The turnover and the catabolic fate of the B apoprotein of very low density lipoprotein (VLDL-B) was studied in 15 normal and hyperlipidemic subjects using reinjected autologous VLDL labeled with radioiodine. The specific radioactivity-time curve of the B apoprotein in total VLDL (Sf20-400) was multiexponential but conformed to a two-pool model during the first 48 h of catabolism. The flux was highest in several hypertriglyceridemic subjects. The mass of pool A exceeded the intravascular content of VLDL-B by 30% on average, indicating extravascular metabolism of VLDL. The two-pool model might reflect the input of several populations of particles or heterogeneity of catabolic processes or pools. The flux of B apoprotein was also measured in several subclasses of VLDL, in smaller intermediate density lipoproteins, and in low density lipoproteins (LDL). In three subjects the flux was similar in Sf 60-400 and in Sf 12-60 lipoproteins, suggesting that VLDL was catabolized at least to a particle in the density range Sf 12-60. Subsequent catabolism appeared to proceed by two pathways: in normotriglyceridemic subjects, B apoprotein flux in the Sf 20-400 and in Sf 12-20 lipoproteins was similar, whereas in hypertriglyceridemic subjects flux through Sf 12-20 accounted for only part of the VLDL-B flux.
Michael F. Reardon, Noel H. Fidge, Paul J. Nestel