Further Studies of Stimulation of Anterior Pituitary Cyclic Adenosine 3',5'-Monophosphate Formation by Hypothalamic Extract and Prostaglandins

Abstract

Abstract Crude ovine hypothalamic extract in vitro increased the formation of cyclic adenosine 3',5'-monophosphate (cyclic AMP) by rat anterior pituitary glands but not by posterior pituitary, pineal, adrenal, or liver. Epinephrine (30 µg per ml) stimulated formation of cyclic AMP in pineal gland and adrenocorticotropic hormone- (8 i.u. per ml) and glucagon-(100 µg per ml) augmented cyclic AMP in adrenal and liver, respectively. Hypothalamic extract also rapidly increased adenyl cyclase activity in homogenates of rat anterior pituitary glands. Although theophylline (10-2 m) inhibited phosphodiesterase activity in anterior pituitary homogenates, hypothalamic extract had no effect on this enzyme either in the presence or absence of theophylline. Theophylline addition increased the concentration of anterior pituitary cyclic AMP and potentiated effects of hypothalamic extract on this parameter, but had no effects on luteinizing hormone release. Hypothalamic extract did not inhibit ATPase activity. Exclusion of Ca2+ from the buffer did not diminish stimulation of cyclic AMP formation by hypothalamic extract. Anterior pituitary cyclic AMP was not increased by high K+ concentration in the incubation medium. Prostaglandins added in vitro also increased formation of cyclic AMP by anterior pituitary, but there was marked variation in their potency. Prostaglandin E1 was the most effective and F1α the least. However, none of the prostaglandins increased luteinizing hormone release in vitro. Hypothalamic extract and prostaglandin E1 stimulated 3H-adenine incorporation into 3H-labeled cyclic AMP in intact anterior pituitary glands. NaF did not increase 3H-adenine incorporation into 3H-labeled cyclic AMP in intact pituitary in vitro, although it markedly increased adenyl cyclase activity in pituitary homogenates. Epinephrine (200 µg per ml) did not modify the stimulation by hypothalamic extract of either cyclic AMP synthesis or luteinizing hormone release. Carbamylcholine (30 µg per ml), dopamine (30 µg per ml), serotonin (30 µg per ml), prostaglandin E1 (10 µg per ml), or histamine (30 µg per ml) added in vitro had no effect on cyclic AMP concentrations in hypothalamic fragments.