Measuring plasma fatty acid oxidation with intravenous bolus injection of 3H- and 14C-fatty acid

Accurate measures of plasma FA oxidation can improve our understanding of diseases characterized by impaired FA oxidation. We describe and compare the 24 h time-courses of FA oxidation using bolus injections of [1-14C]palmitate versus [9,10-3H]palmitate under postabsorptive, postprandial, and walking conditions. Fifty-one men and 95 premenopausal women participated in one condition (postabsorptive, postprandial, or walking), one tracer (14C- or 3H-labeled), and an acetate or palmitate study. Groups were matched for sex, age, and body mass index (BMI). At 24 h, cumulative [3H]acetate recovery as 3H2O was 80 ± 6%, 78 ± 2%, and 81 ± 6% in the postabsorptive, postprandial, and walking conditions, respectively (not significant). Model-predicted maximum [1-14C]acetate recovery as expired 14CO2 was 59 ± 12%, 52 ± 8%, and 65 ± 10% in the postabsorptive, postprandial, and walking condition, respectively (one way ANOVA, P = 0.12). When corrected with the corresponding acetate recovery factors, 24 h time-courses of FFA oxidation were similar between [1-14C]palmitate and [9,10-3H]palmitate in all three conditions. In contrast to previous meal ingestion studies, an acetate-hydrogen recovery factor was needed to achieve comparable oxidation rates using an intravenous bolus of [3H]palmitate. In conclusion, intravenous boluses of [9,10-3H]palmitate versus [1-14C]palmitate gave similar estimates of 24 h cumulative FFA oxidation in age-, sex- and BMI-matched individuals.