On day 14 aldosterone secretion was measured after a 30-min infusion of Ang II (330 ng/min). Ang II infusion increased the peak plasma aldosterone levels to a lesser degree in the OVX+E2 than in the OVX rats (OVX, 1870 +/- 290 pg/ml; OVX+E2, 1010 +/- 86 pg/ml; P < 0.05). Ang II-induced ACTH and aldosterone secretion was also studied in rats that were not treated with DEX. In the absence of DEX, the peak plasma aldosterone response was also significantly decreased (OVX, 5360 +/- 1200 pg/ml; OVX+E2, 2960 +/- 570 pg/ml; P < 0.05). However, E2 also reduced the plasma ACTH response to Ang II (P < 0.05; OVX, 220 +/- 29 pg/ml; OVX+E2, 160 +/- 20 pg/ml), suggesting that reduced pituitary ACTH responsiveness to Ang II contributes to the effect of E2 on Ang II-induced aldosterone secretion. Adrenal AT1 binding studies confirmed that E2 significantly reduces adrenal AT1 receptor expression in both the presence and absence of DEX in NaCl-deprived rats. These results indicate that E2-induced decreases in pituitary and adrenal AT1 receptor expression are associated with attenuated pituitary ACTH and adrenal aldosterone responses to Ang II and suggest that estrogen replacement therapy may modulate Ang II-stimulated aldosterone secretion as part of its well known cardioprotective actions.     

Guanabenz-induced inhibition of aldosterone secretion from isolated rat adrenal glomerulosa cells.

The authors examined the effects of the alpha 2-adrenergic agonist guanabenz and other alpha-adrenergic ligands on aldosterone secretion and cyclic nucleotide content in isolated rat adrenal glomerulosa cells. Guanabenz inhibited aldosterone secretion stimulated by potassium, angiotensin II (AII), and adrenocorticotropic hormone (ACTH), exhibiting IC50 values of 35 microM, 43 microM, and 58 microM for stimulation by 10 mM K+, 1 nM AII, and 10 pM ACTH, respectively. Guanabenz did not affect the cGMP content of purified adrenal glomerulosa cells but inhibited ACTH stimulation of cAMP accumulation. Guanabenz inhibition of ACTH-induced cAMP may represent a mechanism for inhibition of aldosterone secretion, however, guanabenz also inhibited aldosterone secretion stimulated by the cAMP analog dibutyryl cAMP. The effect of guanabenz on the early and late pathways of steroidogenesis was tested in the isolated rat glomerulosa cells using 25-OH cholesterol and steroid precursors to aldosterone. Guanabenz inhibited the steroidogenic response to 25-OH cholesterol stimulation of aldosterone secretion but induced a much smaller inhibition of the steroidogenic response to exogenous pregnenolone, progesterone, and 11-deoxycorticosterone. These results suggested that guanabenz inhibited aldosterone secretion primarily through inhibition of the early component of the steroidogenic pathway prior to pregnenolone formation. The effects of guanabenz were not mimicked by other alpha-adrenergic ligands suggesting that these effects of guanabenz were not mediated through activation of alpha-adrenergic receptors.     

Interaction between serotonin and other regulators of aldosterone secretion in rat adrenal glomerulosa cells

Although serotonin (5HT) is a recognized stimulator of aldosterone secretion in vivo and in vitro, its physiological role as a regulator of mineralocorticoid secretion and its mechanism of action in the adrenal glomerulosa have not been elucidated. To address these questions we studied the interaction of 5HT with other aldosterone regulators in isolated rat adrenal glomerulosa cells. 5HT stimulated aldosterone production 14-fold, with an ED50 of 20 +/- 5 nM, and stimulation was maximal at 0.8 microM. The stimulation of aldosterone production by 5HT was accompanied by a 5-fold increase in cAMP production, with an ED50 of 1 microM. Threshold levels of 5HT (1 nM) potentiated the effect of submaximal concentrations of angiotensin-II (AII), decreasing the ED50 from 1.3 to 0.46 nM and increasing the maximum response in an additive manner. In contrast, the stimulatory effect of 5HT was purely additive to that of submaximal ACTH concentrations. 5HT had no effect on aldosterone secretion stimulated by maximal ACTH concentrations, despite full additivity on cAMP accumulation. Stimulations of steroidogenesis by potassium and 5HT were fully additive at submaximal concentrations, but only partially additive at-maximal levels. To determine the mechanism of the synergistic effects of AII and 5HT, we analyzed the interaction of both stimuli on cAMP accumulation, intracellular calcium, and inositol phosphate formation. Consistent with the inhibitory effect of AII on adenylate cyclase, in the presence of AII the stimulation of cAMP by 5HT was reduced by 18 +/- 3%. 5HT alone had no effect on cytosolic calcium, but significantly enhanced the peak and later phases of the AII-stimulated increase (P less than 0.005). This effect of 5HT was due to calcium influx and not to release from intracellular pools, as shown by suppression of the potentiation in the absence of extracellular calcium and the lack of effect of 5HT on basal or AII-stimulated inositol phosphate formation. The ability of low concentrations of 5HT to potentiate the stimulatory effect of AII on aldosterone secretion suggests that under some physiological conditions, 5HT may play a role in regulating the adrenal sensitivity to AII.     

Characterization of dopamine receptors associated with aldosterone secretion in rat adrenal glomerulosa

Dopamine (DA) may participate in the control of aldosterone secretion. We report that two different receptors for DA are present in rat adrenal glomerulosa: D-1, associated with stimulation of adenylate cyclase, and D-2, whose action inhibits adenylate cyclase. The adenylate cyclase system was stimulated by DA (EC50, 7.2 microM) and different DA agonists. When the D-1 receptor blocker SCH 23390 was added to the incubation medium, DA elicited a dose-dependent inhibition of adenylate cyclase (IC50, 10 microM); (-)sulpiride specifically blocked this effect. Furthermore, DA blocked angiotensin II-induced aldosterone release from glomerulosa slices in vitro. This effect was prevented by (-)sulpiride, but not by SCH 23390. The results suggest that the D-2 receptor acts to inhibit the cAMP-generating system and may be physiologically involved in the regulation of aldosterone secretion.     

Inhibition of aldosterone biosynthesis by atriopeptins in rat adrenal cells

The effect of synthetic atriopeptins on basal and stimulated aldosterone secretion was determined in isolated adrenal glomerulosa cells of the rat. Neither atriopeptin I (1-21) or III (1-24, i.e., the Phe-Arg-Tyr carboxy-terminal extension of atriopeptin I) altered basal aldosterone release. However, if the cells were prepared from adrenals of sodium-depleted rats, the basal aldosterone release was increased by 9-fold, compared with cells from normal rats. This elevated release was inhibited by 32% by atriopeptin I and atriopeptin III. Atriopeptin III was more potent than atriopeptin I. Angiotensin II and adrenocorticotropin stimulated the release of aldosterone in a concentration-related manner. Both atriopeptin I and atriopeptin III inhibited the stimulation by the peptides. Atriopeptin I inhibited angiotensin II- and adrenocorticotropin-induced aldosterone production by 50% at concentrations of 12 and 11 nM, respectively, and 0.5 and 0.2 nM, respectively, for atriopeptin III. Potassium-stimulated aldosterone production was also inhibited by atriopeptin I and atriopeptin III with 50% inhibition at concentrations of 10 and 0.4 nM, respectively. Shorter peptides (1-20, 1-19, and 3-19) were equipotent to atriopeptin I (1-21) as inhibitors of angiotensin II-induced steroidogenesis. To determine the site at which atriopeptins inhibit aldosterone synthesis, we used cyanoketone to inhibit 3 beta-hydroxy-dehydrogenase and dissociate the early and late pathways. Angiotensin II (2 nM) increased the synthesis of pregnenolone (early pathway), as well as the conversion of [3H]corticosterone to [3H]aldosterone (late pathway). Atriopeptin III inhibited basal pregnenolone synthesis by 36% and completely blocked angiotensin II-stimulated synthesis. The peptide similarly inhibited the late pathway.(ABSTRACT TRUNCATED AT 250 WORDS)     

Mechanism of cholinergic stimulation of aldosterone secretion in bovine adrenal glomerulosa cells

The effect of cholinergic stimulation on aldosterone secretion was examined in bovine adrenal glomerulosa cells. Both acetylcholine and carbachol stimulated aldosterone secretion in a dose-dependent manner. Acetylcholine-induced secretion was inhibited by atropine but not by hexamethonium, suggesting that cholinergic agonists act on muscarinic receptors. The mechanisms of cholinergic agonist action were compared with those of angiotensin II. Like angiotensin II, carbachol generated calcium signal in glomerulosa cells. When [3H]inositol-labeled cells were stimulated by carbachol, there was an immediate increase in [3H]inositol trisphosphate, followed by a relatively slow increase in [3H]inositol bisphosphate. Carbachol increased the cytosolic concentration of calcium transiently but not intracellular cAMP. Carbachol caused a rapid 3-fold increase in 45Ca fractional efflux ratio in 45Ca-prelabeled cells both in the presence and absence of extracellular calcium. Carbachol also increased calcium influx; however, carbachol-induced influx was smaller than that of angiotensin II. In a perifusion system, the time course of carbachol-induced aldosterone secretion was biphasic. However, when calcium influx was increased to a value similar to that in angiotensin II-treated cells by combination of carbachol and BAY K-8644, this combination induced a monophasic and sustained secretory pattern. These results indicate that muscarinic cholinergic agonists stimulate aldosterone secretion via the calcium messenger system, and the biphasic secretory response to cholinergic agonist is due to a smaller increase in calcium influx.     

Atrial natriuretic peptide inhibition of calcium ionophore A23187-stimulated aldosterone secretion in rat adrenal glomerulosa cells.

The effect of atrial natriuretic peptide (ANP) on calcium ionophore A23187-stimulated aldosterone secretion was investigated using collagenase-dispersed rat adrenal glomerulosa cell suspensions. A23187 treatment induced a dose-dependent stimulation of aldosterone secretion, exhibiting an EC50 of approximately 75 nM. In agreement with the presumed action of A23187 as a Ca2+ ionophore, stimulation was dependent on the extracellular Ca2+ concentration, being completely inhibited in nominally Ca(2+)-free medium. In such Ca(2+)-free medium, stimulation of aldosterone secretion by bath applied 25-hydroxycholesterol was not inhibited, indicating that cells and biosynthetic pathway enzymes were not inhibited by low extracellular Ca2+ levels. A23187-induced aldosterone secretion was also inhibited by more than 90% when cells were simultaneously treated with ANP. Maximal ANP inhibition of A23187-stimulated aldosterone secretion was not overcome by concentrations of A23187 up to 10 microM or by increasing the extracellular Ca2+ concentration from 1.25 to 5 mM in the presence of A23187 and ANP. Addition of A23187 to ACTH-, angiotensin II-, or K(+)-stimulated glomerulosa cells did not overcome ANP-induced inhibition of aldosterone secretion stimulated by these secretagogues. In contrast to ANP inhibition of Ca(2+)-dependent A23187 stimulation of aldosterone secretion, ANP inhibition of dBcAMP-stimulated aldosterone secretion was readily overcome by increasing the dBcAMP concentration. These results indicated that ANP selectively and noncompetitively inhibited an intracellular step necessary for Ca(2+)-dependent stimulation of the early pathway of aldosterone biosynthesis in rat adrenal glomerulosa cells.     

The mechanism of angiotensin-induced desensitization of adrenal glomerulosa cells

Superfusion of isolated rat adrenal glomerulosa cells for 6 h with a medium containing 2.5 nM angiotensin II (AII) reduces the aldosterone response to AII, corticotropin and potassium. Here we report that under such conditions there is a decrease in the capacity of the cells to form inositol phosphates in response to a subsequent stimulation with AII. The capacity to convert corticosterone to aldosterone is also reduced by a prior exposure to AII. Superfusion with a high-potassium medium has no such an effect. Reduced phosphoinositide response may be responsible for the decreased aldosterone stimulation by AII, the inhibition of the late stage of aldosterone biosynthesis may account for the heterologous character of desensitization.     

Kinetics of cytosolic calcium and aldosterone responses in rat adrenal glomerulosa cells

To evaluate the relationship between cytosolic calcium (Cai) and aldosterone production, rat adrenal zona glomerulosa (ZG) cells were studied during long-term stimulation by different secretagogues. Cai was measured in single ZG cells using microspectrofluorimetry, and aldosterone was determined in cell populations using a superfusion system. For external potassium (K+), Cai increases are sustained, with only a slight decrement over time, a feature shared by aldosterone production. The relationship between aldosterone output and Cai is nonlinear, with a Cai value for half-maximal stimulation of approximately 500 nM. Furthermore, the sustained changes in Cai with external K+ indicate that ZG cells can use an amplitude-based Cai signal to stimulate aldosterone production. Cai changes stimulated by angiotensin-II (Ang-II) show a complex dose-response pattern, with high concentrations (greater than or equal to 1 nM) of Ang-II eliciting a peak-plateau signal and lower doses (0.1 nM to 10 pM) producing repeated Cai oscillations. The peak amplitude of the Cai response in individual cells is not dose dependent, with the ZG cell experiencing peak levels repeatedly at the lowest Ang-II concentrations. However, the Cai transients are more frequent with increasing Ang-II concentrations between 0.1 nM and 10 pM. When integrated over time, the mean Cai signal also shows only modest dose-dependency during the sustained phase of Ang-II stimulation. Unlike the integrated Cai signal, aldosterone production increases steeply between 10 pM and 0.1 nM Ang-II, indicating that the Cai signal is likely to be frequency-based. Conversely, the steroid response to high Ang-II closely mirrors the kinetics of the more sustained Cai signals, including the diminished Cai and aldosterone levels during sustained stimulation with the highest Ang-II doses. Arginine vasopressin stimulated Cai and aldosterone responses, which closely resemble those elicited by 0.1 nM Ang-II, except that both Cai and aldosterone return to basal values within 20 min of continuous presentation of arginine vasopressin. Each ZG secretagogue produces a distinct pattern of Cai and aldosterone response. In addition, Cai response patterns can be divided into two general classes: a sustained Cai response, which appears to modulate cell activation by the amplitude of the Cai signal, and an oscillating Cai response, which uses the frequency of the Cai transients to control the magnitude of stimulation.     

Effect of osmolarity on aldosterone production by rat adrenal glomerulosa cells

The effect of osmotic changes on aldosterone production, [Ca2+]i and voltage-gated Ca2+ currents, was studied in cultured rat glomerulosa cells. Alteration of osmolarity by sucrose addition in the 250-330 mosM range did not influence aldosterone production per se, but it substantially affected K+-stimulated aldosterone production. Hyposmosis markedly increased the hormone response evoked by raising [K+] from 3.6 to 5 mM, whereas hyperosmosis had a mild decreasing effect. Cytoplasmic [Ca2+]i, measured in single glomerulosa cells, did not show detectable change in response to either hyposmotic or hyperosmotic exposure, but the [Ca2+]i signal evoked by elevation of [K+] to 5 mM was augmented in hyposmotic solution. The osmosensitivity of the transient (T)-type and long-lasting (L)-type voltage-gated Ca2+ currents was studied using the nystatin-perforated voltage-clamp technique. Lowering osmolarity to 250 mosM significantly increased the amplitude of the T-type current, and it had a transient augmenting effect on L-type current amplitude. Hyperosmotic solution (330 mosM) reduced L-type current amplitude but did not evoke significant change in T-type current. These results indicate that the responsiveness of rat glomerulosa cells to physiological elevation of [K+] is remarkably influenced by changes in osmolarity by means of modulating the function of voltage-gated Ca2+ channels.     

Signal transduction mechanisms involved in carbachol-induced aldosterone secretion from bovine adrenal glomerulosa cells.

In cultured bovine adrenal glomerulosa cells, diacylglycerol content remains elevated for up to 75 min following the removal of angiotensin II. This maintained increase could provide a mechanism by which angiotensin II pretreatment may prime cells to secrete aldosterone in response to the calcium channel agonist Bay K 8644. In the present study we find that carbachol failed both to produce this persistent diacylglycerol elevation and to exert a priming effect. In addition, because carbachol was also a less potent activator of phospholipase D than angiotensin II, our results implicate phospholipase D in the maintained increase in diacylglycerol content observed following stimulation with and removal of angiotensin II. Carbachol also elicited changes in the radiolabeled levels of both myristate- and arachidonate-containing diacylglycerol. However, the rapid decline in diacylglycerol content following carbachol removal resembled the rapid fall in arachidonate-diacylglycerol; we therefore proposed that the diacylglycerol species generated with carbachol stimulation contains predominantly arachidonic acid. In summary, our results suggest that prolonged elevations in diacylglycerol content following removal of hormones such as angiotensin II, as well as the identity of the diacylglycerol species itself, may be important in the regulation of cellular responses.     

Angiotensin II receptors and aldosterone production in rat adrenal glomerulosa cells.

Specific receptors for angiotensin II (A II) were demonstrated in membrane fractions and collagenase-dispersed cells from the zona glomerulosa of the rat adrenal gland. The equilibrium association constant (Ka) of the A II binding sites was similar in particulate fractions (2.0 +/- 0.4 (SE) X 10(9) M-1) and intact glomerulosa cells (1.8 +/- 0.3 X 10(9) M-1). Specific binding of [125I]iodo-A II was enhanced by increasing sodium concentration, and in the presence of dithiothreitol, EDTA, and EGTA. Plasma membrane fractions prepared by density gradient centrifugation showed increased binding of [125I]iodo-A II, and were correspondingly enriched in adenylate cyclase and sodium-potassium-dependent ATPase. Steroid production by collagenase-dispersed adrenal glomerulosa cells was highly responsive to A II and ACTH. Significant increases in aldosterone and corticosterone production were elicited by A II concentrations as low as 3 X 10(-11) M, equivalent to normal blood levels of A II in rats (5 X 10(-11) M). The maximum increase in aldosterone production, of 6--7 times the basal value, was obtained at 10(-9) M A II. Dispersed capsular cells were also highly sensitive to ACTH, responding to concentrations down to 3 X 10(-12) M with increased aldosterone production, reaching a maximum aldosterone response of 20-fold above the basal value. The magnitudes of the aldosterone and corticosterone responses to A II in capsular and fasciculata-reticularis cells were commensurate with the distribution of A II receptors, which were 11-fold more concentrated in capsular cells. The ability of A II to evoke aldosterone production at physiological concentrations, and the correspondence between A II binding and steroidogenesis in capsular cells, demonstrate the functional importance of A II receptor sites in the zona glomerulosa of the rat adrenal cortex.     

Vasoactive intestinal peptide stimulates adrenal aldosterone and corticosterone secretion

Vasoactive intestinal peptide (VIP)-immunoreactive nerve fibers have been demonstrated in the rat adrenal cortex in close association with zona glomerulosa cells, suggesting neural regulation of adrenocortical cell function (5). The present studies were undertaken to study the possible role of VIP in the regulation of steroid hormone secretion from the outer zones of the normal rat adrenal cortex. Capsule-glomerulosa preparations, consisting of the capsule, zona glomerulosa, and a small but variable portion of the zona fasciculata, were perifused in vitro. To assess the secretory responsiveness of the capsule-glomerulosa preparation, aldosterone and corticosterone release were measured after stimulation with ACTH and angiotensin II. ACTH (10(-12)-10(-8) M) stimulated dose-dependent increases in aldosterone secretion (1.9- to 36.9-fold increases over basal values) and corticosterone secretion (1.4- to 14.0-fold increases over basal values). Angiotensin II (10(-8)-10(-5) M) stimulated dose-dependent increases in aldosterone secretion (1.6- to 8.8-fold increases over basal values). VIP (10(-6)-10(-4) M) stimulated dose-dependent increases in both aldosterone (1.7- to 41.0-fold) and corticosterone secretion (1.8- to 5.3-fold). However, glucagon and (N-Ac-Tyr1-D-Phe2)GRF-(1-29)NH2, peptides structurally related to VIP, stimulated neither aldosterone nor corticosterone secretion, indicating that VIP effects are likely to be specific for this peptide. It is noteworthy that in this preparation, the stimulation of corticosteroid secretion by VIP at 10(-5) and 10(-4) M was comparable to those by 10(-6) M angiotensin II and 10(-9) M ACTH, respectively. These results support the hypothesis that the VIP innervation of the adrenal cortex may contribute directly to the regulation of adrenal steroidogenesis.     

Mechanisms involved in the interaction of dopamine with angiotensin II on aldosterone secretion in isolated and cultured rat adrenal glomerulosa cells.

In a previous study, we have shown that freshly isolated glomerulosa cells possess dopamine (DA) receptors from both DA-1 and DA-2 subclasses, whereas in cultured conditions, cells exhibit dopamine receptors from the DA-1 subclass only. In the present work, we have studied the effect of DA on angiotensin-stimulated glomerulosa cells in these two experimental conditions. Our results demonstrate that in isolated cells, angiotensin II (AT) stimulates inositol phosphate accumulation, calcium influx and steroid secretion. Treatment with pertussis toxin completely blocks AT-stimulated steroid secretion and calcium influx and partially reduces inositol phosphate accumulation. DA alone has no effect on cAMP accumulation. However, in the presence of a specific DA-1 antagonist (SCH 23390), DA reduces intracellular cAMP content. Similarly, DA-like pertussis toxin produces the same inhibitory effects on AT-stimulated cells. The combined influence of DA and pertussis toxin is not additive suggesting that a 'Gi' GTP-binding protein is involved in the DA action. Specific DA antagonists indicate that these inhibitory processes are mediated through the DA-2 receptor subtype. DA may act by decreasing the intracellular calcium concentration since it reduces AT-stimulated Ca2+ influx and that both phospholipase C (PLC) and steroid accumulation are calcium dependent. Yet a direct inhibitory coupling between the DA-2 receptor and PLC may represent a second alternative since DA inhibitory effects are always present when calcium influx is artificially increased or decreased. In cultured cells, we observe an additive effect of DA and AT on aldosterone secretion, which is the result of additive interactions of the second messengers involved, namely cAMP for dopamine and inositol phosphates for angiotensin II. From these studies, we conclude that DA may exert a more versatile effect on aldosterone secretion than previously suspected.     

Dopaminergic modulation of aldosterone secretion in the rat

The dopamine antagonist metoclopramide (MCP) has been shown to acutely stimulate aldosterone secretion in vivo. To determine whether a dopaminergic mechanism is involved in the regulation of aldosterone secretion, we examined the effect of minipump infusion of MCP (iv) and/or angiotensin II (AII;sc) upon plasma aldosterone, adrenal capsular AII receptors, and 18-hydroxylase activity in rats maintained on high sodium intake. During normal sodium intake, plasma aldosterone was elevated from 8.3 +/- 1.3 to 35.4 +/- 3.2 ng/dl after 2-day infusion of a nonnatriuretic dose of AII (25 ng/min) and to 15.0 +/- 1.8 ng/dl after the infusion of 1.2 micrograms/min MCP. AII receptors were unchanged by MCP infusion, and rose from 1014 +/- 98 to 1638 +/- 98 fmol/mg after AII infusion. During high sodium intake, the infusion of either AII or MCP alone produced no change in plasma aldosterone or AII receptors. However, after simultaneous infusion of AII and MCP, plasma aldosterone rose from 4.5 +/- 1.2 to 32.5 +/- 2.7 ng/dl, AII receptors increased from 969 +/- 35 to 1607 +/- 280 fmol/mg, and 18-hydroxylase activity, measured as the conversion of corticosterone to aldosterone by isolated mitochondria, rose from 29.5 +/- 1.67 to 40.6 +/- 2.9 pmol/mg . min. These adrenal responses induced by the combined treatment with AII and MCP were similar to the effects of AII infusion during normal sodium intake, indicating that MCP exerts a permissive action upon the trophic effects of AII on the adrenal cell during high sodium intake. These actions of MCP were completely abolished by the simultaneous infusion of dopamine (2 micrograms/min), suggesting that the effects of MCP on adrenal function are due to its dopaminergic antagonist properties. In collagenase-dispersed adrenal glomerulosa cells, only supraphysiological concentrations of dopamine in the incubation medium (10-100 microns) inhibited basal, AII-stimulated, and ACTH-stimulated aldosterone production, and these inhibitory effects were not reversed by high concentrations of MCP. Also, MCP itself inhibited both basal and stimulated aldosterone production. These results suggest that the stimulatory actions of MCP in vivo are exerted through liberation of other local regulators, rather than directly upon the adrenal glomerulosa cell. These findings have defined a mechanism by which the primary regulatory action of AII upon aldosterone secretion can be modulated during high sodium intake by dopaminergic inhibition of adrenal glomerulosa function.     

Expression of prostaglandin E receptor EP4 subtype in rat adrenal zona glomerulosa: involvement in aldosterone release

We examined the role of prostaglandin (PG) E receptors in the secretion of aldosterone. PGE2 is known to exert its various biological functions by binding to PGE receptors. There are four subtypes of PGE receptors, EP1, EP2, EP3, and EP4. Among the PGE receptors EP2 and EP4 subtypes are coupled to Gs protein and stimulate adenylyl cyclase. In this study, PGE2 caused a dose-dependent increase in aldosterone production from the rat adrenal zona glomerulosa cells in vitro accompanied with an increase in intracellular cAMP concentration. A specific agonist for EP2, butaprost, did not increase the cAMP production or the aldosterone release, suggesting the possibility that EP4 mediates the secretion of aldosterone by PGE2. Northern blot hybridization analysis disclosed that EP4 gene was expressed in the rat adrenal gland but that EP2 gene was not. In situ hybridization revealed that EP4 mRNA is present abundantly in the zona glomerulosa of rat adrenal gland. These findings suggest that the PGE2-EP4 system is involved in the regulation of aldosterone secretion from the rat adrenal gland.