PYRUVATE-DEHYDROGENASE ACTIVITY AND ACETYL GROUP ACCUMULATION DURING EXERCISE AFTER DIFFERENT DIETS

Pyruvate dehydrogenase activity (PDHa) and acetyl group accumulation w ere examined in human skeletal muscle at rest and during exercise afte r different diets. Five males cycled at 75% of maximal O2 uptake (VO2 max) to exhaustion after consuming a low-carbohydrate diet (LCD) for 3 days and again 1-2 wk later for the same duration after consuming a h igh-carbohydrate diet (HCD) for 3 days. Resting PDHa was lower after a LCD (0.20 +/- 0.04 vs. 0.69 +/- 0.05 mmol.min-1.kg wet wt-1; P < 0.05 ) and coincided with a greater intramuscular acetyl-CoA-to-CoASH ratio , acetyl-CoA content, and acetylcarnitine content. PDHa increased duri ng exercise in both conditions but at a lower rate in the LCD conditio n compared with the HCD condition (1.46 +/- 0.25 vs. 2.65 +/- 0.23 mmo l.min-1.kg wet wt-1 at 16 min and 1.88 +/- 0.20 vs. 3.11 +/- 0.14 at t he end of exercise; P < 0.05). During exercise muscle acetyl-CoA and a cetylcarnitine content and the acetyl-CoA-to-CoASH ratio decreased in the LCD condition but increased in the HCD condition. Under resting co nditions PDHa was influenced by the availability of fat or carbohydrat e fuels acting through changes in the acetyl-CoA-to-CoASH ratio. Howev er, during exercise the activation of PDHa occurred independent of cha nges in the acetyl-CoA-to-CoASH ratio, suggesting that other factors a re more important.