The association of acetyl-L-carnitine with glucose and lipid metabolism in human muscle in vivo: the effect of hyperinsulinemia

Metabolism. 1997 Dec;46(12):1454-7. doi: 10.1016/s0026-0495(97)90147-5.


We examined whether hyperinsulinemia is associated with changes in the amount of L-carnitine and acetyl-L-carnitine in the muscle and whether the source of acetyl-coenzyme A (CoA) (glucose or free fatty acids [FFAs]) influences its further metabolism to acetyl-L-carnitine or through tricarboxylic acid in the skeletal muscle of man in vivo. Twelve healthy men (aged 45 +/- 2 years; body mass index, 25.2 +/- 1.0 kg/m2) were studied using a 4-hour euglycemic-hyperinsulinemic clamp (1.5 mU/kg/min) and indirect calorimetry. Although the mean muscle free L-carnitine and acetyl-L-carnitine concentrations remained unchanged during hyperinsulinemia in the group as a whole, the individual changes in muscle free L-carnitine and acetyl-L-carnitine concentrations were inversely related (r = -.72, P < .02). The basal level of acetyl-L-carnitine was inversely related to the rate of lipid oxidation (r = -.70, P < .02). In a stepwise linear regression analysis, 77% of the variation in the change of acetyl-L-carnitine concentrations was explained by the basal muscle glycogen level (inversely) and nonoxidative glucose disposal rate (directly) during hyperinsulinemia (P < .001); by adding the final FFA concentration (inverse correlation) to the model, 88% of the variation was explained (P < .001). In conclusion, (1) hyperinsulinemia does not enhance skeletal muscle free L-carnitine or acetyl-L-carnitine concentrations in-man, and (2) the acetyl group of acetyl-L-carnitine in human skeletal muscle in vivo is probably mostly derived from glucose and not through beta-oxidation from fatty acids.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Acetyl Coenzyme A / analysis
  • Acetyl Coenzyme A / metabolism
  • Acetyl Coenzyme A / physiology
  • Acetylcarnitine / analysis
  • Acetylcarnitine / metabolism*
  • Acetylcarnitine / physiology
  • Adult
  • Calorimetry, Indirect
  • Fatty Acids, Nonesterified / analysis
  • Fatty Acids, Nonesterified / metabolism
  • Glucose / metabolism*
  • Glycogen / analysis
  • Glycogen / metabolism
  • Humans
  • Hyperinsulinism / metabolism*
  • Hyperinsulinism / physiopathology
  • Insulin / pharmacology
  • Linear Models
  • Lipid Metabolism*
  • Male
  • Middle Aged
  • Muscle, Skeletal / chemistry
  • Muscle, Skeletal / metabolism*
  • Muscle, Skeletal / physiology
  • Oxidation-Reduction


  • Fatty Acids, Nonesterified
  • Insulin
  • Acetylcarnitine
  • Acetyl Coenzyme A
  • Glycogen
  • Glucose