Modulation of testicular receptors for LH, FSH and prolactin by the administration of ovine prolactin in mature rat.

To elucidate the role of prolactin on testicular function, we treated mature rats with ovine prolactin (oPRL) and investigated the dose and timedependent changes in testicular LH, FSH and prolactin receptors as well as in serum gonadotropin and steroid levels. Twelve week-old rats were injected sc with a single dose of various amounts of oPRL (0.2, 1 and 5 IU) and killed on the first, second and third days after the treatment. Testicular LH receptor decreased to 59% of the control level as a function of time while prolactin receptor increased to 244% maximally of the control level on the second day. In contrast, FSH receptor changed in a different fashion. Smaller amounts of oPRL (0.2 and 1 IU) raised the receptor level to 193% of the control level on the first day whereas a larger amount (5 IU) did not change the receptor, which tended to remain in a low level throughout the experimental period. The serum FSH level significantly increased in every group on the second day, then returned to the control range by the third day. On the other hand, the serum testosterone level changed in a characteristic manner, decreased significantly in every group on the first day though not in a dose-dependent fashion, returned to normal on the second day and significantly increased in the 0.2 IU group on the third day (p<0.01). Similarly, the serum estradiol level decreased in the oPRL-treated groups on the first day and was restored on the second day. These results suggested that exogenously administered prolactin modulated the testicular LH, FSH and prolactin receptors, which might be subsequently related to the decreases in estrogen and testosterone secretion. These findings with prolactin may be, in part, relevant to hypogonadal function in man with hyperprolactinemia. rat; testis; receptor regulation; LH, FSH and prolactin receptors; hyperprolactinemia.