Effect of acute exercise on amino acid incorporation into the rat myocardium

To determine the effect of acute exercise and recovery on amino acid incorporation into myocardial protein, female Wistar rats (220-240 g) were exercised to exhaustion by swimming. Animals were sacrificed at exhaustion, or 0.5, 1, 2, 4. or 16 h after exercise. Hearts were removed and perfused for 30 min with a Krebs-Henseleit bicarbonate buffer containing; 15 mM glucose, normal plasma levels of amino acids and 0.1 muCi [3H]-phenylalanine per ml of buffer. Immediately following the exhaustive exercise, amino acid incorporation into extramitochondrial, mitochondrial and whole heart protein was decreased by 50, 55, and 43% respectively. Following 2 h of recovery, incorporation of [3H]-phenylalanine returned to normal in all three protein fractions. No stimulation in protein synthesis was observed in any of the cell fractions. In an attempt to estimate the intracellular availability of [3H]-phenylalanine, the TCA soluble radioactivity was determined. No change from rest was observed at exhaustion or throughout recovery suggesting that the amino acid pool size was not altered. These data indicate that exhaustive exercise temporarily reduces myocardial protein synthesis which quickly returns to normal during recovery.