Interaction of progesterone and adrenocorticoids in ultrastructural development of the mammary gland of the rat

Comparative development of rough endoplasmic reticulum (RER) in mammary glands of rats was studied in relation to levels of progesterone and adrenocorticosteroids. The tranquilizer perphenazine was administered to stimulate secretion of prolactin; serum glucocorticoids also increased. When perphenazine was administered after ovulation, serum progesterone was increased 18-fold, but when treatment was begun on proestrus, ovulation was inhibited and serum progesterone increased only 4-fold. Concentrations of progesterone in the breast were approximately 10-fold greater than, but parallel to, serum concentrations. In ovulating rats the RER was poorly developed. In nonovulating rats extensive development of RER occurred. Cortisol acetate given to ovulating, perphenazine-treated rats did not alter levels of serum progesterone, but tissue progesterone was reduced by 50 per cent and development of RER approached that in nonovulating rats. The development of secretory capacity (formation of RER) in the breast appears to depend on the relation between stimulation by glucocorticoid and inhibition by progesterone.