The Effect of Catecholamines on Hormone Release from Anterior Pituitaries and Ventral Hypothalami Incubated <i>in vitro</i>

Abstract

Incubation of pituitaries in the presence of cate-cholamines produced a dramatic inhibition of prolactin release by the glands. The minimal effective dose of both dopamine hydrochloride (DA) and norepinephrine bitartrate (NE) was approximately 0.1 µg/ml, and the inhibition increased with the dose, up to a maximum of 2–8 µg/ml. The higher doses of DA slightly reduced the amount of growth hormone (GH) detected but failed to modify the release of FSH and LH. When hypothalami were coincubated with pituitaries, slight stimulation of release of gonadotropins and GH occurred. The release of prolactin was inhibited, however, suggesting that the hypothalami released hypothalamic neurohormones during the incubation, which then altered the release of anterior pituitary hormones. The inhibitory effect of DA on prolactin release by pituitaries in vitro was completely blocked by haloperidol. This made it possible to study the effect of DA on the release of prolactin inhibiting factor (PIF) from hypothalamic fragments incubated in vitro. Media from such incubations, in the presence or absence of added haloperidol, were capable of further inhibiting the release of prolactm from pituitaries. In similar experiments, NE had no significant effect on PIF release. There was a slight stimulation of GH release when pituitaries and hypothalami were coincubated in the presence of DA. On the other hand, in these experiments, no stimulatory effect of DA on the output of FSH and LH in the coincubation system was observed. The results indicate that DA and NE can profoundly inhibit prolactin release by the incubated pituitary and that DA can stimulate a release of PIF from incubated hypothalami.