THE POSSIBLE ROLE OF OXYTOCIN IN STIMULATING THE RELEASE OF PROLACTIN1

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Abstract
Hypothalamic lesions in the supraoptico-hypophysial tract of lactating rats produceda block of both milk ejection and milk secretion. The defect in milk secretion was correlated with the deficiency in endogenous oxytocin secretion, but there was no correlation between polydipsia and milk ejection or milk secretion. The effective lesions interrupted the supraoptico-hypophysial tract either in the median eminence or in front of this structure. The defect in milk secretion was seen in rats where median eminence, hypophysial portal vessels, and anterior lobe of the pituitary appeared to be essentially normal on histological examination. Pitocin and synthetic oxytocin delayed mammary involution in lactating rats. Pitressin produced a smaller effect. The effect of Pitocin and synthetic oxytocin persisted in rats with hypothalamic lesions. Since a defectin endogenous oxytocin release led to a defect in milk secretion, whereas oxytocin delayed mammaryinvolution, it was postulated that oxytocin may be the neurohumor stimulating the release of lactogenic hormone.