Reduction of milk secretion by prolactin-inhibiting factor: further evidence that exteroceptive stimuli can release pituitary prolactin in rats.

Abstract

A test was devised to ascertain the effect of hypothalamic extracts on milk secretion in the rat. The mammary glands were emptied of milk by 30-min suckling by the pups with the aid of oxytocin injected into the mother. The mothers then were reisolated from the pups for 16 hr, whereupon the milk yield was estimated from the weight loss of the mothers and the weight gain of the pups after 30-min suckling. The injection of either crude extracts of rat stalkmedian eminence (SME) or a purified preparation of ovine prolactin-inhibiting factor (PIF) (T-135) just prior to the first suckling resulted in significantly lesser amounts of milk accumulated during the 16-hr period in comparison with that obtained following injection of saline, rat cerebral cortical extract, the diluent used in the preparation of the PIF, or of other fractions (T-153 or 155) of ovine hypothalamic extract devoid of PIF activity. The reduction in milk secretion from the injection of rat SME or PIF presumably was secondary to the blockade ...