Comparison of the clearances of serum chylomicron triglycerides enriched with eicosapentaenoic acid or oleic acid.
Rat mesenteric lymph chylomicrons containing triglycerides enriched with either [14C]oleic acid (OA) or [14C]-eicosapentaenoic acid (EPA) were prepared by ultracentrifugation of lymph samples collected for 6 hr after a single duodenal infusion of an emulsion containing either fatty acid. These chylomicrons were injected into the jugular vein of recipient rats and, at various time intervals, blood was drawn and serum was assayed for radioactivity. In separate animals, serum lipoprotein fractions were separated by ultracentrifugation, and the redistribution of labeled fatty acid among circulating lipoproteins was determined by liquid scintillation spectrometry. When the early disappearance rates (10 min) of either total serum radioactivity or specifically the chylomicron fraction were compared, there were no differences between the groups receiving OA- or EPA-enriched chylomicrons. However, disappearance rates of EPA-enriched chylomicrons were slower than those of OA-enriched chylomicrons from 25 to 90 min. The small but significant differences in the disappearance rates for the longer time periods cannot be ascertained without further studies. At 5 min after injection of either type of chylomicron, the d less than 1.006 g/ml lipoprotein fraction of serum chylomicrons and very low density lipoproteins contained almost 90% of the original radioactivity. By 240 min, when less than 2% of the radioactivity remained, this radioactivity in the d less than 1.006 g/ml fraction was 43-46%, with concomitant increases in the low and high density lipoprotein fractions and in the lipoprotein-free serum.