Glucocorticoid receptor of rat mammary gland during pregnancy and lactation.

The binding of 3H-dexamethasone to specific cytosol binding sites of rat mammary gland during pregnancy and lactation was characterized and quantified. During the first week of pregnancy the amount of receptor gradually increased and remained at a relatively constant level throughout pregnancy. Maximum concentration of receptor was observed immediately before labor and one day after labor. During lactation the receptor concentration gradually returned to the level observed during pregnancy and then remained at about the same level until the day 21 which was followed by a rapid decrease at the end of lactation period. No significant differences in dissociation constants were noticed during pregnancy and lactation.