Triglyceride removal from very low density lipoproteins in vivo as a function of their triglyceride content

Rabbit very low density lipoproteins (VLDL) were fractionated in 3 subfractions differing in density and triglyceride (TG) content. The fraction of total weight represented by triglycerides was: VLDL1 TG = 71%, VLDL2 TG = 62%, VLDL3 TG = 55%. No other difference in composition was observed. After intravenous administration of radioglycerol all subfractions were labelled and the distribution of radioactivity in their glycerolipids was the same. In 5 rabbits, a biologically labelled triglyceride-rich VLDL1 subfraction preparation was administered and the specific activity of triglyceride was determined in all 3 subfractions in serial samples. A precursor--product relationship between VLDL1 TG and VLDL TG in other subfractions was not observed. In another set of experiments the disappearance rates of VLDL TG from subfractions were determined in recipient rabbits. The half-lives were: VLDL1 TG = 9.5 +/- 1.3 min, VLDL2 TG : 16.0 +/- 1.3 min, VLDL3 TG: 26.9 +/- 1.3 min. It is concluded that triglyceride removal from a VLDL subfraction varies inversely with its triglyceride content. A role for partial VLDL lipolysis in this metabolic heterogeneity was not established.