Effect of endotoxin on P-glycoprotein-mediated biliary and renal excretionof rhodamine-123 in rats

The effects of Klebsiella pneumoniae endotoxin on the biliary excretion and renal handling of rhodamine-123 were investigated in rats at different tim es after intraperitoneal injection (1 mg/kg of body weight). The typical su bstrates for P glycoprotein, i.e., cyclosporine, colchicine, and erythromyc in, inhibited the biliary clearance of rhodamine-123, whereas a substrate f or organic cation transporter, cimetidine, did not inhibit clearance, sugge sting that rhodamine-123 is transported mainly by P glycoprotein. The bilia ry, renal, and tubular secretory clearances of rhodamine-123 and the glomer ular filtration rate significantly decreased 6 h after injection of endotox in but returned to control levels by 24 h. These results suggest that endot oxin-induced decreases in P-glycoprotein-mediated biliary excretion and ren al handling of rhodamine-123 were probably due to impairment of P-glycoprot ein-mediated transport ability. Pretreatment with pentoxifylline (50 mg/kg) significantly inhibited endotoxin-induced increases in tumor necrosis fact or alpha (TNF-alpha) levels in plasma, which ameliorated the endotoxin-indu ced reduction of the biliary excretion of rhodamine-123. It is likely that endotoxin-induced impairment of the transport of rhodamine-123 is caused, i n part, by overproduction of TNF-alpha. The effect of endotoxin on the expr ession of P-glycoprotein mRNA in liver and kidneys of rats was investigated by using a reverse transcriptase PCR. The expression of Mdr1a mRNA in both liver and kidney decreased 6 h after endotoxin injection and returned to c ontrol levels after 24 h, whereas the expression of Mdr1b mRNA in liver inc reased at both times and that in kidney decreased at 24 h. These findings s uggest that K. pneumoniae endotoxin dramatically decreases P-glycoprotein-m ediated biliary and renal excretion of rhodamine-123 probably by decreasing the expression of Mdr1a, which is likely due to increased plasma TNF-alpha levels.