Effect of Anterior Pituitary-Like Hormone on Lactation in the Albino Rat

Abstract

Experimental development of the mammary gland by administration of anterior pituitary-like hormone of pregnancy urine (A.P.L.) has been reported by several investigators. Bradbury 1 observed that the mammary glands of the mouse could be stimulated to develop by A.P.L. treatment, but only in those animals in which the uterus and ovaries were present. Selye, Collip, and Thomson 2 extended these findings to include the albino rat, and noted that increased development of the mammary glands paralleled an increase in the weight of the ovaries of A.P.L.-treated animals. No milk secretion occurred except after removal of the intensely luteinized ovaries, and then only in those animals in which the pituitary was intact.

In addition to a stimulative effect on the mammary gland, A.P.L. has been shown to inhibit milk secretion in normal lactating mice by Enzmann and Pincus, 3 and in normal and ovariectomized lactating mice by De Jongh. 4 Selye, Collip, and Thomson 5 administered A.P.L. and pig pituitary extract on the 3rd or 4th day after initiation of milk secretion in rats and observed an immediate inhibitory effect on lactation, which they suggest is exerted through the hypophysis rather than directly on the mammary glands. The mammary glands showed signs of secretion, but there was apparently lessened activity, since the suckling young of treated animals received little nourishment, lost weight, and eventually died.

The present work was undertaken to determine the effect of A.P.L. alone on lactation in the albino rat. Fifty-three lactating female animals of the Wistar strain and their litters were employed. Insofar as possible, litter-mate mothers were used and distributed among 3 groups: (1) normal untreated controls, (2) physiological saline-injected controls, and (3) Antuitrin St-treated experimental animals.