Measurement of human chylomicron triglyceride clearance with a labeled commercial lipid emulsion

Human chylomicron triglyceride (TG) kinetics has been difficult to determin e directly owing to technical limitations. This report describes a new meth od for studying chylomicron metabolism. Healthy volunteers (n 10) sipped a drink providing 175 mg fat.kg(-1).h(-1) for 7.5 h to produce a steady-state chylomicronemia. A commercial 10% intravenous lipid emulsion was labeled w ith [H-3]triolein, purified by highperformance liquid chromatography, and s terilized. A trace amount of labeled emulsion was injected intravenously 30 min before (i.e., in the fasting state) and 5, 6, and 7 h after sipping be gan (i.e., triplicate determinations in the fed state). Chylomicron half-li ves were calculated from the monoexponential decay curves, and apparent dis tribution volumes were estimated by back-extrapolation to time zero. Plasma and estimated chylomicron TC concentrations increased from 89 +/- 13 and 0 .8 +/- 0.3 to 263 +/- 43 and 91 +/- 39 mg/dL (mean +/- SEM), respectively, with feeding. Tracer-determined chylomicron TG half-lives were 5.34 +/- 0.5 8 and 6.51 +/- 0.58 min during the fasting and fed states, respectively (P< 0.01). The apparent distribution volume during the fasting state was 24% g reater than plasma volume (4515 +/- 308 vs. 3630 +/- 78 mL, P< 0.02), consi stent with significant margination of lipid emulsion particles to endotheli al binding sites. Margination was reduced during the fed state, suggesting that native chylomicrons competed with lipid emulsion particles for endothe lial lipoprotein lipase. The results indicate that a radiolabeled commercia l lipid emulsion is metabolized in a fashion similar to native chylomicron TG, and thus can be used to study chylomicron TG kinetics.