Reflex Stimulation of the Neurohypophysis (Posterior Pituitary Gland) and the Nature of Posterior Pituitary Hormone(s)

Abstract

THE sensory stimulus of suckling evokes nervous reflex release of the oxytocic substance from the neurohypophysis, which in turn stimulates the contractile tissue of the breast and causes a rise of milk pressure in the mammary ducts¹. Electrical stimulation of the nerve supply (the supraopticohypophysial tract) of the neurohypophysis, or injection of posterior pituitary extracts (especially the oxytocic fraction)², elicits similar effects on the breast. Rise in intra-mammary duct pressure produced by injection of the oxytocic substance, or by excitation of the milk ejection reflex alone, does not usually result in free flow of milk to the exterior, possibly because of some sphincter-like mechanism at the nipple. In some cases, however, excitation of the milk ejection reflex results in dribbling of milk from a nipple that is not being suckled or milked ; for example, the flow that may occur from the unsuckled breast of a nursing woman or from the udder of a cow subjected to routine procedures preceding milking.