Studies on the Function of Glucocorticoid in Mouse Mammary Epithelial Cell Differentiation in Vitro

Glucose 6-phosphate dehydrogenase activity is stimulated maximally in mouse mammary epithelial cells in culture in the presence of insulin, hydrocortisone, and prolactin. Insulin, by itself, is a potent stimulus, whereas both hydrocortisone and prolactin require insulin for manifestation of their effects. Time course studies of the change in enzyme activity show that insulin produces approximately a 100% increase in the enzyme activity during the first 48 hours and that thereafter the activity decreases rapidly to the basal level. Addition of prolactin to the insulin-containing medium effects a larger increase up to about 200%, but after 2 days in culture the activity again declines markedly. Hydrocortisone, together with insulin, increases the activity by about 250% and maintains this high level for 4 days in culture. Such an effect of hydrocortisone is also manifested in the presence of insulin and prolactin, and results in a maximal increase in the enzyme activity. The ability of hydrocortisone to facilitate a high level of enzyme activity is mimicked by spermidine, but not by spermine, putrescine, or magnesium ion. Spermidine is effective at a concentration as low as 4 x 10-4 m, which is within the physiological range. This effect of spermidine is specific for hydrocortisone since spermidine does not simulate the effect of either insulin or prolactin.