Stimulatory and inhibitory effects of prostaglandin E 2 on prolactin release in the domestic fowl

Abstract

In vivo prolactin secretion was increased in immature cockerels 20–30 min after the intravenous administration of prostaglandin (PG) E 2 at a dose of 200 μg/kg. The addition of PGE 2 to incubation medium had no direct effect on the release of pituitary prolactin during short-term (3-hr) culture, but augmented the stimulatory effect of hypothalamic tissue on prolactin secretion. The stimulatory effect of serotonin, noradrenaline, acetylcholine, and histamine on hypothalamus-induced prolactin release was also increased when pituitaries were coincubated with 10 −7 M PGE 2, as was the stimulatory effect of thyrotrophin-releasing hormone (TRH) and hypothalamic extract (HE). The long-term (24-hr) preincubation of pituitaries with 10 −7 M PGE 2 reduced the responsiveness of the prolactin-secreting cells to TRH or HE stimulation. PGE 2 treatment also reduced the stimulatory effect of hypothalamic tissue on prolactin release and diminished the stimulatory effect of serotonin on hypothalamus-induced prolactin secretion. A 24-hr preincubation of hypothalamic tissue with 10 −7 M PGE 2 also reduced its stimulatory effect on prolactin release when subsequently incubated with control pituitary glands. These results demonstrate that PGE 2 initially stimulates in vivo and in vitro prolactin secretion in the fowl, possibly by increasing the release of hypothalamic prolactin-releasing activity and/or by increasing pituitary sensitivity to provocative stimuli. Chronic PGE 2 stimulation appears to result in a reduction in pituitary responsiveness to stimulatory influences and in the release of hypothalamic-releasing activity.