Extraction of endogenous plasma triglycerides by the working human forearm muscle in the fasting state

The extraction of triglycerides (TG) by the working forearm was determined in eight healthy fasting men, both by the measurement of chemical arterial-deep venous (a-dv) TG differences and by the a-dv differences in TG radioactivity after endogenous labeling with tritiated palmitate. Measurements were made before and then during nicotinic acid infusion. Correction for plasma water shift in the forearm vasculature was made by estimating the (125I)albumin activity after an intravenous injection. The overall mean value +/- S.E.M. without and with nicotinic acid was for TG arterial concentration (mumol/1) 713 +/- 153 and 695 +/- 140, TG a-dv concentration difference (mumol/1)-14 +/- 7 and -6 +/- 4, TG arterial radioactivity (cpm/ml) 1650 +/- 469 and 1471 +/- 342, TG a-dv radioactivity difference 12 +/- 24 and -2 +/- 13. The average standard errors for the determinations of triglycerides were 0.85% and 1.5% for the chemical and the isotope methods, respectively. In conclusion, no significant average a-dv difference in TG concentration as determined by either the chemical or the isotope method was detected. With the standard errors achieved, however, a-dv differences of less than around 20 mumol/lcould not be discovered. Such an extraction of endogenous plasma TG could, if oxidized, account for about 25% of the oxygen extraction by the eercising forearm.