抄録
In man, studies on VLDL apo-B metabolism indicate that the small particles are derived entirely from larger particles. On the other hand, there is in vivo evidence that triglyceride (TG) in small particles is not derived entirely from larger particles. The above information raises the possibility that newly made TG can be transferred from hepatocyte directly into pre-existing TG-rich particles. In order to persue this possibility we incubated TG-prelabelled rat hepatocytes with human lipoprotein fractions. 3H-glycerol was injected via portal vein 20min before liver perfusion with collagenase. Collected cells were washed 4times and incubated at density ca 4×106 cells/ml with or without a lipoprotein fraction in Tyrode's solution, pH 7.4 with 1% BSA. After 45min incubation at 37°C, the medium was separated from hepatocytes by centrifugation. TG-glycerol specific activities in the medium containing VLDL (sf 60-400) was significantly higher than in medium without lipoprotein addition. The labelled TG appeared to be part of the fraction as judged by ultracentrifugation, hep-Mn and anti-apo-B separation. This transfer of TG from hepatocyte to VLDL did not depend on the synthesis and release of new VLDL particles as it was not accompanied by a change in the production of 14C-leucine labelled VLDL protein and it was not blocked by chloroquine. Less transfer was found from hepatocyte to LDL (sf 0-12) than to VLDL (sf 60-400). These data suggest that newly synthetized TG can directly enter circulating TG-rich particles independent of endogeneous VLDL secretion.
