Effects of induced hypoprolactinemia on testicular function during gonadal maturation in the rat

We have evaluated the effects of hypoprolactinemia during gonadal maturation in the male rat. Intact 30‐day‐old rats were injected daily for 10 days with three different doses of bromocriptine (0.75, 1.5 or 3.0 mg/kg of body weight/day). At the end of the treatment period, the animals were sacrificed, serum was collected for prolactin (PRL), LH, and androgen measurements. Intratesticular testosterone and 5 α‐androstanediol (androstanediol) were measured following celite column chromatography and a specific radioimmunoassay. In addition, the production of androgens by decapsulated testes and dispersed Leydig cells was also studied in vitro. Serum levels of PRL (9.4 ± 1.9 ng/ml) were suppressed to undetectable levels in the three bromocriptine‐treated groups, whereas LH levels were not altered. All three doses of bromocriptine markedly depressed serum testosterone (plus DHT) and androstanediol. Intra‐testicular testosterone and androstanediol were diminished (25% and 35%, respectively, P < 0.05) during hypoprolactinemia. Decapsulated testes and dispersed Leydig cells from bromocriptine‐treated animals showed a significant reduction in the basal secretion of testosterone (plus DHT) and androstanediol, and in androgen responses to submaximal hCG stimulation. Maximal steroidogenic responses from bromocriptine‐treated rats were similar to controls. The present findings show that, during puberty, bromocriptine influences testicular steroidogenesis, and these effects may be partly due to changes in PRL levels. A direct effect of this dopaminergic agonist on the male gonad cannot be completely ruled out.