Biliary secretion of anionic polypeptide fraction is not coupled to that of phospholipids and cholesterol in rats

Abstract

indicate that the biliary secretion rates of APF and of Anionic polypeptide fraction (APF) is a phospholipidphospholipids/cholesterol are not coupled and, thereand calcium-binding apoprotein present in animal and fore, do not support a direct physiological role of APF human bile, predominantly associated with cholesterolsecretion in biliary lipid secretion. APF secretion into phospholipid vesicles. In bile, the protein may play a bile may, at least partially, be controlled by biliary bile physiological role in preventing precipitation of calcium acid secretion. (HEPATOLOGY 1997;25:38-47.) salts. APF has also been suggested to be of regulatory importance in the process of biliary lipid secretion. The aim of the present study was to investigate whether the Anionic polypeptide fraction (APF) is a phospholipid-and secretion rates of APF and that of biliary lipids are cou-calcium-binding apoprotein present in animal and human pled, which would support a physiological role of APF bile, which is predominantly associated with cholesterolin biliary lipid secretion. Biliary secretion rates of bile phospholipid vesicles. APF was originally described as part acids, phospholipids, and cholesterol were experimen-of a biliary lipoprotein complex, present in human bile.1 Pubtally modulated in three different rat models. Secretion lished data indicate that antibodies raised against APF crossrates of APF were compared with that of bile acids, lip-react with calcium-binding protein, which was isolated from ids, and with that of two other biliary proteins, the lyso-cholesterol and pigment gallstones. 2,3 In human cholesterol somal protein b-glucuronidase and apolipoprotein A-I gallstones, APF is associated with the pigments at the inter-(apo A-I). Model 1: diurnal variation in bile formation faces of mucine and pigment. 4 These observations have led during chronic bile diversion; model 2: specific inhibi-to the hypothesis that APF/calcium-binding protein may be tion of biliary phospholipid and cholesterol, but not of involved in the pathogenesis of cholesterol and/or pigment bile acid secretion by infusion of the organic anion, sul-gallstone disease. [5][6][7] Apart from the hypothesized role in gallfated lithocholyltaurine; model 3: acute interruption of stone formation, APF has been suggested to be involved in the enterohepatic circulation in unanesthetized rats. biliary lipid secretion under physiological circumstances. 8-13The diurnal variation in bile formation involved a paral-The preferential association of APF with biliary lipid vesicles lel increase of the biliary secretion rates of bile acids and its amphipathic character could be in agreement with a (/56 { 7%, mean { SD), phospholipids (/53 { 29%), cho-proposed physiological role for APF in biliary lipid secretion. lesterol (/73 { 54%), and APF (/72 { 86%) during the Furthermore, the involvement of APF in intrahepatocytic tarnight phase of the cycle. Infusion of sulfated lithocholyl-geting of plasma-derived lipids was suggested by experiments taurine inhibited biliary p...