MECHANISMS OF HYPERTRIGLYCERIDEMIA IN THE COCONUT OIL CHOLESTEROL-FED RABBIT - INCREASED SECRETION AND DECREASED CATABOLISM OF VERY LOW-DENSITY-LIPOPROTEIN

Rabbits fed a 14% coconut oil/0.5% cholesterol (CNO/Chol) diet develop mild to severe hypertriglyceridemia compared with rabbits fed a 14% olive oil/0.5% cholesterol (OO/Chol) diet. Lipids and apolipoprotein (apo) B were significantly higher in the very low density lipoprotein (VLDL) and intermediate density lipoprotein fractions from CNO/Chol than from OO/Chol rabbits. Yet, the particle diameters of these lipoproteins were similar in both diet groups, indicating that CNO/Chol rabbits had a much larger number of VLDL and intermediate density lipoprotein particles in plasma. Although the composition of CNO/Chol VLDL differed from that of OO/Chol VLDL, the rates of triglyceride hydrolysis of CNO/Chol VLDL and OO/Chol VLDL by postheparin lipoprotein lipase in vitro were the same, suggesting that VLDLs from the two diet groups were equally good substrates for lipoprotein lipase. To determine the mechanisms of hypertriglyceridemia in the CNO/Chol rabbit, triglyceride and apo B of CNO/Chol VLDL and OO/Chol VLDL were labeled with tritium-containing triolein and iodine-131 and injected intravenously into CNO/Chol and OO/Chol rabbits. The fractional clearance rate for triglyceride in OO/Chol rabbits was twice that of CNO/Chol rabbits, which parallels the previously observed differences in postheparin lipoprotein lipase activity. Although the average fractional removal of apo B did not differ between diet groups, there was a significant inverse relation between plasma cholesterol and apo B fractional clearance rate. We conclude that the hypertriglyceridemia and the enhanced hypercholesterolemia in the CNO/Chol rabbit results primarily from increased hepatic secretion of VLDL and a modest decrease in VLDL triglyceride clearance capacity.