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Influence of Hormones on Enzyme Activity in Mouse Mammary Gland in Vitro

Department of Zoology, Michigan State University, East Lansing 48823

ABSTRACT

Organ cultures of the mouse mammary gland have been concerned largely with the hormonal induction of secretory responses in nonsecretory prelactating tissue taken at mid-pregnancy. The impetus for these in vitro studies derives from experimentation with endocrinectomized mice wherein prolactin and cortisol initiated secretion in mammary glands in which lobulo-alveolar growth had been initiated by ovarian hormones and prolactin (29). Lobulo-alveolar formation which normally precedes lactational development does not appear to be a strict requirement for cellular function inasmuch as milk protein synthesis can be hormonally-induced in vitro in embryonic (5) and prepubertal (47) mammary tissue devoid of alveoli. These latter findings indicate that lobulo-alveolar formation can be dissociated from secretory development but do not necessarily imply that the status of the mammary cells is not important in the normal sequence of events leading to secretory function. For example, mammary explants from late pregnancy are more sensitive to hormonal stimulation than those from midpregnancy, and explants from involuted glands are even less responsive than the latter (31, 34).