FACTORS INFLUENCING LOBULO-ALVEOLAR DEVELOPMENT AND MAMMARY SECRETION IN THE RAT1

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Abstract
During pregnancy, the mammary gland of the rat undergoes a marked transformation so that, near the end of gestation, it consists of grape-like clusters of alveoli in lobule formation. Two days before parturition, secretion within the alveoli becomes visible (Turner and Schultze, 1931). Full development of the mammary gland, therefore, is attained when lobulo-alveolar development with secretion is established. In the absence of pregnancy, full development of the mammary gland has been produced experimentally in rats by injection of the gonadotropic substance from the urine of pregnant women (Selye et al., 1933). This hormone causes intense luteinization of the ovaries and complete lobulo-alveolar development of the gland but no secretion. If the stimulated ovaries are excised, secretion will follow about thirty-six hours later and the gland will then present the appearance of full development.