Interaction of carnitine with insulin-stimulated glucose metabolism in humans.
To characterize the interactions of carnitine with glucose metabolism, we administered L-carnitine as a primed (3 mmol) constant (17 mumol/min) intravenous infusion to healthy young volunteers during short-term (2 h) euglycemic hyperinsulinemia. In comparison with a control (saline) infusion, exogenous carnitine administration resulted in a stable, fourfold increase in basal serum carnitine levels (160 +/- 14 vs. 36 +/- 2 microM, P less than 0.001). At similar steady-state plasma insulin levels (75 microU/ml), carnitine infusion was associated with a 17 +/- 3% stimulation of whole body glucose utilization (6.56 +/- 0.60 vs. 5.57 +/- 0.44 mg.min-1.kg-1, P less than 0.001). This effect was more pronounced in the subjects with higher rates of glucose disposal (r = 0.65, P less than 0.05). Net rates of insulin-induced glucose oxidation (measured by continuous, computerized indirect calorimetry) were similar with or without carnitine (1.67 +/- 0.23 vs. 1.65 +/- 0.10 mg.min-1.kg-1, respectively). As a consequence, the carnitine-induced enhancement of total glucose metabolism was quantitatively accounted for by a 50% increase in nonoxidative glucose disposal (2.89 +/- 0.81 vs. 1.92 +/- 0.51 mg.min-1.kg-1, P less than 0.05). The inhibitory effect of insulin on net lipid oxidation was not altered by carnitine (-0.67 +/- 0.09 vs. -0.62 +/- 0.06 mg.min-1.kg-1). Circulating levels of free fatty acids (FFA), glycerol, and beta-hydroxybutyrate fell in parallel during insulin infusion in the test and control study, and blood lactate concentrations rose by similar amounts (approximately 0.35 mM).(ABSTRACT TRUNCATED AT 250 WORDS)
Ferrannini
E
E
Metabolism Unit, Consiglio Nazionale della Ricerche Institute of Clinical Physiology, Pisa, Italy.
Buzzigoli
G
G
Bevilacqua
S
S
Boni
C
C
Del Chiaro
D
D
Oleggini
M
M
Brandi
L
L
Maccari
F
F
D000328:Adult; D001786:Blood Glucose / Q000378:metabolism; D002331:Carnitine / Q000494:pharmacology*; D005260:Female; D005947:Glucose / Q000378:metabolism*; D015309:Glucose Clamp Technique; D006801:Humans; D007328:Insulin / Q000097:blood / Q000494:pharmacology*; D007700:Kinetics; D007773:Lactates / Q000097:blood; D008297:Male; D011773:Pyruvates / Q000097:blood; D012016:Reference Values
D001786:Blood Glucose; D007328:Insulin; D007773:Lactates; D011773:Pyruvates; D005947:Glucose; D002331:Carnitine