Endothelin-1 and -3 induce choleresis in the rat through ETB receptors coupled to nitric oxide and vagovagal reflexes

Abstract

We have reported previously that centrally applied ET (endothelin)-1 and ET-3 induce either choleresis or cholestasis depending on the dose. In the present study, we sought to establish the role of these endothelins in the short-term peripheral regulation of bile secretion in the rat. Intravenously infused endothelins induced significant choleresis in a dose-dependent fashion, being ET-1 more potent than ET-3. Endothelins (with exception of a higher dose of ET-1) did not affect BP (blood pressure), portal venous pressure or portal blood flow. ET-1 and ET-3 augmented the biliary excretion of bile salts, glutathione and electrolytes suggesting enhanced bile acid dependent and independent bile flows. ET-induced choleresis was mediated by ETB receptors coupled to NO and inhibited by truncal vagotomy, atropine administration and capsaicin perivagal application supporting the participation of vagovagal reflexes. RT (reverse transcription)?PCR and Western blot analysis revealed ETA and ETB receptor expression in the vagus nerve. Endothelins, through ETB receptors, augmented the hepatocyte plasma membrane expression of Ntcp (Na+ /taurocholate co-transporting polypeptide; Slc10a1), Bsep (bile-salt export pump; Abcb11), Mrp2 (multidrug resistance protein-2; Abcc2) and Aqp8 (aquaporin 8). Endothelins also increased the mRNAs of these transporters. ET-1 and ER-3 induced choleresis mediated by ETB receptors coupled to NO release and vagovagal reflexes without involving haemodynamic changes. Endothelin-induced choleresis seems to be caused by increased plasma membrane translocation and transcriptional expression of key bile transporters. These findings indicate that endothelins are able to elicit haemodynamic-independent biological effects in the liver and suggest that these peptides may play a beneficial role in pathophysiological situations where bile secretion is impaired. Key words: bile salt, bile secretion, endothelin receptor, hepatic transporter.