Role of Glucocorticoid Receptor and Pregnane X Receptor in Dexamethasone Induction of Rat Hepatic Aryl Hydrocarbon Receptor Nuclear Translocator and NADPH-Cytochrome P450 Oxidoreductase.

The aryl hydrocarbon receptor (AHR) nuclear translocator (ARNT), as the AHR's heterodimerization partner, and NADPH-cytochrome P450 oxidoreductase (POR), as the key electron donor for all microsomal P450s, are independent and indispensable components in the adaptive and toxic responses to polycyclic aromatic hydrocarbons. Expression of both ARNT and POR in rat liver is induced by dexamethasone (DEX), a synthetic glucocorticoid known to activate both the glucocorticoid receptor (GR) and the pregnane X receptor (PXR). To better understand the role of GR and PXR in the in vivo DEX induction of rat hepatic ARNT and POR at the mRNA and protein levels, we studied the following: 1) the effects of DEX doses that activate GR (≥0.