Non-invasive observation of acetyl-group buffering by H-1-MR spectroscopy in exercising human muscle

The observation of a previously unidentified peak in localized H-1 magnetic resonance (MR) spectra of human muscle during and after a work load is rep orted. Basic NMR properties of this resonance, as well as physiologic circu mstances of its observation, suggest that it is due to the acetyl group of acetylcarnitine. The relatively large pool of muscular carnitine acts as a buffering system stabilizing the ratio of acetylated to free coenzyme A. Fr ee carnitine can be acetylated to a large extent whenever a mismatch occurs between the fluxes through pyruvate dehydrogenase and the TCA cycle. Resul ts of initial applications of H-1 MR spectroscopy in several muscles and un der different exercise regimes are in agreement with earlier invasive measu rements of acetylcarnitine. It is demonstrated that the detailed dynamics o f acetyl group formation are now likely to be observable non-invasively in humans by localized H-1 magnetic resonance spectroscopy on standard MR imag ing systems, and that acetylcarnitine buffering as a function of exercise t ype, oxygenation states, diet and pathology could thus be studied repeatedl y and in various muscle groups with much improved temporal resolution. Copy right (C) 1999 John Wiley & Sons, Ltd.