Sodium arsenite induced alterations in bilirubin excretion and heme metabolism.

The acute administration of sodium arsenite (AsIII) to rats resulted in a biphasic alteration of the hepatic cytosolic "free" heme pool. The first stage was an increase in the cytosolic "free" heme without significant effects on the content of cytochrome P-450 or on bilirubin excretion. The second stage consisted of a continuous fall of the cytosolic "free" heme and of the content of cytochrome P-450. These changes were concurrent with an eight-fold increase in heme oxygenase activity and associated with marked elevations in the biliary excretion of bilirubin. The bile was collected from chronically cannulated rats to avoid artifacts related to anesthesia or post anesthetic effects. The rapid increase in biliary excretion of labeled heme degradation products indicated an increased breakdown of newly synthesized heme. Immunoelectrophoresis of bile proteins showed an altered pattern of bile protein excretion. The increased biliary haptoglobin suggested some hemolysis, while the reduction in the free immunoglobulin A (IgA) secretory component showed an AsIII-related decreased protein transport across hepatocytes to bile. Further research is required to assess the direct role of an increased heme degradation in the genesis of the hepatotoxic effects of AsIII.