The mechanism of hormonal receptor regulation in the rat ovary following administration of gonadotropin and prolactin.

In order to understand the role of hormonal receptors in patients with hyperprolactinemia, changes in the ovarian receptors for prolactin and LH and in the serum hormone levels were studied in mature female rats. Wistar-Imamichi strain rats were pretreated with ovine prolactin (oPRL; 1IU), hCG (10IU) or hMG (20IU) for 4 days and oPRL, hCG, oPRL plus hCG for 8 days. The ovarian LH receptor levels fell significantly in rats stimulated with hCG, oPRL or hCG plus oPRL for 4 or 8 days. The serum estradiol level rose with hCG, and fell with oPRL. Combined treatment with oPRL and hCG synergistically reduced LH receptor to below the control level, and the estradiol level near the control compared with that by hCG alone. A decrease in LH receptor (60%) after the 4-day treatment with oPRL was further lowered to 53% of the control level after the 8 day treatment. Prolactin receptor levels rose with hCG after the 4-day administration, and then returned to normal after the 8-day treatment. The hMG treatment for 4 days raised the serum estradiol and progesterone levels to 9 times and twice those of the controls, respectively, without changing ovarian receptor levels. Prolactin seems to lower the ovarian LH receptor levels under certain conditions, and this may be one of the causes of the refractory reaction to gonadotropin therapy in patients with hyperprolactinemia.