Metabolism of cyhlomicrons in perfused adipose and mammary tissue of the rat

Abstract

Perfused adipose and mammary tissues of the rat were used to study the role of capillary endothelium and lipoprotein lipase in the metabolism of chylomicrons. Triacylglycerol of chylomicrons was hydrolyzed stepwise during uptake by both tissues, first to di- or monoacylglycerol and fatty acid, and then to glycerol and fatty acid. Cytochemical studies in perfused adipose tissue showed that lipolysis occurred at the luminal surface of capillaries, within vacuoles and microvesicles in the endothelium, and between the endothelium and pericytes. Radioautography of perfused lactating mammary tissue showed that acyl and glyceryl moieties derived from chylomicron triacylglycerol were both incorporated into milk lipid droplets. Perfused lactating mammary tissue also took up cholesterol from chylomicrons. There was marked reduction of lipoprotein lipase activity and uptake of both triacylglycerol and cholesterol in perfused mammary tissue of hypophysectomized lactating rats. It is proposed that uptake of triacylglycerol by extrahepatic tissues requires the direct action of lipoprotein lipase, while uptake of cholesterol is dependent on reduction of the triacylglycerol core volume, resulting from action of the enzyme on the core and uptake of lipolytic products by the tissue.