Aortic accumulation and plasma clearance of beta-VLDL and HDL: effects of diet-induced hypercholesterolemia in rabbits.

To assess the role of beta-VLDL in diet-induced atherogenesis, the in vivo metabolism and aortic accumulation of 125I-labeled beta-VLDL were investigated in cholesterol-fed rabbits and chow-fed controls. 125I-labeled HDL and 125I-labeled albumin were studied for comparison. The fractional catabolic rate of 125I-labeled beta-VLDL was reduced in cholesterol-fed rabbits (0.011 vs 0.139 hr-1), but due to the high endogenous pool, the total beta-VLDL flux was very high (13.1 vs less than 1.1 mg/kg per 24 hr). These results suggest that elevated levels of beta-VLDL during cholesterol feeding were due to an enhanced rate of synthesis, a finding confirmed in hypercholesterolemic rabbits subjected to plasmapheresis. Following acute reduction of plasma cholesterol by plasmapheresis, the quantitative increases in beta-VLDL cholesterol concentrations (210 to 364 mg/dl) over the subsequent 24 hr were in agreement with the rise calculated from the plasma clearance kinetics of 125I-labeled beta-VLDL (378 mg/dl per 24 hr). Aortic accumulation of beta-VLDL in hypercholesterolemic rabbits was increased greater than 15-fold over controls. Accumulation was predominantly in the intimal atheromatous lesions. The fractional catabolic rate of 125I-labeled HDL was increased during cholesterol feeding (0.037 vs 0.021 hr-1). A decreased rate of synthesis appeared to be responsible for the markedly depleted plasma HDL. HDL accumulation within the aorta was attenuated greater than 9-fold in cholesterol-fed rabbits compared to those fed normal chow. Plasma kinetics and aortic accumulation of 125I-labeled albumin were similar in hypercholesterolemic and control rabbits.(ABSTRACT TRUNCATED AT 250 WORDS)