Chylomicron catabolism differs between Hooded and albino laboratory rats

To extend previous reports that some aspects of lipid metabolism are different between Hooded and albino strains of laboratory rats, thoracic duct lymph chylomicrons were collected and their composition and metabolism were compared in this study. Chylomicrons from Hooded rats had more core components and fewer surface components than albino rats. After adding 1% cholesterol to the diet the ratio of cholesterol:phospholipid was higher in Hooded rat chylomicrons. Nascent lymph chylomicrons from Hooded rats contained less apolipoprotein A-IV, but after incubation with serum there was a gain of apolipoprotein A-IV and a loss of A-I from both types of chylomicron. The ratio of apoC to apoE was higher in Hooded than in albino rats. The metabolism of injected chylomicrons was slower in Hooded rats. Twenty minutes after a single injection, only 1-3% of chylomicron triacylglycerol and 8-13% of chylomicron cholesteryl ester remained in the plasma of albino rats, compared with 6-12% of triacylglycerol and 30-33% of cholesteryl ester in Hooded rats. At 30 min in the Hooded rats, the uptake of injected chylomicron cholesterol into the liver was decreased whereas uptake into other tissues, notably adipose tissue and muscle, was increased. During the steady intravenous injection of chylomicrons from the same strain, the fractional clearance rate of chylomicron triaclyglycerol was about three-fold faster in albino rats than in Hooded rats, and the fractional clearance rate of chylomicron cholesteryl ester was 70% faster in albino rats. When chylomicrons were allowed to circulate for 30 min after injection into functionally hepatectomized rats, with or without heparin, the remnant formation and chemical composition were similar in Hooded and albino rats. Hence the deficiency in chylomicron metabolism in Hooded rats was not due to an absolute impairment in the formation of remnants by the action of lipoprotein lipase in peripheral tissues, although our findings were most likely accounted for by some relative impairment of remnant formation in the Hooded strain. The deficiency in chylomicron metabolism correlated with an increased cholesterolemic response in Hooded rats compared with albino rats when 1% cholesterol was added to the diet.-Jeffery, F., and T. G. Redgrave. Chylomicron catabolism differs between Hooded and albino laboratory rats.