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 time-dependent 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 less than 0.01). Similarly, the serum estradiol level decreased in the oPRL-treated groups on the first day and was restored on the second day.(ABSTRACT TRUNCATED AT 250 WORDS)