Prolactin-Releasing and Release-Inhibiting Factor Activities in the Bovine, Rat, and Human Pineal Gland:In Vitroandin VivoStudies

Abstract

The effects of crude extracts of bovine, rat, and human pineal glands on prolactin (PRL) release were studied using an in vitro system. In addition, the effects of a known pineal constituent, arginine vasotocin (AVT), and crude bovine pineal extract (bPE) on PRL secretion were studied in vivo. Normal malerathemipituitaries(HP), incubated with bPE (13 ing tissue/HP) released 200%, 150%, and 285% more PRL into the medium than did their corresponding untreated control halves incubated in either Medium 199 alone, hypothalamic extract, or cerebral cortical extract, respectively. HP incubated with either rat (6 mg of tissue/HP) or human (25 mg of tissue/HP) pineal extract released 110% and 75% more PRL, respectively, than did their corresponding untreated control halves. HP exposed to 10 mg tissue eq of either bovine pineal fraction A₁ or bovine pineal fraction A₃ released 88% and 63%, respectively, less PRL than did their corresponding untreated control halves incubated in Krebs-Ringer Bicarbonate (KRB) medium. Quantities of melatonin, thyrotropin-re-1easing hormone (TRH), or estrogen, comparable to those found in the pineal, had no significant effect on PRL secretion in vitro. The iv injection of either bPE (90 mg tissue/rat) or AVT (10 μg/rat) into estrogen and progesteronetreated male rats resulted in a 40% and 138% increase, respectively, in plasma PRL titers, 10 min after injection, over pre-injection control levels. The per cent of increase in plasma PRL levels in these animals was significantly greater than that observed in control rats receiving either saline or cortical extract. The results suggest that crude extracts of pineal glands of three different species contain prolactinreleasing factor (PRF) activity which is probably not due to any endogenous melatonin, TRH, or estrogen that may be present. Conversely, two bovine pineal fractions, A₁ and A₃, appeared to exhibit prolactininhibiting factor (PIF) activity. We have concluded that the pineal gland may serve as an alternate or supplemental source of PRF and/or PIF. (Endocrinology99: 152, 1976)