Acetyl coenzyme A and acetylcarnitine concentration and turnover rates in muscle and liver of the ketotic rat and guinea pig.

Fasting ketosis caused no change in liver acetylcarnitine concentration but caused a decrease in muscle acetylcarnitine to one-half the control level. The combined acetyl coenzyme A and acetylcarnitine turnover rates for control and ketotic liver were, respectively, 4.66 and 10.90 mpmoles per g (fresh weight) per min; for normal and ketotic muscle the corresponding figures were 8.23 and 4.52 mpmoles per g (fresh weight) per min. With respiratory activity unchanged in ketotic liver, any increase in acetyl-CoA or acetylcarnitine turnover rate must reflect an increased rate of acetoacetate synthesis. By contrast, ketotic muscle was characterized by a decreased acetyl-CoA or acetylcarnitine turnover rate, a decreased acetylcarnitine pool size, a shift to a more oxidized state as indicated by measured ratios of lactate to pyruvate, and an increased specific activity of acetyl-CoA and acetylcarnitine. These results explain a previously reported observation that fasted ketotic guinea pigs that have received injections of acetate-l J4C expire less Co2 but more 14C02 than their appropriate controls.