Effects of proopiomelanocortin peptides and angiotensin II on steroidogenesis in isolated aldosteronoma cells.

Cells isolated from five aldosterone-producing adenomas were used to study glucocorticoid and aldosterone production in response to ACTH, angiotensin II (A II), and peptides derived from proopiomelanocortin (POMC), viz. the 16K N-terminal fragment (16K) and its derivative, gamma 3MSH and the C-terminal fragment beta-lipotropin (beta LPH) and its derivative beta-endorphin. At concentrations similar to those of ACTH and A II (10(-12)-10(-10) M), 16K, gamma 3MSH, and beta LPH selectively stimulated aldosterone production, which reached levels close to those obtained with A II. ACTH, however, was the most effective stimulant of steroidogenesis. The 16K, gamma 3MSH, and beta LPH peptides potentiated the action of ACTH, particularly in the case of aldosterone production. beta-Endorphin, whether used alone or in association with ACTH, had no effect on steroidogenesis at the dose used (10(-10) M). The principal glucocorticoid products of the adenoma cells were cortisol and corticosterone. The ratios of corticosterone to cortisol (B/F) and aldosterone to corticosterone (A/B) varied considerably from one adenoma to another, both basally and in response to ACTH. Nevertheless, within individual adenomas, the mean B/F ratio induced by ACTH [0.280 +/- 0.013 (+/- SEM)] was significantly larger than that induced by A II (0.127 +/- 0.007; P less than 0.001). By contrast, the A/B ratio in response to ACTH (0.061 +/- 0.003) was significantly smaller than that in response to A II (0.159 +/- 0.010; P less than 0.001). The values obtained with 16K (B/F, 0.106 +/- 0.010; A/B, 0.192 +/- 0.028) and gamma 3MSH (B/F, 0.122 +/- 0.012; A/B, 0.178 +/- 0.020) were close to those obtained with A II. 16K and gamma 3MSH potentiated ACTH's effect on steroidogenesis mainly by increasing the A/B ratio from 0.061 +/- 0.003 for ACTH alone to 0.100 +/- 0.008 for 16K plus ACTH (P less than 0.005) and to 0.092 +/- 0.005 for gamma 3MSH plus ACTH (P less than 0.001). The findings suggest that the stimulation of aldosterone production by 16K and gamma 3MSH in aldosteronoma cells is of the A II type and that these peptides may play a role in the genesis of primary aldosteronism.

Inhibition of cortisol production in isolated guinea-pig adrenal cells.

Cortisol, added to 1 ml incubation medium containing 3-4 X 10(5) isolated guinea-pig adrenal cells, provoked a decrease in basal and ACTH (250 pg)-stimulated cortisol production, in correlation with the amounts used (50 ng-2,000 ng). A decrease in aldosterone production could be seen when cortisol concentrations reached or exceeded 1,000 ng/ml. There were no variations in either androgens (delta 4-androstenedione, dehydropiandrosterone) or 17-hydroxyprogesterone. Only 11-deoxycortisol was slightly increased. Using increasing concentrations of ACTH (50-250 pg), both in the absence and in the presence of 1,000 ng cortisol, it was noted that the inhibition induced by cortisol was of a competitive type and could be overcome by ACTH. This decrease in cortisol was concomitant with an increase in 11-deoxycortisol. Neither corticosterone nor dexamethasone reduced cortisol production. In addition, it was shown that the conversion of tritiated 11-deoxycortisol to radioactive cortisol increased significantly under the influence of 250 pg ACTH (mean relative variation of 21.7% +/- 7.7 (SEM), n = 6, P less than 0.05); but decreased significantly under the combined effect of 1,000 ng exogenous cortisol and the same dose of ACTH: (mean relative variation of 4.3% +/- 1 (SEM), n = 8, P less than 0.005). There is therefore reason to believe that the concentrations of cortisol at the adrenal level modulate the stimulation induced by ACTH and that this self-adjustment forms part of the control mechanisms involved in corticosteroidogenesis.

Effects of cyproterone acetate on adrenal steroidogenesis in vitro.

The effects of cyproterone acetate (CA) on steroidogenesis in isolated guinea-pig adrenal cells have been investigated by measuring the production of cortisol, its immediate precursors (11-deoxycortisol and 17-hydroxyprogesterone), and adrenal androgens (delta 4-androstenedione and dehydroepiandrosterone). Used at a dose of 2 micrograms/ml, CA provoked a sharp drop in the production of cortisol, aldosterone and 11-deoxycortisol. By contrast, 17-hydroxyprogesterone, delta 4-androstenedione and dehydroepiandrosterone were increased, which suggests that 21-hydroxylase activity is inhibited. With concentrations above 2 micrograms/ml CA, it would seem to be the 3-beta-ol-dehydrogenase-delta 4,5-isomerase complex that is affected, since dehydroepiandrosterone exhibited a sudden increase, whereas 17-hydroxyprogesterone and delta 4-androstenedione showed a relative decrease. The enzymatic system or systems involved therefore appear to be linked to the concentration of CA used but, whatever the case, the drop in cortisol production is accompanied by a decrease in aldosterone and an increase in adrenal androgen levels.

Responses of isolated guinea-pig adrenal cells to ACTH and pro-opiocortin-derived peptides.

A comparison of the responses of isolated guinea-pig adrenal cells to ACTH and pro-opiocortin-derived peptides was carried out by measuring cortisol, aldosterone, androstenedione and dehydroepiandrosterone production. With concentrations below 10,000 pg/ml, no steroidogenic activity was found in response to either beta-LPH, gamma-LPH, gamma 3-MSH or the 16K fragment, whether assayed alone or in association with ACTH. At concentrations above 10,000 pg/ml, gamma-LPH (100 ng), the 16K fragment (100 ng) and beta-endorphin (500 ng) proved to be totally inactive. beta-LPH from 25 to 250 ng, however, exhibited a significant though slight stimulatory effect on cortisol, aldosterone and androstenedione production. Its effectiveness on aldosterone production was especially marked, but the extent of the response was modest in view of the concentrations used.