Increased paracellular permeability in intrahepatic cholestasis induced by carmustine (BCNU) in rats

Carmustine [i.e., 1,3-bis(2-chloroethyl)-1-nitrosourea (BCNU)] is a drug with cholestatic potency both in experimental animals and in humans. To study the mechanisms involved in the development of the hepatic lesions, early changes in liver function in rats pretreated with the drug were investigated. Dosages and sampling times that did not result in hepatocellular injury, as indicated by release of marker enzymes, were applied. In isolated perfused livers from pretreated rats, bile flow and maximal secretion rate of taurocholate were decreased. An increase in biliary [14C]sucrose clearance suggested enhanced permeability of the bile tract and was correlated with increased inorganic phosphate concentration in bile. To assess the contribution of paracellular and transcellular pathways of sucrose, [14C]sucrose access into bile was analyzed by biliary off-kinetics after omission of the radioactive marker from the perfusion medium. An improved method was developed to quantitate the permeability of the bile tract by applying the classical flow equation to the paracellular portion of biliary sucrose clearance. With this method it was shown that pretreatment of rats with BCNU resulted in an increase in both diffusion and convection of paracellular sucrose from perfusate into bile. Accordingly, the fast access of horseradish peroxidase from perfusate into bile was facilitated in isolated perfused livers of BCNU-treated rats. The results indicate that an increase in paracellular permeability is an early alteration that may contribute to the development of hepatotoxic lesions caused by BCNU. It is shown that inert solute clearance can be used to assess paracellular permeability if the paracellular fraction is determined.