Comparison of the biopotency of corticosterone and dexamethasone acetate in glucocorticoid receptor down regulation in rat liver

The effects of long treatment with dexamethasone 21-acetate and corticosterone on the glucocorticoid receptor in rat liver cytosol were compared. Dexamethasone acetate (5 micrograms/ml or 10 micrograms/ml water) or corticosterone (100 micrograms/ml water) was given to adrenalectomized animals as drinking solution for 6 days, and glucocorticoid receptor concentration was determined at 0, 12, 24, 48 and 72 h after steroid withdrawal. Dexamethasone acetate caused a dose dependent depletion of cytosol receptor. There was no measurable binding at time 0; the values of Bmax for the glucocorticoid receptor with decreased at 12, 24 and 48 h after the steroid withdrawal. Increased dissociation constant (Kd) were calculated for 12 and 24 h samples. The effect of corticosterone on receptor depletion was less pronounced. Bmax for the receptor was decreased at 0, 12, 24 h after steroid withdrawal with no change in Kd. The extent of steroids-induced receptor depletion showed good correlation with the induction of tyrosine aminotransferase (TAT), however, maximum TAT activity measured immediately after withdrawal of dexamethasone acetate was lower than that found after a single injection of dexamethasone acetate. We conclude that both steroids cause down regulation of the glucocorticoid receptor in rat liver cytosol, with both the extent and the duration of depletion being dependent on the biopotency of the glucocorticoid.