Abstract
Cholestasis was induced by administration of ethinylestradiol (E. E.) to rats. E. E. treatment of rats increased phospholipid and cholesterol concentration and alkaline phosphatase activity in their sera. From the livers of E. E. -treated rats, the liver plasma membranes were isolated and fractionated into two subfractions, of which the low density fraction was mainly derived from the bile canalicular surface and the high density one from the other surface areas. Na-K ATPase activity was decreased in both of the subfractions. Mg-ATPase and leucyl-β-naphthylamidase activity were elevated in the heavy fraction. 5'-Nucleotidase activity was decreased in the light fraction. Alkaline phosphatase activity was increased markedly in both of the subfractions. Cholesterol and phospholipid contents were not changed significantly in both of the subfractions. The reduction of Na-K ATPase activity in the bile canalicular surface brought about the decrease of bile acid-independent fraction of bile formation. The reduction of the activity in the basolateral surface caused the loss of the Na+- gradient across the plasma membrane and decreased the uptake of bile acids, leading to the reduction of bile formation.
