Cholestasis induced by scillaren administration, bicarbonate deprivation, or reduced hepatic blood flow

Abstract

Hepatocytic morphologic changes associated with bile salt-induced choleresis have been well studied; however, changes associated with alterations in the bile salt-independent fraction of bile flow (BSIF) have not been examined. We diminished bile flow in the perfused rat liver by two means which are thought to decrease BSIF: bicarbonate deprivation and treatment with scillaren, a cardiac glycoside which inhibits Na +,K +-ATPase. Perfusate flow, bile flow, biliary bile acid excretion, and, in two experiments, perfusate calcium concentration were monitored. No morphologic changes occurred in the livers in which BSIF had been reduced by 50% by bicarbonate removal. In scillaren-treated livers both functional and morphologic changes occurred. In contrast to previous reports, scillaren (1.8 × 10 −4 to 7.2 × 10 −4 M) reduced blood flow at the same time that it reduced BSIF proportionately. The bile salt-dependent fraction (BSDF) of bile flow was not reduced. Gross mottling appeared at the periphery of the lobes and microscopy revealed changes indicative of circulatory shutdown in sinusoids and ischemic damage to hepatocytes in such areas. Elsewhere, hepatocytes with membranes and organelles morphologically normal became widely separated at their lateral intercellular surfaces, while tight junctions (and hence bile canaliculi) remained intact. These latter changes occurred predominantly in hepatic acinar zone 1 (periportal zone) and could be reproduced by removal of Ca 2+ from the perfusate, yet perfusate Ca 2+ levels did not change with addition of scillaren. The same changes also developed when perfusate flow was reduced to a level comparable to that induced by higher doses of scillaren. It is concluded that (1) 50% reduction in BSIF by bicarbonate deprivation occurs without change in hepatic ultrastructure, (2) inhibition of bile flow by scillaren is associated with a decrease in hepatic blood flow and focal ischemic injury so that its effect on bile flow is not exclusively attributable to the inhibition of Na +,K +-ATPase, and (3) marked reduction in perfusate flow either by restriction of portal inflow or by administration of scillaren causes a partial separation of interhepatocellular adhesion in acinar zone 1.