Hyperprolactinemia enhances LH-stimulated 4-ene-5 alpha-reductase activity but inhibits LH-induced 17-hydroxylase activity in testes of hypophysectomized immature rats.

Two pituitaries from 7-week old female rats (Sprague-Dawley strain) were grafted under the capsule of the left kidney of 21-day old male rat. The pituitary grafted and sham-operated rats were hypophysectomized at 27 days of age. The hypophysectomized rats, in groups of 4, were given daily injections of 9 micrograms NIAMDD-oLH-23 (minimum effective dose) or saline for 3 days starting from day 29. Testicular homogenates were incubated with [3H]progesterone or [14C]4-androstene-3,17-dione, and enzyme activities per testes were estimated. Testicular HCG-binding sites were also measured. Hypophysectomy caused significant decreases in activities of testicular 5 alpha-reductase, 17-hydroxylase, and 17 beta-hydroxysteroid oxidoreductase. These decreased enzyme activities were significantly stimulated by LH treatment. Although pituitary grafts alone showed no effects on these enzyme activities in the testes of the hypophysectomized rats, the grafts significantly enhanced LH-stimulated 5 alpha-reductase activities but inhibited LH-stimulated 17-hydroxylase activity. Testicular LH/HCG receptors were significantly increased by the grafts, especially in the presence of LH, without affecting affinity for HCG. The present results demonstrate for the first time that hyperprolactinemia directly stimulates LH-stimulated 5 alpha-reductase activity in rat testes. The results also show that the same grafts directly inhibit LH-stimulated 17-hydroxylase activity, probably via postreceptor mechanisms.