Effects of prolactin and bromocryptine on the regulation of testicular luteinizing hormone receptors in mice

The binding of luteinizing hormone (LH) to testicular homogenates increased gradually in mice from 15 to 60 days of age, while the level at 90 days was almost the same as that at 60 days. The plasma concentration of prolactin (PRL) increased significantly from 15 to 40 days and thereafter remained constant. In order to ascertain the influence of PRL on testicular receptors for LH, bromocryptine was injected subcutaneously for 10 days into immature (20-day-old) and adult (90-day-old) mice. In 20-day-old mice, treatment with bromocryptine significantly reduced the plasma levels of PRL but had no significant effects on the binding of LH to receptors in 30-day-old mice. However, in 90-day-old mice, treatment with bromocryptine led to a significant reduction in numbers of receptors for LH 10 days later. There was no difference in dissociation constants (Kd) between groups of oil-injected (Kd = 6.5 x 10(-10) M) and bromocryptine-injected (Kd = 4.6 x 10(-10) M) mice. The reduction in binding of LH per testis of 100-day-old mice after treatment with bromocryptine was eliminated by the simultaneous administration of ovine (o) PRL. The plasma level of follicle-stimulating hormone (FSH) in 100-day-old mice, which tended to be decreased as a result of treatment with bromocryptine, was markedly increased by treatment with oPRL. There were no distinct changes in binding of FSH in any of the groups.(ABSTRACT TRUNCATED AT 250 WORDS)