Stability of receptor complexes in the rat liver bound to glucocorticoids of different biopotencies

To examine the behavior in the receptor-acceptor system of glucocorticoids of different biopotencies, the stability of receptor complexes of dexamethasone (Dex), prednisolone (Pred) and corticosterone (Cort) in cytosols, nuclei and nuclear extracts from the rat liver was compared. Receptor complexes bound to these ligands were relatively stable at 0 degrees C, but at 25 degrees C a rapid liberation of ligands was observed. However, differences in the rate of temperature-dependent decay of these receptor complexes were obvious; the Dex receptor complex was the most stable, the receptor complex bound to Cort liberated the ligand most rapidly and the stability of the Pred-receptor complex was the intermediate of these two. The addition of molybdate and dithiothreitol stabilized the receptor complexes in cytosols but these agents accelerated the liberation of ligands from the complexes in nuclei and nuclear extracts. Among the factors examined, only bovine serum albumin decreased the rate of decay in the nuclear-bound receptor complexes. From these observations, it appears likely that different mechanisms may contribute to the dissociation of ligand from receptor complexes in cytosols, nuclei and nuclear extracts.