BILE FORMATION AND HEPATIC PLASMA-MEMBRANE COMPOSITION IN GUINEA-PIGS AND RATS

We compared bile formation, and biliary and liver plasma membrane composition in guinea-pigs and rats in an attempt to explain the observation that the bile flow rate and the bile acid independent fraction of bile flow (BAIF) in guinea-pigs is about five to seven times higher than in rats, Analysis of electrolytes in bile showed that bicarbonate was significantly [acid] higher in guinea-pigs while Cl-, phosphate and Ca2+ were markedly lower than in rats, High bile independent secretion in guinea-pigs was associated with a significantly lower concentration of total bile acid, phospholipid and cholesterol than in rats, Bile acid distribution studies showed that glycine conjugated chenodeoxycholate and ketolithocholate were the main bile acids in guinea-pigs, while taurine conjugated cholate and muricholate were the predominant bile acids in rats, Total fatty acid analysis of bile indicated that in rats the major fatty acids were palmitic acid (C16:0) and linoleic acid (C18:2, n-6), In guinea-pigs, the contribution of these fatty acids was lower than in rats and compensated with a significantly higher percentage of oleic acid (C18:1, n-9), Concentrations of anionic polypeptide fraction (APF), an acidic calcium binding apoprotein closely associated with biliary phospholipid and cholesterol secretion was also significantly lower in guinea-pigs, Canalicular plasma membrane analysis showed that as compared with rats, specific activities of Na+,K+ ATPase, and cholesterol and phospholipid content were markedly lower in guinea-pigs, Total fatty acid analysis of the membrane revealed that palmitic acid (C16:0), stearic acid (C18:0) and linoleic acid (C18:2, n-6) were the predominant fatty acids in guinea-pigs, while palmitic acid (C16:0), stearic acid (C18:0) and arachidonic acid (C20:4, n-6) were the most important in rats, Thus, high bile flow rate and BAIF in the guinea-pig may be attributed to the low bile acid concentration (below the critical micellar concentration), secretion of hypercholeretic bile acids (e.g. ketolithocholate) and high bicarbonate output.