Fatty acid oxidation intermediates and the effect of fasting on oxidation in red and white skeletal muscle.

In vitro oxidation of U-[14C]glucose-6-phosphate, 2-[14C]pyruvate, and 1-[14C]pyruvate was significantly reduced in red skeletal muscle from fasting rats. Over the same time interval of fasting, 1-[14C]palmitate oxidation remained unchanged. Pyruvate dehydrogenase activity, assayed before in vitro activation, was also reduced in red muscle. Long chain acylcarnitine and long chain acyl CoA increased over the same time period in red muscle. Changes in long chain fatty acid derivatives and pyruvate oxidation were much less dramatic in white muscle. We propose that the rise in levels of long chain fatty acid derivatives may be directly related to the inhibition of carbohydrate oxidation during fasting in red skeletal muscle.