Long-term administration of L-carnitine to humans: effect on skeletal muscle carnitine content and physical performance.
BACKGROUND
Long-term administration of high oral doses of L-carnitine on the skeletal muscle composition and the physical performance has not been studied in humans.


METHODS
Eight healthy male adults were treated with 2 x 2 g of L-carnitine per day for 3 months. Muscle biopsies and exercise tests were performed before, immediately after, and 2 months after the treatment. Exercise tests were performed using a bicycle ergometer for 10 min at 20%, 40%, and 60% of the individual maximal workload (P(max)), respectively, until exhaustion.


RESULTS
There were no significant differences between V(O(2)max), RER(max), and P(max) between the three time points investigated. At submaximal intensities, the only difference to the pretreatment values was a 5% increase in V(O(2)) at 20% and 40% of P(max) 2 months after the cessation of the treatment. The total carnitine content in the skeletal muscle was 4.10 +/- 0.82 micromol/g before, 4.79 +/- 1.19 micromol/g immediately after, and 4.19 +/- 0.61 micromol/g wet weight 2 months after the treatment (no significant difference). Activities of the two mitochondrial enzymes citrate synthase and cytochrome oxidase, as well as the skeletal muscle fiber composition also remained unaffected by the administration of L-carnitine.


CONCLUSIONS
Long-term oral treatment of healthy adults with L-carnitine is not associated with a significant increase in the muscle carnitine content, mitochondrial proliferation, or physical performance. Beneficial effects of the long-term treatment with L-carnitine on the physical performance of healthy adults cannot be explained by an increase in the carnitine muscle stores.
Wächter
Sandra
S
Institute of Clinical Pharmacology, University of Berne, Switzerland.
Vogt
Michael
M
Kreis
Roland
R
Boesch
Chris
C
Bigler
Peter
P
Hoppeler
Hans
H
Krähenbühl
Stephan
S
D000328:Adult; D015308:Anaerobic Threshold / Q000187:drug effects; D002331:Carnitine / Q000097:blood / Q000494:pharmacology* / Q000652:urine; D002851:Chromatography, High Pressure Liquid; D005080:Exercise Test; D006801:Humans; D019344:Lactic Acid / Q000097:blood; D009682:Magnetic Resonance Spectroscopy; D008297:Male; D008931:Mitochondria, Muscle / Q000187:drug effects / Q000201:enzymology / Q000648:ultrastructure; D018485:Muscle Fibers, Skeletal / Q000187:drug effects; D018482:Muscle, Skeletal / Q000166:cytology / Q000187:drug effects* / Q000378:metabolism*
D019344:Lactic Acid; D002331:Carnitine