Regulation of plasma long-chain fatty acid oxidation in relation to uptake in human skeletal muscle during exercise
American Journal of Physiology. Endocrinology and Metabolism
Roepstorff, Carsten, Bodil Vistisen, Kirstine Roepstorff, and Bente Kiens. Regulation of plasma long-chain fatty acid oxidation in relation to uptake in human skeletal muscle during exercise. Am J Physiol Endocrinol Metab 287: In the present study, we investigated possible sites of regulation of long-chain fatty acid (LCFA) oxidation in contracting human skeletal muscle. Leg plasma LCFA kinetics were determined in eight healthy men during bicycling (60 min, 65% peak oxygen uptake) with either
... take) with either high (H-FOX) or low (L-FOX) leg fat oxidation (H-FOX: 1,098 Ϯ 140; L-FOX: 494 Ϯ 84 mol FA/min, P Ͻ 0.001), which was achieved by manipulating preexercise muscle glycogen (H-FOX: 197 Ϯ 21; L-FOX: 504 Ϯ 25 mmol/kg dry wt, P Ͻ 0.001). Several blood metabolites and hormones were kept nearly similar between trials by allocating a preexercise meal and infusing glucose intravenously during exercise. During exercise, leg plasma LCFA fractional extraction was identical between trials (H-FOX: 17.8 Ϯ 1.6; L-FOX: 18.2 Ϯ 1.8%, not significant), suggesting similar LCFA transport capacity in muscle. On the contrary, leg plasma LCFA oxidation was 99% higher in H-FOX than in L-FOX (421 Ϯ 47 vs. 212 Ϯ 37 mol/min, P Ͻ 0.001). Probably due to the slightly higher (P Ͻ 0.01) plasma LCFA concentration in H-FOX than in L-FOX, leg plasma LCFA uptake was nonsignificantly (P ϭ 0.17) higher (25%) in H-FOX than in L-FOX, yet the fraction of plasma LCFA uptake oxidized was 61% higher (P Ͻ 0.05) in H-FOX than in L-FOX. Accordingly, the muscle content of several lipidbinding proteins did not differ significantly between trials, although fatty acid translocase/CD36 and caveolin-1 were elevated (P Ͻ 0.05) by the high-intensity exercise and dietary manipulation allocated on the day before the experimental trial. The present data suggest that, in contracting human skeletal muscle with different fat oxidation rates achieved by manipulating preexercise glycogen content, transsarcolemmal transport is not limiting plasma LCFA oxidation. Rather, the latter seems to be limited by intracellular regulatory mechanisms. plasma membrane fatty acid-binding protein; cytosolic fatty acidbinding protein; fatty acid translocase; caveolin CIRCULATING LONG-CHAIN FATTY ACIDS (LCFA) are an important energy source for human skeletal muscle during moderateintensity exercise. On the whole body level, previous studies have suggested that when LCFA availability or exercise intensity is manipulated, systemic plasma LCFA oxidation during exercise is regulated at the entrance of LCFA into mitochondria (6, 35). However, whole body measurements of plasma LCFA kinetics do not accurately reflect plasma LCFA kinetics in skeletal muscle (12, 31); therefore, studies in human skeletal muscle are warranted.