Effects of L-, D-, and DL-carnitine on morphometric parameters of skeletal muscle and exercise performance of laboratory animals receiving carnitine-deficient diet.

Serum concentration of L-carnitine, the mean thickness of the skeletal muscle fiber, and exercise performance in the forced swimming test decreased in rats receiving a carnitine-deficient diet. Treatment with L-carnitine compensated for carnitine deficiency, while racemate and D-stereoisomer did not increase its level. L-Carnitine, but not racemate and D-stereoisomer, promoted recovery of the skeletal muscle fiber thickness and exercise performance of rats.