Further studies on the mechanisms controlling prostaglandin biosynthesis in the cat adrenal cortex: the role of calcium and cyclic AMP.

In light of previous studies which have implicated prostaglandin (PG) formation as a link in ACTH-induced steroid production by isolated cat adrenocortical cells, experiments were carried out to provide additional information regarding the role of PGs in adrenal steroidogenesis and their interactions with calcium and cyclic AMP. Perfusion of cat adrenal glands with Locke's solution plus beta(1-24)-ACTH resulted in an immediate increase in PGF2alpha release, which rapidly declined to basal levels after the stimulus was withdrawn. In contrast, maximal rates of steroid release were manifest some 30 min after removal of ACTH. ACTH and its onitrophenyl sulfenyl derivative (NPS-ACTH) increased PG (PGF2alpha and PGE2) and steroid release by trypsin-dispersed cat cortical cells, but NPS-ACTH, unlike ACTH, did not augment cortical cyclic AMP levels. In this same preparation, indomethacin completely blocked ACTH and NPS-ACTH facilitated PGF2alpha and PGE2 release but failed to suppress steroid release markedly. Calcium-deprivation blocked PG and steroid release evoked by these two polypeptides, and depressed PG release elicited by monobutyryl cyclic AMP (bcAMP) without affecting steroid release. These experiments offer additional evidence to support the concept that PGs play a role in the mode of action of ACTH; however, they do not appear to be obligatory intermediates in the steroidogenic process. The importance of calcium in regulating PG formation is discussed with special regard for the idea that this cation has a direct action on the enzyme systems which control PG synthesis.     

Corticosteroid and ribonucleic acid synthesis in isolated adrenal cells: Inhibition by actinomycin D

Both adrenocorticotrophic hormone (ACTH) and cyclic AMP rapidly stimulate corticosterone synthesis in isolated adrenal cells prepared by collagenase disaggregation of decapsulated rat glands. This steroidogenic response is not accompanied by any acute increase in the incorporation of [³H]uridine into acid insoluble RNA; indeed a slight decrease is observed during the incubations. A wide variety of different effects of actinomycin D on adrenal steroidogenesis have previously been reported. The effects of a range of actinomycin D concentrations (1–50 μmol/l) on the steroidogenesis brought about by different concentrations of ACTH (0.1–100. mi.u./ml) and cyclic AMP (1–5 mmol/l) were therefore examined. Actinomycin D (1 μmol/l) inhibits overall RNA synthesis by over 91% but has little or no effect on the cellular response to low concentrations of ACTH, although both basal (non-stimulated) corticosterone output and cyclic AMP stimulated steroidogenesis are appreciably inhibited (by 29–54%). Even at very high doses of actinomycin D (50 μmol/l), which inhibit RNA synthesis by 96% a substantial steroidogenic stimulation is obvious at all concentrations of ACTH and cyclic AMP studied. There is a greater inhibition of stimulated steroidogenesis not only with increasing actinomycin D concentrations, but also with increasing time of cellular exposure to actinomycin D. It is concluded that the acute steroidogenic ACTH mechanism does not require newly synthesized RNA and that if the inhibition by actinomycin D is simply due to an effect on synthesis of various RNA species, then the shortest estimate of the half-life of any RNA involved is 70 min.     

Lipoxygenase products as common intermediates in cyclic AMP-dependent and -independent adrenal steroidogenesis in rats

Aldosterone secretion from adrenal glomerulosa cells can be stimulated by angiotensin II (AII), extracellular potassium and ACTH. Mitochondria from these cells respond to intracellular factors generated by AII (cyclic AMP (cAMP)-independent steroidogenesis) and ACTH (cAMP-dependent steroidogenesis), suggesting that the two-signal-transduction mechanisms are linked by a common intermediate. We have evaluated this hypothesis by stimulating mitochondria from the unstimulated zona glomerulosa with a subcellular post-mitochondrial fraction (PMF) obtained from the zona glomerulosa after stimulation with AII or from the fasciculata gland after stimulation with ACTH; the subcellular fractions were also tested on mitochondria from fasciculata cells. PMFs obtained after incubation of adrenal zona glomerulosa with or without AII (0.1 microM) or ACTH (0.1 nM) were able to increase net progesterone synthesis 4.5-fold in mitochondria isolated from unstimulated rat zona glomerulosa. AII-pretreated PMFs from the zona glomerulosa also stimulated steroidogenesis by mitochondria from zona fasciculata cells. Separate experiments showed that inhibitors of arachidonic acid release and metabolism (bromophenacyl bromide, nordihydroguaiaretic acid, caffeic acid or esculetin) blocked corticosterone production in fasciculata cells stimulated with ACTH, suggesting that arachidonic acid could be the common intermediate in the actions of AII and ACTH on steroid synthesis. Evidence to support this concept was obtained from experiments in which the formation of an activated PMF by treatment of zona fasciculata with ACTH was blocked by the presence of the same inhibitors. Moreover, the inhibitory effects of these substances on PMF activation by ACTH were overcome by exogenous arachidonic acid and, in addition, arachidonic acid release was stimulated by ACTH.(ABSTRACT TRUNCATED AT 250 WORDS)     

Studies on cyclic nucleotides in the adrenal gland. VIII. Effects of angiotensin on adenosine 3',5'-monophosphate and steroidogenesis in the adrenal cortex.

Effects of angiotensin II on corticoid biogenesis and cAMP levels in the zona fasciculata-reticularis (the decapsulated fraction) and the zona glomerulosa (the capsular fraction) from the rat adrenal gland have been studied. Angiotensin II exclusively stimulated steroidogenesis in the zona glomerulosa without stimulation of the cAMP system, suggesting that steroidogenic action of this polypeptide does not involve the adenylate cyclase system. Angiotensin II was also found to stimulate cAMP-phosphodiesterase activity in the zona glomerulosa. An elevation of calcium concentration in the incubation medium has been observed to be effective in stimulating the production of aldosterone and cAMP by the capsular fraction. Angiotensin II caused a significant enhancement of the steroidogenic response of the capsular fraction to increasing calcium concentration regardless of the response of the cAMP system to calcium. This steroidogenic effect of angiotensin II was completely abolished by calcium antagonists added to the incubation medium without any inhibitory effect on the calcium-induced accumulation of tissue cAMP. These results suggest that angiotensin II acts on the adrenal II acts on the adrenal glomerulosa cell to increase intracellular calcium, which in turn directly stimulates steroidogenesis concomitant with the increased activity of phosphodiesterase.     

Excitation-secretion coupling: involvement of potassium channels in ACTH-stimulated rat adrenocortical cells

The mechanism by which ACTH stimulates calcium influx and steroid secretion was studied using rat adrenal glomerulosa cells, which were either freshly isolated or maintained in primary culture for 3 days. The potassium channel blocker tetraethylammonium chloride (TEA) stimulated twofold both corticosterone and aldosterone secretion; this stimulation was lower than that induced by ACTH at low concentrations (10 pmol/l). However, TEA and ACTH induced similar increases in Ca2+ influx and inositol phosphate accumulation. The three responses (steroid secretion, calcium influx and inositol phosphate accumulation) induced by TEA or low concentrations of ACTH were blocked by CoCl2. The greater stimulatory effect on steroid secretion of 10 nmol ACTH/l was decreased but not blocked by CoCl2. These data further document the complex mechanism of action of ACTH. It is postulated that, at low concentrations, ACTH binds preferentially to the high-affinity site of its receptor, leading to calcium influx by depolarization of the membrane potential, and to steroid secretion predominantly through an inositol phosphate- and Ca2+-stimulated pathway and also a cyclic AMP pathway. At higher concentrations, the hormone also binds to the low-affinity site of its receptor, largely stimulating cyclic AMP production and further increasing steroid secretion.     

Comparative effects of prostaglandins and ACTH on the production of corticosterone and cyclic AMP in isolated adrenal gland cells of rats

The authors compared the effect of prostaglandin PGE2 and ACTH on corticosterone and cAMP production in isolated adrenal cells of rats. PGE2 stimulated steroidogenesis in the concentrations of 0.01-1.10 micrograms/ml and the maximum stimulation (2.5-fold) was observed in the PGE2 concentration of 0.1 micrograms/ml. ACTH stimulated steroidogenesis 12-fold as compared to PGE2. In combined addition of different PGE2 doses and the physiological ACTH dose (5 pg/ml) their steroid effects were summated. The results obtained are indicative of the fact that PGE2 is no mediator of the ACTH effect but that it is capable of potentiating this effect. Like ACTH, PGE2 raised the cAMP level in the adrenal gland. In concentrations causing a similar to ACTH increase in the cAMP level, PGE2 stimulated steroidogenesis to a lesser degree than ACTH, and in this connection a possibility of the existence of two cAMP foci in the adrenal gland is discussed. It is assumed that one of the foci is related and the other is not related with steroidogenesis, and PGE2 stimulates mainly the second focus.     

Lactic acid and steroid production by intact mouse adrenal glands and cell suspensions: effects of nucleotide derivatives and substrates

The effects of the dibutyryl derivatives of cyclic GMP and cyclic AMP on lactic acid and steroid production were compared in intact mouse adrenal glands at concentrations of 0.5-1 mmol/l and in mouse adrenal cell suspensions at concentrations of 0.01-1 mmol/l. The dibutyryl derivative of cyclic GMP had little or no effect on lactic acid production in either tissue preparation. It caused a slight stimulation of corticosteroid output in intact glands at a concentration of 1 mmol/l, amounting to one-tenth of the response observed with 1 mM-dibutyryl cyclic AMP. Dose-dependent increases in lactic acid and steroid production were obtained with dibutyryl cyclic AMP in cell suspensions. AMP and GMP increased lactic acid but not steroid production. All the substrates tested (glucose, glucose-6-phosphate, fructose, fructose-6-phosphate, fructose-1,6-diphosphate, 10 mmol/l; pyruvate and glycerol, 20 mmol/l) stimulated basal glycolysis in intact glands and cell suspensions and none affected basal steroid production significantly. By far the greatest increase in lactic acid production was noted with fructose-1,6-diphosphate. However, only glucose and, in unsectioned glands, pyruvate exerted a potentiating effect on the glycolytic response to ACTH. Glucose potentiated the steroidogenic response to ACTH also, but only in intact glands. The relative ineffectiveness of dibutyryl cyclic GMP is in accord with the species-dependent differing responses to the free form of the cyclic nucleotides noted in mouse and rat adrenal glands. The substrate requirements are in keeping with a rate-limiting role of phosphofructokinase and an action of ACTH at some site between the entry of glucose into the cell and the formation of fructose-1,6-diphosphate.     

Effect of cyclic AMP and Ca++ on steroidogenesis by rat adrenal mitochondrial fraction. Studies on the mechanism of ACTH action (I) (author's transl)]

Despite the accumulation of a number of studies, the mechanism of action of ACTH remains to be clarified. Although it is now clear that cyclic AMP acts as a intracellular mediator of ACTH action, the mechanism of its action on the stimulation of steroidogenesis is not known. The present studies were carried out to test the hypothesis that cyclic AMP might act directly on adrenal mitochondrial fraction to stimulate the metabolism of cholesterol to pregnenolone and progesterone, and to determine whether Ca++ might modulate the action of cyclic AMP. Adrenal mitochondria were obtained from male Sprague-Dawley rats pretreated with dexamethasone. Steroidogenesis by the mitochondrial fraction from cholesterol-4-14C (0.2-0.25 muCi, 3.6-4.5 mmumole/sample) were measured in a system containing 20 mM tris-HCl buffer (pH 7.4), 11.5 mM NaCl, 15.4 mM KCl, 70 mM sucrose, 10 mM sodium succinate and mitochondrial fraction (0.16-0.22 mg protein/sample). Incubations were performed at 37 degrees C, with shaking, in the presence or absence of cyclic AMP, cyclic GMP and cycloheximide. After incubation, the medium was extracted with chloroform, and the extracts were analyzed by thin-layer chromatography. And the radioactivity of the separated steroids was measured. The products from cholesterol-4-14C were mainly pregnenolone and progesterone, and the other products were almost negligible. Cyclic AMP effected the formation of pregnenolone and progesterone by mitochondria. Cyclic AMP exerted its effect even at low concentrations (5 X 10(-6) approximately 5 X 10(-5)M), which was presumably near the intracellular level. On the other hand, cyclic GMP (5 X 10(-5) M) failed to enhance steroidogenesis. The effect of Ca++ on the action of various concentrations (5 X 10(-6) approximately 3 X 10(-3) M) of cyclic AMP was also clearly demonstrated. Addition of Ca++ (1 mM) to the incubation medium intensified the stimulatory effect of cyclic AMP in each concentration. And in the presence of Ca++, the most effective level of cyclic AMP was shifted from 5 X 10(-4) approximately 3 X 10(-3)M to the lower concentration (5 X 10(-5)M). In addition, cyclic AMP action was modified by the changes in the concentration of Ca++ in the medium. At concentration of 10(-6) M of Ca++, steroid formation of mitochondria was maximally activated by cyclic AMP. These observations suggest that cyclic AMP enhances steroidogenesis by acting directly on adrenal mitochondria to stimulate pregnenolone and progesterone formation from cholesterol, and that Ca++ plays a significant role in its action.     

Dependence of aldosterone stimulation in adrenal glomerulosa cells on calcium uptake: effects of lanthanum nd verapamil

The calcium dependence of steroidogenic responses to angiotensin II, potassium, and ACTH was analyzed in isolated adrenal glomerulosa cells incubated with inhibitors of calcium uptake. Both lanthanum and verapamil reduced the stimulation of aldosterone production by each regulator in a dose-dependent manner, with only a moderate decrease in basal steroid production. The stimulation of aldosterone and cAMP production by ACTH was blocked by both antagonists, and the degree of inhibition was dependent on the concentration of ACTH employed. Increasing concentrations of verapamil caused an increase in th ACTH concentration required for half-maximal stimulation as well as a reduction in the maximum production of aldosterone. Aldosterone production by glomerulosa cells in response to angiotensin II or potassium was also decreased by lanthanum and verapamil, with no change in the concentration of angiotensin II required for half-maximal stimulation of steroidogenesis. Stimulation of pregnenolone synthesis by angiotensin II was also inhibited by verapamil, indicating that calcium is required for the action of angiotensin II at an early step in the steroidogenic pathway. The inhibitory action of verapamil upon angiotensin-stimulated aldosterone production was overcome by increasing concentrations of calcium. Neither of the calcium antagonists affected the binding of angiotensin II to glomerulosa cells, placing the calcium requirement for the action of angiotensin II at a postreceptor locus. These results provide further evidence that angiotensin II and potassium increase aldosterone production in adrenal glomerulosa cells through a calcium-dependent mechanism, and indicate that calcium uptake is an essential requirement for the stimulation of aldosterone production by these two effectors.     

Effects of ACTH and its O-nitrophenyl sulphenyl derivative on adrenocortical function in vivo.

Both ACTH and NPS-ACTH in which the single tryptophan residue of the hormone is modified were able to stimulate adrenal corticosterone concentration to the same extent in hypophysectomized rats, although a higher dose of NPS-ACTH was required. ACTH stimulated adrenal cyclic AMP levels 120-fold in hypophysectomized rats whereas NPS-ACTH caused a marginal increase. In the case of ACTH, low doses of the hormone capable of producing maximal stimulation of corticosterone synthesis did not produce any detectable change in cyclic AMP concentration. The rates of secretion of corticosterone induced by ACTH and NPS-ACTH in vivo were the same. NPS-ACTH was found to be 1.2% as potent as ACTH. The role of cyclic AMP in adrenal repair was investigated by administering equipotent doses of ACTH or NPS-ACTH to hypophysectomized rats. In adult rats both failed to produce a significant increase in adrenal weight. Adrenal function (measured by responsiveness to exogenous ACTH in vitro) was restored by NPS-ACTH but not to the same degree as ACTH. In hypophysectomized weanling rats, ACTH produced a small but significant increase in adrenal weight but NPS-ACTH did not. These results suggest that an increase in adrenal cyclic AMP may not be obligatory for the stimulation of steroidogenesis by ACTH and that some of the trophic actions of the hormone may be mediated by cyclic AMP.     

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.     

Stimulation of steroidogenesis by forskolin in rat adrenal zona glomerulosa cell preparations.

The actions of forskolin have been investigated to determine to what extent its effects on steroidogenesis in rat adrenal preparations are dependent on activation of adenylate cyclase. In zona glomerulosa preparations, stimulation of both aldosterone and corticosterone production was obtained at concentrations of forskolin between 1 and 10 mumol/l. The effects of 10 mumol forskolin/l were additive with those of low doses (1 pmol/l) of corticotrophin (ACTH), but not with those of high doses (1 nmol/l) of ACTH. In contrast, in zona fasciculata/reticularis cells, doses of forskolin up to 10 mumol/l produced no significant stimulation of corticosterone production either alone or in the presence of ACTH (1 pmol/l and 1 nmol/l). The response to 1 nmol ACTH/l was attenuated in the presence of forskolin (10 mumol/l) in both zona glomerulosa and zona fasciculata/reticularis cell preparations. Cyclic AMP production increased progressively with dose up to 100 mumol forskolin/l in zona glomerulosa cells, whereas corticosterone production was maximal between 10 and 30 mumol forskolin/l and decreased at 100 mumol forskolin/l. In zona fasciculata/reticularis cells, cyclic AMP production was also increased by forskolin (1 and 10 mumol/l). The stimulation of zona glomerulosa steroidogenesis by forskolin (1-10 mumol/l) and ACTH (1-100 pmol/l) were both reduced by the adenylate cyclase inhibitor, N6-phenylisopropyladenosine (100 mumol/l). The calcium channel inhibitor, nifedipine, only reduced the steroidogenic response to forskolin (3 mumol/l) at doses of 300 mumol/l whereas the response to 8.4 mmol K+/l was inhibited at 10 mumol nifedipine/l.(ABSTRACT TRUNCATED AT 250 WORDS)     

Regulation of ornithine decarboxylase activity by corticotropin in adrenocortical tumor cell clones: roles of cyclic AMP and cyclic AMP-dependent protein kinase.

In Y1 adrenocortical tumor cells, corticotropin (ACTH), cyclic AMP, and 8-bromoadenosine 3',5'-monophosphate (8BrcAMP) stimulated ornithine decarboxylase activity (L-ornithine carboxy-lyase, EC 4.1.1.17) and steroidogenesis. The concentrations required for half-maximal activation of ornithine decarboxylase were 60 pM for ACTH and 1 mM for 8BrcAMP; the concentrations required for half-maximal activation of steroidogenesis were 50 pM for ACTH and 0.2 mM for 8BrcAMP. Ornithine decarboxylase activity increased 1.5 hr after the addition of these agents, reached a maximum between 4 and 6 hr, and then declined. Mutant clones with impaired ACTH-responsive adenylate cyclase systems [ATP pyrophosphate-lyase (cyclizing), EC 4.6.1.1]did not respond to ACTH with increased ornithine decarboxylase activity, but they responded normally to added cyclic AMP. These results indicate that adenylate cyclase and cyclic AMP are necessary for the stimulation of ornithine decarboxylase activity by ACTH. In a series of Y1(Kin) mutants with altered cyclic AMP-dependent protein kinase activities (ATP:protein phosphotransferase, EC 2.7.1.37), the effects of ACTH on ornithine decarboxylase also were attenuated. These findings suggest that cyclic AMP-dependent protein kinase also plays a necessary role in the stimulation of ornithine decarboxylase activity by ACTH. The effects of ACTH on ornithine decarboxylase in the Kin mutants, however, were quantitatively different from the effects on steroidogenesis and did not closely reflect the degree of defect in cyclic AMP-dependent protein kinase activity. These differences suggest that the pathways of ACTH action leading to stimulation of steroidogenesis and ornithine decarboxylase activity diverge subsequent to activation of the protein kinase.     

Effect of calcium on steroidogenesis in isolated human adrenal cells (author's transl)]

Isolated adrenal cells were obtained surgically from patients with primary aldosteronism, breast cancer, or Cushing's syndrome. They were prepared by the modification of Sayers method, and incubated at 37 degrees C for 2 hours under 95% O-2-5% CO-2, in the medium of calcium-free Krebs-Ringer bicarbonate buffer containing 0.2% glucose and 0.5% bovine serum albumin, to which various doses of calcium, ACTH, dibutyryl cyclic AMP or cycloheximide were added. Steroid production was measured by the method of Silber et al. In isolated normal adrenocortical cells, 11-OHCS was produced by calcium alone in the absence of ACTH or dibutyryl cyclic AMP, while it was not produced by ACTH alone without calcium. 11-OHCS production by ACTH was decreased in the high concentration of calcium (10.16 mM, 12.70 mM). Cycloheximide partially blocked an increase in 11-OHCS synthesis induced by calcium. These data suggest that adenyl cyclase of human adrenocortical cells may be stimulated by calcium alone, supporting the notion that calcium is a second messenger. The ratio of 11-OHCS production by calcium alone to that by dibutyryl cyclic AMP was higher in adenoma cells than in normal cells. This may account for the character of autonomic steroid production in adrenocortical adenoma cells.     

Role of calcium in luteinizing hormone-induced progesterone and cyclic AMP production in granulosa cells of the hen (Gallus domesticus)

The effects of calcium on steroidogenesis and cyclic AMP production in chicken granulosa cells were examined. For the expression of full steroidogenic effects by LH, forskolin, and 8-bromo cyclic AMP the presence of calcium in the incubation medium was essential, the optimal concentration being 1 mM. Moreover, calcium antagonists (verapamil, TMB-8) significantly suppressed steroidogenesis in response to all three agonists. The metabolism of 25-hydroxycholesterol and the conversion of pregnenolone to progesterone, however, were not affected by the lack of calcium or by coincubation with calcium antagonists. LH-stimulated cyclic AMP production was also suppressed in calcium-deficient medium and in the presence of the putative calcium channel blocker, verapamil. However, TMB-8 did not affect LH-induced cyclic AMP production. Moreover, neither forskolin- nor IBMX-induced cyclic AMP accumulation was significantly affected by lack of calcium or verapamil. These results are interpreted to indicate that the continuous presence of extracellular calcium is essential for hormonal regulation of steroidogenesis and is important for events both proximal and distal to cyclic AMP generation up to pregnenolone synthesis.     

Cyclic AMP levels in purified rat adrenal zonae fasciculata and reticularis cells and the effect of adrenocorticotrophic hormone

Cyclic AMP levels were measured in combined cells and supernatant fraction from incubations of dispersed rat adrenal zona fasciculata and zona reticularis cell preparations purified by unit gravity sedimentation. These measurements were correlated with deoxycorticosterone (DOC) and corticosterone outputs from the cells in the presence or absence of ACTH. Similar measurements of cyclic AMP outputs were made for unpurified dispersed, decapsulated rat adrenal cell preparations and they were found to correspond to previously reported measurements made by other workers on such preparations. The response of the purest zona reticularis cells to ACTH in terms of cyclic AMP output was 28-fold lower than that of the purest zona fasciculata cells (compared with a fivefold lower DOC output and a 20-fold lower corticosterone output) and the response to ACTH of the mixed-cell preparations was related to the number of zona fasciculata cells in the preparation, i.e. the greater the proportion of zona fasciculata cells in the preparation the greater the response in terms of both outputs of cyclic AMP and of either of the two steroids measured. This correlation is in accordance with the theory that cyclic AMP may be the secondary messenger for both zona fasciculata and zona reticularis cells of the rat adrenal cortex in mediating the response to an ACTH stimulus.     

On the role of protein synthesis in the response of adrenal tumor cells to ACTH.

Y-1 adrenal tumor cells were incubated with aminoglutethimide with and without ACTH. Greater production of pregnenolone from endogenous cholesterol was observed (after washing to remove aminoglutethimide) in mitochondria from cells incubated with aminoglutethimide and ACTH than in those from cells incubated with aminoglutethimide alone. This response was inhibited by cycloheximide and puromycin but not by chloramphenicol or actinomycin D. ACTH increased the incorporation of [3H]tyrosine into protein associated with mitochondria but not into total cell protein or protein of postmitochondrial supernatant. This response did not require aminoglutethemide block and was inhibited by cycloheximide and puromycin but not by chloramphenicol or actinomycin D. Dibutyryl cyclic AMP produced both of these responses (increased production of pregnenolone and synthesis of protein associated with mitochondria). The concentration of cycloheximide required to cause 50% inhibition of the responses to ACTH and dibutyryl cyclic AMP was approximately the same for steroidogenesis by whole cells, for production of pregnenolone by isolated mitochondria, for incorporation of [3H]tyrosine into Y-1 cell protein and for the increase in synthesis of protein associated with mitochondria produced by ACTH (0.08--0.2 microgram/ml). Disc gel electrophoresis revealed that the increased incorporation of [3H]tyrosine involved two proteins corresponding to molecular weight of approximately 27,000 and 13,000 respectively. These observations suggest that ACTH promotes synthesis of protein(s) by cytoplasmic ribosomes on stable messenger RNA, that the protein(s) becomes associated with mitochondria and that the protein(s) includes one or more which are associated with the increase in production of pregnenolone produced in mitochondria by the addition of ACTH to adrenal cells.     

Lack of effect of angiotensin on levels of cyclic AMP in isolated adrenal zona glomerulosa cells from the rat

The effects of pure [Asp1,Val5]- and [Asn1,Val5]-angiotensin II and also [des-Asp1,Ile5]-angiotensin II (angiotensin III) on cyclic AMP and steroid outputs by dispersed rat capsular cells, comprising 95% zona glomerulosa and 5% zona fasciculata cells, have been studied. The results showed that [Asp1, Val5]-and [Asn1, VAl5]-angiotensin II, at doses between 2.5 X 10(-11) and 2 X 10(-4) mol/l, which produced typical increases in steroidogenesis, failed to increase output of cyclic AMP. This lack of effect was observed whether the nucleotide was measured by radioimmunoassay or by adrenal binding protein and under the same conditions in which 8.4 mM-K+ consistently increased the output of cyclic AMP. Instead the results showed a small but significant decrease in cyclic AMP output with angiotensin II. Similar results were obtained with incubations for 60 rather than 120 min and with medium containing a concentration of 5 or 40 g bovine serum albumin/l. Although the levels of cyclic AMP were generally higher in the presence of the phosphodiesterase inhibitor, 3-isobutyl-1-methylxanthine, the same decrease relative to basal outputs was observed with angiotensin II which increased steroidogenesis. Angiotensin III also failed to increase output of cyclic AMP at doses (2.5 X 10(-9) to 2.5 X 10(-6) mol/l) which produced increases in steroid output equivalent to those with angiotensin II. These results indicate that angiotensin II and III can act through a cyclic AMP-independent mechanism.     

In vitro ACTH stimulation of corticosterone output in relation to cyclic nucleotide alterations in the crocodilian (Caiman sclerops) adrenal.

As ACTH increases cyclic GMP (cGMP) levels in the crocodilian adrenal, the cyclic AMP (cAMP) mechanism of ACTH action in corticosterone output was evaluated in Caiman sclerops. In vitro production of cAMP and corticosterone was determined by radioimmunoassay (RIA). Control adrenals showed a significant increase in cAMP levels above that occurring in normal and zero-time adrenals. In addition, a basal level of corticosterone output was present. Porcine ACTH produced a log-dose depression of cAMP levels below the control level. This inhibitory action was shared by Caiman ACTH. Both porcine and Caiman ACTH significantly increased Caiman corticosterone output. In contrast to the reptilian response, rat adrenals used as reaction controls responded to both porcine and Caiman ACTH with increased cAMP levels and corticosterone output. The $\text{cAMP}\text{cGMP}$ ratios in Caiman adrenals pursuant to ACTH stimulation demonstrated that increased steroid output was coincident with the lowest nucleotide ratio. A high degree of correlation exists between total steroid output and nucleotide ratio; however, evidence suggests that additional factors may also be involved.