The effect of a placental mammotrophin and cortisol on the ultrastructure of rat mammary gland in organ culture.

Mammary gland explants obtained from 13 days pregnant rats were cultured for 3, 6 and 9 days in the presence of serum of either virgin rats or 13 days pregnant rats. Insulin was added alone or in combination with cortisol. The way these different forms of treatment affected the ultrastructure was studied. With virgin rat serum plus insulin alone the mammary gland regressed to a lower state of development comparable to that of the virgin rat in vivo. When virgin rat serum was replaced by 13 days pregnant rat serum--which contains rat chorionic mammotrophin--the initial development was maintained, but synthesis of secretory products ceased. When cortisol was added to the virgin rat serum plus insulin, cortisol maintained the differentiated state originally present. Even some secretory activity was induced, but at a minimal level. With cortisol added to the pregnant rat serum plus insulin, the explants were stimulated to synthetize the extrude secretion products.