Aldosterone production and hormone responsiveness in adrenal glomerulosa cells from cows of different ages

Aldosterone production by suspensions of adrenal glomerulosa cells obtained from young and old cows was measured. Basal steroidogenesis was lower in cells from old cows, as were the responses to angiotensin II (AII), potassium, ACTH and dibutyryl cyclic AMP. Receptors for AII and aldosterone production from added progesterone were the same in old and young cells. Synthesis of pregnenolone from endogenous precursor, the 'early pathway' of aldosteronogenesis, was lower in old cells than in young. AII-stimulated incorporation of 32P into phosphatidylinositol and the change in 45Ca2+ flux induced by AII were diminished in old cells. Overall protein synthesis, measured by 3H leucine incorporation, was lower in old cells than young, but was not affected by AII in either. Diminished responsiveness of adrenal glomerulosa cells from old animals results from a change in postreceptor events that affect the early pathway of aldosteronogenesis.

The antihypertensive effect of lisinopril compared to atenolol in patients with mild to moderate hypertension

In a multicenter, parallel, double-blind study, lisinopril was compared with atenolol in the treatment of mild to moderate essential hypertension. Four hundred ninety patients were randomized to a once-a-day treatment with lisinopril 20 mg or atenolol 50 mg for 4 weeks, and the doses of lisinopril or atenolol were increased up to 80 mg or 200 mg, respectively, at 4-week intervals if sitting diastolic blood pressure (SDBP) was not well controlled. Hydrochlorothiazide (HCTZ) 12.5 or 25 mg was added after 12 weeks, if necessary, and titrated upward after 4 weeks to a maximum dose of 25 or 50 mg/day. Lisinopril and atenolol reduced SDBP to a similar extent. All reductions from baseline in sitting diastolic and systolic blood pressure were significant (less than 0.01). Lisinopril produced a significant (less than 0.01) greater reduction in sitting systolic blood pressure (SSBP) than atenolol. Addition of HCTZ caused further blood pressure reductions (p less than 0.01). Five patients (1.7%) on lisinopril and four (2.0%) on atenolol developed skin rashes during weeks 1-12. Two patients (0.7%) on lisinopril 80 mg developed proteinuria (greater than 1 g/day). Cough occurred more often with lisinopril (4.5%), and elevated triglycerides occurred more often with atenolol (2.0%).

Atrial natriuretic peptide inhibits protein phosphorylation stimulated by angiotensin II in bovine adrenal glomerulosa cells

Bovine adrenal glomerulosa cells were incubated with 32PO4 and either angiotensin II, atrial natriuretic peptide, or both. Solubilized cells were subjected to one-dimensional gel electrophoresis. Autoradiography and scintillation counting of gels showed that angiotensin increased labeling of one band, with an apparent molecular weight of 17,600. Atrial natriuretic peptide inhibited the angiotensin effect. Together with earlier results, this observation suggests that atrial natriuretic peptide affects aldosteronogenesis at the level of protein phosphorylation, but not by altering angiotensin receptors, calcium fluxes or phosphoinositide metabolism.

Fatty acid effects on angiotensin receptors

Saturated and unsaturated fatty acids were tested for their ability to inhibit specific binding of angiotensin to receptors in bovine adrenal glomerulosa and fasciculata cells, and homogenates of tissue from bovine adrenal and renal artery. Several naturally occurring fatty acids were inhibitory. The most potent fatty acids in the angiotensin-adrenal system were unsaturated C-18, C-20, and C-22 congeners, including oleic, linoleic, and arachidonic acids. These fatty acids inhibited angiotensin binding to adrenal glomerulosa cells by 50% at concentrations between 4 and 8 X 10(-6) M. Inhibition by linoleic acid was predominantly competitive, reducing receptor affinity by approximately 50% at the ID50 of the fatty acid. Renal artery binding sites were more sensitive than adrenal sites to linoleic, linolenic, and trans-vaccenic acids, but not to other fatty acids. Inhibition was not affected by indomethacin, nordihydroguaretic acid, or a guanosine triphosphate analogue. Fatty acids inhibiting the angiotensin-adrenal system had no effect on angiotensin antibody, adrenal receptors for atrial natriuretic factor, or myometrial receptors for bradykinin. Some fatty acids nonspecifically inhibited aldosterone production, blocking the response to angiotensin and substrate concentrations of corticosterone. This inhibition was apparently unrelated to effects on receptors. Albumin in the buffer partly neutralized the effects of added fatty acids. Pretreatment of fresh adrenal cells with albumin increased their ability to bind angiotensin. This was reversed by adding back the lipids absorbed to the albumin in the wash. Results suggest that endogenous fatty acids can regulate angiotensin receptors.

Platelet angiotensin receptors in young and old humans

Platelets from healthy human volunteers were studied for angiotensin II (AII) binding sites. Platelets were isolated from whole blood by differential centrifugation, and binding sites were analyzed by Scatchard plots of radioactive ligand binding data. The number of platelet AII receptor sites was significantly higher in human beings of advanced age compared with younger persons. The affinity of receptor sites was not different in young and old participants. The increased number of binding sites bore no relationship to salt intake as documented by history, plasma renin activity, or blood pressure. A significant portion of the increase in platelet AII receptor sites in older adults in this study is related directly to the age of the individuals.

Inhibition of aldosterone synthesis by atrial natriuretic factor

Atrial natriuretic factor (ANF) inhibits basal and stimulated aldosterone synthesis in adrenal glomerulosa cells. ANF probably acts through specific membrane receptors. Alterations in cyclic GMP and cyclic AMP levels do not account for ANF's inhibitory effect. ANF does not block angiotensin II (AngII) receptors nor does it interfere with phosphoinositide metabolism or calcium movements stimulated by adrenal agonists. ANF does not inhibit protein synthesis nor does it work by inhibiting NA+,K+-ATPase or depleting cell potassium. ANF decreases conversion of endogenous cholesterol to pregnenolone, the step stimulated by adrenocorticotropin and AngII. ANF does not affect the conversion of 20-alpha-hydroxycholesterol, which easily penetrates mitochondrial membranes to the site of the cholesterol side-chain cleavage enzyme. These results suggest that ANF inhibits the ability of endogenous cholesterol to reach or interact with the side-chain cleavage enzyme. ANF does not act like a calcium channel-blocking agent. However, ANF is less effective at high-calcium concentrations, which suggests that it may inhibit a step that calcium stimulates. Understanding ANF action will probably require identification of the specific biochemical changes (mediators) that it induces. Parallel efforts to understand how other agents stimulate steroidogenesis (particularly in the areas of protein synthesis, protein phosphorylation, and cholesterol movements) will further this understanding.

Effects of pH on adrenal angiotensin receptors and responses

Ambient hydrogen ion concentration modulates the effects of angiotensin II (AII) on adrenal aldosterone secretion, but the mechanism of this modulation is unknown. We examined the influence of pH on AII receptors and responses in bovine adrenal glomerulosa cells. Lowering pH from 7.4 to 6.8 increased AII binding 20.5% and increased maximal All-stimulated aldosterone secretion 43%. By contrast, at pH 8.0, All binding and stimulation of aldosteronogenesis fell by 56.6% and 39%, respectively. Effects on All binding intermediate to these changes were observed at pH 7.1 and 7.7. Similar effects of altered pH were observed on All binding to a crude membrane fraction of bovine glomerulosa cells. Analysis indicated that pH primarily affected receptor number rather than affinity. In studies of proposed postreceptor mediators of All actions, pH had no effect on All stimulation of phosphatidylinositol turnover or All inhibition of calcium influx. The results show that pH affects All interaction with its receptors. The larger magnitude of the change in aldosterone compared with receptor binding suggests that a postreceptor step is also altered by pH; however, this postreceptor step is not reflected in calcium influx or phospholipid turnover.

Effects of ouabain and potassium on protein synthesis and angiotensin-stimulated aldosterone synthesis in bovine adrenal glomerulosa cells

Ouabain (1 microM and below) inhibited both basal and angiotensin II-stimulated aldosterone synthesis in bovine adrenal glomerulosa cells. Ouabain had no effect on binding of 125I-labeled angiotensin, on angiotensin's effects on 45Ca2+ fluxes, or on 32PO4 incorporation into phosphatidylinositol. This spectrum of activities resembles that of the protein synthesis inhibitor cycloheximide, which also blocks aldosterone synthesis. Ouabain was, therefore, tested for its effect on protein synthesis, as measured by uptake of [3H]leucine into acid-precipitable material. Ouabain inhibited protein synthesis at concentrations similar to those that depressed aldosterone synthesis, but did not block uptake of the nonmetabolized amino acid [carboxyl-14C]aminocyclopentane-1-carboxylic acid, nor the entrance of [3H]leucine into cells. When cells previously loaded with 86Rb+ were treated with 1 microM ouabain, they lost approximately half of the accumulated radioactivity in 30 min. When cells were incubated in potassium-free buffer, both protein and aldosterone synthesis were severely inhibited. Increased extracellular potassium reversed ouabain's inhibition of protein and aldosterone synthesis in parallel. Pregnenolone synthesis was inhibited by ouabain, and elevated potassium overcame that blockade. Ouabain did not block aldosterone synthesis from exogenous progesterone. These data fit a model in which ouabain causes loss of cell potassium, which, in turn, depresses protein synthesis. Since protein synthesis is necessary for angiotensin II stimulation of cholesterol side-chain cleavage, ouabain depresses that step, pregnenolone synthesis, and thus, aldosterone synthesis.

Veratridine, angiotensin receptors and aldosteronogenesis in bovine adrenal glomerulosa cells

Veratridine inhibited angiotensin binding to its receptors in bovine adrenal glomerulosa cells and vascular smooth muscle. Fifty percent inhibition of adrenal receptors required about 2 X 10(-5) M veratridine. Receptors from vascular tissue were less sensitive. Graphic analysis showed that inhibition resulted primarily from a reduction of receptor number. Angiotensin stimulation of phosphatidylinositol turnover and of aldosterone production was inhibited by veratridine. Analogues of veratridine varied in their receptor inhibitory potency, but these variations did not correlate with the potencies of analogues as hypotensive agents or inhibitors of aldosteronogenesis. Very low extracellular sodium concentrations inhibited the adrenal effects of angiotensin. Neither veratridine nor grayanotoxin, both of which open sodium channels in excitable tissues, had a detectable effect on sodium fluxes in adrenal cells. Inhibition of aldosteronogenesis by veratridine is more likely the result of receptor and post-receptor effects than an alteration of the sodium channel.

Angiotensin effects on calcium and steroidogenesis in adrenal glomerulosa cells

We investigated the role of cellular calcium pools in angiotensin II-stimulated aldosterone synthesis in bovine adrenal glomerulosa cells. Angiotensin II decreased the size of the exchangeable cell calcium pool by 34%, consistent with previous observations that angiotensin II causes decreased uptake of 45Ca+2 into cells and increased efflux of 45Ca+2 from preloaded cells. Atomic absorption spectroscopy showed that angiotension II caused a decrease of 21% in total cellular calcium. Angiotensin II caused efflux of 45Ca+2 in the presence of EGTA and retarded uptake of 45Ca+2 when choline was substituted for sodium, suggesting that hormone effects on calcium pools do not involve influx of trigger calcium or sodium. Cells incubated in calcium-free buffer and 0.1 mM or 0.5 mM EGTA synthesized reduced (but still significant) amounts of the steroid in response to hormone. Cells incubated in increasing concentrations of extracellular calcium contained increasing amounts of intracellular calcium and synthesized increasing amounts of aldosterone in response to angiotensin II. These results point to the participation of intracellular calcium pools in angiotensin II-stimulated steroidogenesis and the importance of extracellular calcium in maintaining these pools.

Actions of synthetic atrial natriuretic factor on bovine adrenal glomerulosa

Synthetic atrial natriuretic factor (ANF) inhibited aldosterone production by suspensions of bovine adrenal glomerulosa cells. Inhibition by ANF was most pronounced when basal aldosterone production was measured. The effects of angiotensin II (AII), N6,O2'-dibutyryl-adenosine 3':5'-cyclic monophosphate (dibutyryl cyclic AMP), and elevated potassium were also inhibited by ANF. Inhibition could be partially overcome by high doses of agonist. Inhibition was localized to the early pathway of aldosteronogenesis, to a step before cholesterol side-chain cleavage. ANF had no effect on binding of AII to receptors, on the stimulation by AII of phospholipid turnover, or on the alteration by AII of calcium fluxes.

Androgen modulation of adrenal angiotensin receptors

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

Identification of the cycloheximide-sensitive site in angiotensin-stimulated aldosterone synthesis

We have investigated the action of a protein synthesis inhibitor on the ability of angiotensin II (AII) to stimulate steroid synthesis. Isolated bovine adrenal glomerulosa cells were incubated in the presence and absence of angiotensin and cycloheximide, and the effects of the inhibitor on six cellular processes were measured. Cycloheximide at 7 and 28 microM inhibited the ability of the hormone to stimulate aldosterone synthesis. These concentrations of cycloheximide blocked protein synthesis by 72 and 79% respectively. Cycloheximide did not block receptor binding of angiotensin, the effect of angiotensin on [32P]phosphate incorporation into phosphatidylinositol, nor the ability of the hormone to alter 45Ca2+ fluxes. Mitochondrial conversion of cholesterol to pregnenolone is thought to be the rate-determining step in corticosteroid synthesis. Mitochondria isolated from cells treated with angiotensin made pregnenolone at a higher rate than control mitochondria. Cycloheximide blocked this effect when it was present in the cell incubation medium with angiotensin. Cycloheximide added directly to mitochondria had no effect on pregnenolone synthesis. Cycloheximide also blocked AII stimulation of pregnenolone synthesis in intact cells. We propose that protein synthesis is required for angiotensin to exert its stimulatory effects at one particular locus: activation of mitochondrial pregnenolone synthesis. Protein synthesis is not required for other angiotensin-stimulated processes in bovine adrenal glomerulosa cells.

Angiotensin and prostaglandin interactions in cultured kidney tubules

Angiotensin and prostaglandin interactions in cultured kidney tubules were studied in tissue from fetal calves. Methods were developed for the isolation and culture of renal proximal tubule cells. Tubule cells survived three generations in culture. They had microvilli and flagellae characteristic of proximal tubule cells. Binding of 125I-angiotensin II to receptor-like sites in cells and homogenates was partially saturable, and the saturable binding was reversed by excess unlabeled hormone. Two types of binding sites were identified by Scatchard analysis. The higher-affinity site had a dissociation constant of 5 X 10(-10)M. PGE2 and PGA2 inhibited angiotensin binding. PGF2 alpha had no effect. Cultured tubule cells were loaded with 22Na+ by incubation in hypoxic medium free of potassium and glucose. Cells extruded the sodium when oxygen, glucose, and potassium were added. The rate of extrusion was accelerated by angiotensin II at concentrations of 10(-10)M and 10(-9)M. Higher concentrations had less effect. The primary prostaglandins PGA2 and PGF2 alpha inhibited 22Na+ efflux at 6 X 10(-7)M. Angiotensin had no detectable effect on sodium efflux in the presence of PGA2. Angiotensin apparently reversed inhibition of efflux by PGF2 alpha. Our findings suggest that prostaglandins affect angiotensin receptors in renal tubule cells. Prostaglandins also have direct effects on sodium efflux in these cells under the experimental conditions described.

Effects of angiotensin II and dibutyryl cyclic adenosine monophosphate on phosphatidylinositol metabolism, 45Ca2+ fluxes, and aldosterone synthesis in bovine adrenal glomerulosa cells

Angiotensin II (AII) and N6,O2'-dibutyryladenosine 3':5'-cyclic monophosphate (dibutyryl cyclic AMP) both stimulated aldosterone synthesis in bovine adrenal glomerulosa cells. AII altered 45Ca2+ fluxes and increased 32PO4 incorporation into phosphatidylinositol in these cells, whereas dibutyryl cyclic AMP did not affect either process. Neither AII nor dibutyryl cyclic AMP increased the mass of phosphatidylinositol. Both agents are known to stimulate pregnenolone synthesis. Thus, although dibutyryl cyclic AMP and AII may increase aldosterone synthesis at a common site (pregnenolone synthesis), they do so by different mechanisms. AII stimulation of phosphatidylinositol labeling by 32PO4 (the "PI effect") was blocked when cells were incubated in a medium containing both EGTA and the calcium antagonist, 8-(N,N-diethylamino)-octyl 3,4,5-trimethoxy-benzoate hydrochloride (TMB-8), suggesting a calcium requirement for the PI effect.

Cholesteryl hemisuccinate alters membrane fluidity, angiotensin receptors, and responses in adrenal glomerulosa cells

We examined the effects of cholesteryl hemisuccinate on membrane fluidity and angiotensin II (AII) actions in bovine adrenal glomerulosa cells. Incubating cells with cholesteryl hemisuccinate decreased membrane fluidity and markedly inhibited AII binding. The effect on binding was characterized by a decrease in AII receptor number. The effects of AII on phosphatidyl inositol turnover and calcium fluxes, proposed intermediaries of AII actions on aldosterone secretion, were less impaired than AII binding by cholesteryl hemisccinate. AII stimulation of aldosterone secretion was preserved despite the decrease in AII binding after cholesteryl hemisuccinate treatment. These results indicate that AII binding can be dissociated from its effects on aldosteronogenesis by a reagent that alters membrane fluidity.

The possible biological role of aldosterone metabolites

Following the incubation of aldosterone with microsomes from liver of adrenalectomized male rates, a previously unidentified polar neutral metabolite of aldosterone, designated "peak A" material, was isolated and purified using high pressure liquid chromatography. This peak A material, which contains a reduced hydroxylated metabolite of aldosterone, was shown to possess 2% to 3.5% of the mineralocorticoid activity relative to aldosterone. When bovine adrenal glomerulosa cells were incubated with peak A material (3 and 10 micrograms/ml), the binding of 125I-angiotensin II was inhibited by 20% and 36%, respectively. The mineralocorticoid activity of the six possible ring A reduced metabolites was tested. The 5 alpha-reduced metabolites were more potent than the 5 beta-, and the 3 alpha- were more potent than the 3 beta-reduced metabolites. The renal and extrarenal transformations of aldosterone to the polar and nonpolar (reduced) metabolites and their possible role in the accepted mechanism of action of aldosterone is discussed.

Aspects of angiotensin action in the adrenal. Key roles for calcium and phosphatidyl inositol

The steps between exposure of bovine adrenal glomerulosa cells to angiotensin and the stimulated increase in aldosterone production were studied in two ways. Binding of angiotensin to receptors, and hormone effects on phosphatidyl inositol turnover, 45Ca2+ fluxes, and aldosterone production were measured directly. Other potential intermediate steps were investigated indirectly by use of inhibitors. Angiotensin slowed calcium influx and accelerated phosphatidyl inositol turnover in proportion to hormone dose. The effects correlated with receptor binding and aldosterone production. None of the inhibitors tested, except saralasin, inhibited angiotensin's effect on phosphatidyl inositol turnover. Altered calcium flux and stimulated aldosterone production were affected by the calmodulin inhibitor trifluoperazine and the intracellular calcium antagonist 8-(N,N-diethylamino)-octyl 3,4,5-trimethoxybenzoate hydrochloride (TMB-8). Several reagents did not affect angiotensin binding, its effect on phosphatidyl inositol, or 45Ca2+ flux, but severely inhibited steroidogenesis. These included the phospholipase A2 inhibitor mepacrine, the protein synthesis inhibitor cycloheximide, and the Na+/k+-ATPase inhibitor ouabain. Colchicine had very little effect on the processes we measured, suggesting that microtubules play no role in angiotensin action in the adrenal. Based o these observations, we propose that angiotensin II affects the adrenal glomerulosa cell by first interacting with receptors, then increasing phosphatidyl inositol turnover, then altering cellular calcium distribution. Step distal to altered calcium distribution that contribute to increased steroid output include altered phospholipid metabolism, protein synthesis, and Na/k metabolism.

The effect of prolactin on human aldosterone-producing adenomas in vitro

There is evidence for an unidentified aldosterone-stimulating factor of pituitary origin. We measured the effect of ovine PRL (oPRL) on aldosterone secretion by isolated cell suspensions of human aldosterone-producing adenomas (APAs) and compared it to the effects of angiotensins, ACTH, and potassium (K+). In the first APA, the aldosteronotropic action of large doses of oPRL was double that of angiotensin II (AII); the response to ACTH was triple that to AII, while K+ had a small stimulatory effect. Results with the second APA showed that physiological concentrations of oPRL caused a response nearly double that to AII, but, once again, less than the response to ACTH; K+ was inert. ACTH contamination of the oPRL preparation was too minute to account for these findings. We conclude that oPRL possesses aldosterone-stimulating activity in APAs greater than that of angiotensins and potassium, but less that that of ACTH. These data suggest a role for PRL in aldosterone secretion by aldosterone-producing adenomas.

Steroids as potential modulators of angiotensin receptors in bovine adrenal glomerulosa and kidney

To test the hypothesis that there is feedback inhibition of adrenal angiotensin receptors by substances released in response to the peptides, we measured binding of labeled angiotensins in the presence of various steroids. Approximately half of the 70 steroids tested inhibited binding of labeled angiotensin II and III to intact and broken cells from bovine adrenal glomerulosa and kidney, but the concentrations required for inhibition were relatively high. The most potent inhibitors were 3 alpha, 5 beta tetrahydroaldosterone and tetrahydrodeoxycorticosterone (ID50 = 8 x 10-5 M). Kinetic analysis showed that inhibition was mostly competitive. among steroids whose reduced congeners were tested, potency increased in the sequence: parent steroid less than 5 alpha dihydroderivative less than 5 beta dihydro derivative less than 3 alpha, 5 beta tetrahydro-derivative. Tetrahydrodeoxycorticosterone inhibited aldosteronogenesis by intact cells at concentrations that inhibited angiotensin binding. Steroids differentially inhibited binding of labeled angiotensins in II and III, and discriminated between receptors in adrenal glomerulosa and kidney. The results provide additional evidence for heterogeneity of angiotensin receptors, and lead to the prediction that any normal or pathological inhibition of angiotensin receptors by steroids will be mediated by reduced derivatives.

Angiotensin alters 45Ca2+ fluxes in bovine adrenal glomerulosa cells

Angiotensin II stimulated 45Ca2+ release from bovine adrenal glomerulosa cells. It also decreased the influx of 45Ca2+ into glomerulosa cells. The effects were observed within 2 min of hormone addition and were blocked by Saralasin a competitive inhibitor of angiotensin. Des-Phe8-angiotensin II, a biologically inert analog, was inactive in this system. Angiotensin II also inhibited the influx of 133Ba2+ and 54Mn2+, whereas 51Cr6+ and 57Co2+ were unaffected. Alterations in 45Ca2+ fluxes were seen with concentrations of angiotensin that stimulate aldosterone biosynthesis in bovine glomerulosa cell preparations. These results suggest that calcium plays a key role in angiotensin-stimulated aldosteronogenesis.