Depletion of high energy phosphates implicates post-exercise mortality in carp and trout; an in vivo 31P-NMR study

Metabolic responses to exhaustive exercise change markedly during the protracted non-trophic spawning migration of the lamprey Geotria australis

Adults of the Southern hemisphere lamprey Geotria australis were subjected to an exercise/recovery regime at the commencement and end of their 12-15 month non-trophic, upstream spawning migration. In early (immature) migrants and pre-spawning females, muscle glycogen was markedly depleted during exercise, but became rapidly replenished. As muscle lactate rose during exercise and peaked 1-1.5 h into the recovery period, and therefore after muscle glycogen had become replenished, it cannot be the direct source for that replenishment. However, both plasma lactate and glycerol (but not muscle glycerol and glucose) rose sharply during exercise and then declined markedly during the first 0.5 h of recovery and thus exhibited the opposite trend to that of muscle glycogen, implying that these limited pools of glycogenic precursors contribute to glycogen replenishment. Although plasma glucose rose following exercise, and consequently could also be a precursor for muscle glycogen replenishment, it remained elevated even after muscle glycogen had become replenished. While resting pre-spawning females and mature males retained high muscle glycogen concentrations, this energy store became permanently depleted in females during spawning. In mature males, muscle glycogen remained high and lactate low during the exercise/recovery regime, whereas muscle glycerol declined precipitously during exercise and then rose rapidly. In summary, vigorous activity by G. australis is fuelled extensively by anaerobic metabolism of glycogen early in the spawning run and by pre-spawning females, but by aerobic metabolism of its energy reserves in mature males.

Effects of exercise on L-carnitine and lipid metabolism in African catfish (Clarias gariepinus) fed different dietary L-carnitine and lipid levels

African catfish (Clarias gariepinus) were fed four isonitrogenous diets (34 % crude protein), each containing one of two lipid (100 or 180 g/kg) and two L-carnitine (15 or 1000 mg/kg) levels. After 81 d of feeding, thirty-two fish (body weight 32 g) from each dietary group were randomly selected, sixteen fish were induced to a 3-h swim (speed of 1.5 body length (BL)/s), while the other sixteen fish were kept under resting condition. Fish fed 1000 mg L-carnitine accumulated 3.5 and 5 times more L-carnitine in plasma and muscle, respectively, than fish fed the 15 mg L-carnitine. Muscle L-carnitine content was significantly lower in exercised fish than in rested fish. High dietary lipid level (fish oil) led to an increase in muscle n-3 PUFA content and a decrease in SFA and MUFA content. In liver, the increase in dietary lipid level resulted in an increased levels of both n-6 and n-3 PUFA. L-carnitine supplementation significantly decreased n-3 PUFA content. Exercise decreased n-3 PUFA in both muscle and liver. Plasma lactate and lactate dehydrogenase, normally associated with increased glycolytic processes, were positively correlated with exercise and inversely correlated with dietary L-carnitine level. L-carnitine supplementation reduced significantly the RQ from 0.72 to 0.63, and an interaction between dietary L-carnitine and lipid was observed (P < 0.03). Our results indicate that an increase in fatty acids (FA) intake may promote FA oxidation, and both carnitine and exercise might influence the regulation of FA oxidation selectivity.

Differential recovery from exercise and hypoxia exposure measured using 31P- and 1H-NMR in white muscle of the common carp Cyprinus carpio

Phosphocreatine (PCr) was reduced to equivalent levels in carp white muscle by high-intensity exhaustive exercise and exposure to hypoxia at 15 degrees C and 25 degrees C in order to assess the influence of intracellular pH (pH(i)), temperature and lactate levels on PCr recovery in vivo. High-intensity exercise resulted in a significantly lower pH(i) compared with hypoxia exposure and the rate of PCr depletion and tissue acidification during hypoxia exposure was significantly higher in carp held at 25 degrees C compared with those at 15 degrees C. During recovery, PCr and pH(i) returned towards normoxia/resting levels at a faster rate following hypoxia exposure than after exercise. The lower pH(i) in exercised carp caused a greater perturbation to cellular energy status (assessed as the free energy of ATP hydrolysis; DeltafG') and resulted in a higher [ATP]/[ADP(free)] ratio, which may limit mitochondrial ATP production and contribute to the slower recovery from exercise compared with recovery from hypoxia exposure. Rates of recovery from exercise and hypoxia exposure were not affected by acclimation temperature (15 and 25 degrees C), suggesting that the processes involved in acclimation compensate for the Q(10) effects of temperature on metabolic processes. Finally, using a dual 31P-NMR and 1H-NMR analysis technique, we demonstrated that the greater tissue acidification observed after high-intensity exercise compared with hypoxia exposure occurred at similar white muscle lactate concentrations.