Modulation of ovarian LH receptor and serum hormone levels in rats with hyperprolactinemia induced by administration of ovine prolactin or sulpiride.

Hyperprolactinemia was experimentally produced in rats by administration of ovine prolactin (oPRL) and sulpiride, and tried to evaluate the effect of hyperprolactinemia on ovarian receptor for luteinizing hormone (LH) as well as that on serum gonadotropin and steroid hormone levels. Wistar-Imamichi strain mature female rats showing 4-day estrous cycles were treated with various doses of oPRL or sulpiride twice a day for 4 days from diestrus. They were killed on the fifth day. Binding of ovarian LH receptors was reduced by a small dose of oPRL (0.1 IU) or sulpiride (0.25 mg) and restored to normal by larger doses of oPRL. However, larger doses of sulpiride (50 or 100 mg) increased the receptor bindings beyond the control level (4.39 +/- 0.40 ng/mg homogenate protein). Serum prolactin levels decreased in rats treated with larger doses of oPRL, but increased with larger doses of sulpiride. Serum LH levels increased with both agents. Although the ovaries treated with either oPRL or sulpiride suggested the lack of ovulation, there were no significant changes of steroid hormones in oPRL groups. In contrast, sulpiride treatment resulted in a reduction of estradiol and an increase of progesterone secretion, suggesting the prolonged effect of the drug. Thus, prolactin appeared to act on the rat ovarian LH receptors in two different manners in hyperprolactinemia, depending on the amount of this hormone or a ratio of prolactin to LH.