A new method for the study of chylomicron kinetics in vivo

Our understanding of the metabolism of chylomicrons, the lipoprotein that transports dietary fat from the intestine to peripheral tissues, is incomplete. The present studies were conducted to determine whether a labeled intravenous lipid emulsion could be used to estimate chylomicron triglyceride (TG) rate of appearance (R(a)) and thereby quantify the rate of intestinal fat absorption. After an overnight fast, healthy volunteers (n = 6) sipped a ³H-labeled drink over 6.5 h at a rate of 175 mg fat·kg^-1·h^-1, Beginning at hour 5, an HPLC-purified, ¹⁴C-labeled lipid emulsion was infused intravenously for 90 min. During the study, plasma total and chylomicron TG concentrations increased from 100 ± 21 to 237 ± 40 mg/dl and from undetectable 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 summary, a radio-labeled intravenous lipid emulsion is able to accurately estimate chylomicron TG R(a) and therefore can be used to measure in vivo fat absorption rates.