Plasma apolipoprotein A-I levels and bile lipid secretion during thoracic duct drainage in the rat

A large part of the circulating apolipoprotein A-I (apoA-I) is produced by the intestine. Yet the plasma levels of apoA-I are retained or even increased in rats with thoracic duct drainage (Johansson, B. and Nilsson, A, (1981) FEBS Lett. 130, 305-308 and Franzén, J. et al. (1987) Biochim. Biophys. Acta 918, 11-15). In this study we examined the effects of biliary drainage and of combined biliary and lymphatic drainage on the plasma apoA-I levels, and also the effects of lymphatic drainage on the output of biliary lipids in the rat. 63 h of biliary drainage caused a 40% decrease of the serum apoA-I concentration. In contrast the concentration in rats with combined thoracic duct and biliary drainage was 153% of that in control rats. The biliary secretion of bile acids, phosphatidylcholine and cholesterol declined to a lower level in rats with combined thoracic duct and biliary drainage, but increased at the later time intervals to the same levels as in rats with bile fistulas only. Intravenous chyle infusion 3-36 h after commencing the biliary drainage did not prevent the decrease in biliary lipid output. The study thus provided no evidence that the reduced hepatic inflow of apoB-containing lipoproteins during biliary drainage is of importance for the reduced biliary lipid output. The loss of all the chyle lipoproteins leads, however, to an even more pronounced decrease in the biliary lipid secretion. The drainage of all the chyle constituents also leads to an increased apoA-I synthesis that more than compensates for the apoA-I loss in chyle, whereas biliary drainage only lowers the plasma apoA-I levels.