The Effect of Short-Term Intermittent Aerobic Exercise Training on the Carbohydrate Metabolism of Goldfish (Carassius Auratus) Subject to Environmental Hypoxia
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Goldfish subjected to an intermittent short-term aerobic exercise training regime prior to acute hypoxic exposure demonstrated a shift in hypoxia response. Intermittent aerobic training enhanced the aerobic potential of goldfish in the red muscle by increasing maximal activity of citrate synthase by 72% and reduced pyruvate kinase activity by 21% in white muscle. Across red and white muscle tissue, aerobic training caused a decrease in glycogen storage by 19% and 32%, respectively. Liver glycogen stores remained unchanged by training during normoxia. Subsequent hypoxic exposure demonstrated a significant training effect with a77% glycogen depletion in the liver of trained fish compared to a 53% depletion in untrained fish. Hypoxia caused glycogen depletion, glucose mobilization, and ATP depletion in trained and untrained fish muscle tissue. Meanwhile, the liver of trained recovered ATP slower than untrained fish and both liver and plasma had greater lactate accumulation by 1 h hypoxic recovery in trained fish. Alcohol dehydrogenase maximal activity of trained fish responded to hypoxia with a 50% reduction and trained white muscle significantly reduced alcohol dehydrogenase activity during hypoxic recovery. Ethanol was produced with and without training preconditioning in response to hypoxia in red muscle; however, trained fish white muscle showed an ethanol accumulation trend following training and 12 h hypoxia that was significantly cleared during recovery. Ethanol accumulation in white muscle of trained fish may reveal greater perturbation caused by training and hypoxia and/or some developed mechanism for ethanol retention. In effect, this training regime created a very different metabolic profile in goldfish such that during environmental oxygen limitation, trained fish may experience an enhanced metabolic perturbation and greater glycogen depletion which may compromise hypoxic tolerance.