Estrogen and progesterone augment growth responsiveness of mammary tissue to cholera toxin

Second (thoracic) mammary glands of endocrine intact mice were removed intact and incubated in Dulbecco's Modified Eagle's Medium supplemented with insulin, aldosterone, and cholera toxin. Insulin and aldosterone resulted in relatively little mammary development. However, insulin, aldosterone, and cholera toxin substantially increased mammary development, as assessed by development scores and DNA after 6 d of culture. Ovariectomy abolished the ability of cholera toxin to augment mammary development in vitro. Estradiol and progesterone injections for 3 d partly restored responsiveness of mammary tissue to cholera toxin, whereas responsiveness was greater after 6 d of injection than in endocrine-intact mice. Additionally, cyclic AMP-dependent protein kinase (kinase A) activity of fourth (inguinal) mammae was increased after as little as 3 d of estradiol and progesterone treatment. Cholera toxin induced phosphorylation of at least one protein was also increased by estradiol and progesterone. Because cholera toxin is a potent activator of adenylate cyclase, these findings suggest that estradiol and progesterone interact with cyclic AMP active agents to promote mammary development. This interaction may be mediated, at least in part, by increased kinase A activity and increased kinase A substrate availability.