Progesterone and glucocorticoid in relation to the growth and differentiation of mammary epithelium

In pursuit of a model system in which to determine whether exposure to progesterone is necessary for mammary epithlial cells to develop their differentiative potential, hormone-dependent growth of the mammary epithelial rudiment in adult male mice has been reexplored. The formation of ductal cells can be effected by administration of estradiol in the absence of endogenous progesterone and glucocorticoid, using adrenalectomized-castrated animals. The resulting epithlium contains three times more lactose synthetase activity, per epithelial cell, than that in midpregnant mice. The blood spermidine level in these doubly operated animals was similar to the concentration of spermidine required to substitute effectively for glucocorticoid during mammary differentiation in vitro, It is suggested that spermidine can partially supplant glucocorticoid in vivo in milk protein synthesis. It is also concluded that, unlike other secondary sex tissues, mammary cells do not require exposure to progesterone during their ontogeny in order to realize their differentiative potential. The positive role of this steroid in mammary development is apparently limited to its effect on the formation of alveolar structures.