title: Regulation of plasma long-chain fatty acid oxidation in relation to uptake in human skeletal muscle during exercise.
abstract: 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 high (H-FOX) or low (L-FOX) leg fat oxidation (H-FOX: 1,098 +/- 140; L-FOX: 494 +/- 84 micromol FA/min, P < 0.001), which was achieved by manipulating preexercise muscle glycogen (H-FOX: 197 +/- 21; L-FOX: 504 +/- 25 mmol/kg dry wt, P < 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 +/- 1.6; L-FOX: 18.2 +/- 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 +/- 47 vs. 212 +/- 37 micromol/min, P < 0.001). Probably due to the slightly higher (P < 0.01) plasma LCFA concentration in H-FOX than in L-FOX, leg plasma LCFA uptake was nonsignificantly (P = 0.17) higher (25%) in H-FOX than in L-FOX, yet the fraction of plasma LCFA uptake oxidized was 61% higher (P < 0.05) in H-FOX than in L-FOX. Accordingly, the muscle content of several lipid-binding proteins did not differ significantly between trials, although fatty acid translocase/CD36 and caveolin-1 were elevated (P < 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.
authors.affiliation: The Copenhagen Muscle Research Centre, Institute of Exercise and Sport Sciences, Department of Human Physiology, Universitetsparken 13, DK-2100 Ø, Denmark. croepstorff@ifi.ku.dk
authors.forename: Carsten
authors.initials: C
authors.lastname: Roepstorff
authors.forename: Bodil
authors.initials: B
authors.lastname: Vistisen
authors.forename: Kirstine
authors.initials: K
authors.lastname: Roepstorff
authors.forename: Bente
authors.initials: B
authors.lastname: Kiens
mesh_terms: D000328:Adult; D015153:Blotting, Western; D018955:CD36 Antigens / Q000378:metabolism; D002352:Carrier Proteins / Q000378:metabolism; D051242:Caveolin 1; D051244:Caveolin 3; D022461:Caveolins / Q000378:metabolism; D004032:Diet; D004435:Eating / Q000502:physiology; D015444:Exercise / Q000502:physiology*; D050556:Fatty Acid-Binding Proteins; D005227:Fatty Acids / Q000097:blood*; D005947:Glucose / Q000008:administration & dosage / Q000494:pharmacology; D006003:Glycogen / Q000378:metabolism; D006801:Humans; D007262:Infusions, Intravenous; D007866:Leg / Q000502:physiology; D008297:Male; D009119:Muscle Contraction / Q000502:physiology; D018482:Muscle, Skeletal / Q000378:metabolism*; D027361:Organic Anion Transporters / Q000378:metabolism; D010084:Oxidation-Reduction; D015656:Respiratory Mechanics / Q000502:physiology; D012508:Sarcolemma / Q000378:metabolism
chemical_list: C495540:CAV1 protein, human; D018955:CD36 Antigens; D002352:Carrier Proteins; D051242:Caveolin 1; D051244:Caveolin 3; D022461:Caveolins; D050556:Fatty Acid-Binding Proteins; D005227:Fatty Acids; D027361:Organic Anion Transporters; D006003:Glycogen; D005947:Glucose