EFFECT OF CHLORPROMAZINE ON HEPATIC PERFUSION AND BILE SECRETORY FUNCTION IN THE ISOLATED PERFUSED RAT-LIVER

Abstract

The hepatoxicity of CPZ [chlorpromazine] was studied in the isolated perfused rat liver in order to more closely define possible mechanisms of phenothiazine-induced cholestasis. Perfusate concentrations of CPZ were increased from 5 .times. 10-6 M to 5 .times. 10-4 M until bile secretion was significantly inhibited. Measurements were then made of determinants of bile secretory function, including the magnitude of lobar distribution of perfusate flow, BAIF [bile acid-independent bile flow], and liver plasma membrane enzyme activity, Na+, K+-ATPase, Mg2+-ATPase and 5''-nucleotidase. BAIF diminished significantly from control values of 1.76 .+-. 0.07 .mu.l min-1 g-1 of liver to 1.34 .+-. 0.15 and 0.80 .+-. 0.09 following 2.5 and 5 .times. 10-4 M CPZ, respectively. Perfusate flow also diminished from 5.64 .+-. 0.44 to 1.24 .+-. 0.12 ml min-1 g-1 of liver 20 min following 5 .times. 10-4 M CPZ and was associated with reduced flow to peripheral areas of the hepatic lobes as demonstrated by Tc-HAM [Tc99m human serum albumin microspheres]. By 30 min, perfusate flow had returned to baseline values. CPZ also transiently diminished the excretion of bile acids in livers receiving a constant infusion of 40 .mu.mol h-1 sodium taurocholate. Defects in hepatic perfusion could not account entirely for the impairment in BAIF, since comparable mechanical restriction of perfusate flow in controls only diminished BAIF to 1.49 .+-. 0.08 .mu.l min-1 g-1 of liver. CPZ significantly reduced the specific activity of Mg2+-ATPase and 5''-nucleotidase but did not affect Na+,K+-ATPase in liver plasma membrane isolated 20 min after 5 .times. 10-4 M CPZ. CPZ also resulted in a profound shift in the recovery of protein in isolated liver plasma membrane fractions from the light to heavier fractions. These findings, together with previous observations demonstrating alterations in hepatic ultrastructure, indicate that CPZ interacts in a complex manner with hepatocyte plasma and cytoplasmic membrane components and suggest that these drug-membrane interactions independently result in diminished hepatic perfusion, impairment of bile acid excretion and inhibition of bile acid-independent bile secretion.