Effects of L-Dopa on Serum Prolactin and PIF in Intact and Hypophysectomized, Pituitary-Grafted Rats

Abstract

The effects of L-dopa were assessed on serum prolactin, on hypothalamic prolactininhibiting factor content and on serum prolactin releasing activity in hypophysectomized female rats with or without an anterior pituitary (AP) graft and in intact female rats. In 2 separate experiments a single ip injection of L-dopa in hypophysectomized rats with an AP graft decreased serum prolactin concentration by 50–60% within 2 hr. L-Dopa increased hypothalamic PIF content by 35% and the blood serum from these rats decreased pituitary prolactin release in vitro by 65%. In hypophysectomized rats with no AP transplant, L-dopa elicited similar changes in the ability of the hypothalamus and serum to influence prolactin release. In intact rats, injection of L-dopa depressed serum prolactin concentration, increased hypothalamic PIF content and evoked the presence of prolactin inhibiting activity in the serum. These results suggest that L-dopa inhibits pituitary prolactin release by increasing hypothalamic synthesis and release of PIF. (Endocrinology91: 868, 1972)