The uptake and metabolism of [ ''C]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 ['4C]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 fatsupplemented groups, the oxidation of ['4C]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 ['4C]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.
Perfused rat liver: Dietary fat: ChylomicronsChylomicron remnants are formed by the action of lipoprotein lipase (EC 3.1.1.34) on triacylglycerol-rich chylomicrons, and are responsible for the delivery of dietary cholesterol and some triacylglycerol to the liver (Redgrave, 1970). Several studies have shown that the type of dietary fat from which chylomicrons and chylomicron remnants are derived influences their removal by the liver. Livers from dogs and rats are reported to remove [3H]-or [ 14C]fatty acid derived from labelled chylomicrons more rapidly when they are derived from cream as compared with maize oil (Nestel & Scow, 1964;Floren & Nilsson, 1977). Also, in human subjects, retinyl palmitate-labelled chylomicrons and chylomicron remnants derived from soyabean oil or cream are removed more rapidly from the circulation than those derived from olive oil (De Bruin et al. 1993). In this laboratory we have shown that ['4C]oleate-labelled fish oil and butter fat chylomicron remnants (labelled predominantly in triacylglycerol) are taken up by the perfused rat liver more rapidly than those derived from olive, maize or palm oils (Lambert et al. 1995). Taken together these studies show that chylomicron remnants derived from milk fat (cream or butter fat), soyabean oil or fish oil tend to be taken up more rapidly by the liver than those derived from olive, maize or palm oils. As fat-supplemented diets were not used in these studies, the differential uptake of the remnants can be attributed to the fatty acid composition of the particles themselves, which is largely dete...