New aspects of androgens, prolactin, and ACTH interaction in men.

Some endocrine effects of prolactin (PRL), ACTH, and corticosteroids in testicular function were evaluated by measuring, in normal men, the effects of short-term experimental stimulation and suppression of either plasma PRL levels or adrenal function on plasma androgen profile. PRL levels were increased by administration of metoclopramide or sulpiride or suppressed with bromocryptine. Long-acting testosterone (T) was injected at 8 a.m. on one day in a control period and during a 9-day period of metoclopramide administration. PRL increase was accompanied by a rise in plasma 17-hydroxyprogesterone and T, whereas PRL suppression induced an increase in 5 alpha-dihydrotestosterone (DHT) plasma levels. Peripheral converions of T into DHT and androstenedione, noted after T injection, decreased during concomitant metoclopramide administration. Plasma testicular androgen levels were lowered after long-acting ACTH injections as well as after 24-hr cortisol administration, but the metoclopramide-induced PRL increase appeared to prevent the suppressive effects of ACTH on plasma T. A low-dose dexamethasone treatment did not modify testicular androgen levels. Experimentally induced hyperprolactinemia may have a stimulatory effect on testicular androgen secretion as well as a lowering action on 5 alpha reduction and oxidative T metabolism in man. On the other hand, ACTH-induced androgen suppression seems to be mediated through high circulating levels of corticosteroids; furthermore, PRL and corticosteroids might have reciprocal influences that modulate their effects on testicular function.