Prostaglandin-induced release of pituitary gonadotropins: Central nervous system and pituitary sites of action

Prostaglandins were injected either intravenously, intraventricularly, or into the anterior pituitary gland to evaluate their possible participation in the control of gonadotropin release. Their effect on plasma LH and FSH was determined by radioimmunoassay. Intravenous injection of prostaglandin E₂ (PGE₂) produced a slight increase in plasma LH but not FSH in ovariectomized animals. Prostaglandin E₁ (PGE₁), PGF_lα and PGF_2α were ineffective. Third ventricular (3rd V) injections of PGE₂ induced a marked increase in plasma LH in ovariectomized rats. The increase was much greater than that observed following iv injection, and PGE₁, F_lα or F_2α were ineffective. A slight increase in plasma FSH also followed 3rd V injection of PGE₂. Ovariectomized animals were injected SC 48 hr prior to the experiment with estradiol benzoate (10 µg) to sensitize the pituitary gland to the gonadotropin-releasing factor(s). In these animals 3rd V injections of PGE₂ produced a dose-related increase in plasma LH. In addition, a significant increase was also obtained with PGE₁. The other prostaglandins and the diluent were again ineffective. Intrapituitary injections of PGE₂ and E₁ were ineffective in ovariectomized animals but PGE₂ produced a small increase in LH in the estrogenprimed rats. The results indicate that PGE₂ and to a lesser extent PGE₁ have a specific effect in stimulating the release of LH by the adenohypophysis. The principal site of action appears to be on the central nervous system (CNS) with another less important site on the anterior pituitary itself. The findings suggest that PGE₂ and possibly PGE₁ are involved in neural control of pituitary gonadotropin release.