Role of cortisol in mammary gland development. The role of cortisol is shown for the different post-embryonic developmental stages of the mammary gland. Other hormones involved in the different developmental stages are also listed. Estrogen and progesterone promote ductal system proliferation during puberty. However, the DNA binding function of the glucocorticoid receptor also appears to be required. During pregnancy, cortisol contributes to lobuloalveolar development of the mammary gland, in conjunction with estrogen and progesterone. Prolactin and cortisol prepare the mammary cells for lactation and stimulate milk protein production following parturition. In addition, cortisol contributes to the maintenance of lactation by suppressing involution. ER, endoplasmic reticulum.