Effects of Oxytocin and Blocking Agents upon Pituitary Lactogen Discharge in Lactating Rats.

Abstract

The effect of various compounds upon release of lactogenic hormone from the hypophysis in response to nursing stimuli has been studied in 14-day postpartum lactating rats. Atropine, Dibenamine [N-(2-chloroethyl) dibenzylamine] and Nembutal (pentobarbital sodium) effectively blocked pituitary lactogen discharge since 30 minutes nursing evoked no decline (2.35, 2.39 and 2.46 Reece-Turner units/100 g, respectively) from previously obtained control prenursing level (2.44 R-T units/100 g). The normal level following 30 minutes nursing was previously determined as 1.66 R-T units/100 g. Since Dibenamine is a potent adrenergic blocking agent and atropine a cholinergic blocking, it is suggested cholinergic and adrenergic links are involved in the reflex arc responsible for lactogen discharge from rat pituitary gland. Oxytocin injected intravenously into Nembutal-anaesthetized lactating rats in physiological doses failed to alter pituitary lactogen (2.49 R-T units/100 g) from the control prenursing level. Amounts of oxytocin 30 and 60 x this dose produced but a slight discharge. These results suggest oxytocin has no stimulatory effect upon pituitary lactogen release in the lactating rat, and are contrary to the recent hypothesis that oxytocin is a humoral link involved in lactogen discharge.