Different pathomechanisms of altered biliary leukotriene C 4 elimination in isolated perfused rat livers

Abstract

Hepatic retention of cysteinyl leukotrienes is a consequence of impaired bile secretion and may be involved in the pathogenesis of intrahepatic cholestasis. In order to assess the mechanisms of altered biliary leukotriene elimination, we studied the secretion and metabolic pattern of leukotriene C 4 (LTC 4) in bile early in the alterations of bile formation by xenobiotics. To this end, rats were pretreated with α-naphthylisothiocyanate (ANIT), ethionine (ETH), or estradiol valerate (EV) at doses which did not increase serum marker enzymes of cholestasis. Bile secretion was assessed in perfused livers isolated from the treated rats. In all models, the access of [ 14C]sucrose into bile was increased, indicating increased permeability of the bile tract. Biliary recovery of radioactivity infused as [ 3H]LTC 4 was decreased by ANIT and ETH while 3H-efflux into the perfusate was increased concomitantly. The secretion rate of 3H-radioactivity into bile was correlated with that of [ 14C]taurocholate infused at the same time. After pretreatment with ANIT (but not in the other models) the venous efflux of [ 3H]LTC 4-derived radioactivity was correlated with the access of [ 14C]sucrose into bile. Accordingly, only after ANIT pretreatment was increased [ 14C]sucrose clearance into bile associated with greatly enhanced biliary access of [ 32P]phosphate. Thus, altered charge selectivity of the paracellular pathway appears to be a prerequisite for reflux of cholephilic anions. HPLC analysis of [ 3H]LTC 4-derived radioactivity in bile revealed that in all models of altered bile secretion the relative amount of LTD 4 in bile was elevated. These results demonstrate differential changes in hepatobiliary transport and metabolism of LTC 4 in developing cholestasis. ANIT inhibits leukotriene secretion by increasing paracellular permeability with loss of charge selectivity. In contrast, ETH treatment inhibits transcellular transport while treatment with EV only results in enhanced LTC 4 metabolism.