Dexamethasone modulation of multidrug transporters in normal tissues.

The expression of P-glycoprotein (P-gp) and canalicular multispecific organic anion transporter (cMOAT or Mrp2) was evaluated by Western blotting analysis of rat tissues isolated following daily administration (1 mg kg(-1) day(-1)) of dexamethasone over 4 days. Dexamethasone rapidly increased P-gp expression more than 4.5- and 2-fold in liver and lung, respectively, while it was decreased 40% in kidney. cMOAT expression was increased 2-fold in liver and kidney following dexamethasone treatment. The levels of both proteins returned to control values by 6 days after the conclusion of dexamethasone administration. These results indicate that dexamethasone can modulate P-gp and cMOAT expression in specific rat tissues and may have significant relevance for patients treated with dexamethasone as a single agent or in combination therapy with other drugs.