Acutely Hypoxic Conditions

Skeletal muscle CoA and carnitine metabolism were investigated in six human volunteers at rest and after exhaustive exercise under normoxic and hypoxic conditions. In comparison to the values at rest, exhaustive exercise was associated with a threeto fourfold increase in the skeletal muscle lactate, and with a twofold increase in the acetyl-CoA content, both under normoxic and hypoxic conditions. Since exercise did not significantly affect the skeletal muscle CoA radical (CoASH), total acid-soluble, or total CoA contents, the increase in the acetyl-CoA content was at the expense of short-chain acyl-CoAs different from acetyl-CoA. With exhaustive exercise, the skeletal muscle acetylcarnitine and short-chain acylcarnitine contents increased by a factor of three to four both under normoxic and hypoxic conditions. In contrast to the CoA pool, these increases were associated with a decrease in the free carnitine content, whereas the total acid-soluble and total carnitine contents were not affected by exercise. After exhaustive exercise, the skeletal muscle acetyl-CoA/CoASH ratio showed a linear correlation with the corresponding acetylcarnitine/free carnitine ratio. The plasma short-chain acylcarnitine concentration increased by a factor of two to three during exercise, and was not significantly different from the values at rest 40 min after completion of exercise. Thus, the current studies illustrate the close interaction between the CoA and carnitine pools in the exercising human skeletal muscle, and they underscore the important role of carnitine in maintaining the muscular CoASH content during exhaustive exercise. (J. Clin. Invest. 1994. 94:1490-1495.)