CARNITINE METABOLISM DURING EXERCISE

Carnitine is an important cofactor for normal cellular metabolism. opt imal utilization of fuel substrates for ATP generation by skeletal mus cle during exercise is dependent on adequate carnitine stores. During short periods of exercise the skeletal muscle carnitine pool is largel y segregated from extracellular carnitine. In normal human subjects, o nly minimal changes in the muscle carnitine pool are observed during e xercise at work loads below the lactate threshold. In contrast, at wor k-loads above the lactate threshold the muscle total carnitine is redi stributed from carnitine to acetylcarnitine, with the acetylcarnitine content correlated with the muscle acetyl-CoA and lactate contents. In contrast, in patients with peripheral arterial disease, an accumulati on of acylcarnitines is observed at all work loads. Patients with chro nic renal failure who are on hemodialysis demonstrate a poor exercise capability which is correlated with a decrease in muscle carnitine con tent. Carnitine supplementation has been shown to improve exercise tol erance in both peripheral arterial disease and hemodialysis patients. Further work is needed to define the mechanism by which exogenous carn itine improves exercise performance in order to better define potentia l patient populations for therapy and to facilitate optimal dosing reg imens.