A new method for the study of chylomicron kinetics in vivo

Our understanding of the metabolism of chylomicrons, the lipoprotein that t ransports dietary fat from the intestine to peripheral tissues, is incomple te. The present studies were conducted to determine whether a labeled intra venous lipid emulsion could be used to estimate chylomicron triglyceride (T G) rate of appearance (R-a) and thereby quantify the rate of intestinal fat absorption. After an overnight fast, healthy volunteers (n = 6) sipped a H -3-labeled drink over 6.5 h at a rate of 175 mg fat.kg(-1).h(-1). Beginning at hour 5, an HPLC-purified, C-14-labeled lipid emulsion was infused intra venously for 90 min. During the study, plasma total and chylomicron TG conc entrations increased from 100 +/- 21 to 237 +/- 40 mg/dl and from undetecta ble to steady-state levels of 35 +/- 13 mg/dl, respectively. After a minor correction for VLDL contamination, tracer-determined chylomicron TG R-a was 175 +/- 30 mg.kg(-1).h(-1), equal to the presumed ingestion rate. In summa ry, a radiolabeled intravenous lipid emulsion is able to accurately estimat e chylomicron TG R-a and therefore can be used to measure in vivo fat absor ption rates.