EFFECT OF BREFELDIN-A ON TRANSCYTOTIC VESICULAR PATHWAY AND BILE SECRETION - A STUDY ON THE ISOLATED-PERFUSED RAT-LIVER AND ISOLATED RAT HEPATOCYTE COUPLETS

This study investigated the effect of Brefeldin A (BFA) on the transcy totic vesicular pathway labeled with horseradish peroxidase (HRP) in b oth isolated rat hepatocyte couplets (IRHC) and the isolated perfused rat liver (IPRL). To evaluate the role of the transcytotic vesicular p athway on bile secretion, the effect of BFA on bile secretion in the I PRL was then investigated. In the basolateral area of IRHC, BFA showed no effect on the density and percentage of area of HRP-labeled vesicl es. However, HRP-labeled vesicles tended to accumulate in the juxtanuc lear area of BFA-treated hepatocytes (P < .001 vs. controls). In the p ericanalicular area, on the other hand, HRP-labeled vesicles were depl eted compared with controls (P < .001). In keeping with these findings , although the early peak remained unchanged, BFA inhibited as much as 50% of the late peak of HRP excretion in bile, after a pulse load of HRP in the IPRL. Bile flow and the biliary secretion of bile salts (BS ) and phospholipids were not modified by BFA in isolated Livers perfus ed without BS in the perfusate or with 1 mu mol/min taurocholate (TCA) . In BFA-treated livers, peak bile how and BS output decreased by 20% (P < .05 vs. controls) only when a 5 mu mol TCA bolus was administered . In conclusion, this study demonstrates that BFA inhibits the transcy totic vesicular pathway in the liver. However, BFA has no significant effect on bile secretion either in basal conditions or during perfusio n with physiological amounts of BS. BFA slightly decreases bile dow an d BS output only after an overload of BS, providing evidence against t he physiological relevance of the transcytotic vesicular pathway in th e process of bile formation.