Rates of removal and degradation of chylomicron remnants by isolated perfused rat liver.

Chylomicron remnants are removed intact by isolated perfused rat livers and their lipid components are metabolized by the liver (Biochim. Biophys. Acta 488: 464, 1977). The present study provides quantitative information regarding these processes. When the lipoprotein concentration of the perfusate was constant, the removal of chylomicron remnants increases lineraly for 17 min. The rate of remnant removal was a hyperbolic function of the perfusate's remnant concentration. The removal rate had aV max of 28microgram cholesterol per g liver per min and an apparent Km of 64 microgram cholesterol per ml perfusate. Feeding the liver donors a diet containing 1% cholesterol or 4% cholesterol and 1% cholic acid failed to alter the hepatic removal rate. The cholesteryl ester removed from the remnants was hydrolyzed at a rate that was a small fraction of the removal rate (about 0.5% of removed cholesteryl ester per min). The rate of cholesteryl ester hydrolysis did not appear to approach saturation in the range studied. Studies of the lysosomal cholesteryl ester hydrolase suggested that this enzyme was not responsible for limiting the initial rate of hydrolysis, raising the possibility that the degradation rate is determined by the movement of the removed remnant to the site of hydrolysis.