The hypothesis that hepatic lipase mediates the differential hepatic uptake of chylomicron remnants of different fatty acid composition, demonstrated in previous work from our laboratory, was tested by investigating the effect of antibodies to the enzyme on the uptake of remnants enriched with saturated or n-3 polyunsaturated fatty acids by the perfused rat liver. After perfusion of rat livers with polyclonal antibodies to rat hepatic lipase raised in rabbits or with rabbit non-immune serum for 15 min, [3H]oleate-labelled chylomicron remnants, derived from chylomicrons of rats given a bolus of either palm (rich in saturated fatty acids) oil or fish (rich in n-3 polyunsaturated fatty acids) oil, were added. The disappearance of radioactivity from the perfusate during 120 min and its recovery in the liver at the end of the experiments were then measured. Although the rabbit anti-rat hepatic lipase antiserum was shown to inhibit hepatic lipase activity by up to 90 %, and to bind extensively to hepatic sinusoidal surfaces when added to the perfusate, radioactivity from remnants of chylomicrons from rats given a bolus of fish oil as compared with palm oil disappeared from the perfusate and appeared in the liver more rapidly in the presence both the antiserum and the non-immune serum, and the differences between the uptake of the two types of remnants were similar. We conclude, therefore, that differential interaction with hepatic lipase is not responsible for the differences in the rate of removal of chylomicron remnants of different fatty acid composition from the blood.

The uptake and metabolism of [14C]oleate-labelled chylomicron remnants derived from olive oil, maize oil, palm oil, fish oil or butter fat was investigated using perfused livers from rats fed on the corresponding fat-supplemented diet (providing 40 % of the dietary energy) or a low-fat diet for 21 d. The percentage of added [14C]oleate-labelled remnant removed from the perfusate was similar for livers from rats fed on the fat-supplemented diets irrespective of the type of fat fed, whereas livers from rats fed on the low-fat diet removed more labelled fish oil and butter fat remnants than olive, maize or palm oil remnants. Following hepatic uptake in the fat-supplemented groups, the oxidation of [14C]oleate-labelled remnant lipid from maize oil, fish oil, and butter fat remnants was greater than that of the lipids from olive and palm oil remnants, although only the oxidation of lipids from maize and palm oil remnants was increased by prior fat-supplementation of the diet. In addition, the livers from rats fed on the fish-oil-supplemented diet incorporated more [14C]oleate-labelled remnant lipid into phospholipid compared with the livers from rats fed on the other fat-supplemented diets or the low-fat diets. These investigations show that both prior fat feeding and the composition of the fat fed, as well as the fatty acid composition of the chylomicron remnant particles themselves, influence the uptake and metabolism of chylomicron remnants by the liver.