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To determine the preferred infusion-sampling mode for isotopic studies of free fatty acid (FFA) metabolism, tracer ( 14Cpalmitate) was infused into the left ventricle of five anesthetized dogs, and tracee (3Hpalmitate) was infused into three separate peripheral veins of each dog. The 14Cpalmitate specific activity (SA) was lower in mixed venous than arterial blood, and 3Hpalmitate SA was equal in both sites. The actual infusion rate of 3Hpalmitate 2.15 +/- 0.31 X 10(5) disintegrations/min (dpm).kg-1.min-1 could be accurately predicted (2.14 +/- 0.32 X 10(5) dpm.kg-1.min-1) using the known 14Cpalmitate infusion rate and the arterial plasma 14C-to-3Hpalmitate ratio. In contrast, the mixed venous 14C-to-3Hpalmitate ratio resulted in overestimates (P less than 0.05) of the actual 3Hpalmitate infusion rate. In summary, venous tracer infusion with arterial blood sampling for FFA tracer studies provides the most accurate estimates of tracee rate of appearance.
Jensen et al. (1988) studied this question.