Is Free Carnitine Visible in 1H-MR Spectra of Skeletal Muscle?

Andreas Boss¹, Roland Kreis¹, Pierre Saillen¹, Chris Boesch¹, Peter Vermathen¹

The exercise-induced production of intramyocellular acetylcarnitine is mirrored by decreased free carnitine. In ¹H MR-spectra of muscle it was observed that trimethylammonium, supposedly with contributions from both, acetylcarnitine and carnitine, was increased after exercise. We applied spectroscopic imaging in 8 runners (calf) and 8 cyclists (thigh) and found that the change of trimethylammonium was significantly correlated with the exercise-induced production of acetylcarnitine in calf (R²=0.55, p<0.001) and thigh (R²=0.27, p<0.001). The present results suggest that the increase of trimethylammonium resulted at least partly from acetylcarnitine production and, hence, that free carnitine is largely invisible in ¹H MR-spectra of the muscle.