DOES PREGNANCY SUPPRESS THE LACTOGENIC HORMONE OF THE PITUITARY12

Abstract

The various theories which seek to explain the absence of milk secretion during pregnancy and its elaboration after parturition are reviewed. Most of these theories fail to take into account the important role of the lactogenic hormone of the ant. pituitary. Quantitative work on the lactogenic hormone has already demonstrated the very significant fact that this hormone remains low during pregnancy but that it increases several fold following parturition. Insufficient lactogenic hormone in the pituitary is considered the basic reason lactation does not take place during pregnancy. The agent responsible for the increase in lactogenic hormone following parturition is unknown at present. Pregnancy in rabbits has no effect on the lactogenic hormone. On the 20th day post partum the lactogen content of the pituitaries of rabbits during a period of simultaneous lactation and pregnancy was just as high as the pituitaries of rabbits that were only lactating. Also the lactogen content in the pituitaries of rabbits which were ovariectomized on the 20th day of pregnancy and killed 2-5 days later was not significantly greater than in unoperated 20-day pregnant rabbits. The placentas of 3 pregnant-lactating rabbits were shown to contain lactogen. Pregnancy evidently has no inhibiting effects on the lactogenic hormone of the pituitary. Copious lactation can be initiated only when there is a well developed mammary gland present, and when there is a high lactogen content in the ant. pituitary.