Effect of adrenodemedullation on decline in muscle malonyl-CoA during exercise

Malonyl-CoA is an inhibitor of carnitine palmitoyltransferase, a rate-limiting enzyme of fatty acid oxidation. Previous studies have indicated that muscle malonyl-CoA declines in rats during treadmill running. This decrease may be important for allowing an increased rate of fatty acid oxidation during prolonged exercise. This study was designed to determine whether epinephrine is essential for inducing the decline in muscle malonyl-CoA during exercise. Male Sprague-Dawley rats underwent adrenodemedullation (ADM) or sham operation. After allowing 3 wk for recovery, rats were killed (pentobarbital anesthesia) at rest or after running at 21 m/min up a 15% grade for 60 min. Red quadriceps malonyl-CoA decreased from 2.6 +/- 0.3 to 0.8 +/- 0.07 nmol/g in sham-operated rats and from 2.2 +/- 0.3 to 0.8 +/- 0.1 nmol/g in ADM rats. White quadriceps malonyl-CoA decreased to similar levels during exercise in both sham-operated and ADM rats. A second experiment on 24-h fasted rats also showed no impairment in the exercise-induced decline in red quadriceps malonyl-CoA as a result of adrenodemedullation. The hormones of the adrenal medulla are therefore unessential for inducing the decline in malonyl-CoA during exercise.