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

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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 stud- ies derives from experimentation with endo- crinectomized mice wherein prolactin and cor- tisol initiated secretion in mammary glands in which lobulo-alveolar growth had been initi- ated by ovarian hormones and prolactin (29). Lohulo-alveolar formation which normally pre- cedes lactational development does not appear to be a strict requirement for cellular function inasmuch as milk protein synthesis can be hor- monally-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 neces- sarily imply that the status of the mammary cells is not important in the normal sequence of events leading to secretory function. For ex- ample, mammary explants from late pregnancy are more sensitive to hormonal stimulation than those from midpregnaney, and explants from involuted glands are even less responsive than the latter (31, 34). The three hormones, insulin, prolactin, and adrenal eorticosteroid, appear to play impor- tant roles in the secretory development of mammary explants in which many of the struc- tural and functional features parallel those of lactating tissue in vivo. The nmltiplicity of the events associated with the capacity of mam- mary cells to secrete milk in vitro has stimu- lated inquiry into the individual roles of these hormones, their time sequence of effect, and the interlinking of the effects as an initial step in elucidating hormonal control mechanisms. Some of the work has been the subject of re- cent reviews (12, 42, 44), and Denamur (6) has discussed comparative aspects of lacto- genie responses in mammary culture. The observation that lactation is accom-