Mechanism of abnormal production of adrenal androgens in patients with adrenocortical adenomas and carcinomas.

The production of adrenal androgens can be modulated by the activities of steroidogenic enzymes and by the electron transfer system, NADPH-cytochrome P450 reductase (Red) and cytochrome b5 (b5), both of which have been shown to increase 17,20-lyase activity in vitro. To clarify the mechanism of diminished secretion of adrenal androgens in patients with adrenocortical adenoma and Cushing's syndrome and of excess secretion in patients with adrenocortical carcinoma, we investigated the enzymatic activities of cytochrome P45017 alpha, 3 beta-hydroxysteroid dehydrogenase (3 beta-HSD), and Red as well as the content of b5 in five adenomas, three carcinomas, and two normal adrenal glands. An in vitro enzyme assay using a microsomal fraction of the tissues indicated that all the tumors had almost the same degree of 17 alpha-hydroxylase activities as the normal adrenals. However, the relative activity ratio of 17,20-lyase to 17 alpha-hydroxylase of the three adenomas was markedly diminished, and 3 beta-HSD activity was apparently lower in the three carcinomas. The messenger RNA concentrations of P45017 alpha were similar in all tumors, whereas those of 3 beta-HSD were markedly lower in the carcinomas than in other tissues. Both the content of b5 and the activity of Red were significantly lower in the adenomas. These results suggest that low concentrations of adrenal androgens in patients with adrenocortical adenomas are mainly due to low 17,20-lyase activity, which may be explained in part by a lower content of b5 and Red. In addition, high concentrations of adrenal androgens in patients with adrenocortical carcinoma are mainly due to the diminished activity of 3 beta-HSD.