The effects of prolactin on rat testicular steroidogenic enzyme activities

To investigate whether hyperprolactinemia directly affects rat testicular steroidogenesis, we examined the effects of prolactin (PRL) on microsomal 3β-hydroxysteroid dehydrogenase (3β-HSD), 17-hydroxylase (17-OH), 17,20-desmolase (17,20-D), 17-ketosteroid reductase (17-KSR) and aromatase enzyme activities. Adult hypophysectomized, gonadotropin-treated Fisher rats were rendered hyperprolactinemic by isografting pituitaries under the kidney capsule. The controls received skeletal muscle. All rats were sacrificed 7 days later and serum PRL was measured in each animal. PRL levels were 198 ± 14 ng/ml in the hyperprolactinemic rats and 4.3 ± 0.6 ng/ml in the controls (P<0.001). The testes were resected, pooled according to PRL levels, and microsomes were prepared from each pool. The activities of the 3β-HSD, 17-OH, 17,20-D, 17-KSR and aromatase were measured using as substrates ¹⁴C dehydroepiandrosterone, progesterone, 17-hydroxyprogesterone, androstenedione and testosterone, respectively. Hyperprolactinemia was associated with significant decreases in 3β-HSD, 17-OH, 17,20-D, 17-KSR and aromatase activities when compared to controls (P<0.005). We conclude that prolactin may have a direct effect on rat testicular steroidogenesis which appears to be independent of changes in gonadotropin secretion.