Association between muscle acetyl-CoA and acetylcarnitine levels in the exercising horse.

The study investigates the relationship between the levels of acetyl-CoA and acetylcarnitine in the muscle of racing horses during and after treadmill exercise. The researchers found that, with increased workout intensity, both acetyl-CoA and acetylcarnitine levels rose, suggesting acetyl-CoA conversion to acetylcarnitine for redistribution within cells.

Increased Acetyl-CoA and Acetylcarnitine During Exercise

• During treadmill exercise that lasted two minutes and had intensifying levels, the team of researchers noted increased amounts of acetyl-CoA and acetylcarnitine in the working muscles of Thoroughbred horses.
• When these horses were exercising at high-intensity levels, a plateau, or a state of little or no change after a time of activity or progress, was reached for both acetyl-CoA (approximately 50 mumols/kg dry muscle) and acetylcarnitine (around 20 mmol/kg dry muscle).

Post-exercise Correlation

• After exercise, concentrations of acetyl-CoA and acetylcarnitine were significantly correlated. The researchers noted that roughly 350 mumols of acetylcarnitine accumulated for every 1 mumol acetyl-CoA.
• In this study, the relationship between acetylcarnitine and acetyl-CoA indicates that equilibrium was maintained and that neither acetylcarnitine transferase nor carnitine/acetylcarnitine translocase were the limiting factor in this process.

Mechanism of Action: Acetyl-CoA Generation

• Under the exercise conditions used, it is likely that most of the acetyl-CoA formed is generated through the intramitochondrial decarboxylation of pyruvate. In other words, during exercise, pyruvate inside mitochondria is broken down to generate acetyl-CoA.

Redistribution via Acetylcarnitine

• The acetyl group of acetyl-CoA is considered to be redistributed throughout the entire cell through the creation of acetylcarnitine, which crosses the mitochondrial membrane easily.
• Even with this redistribution, the close correspondence between acetylcarnitine and acetyl-CoA levels means that balance is preserved within the cell.

Open Questions

• There remain questions about whether the changes observed in acetyl-CoA and acetylcarnitine directly relate to exercise or to the muscle state ten seconds or more after exercise.