Selective biliary lipid secretion at low bile-salt-output rates in the isolated perfused rat liver. Effects of phalloidin

At high bile-salt-secretion rates the biliary secretion of phospholipids and cholesterol is dependent on that of the bile salts. However, at low bile-salt outputs some secretion remains. Isolated perfused rat livers were used in these experiments in order to study the bile-salt-independent secretion of biliary lipids. The livers were isolated and saline (0.9% NaCl), or phalloidin dissolved in saline, was added to the perfusion fluid after 1 h of liver isolation. The concentration and output of cholesterol was significantly decreased in phalloidin-treated livers compared with the controls, whereas there was no significant decrease in phospholipids; the secretion of cholesterol and phospholipids can thus be uncoupled from each other by the action of phalloidin. These experiments suggest that a proportion of cholesterol gets into bile independently of bile salts and phospholipids. These findings are discussed in relation to the supersaturation of some biles with cholesterol and its relationship to the bile-salt-independent fraction of cholesterol.