No correlation between binding of glucocorticosteroids to specific cytoplasmic proteins in vivo and enzyme induction in the rat liver.

Time- and dose-dependence of the formation of the different cytoplasmic hormone-protein complexes were studied in the rat liver after administration in vivo of [3H]cortisol or [3H]dexamethasone and compared with the stimulation of RNA polymerase B and induction of tyrosine aminotransferase and tryptophan oxygenase. No correlation could be found between formation in vivo of any of the five cytoplasmic hormone-protein complexes found and stimulation of RNA polymerase B activity or enzyme induction. After administration of [3H]cortisol, different metabolites of cortisol could be demonstrated in the isolated hormone-protein complexes. No time- or dose-dependence of the metabolite patterns could be observed after application of hormone doses that were in the range of the biologically active doses. After administration of [3H]dexamethasone, the same hormone-protein complexes were observed, which contained, however, the injected steroid instead of metabolites. These results seem to indicate that the cytoplasmic binding components present in the rat liver are enzymes involved in the metabolism of the glucocorticosteroids and that dexamethasone binds to these enzymes as a substrate analogue.