In vivo determination of very-low-density lipoprotein-apolipoprotein B100 secretion rates in humans with a low dose of L-[1-13C]valine and isotope ratio mass spectrometry

The aim of the present study was to determine the rate of very-low-density lipoprotein (VLDL)-apolipoprotein (apo) B100 secretion in humans with a minimized amount of L-[1-C-13]valine infusion in combination with the use of gas chromatography/combustion/isotope ratio mass spectrometry (GC/C/IRMS) analysis. To compare this method with the conventional gas chromatography/mass spectrometry (GC/MS) technique, two different dosages of L-[1-C-13]valine and both analytical techniques were compared in a single study. A priming dose of L-[1-C-13]valine (2 mu mol/kg) followed by a constant infusion (2 mu mol/kg/h) was given for 3 h, directly followed by a second priming dose (15 mu mol/kg) and a constant infusion (15 mu mol/kg/h) for 4 h. The fractional secretion rate obtained by GC/C/IRMS measurements from the first 3 h of infusion (mean +/- SD: 0.22 +/- 0.09 pools/h) was similar to that obtained by GC/MS during the last 4 h of infusion (0.23 +/- 0.07 pools/h; P = 0.56). In conclusion, superior analytical accuracy and sensitivity of GC/C/IRMS enable measurements of VLDL-apo B100 secretion with much lower doses of L-[1-C-13]valine and allow for reduction of experimental costs. (C) 1998 Academic Press.