The effects of endogenous opioid peptides on exercise performance

In the classic paradigm, the limit to endurance of exercise is explained in terms of metabolic capacity. However fatigue is determined by a complex interplay amongst many factors. The sensation of fatigue during physical exercise may arise not only from peripheral sources of exhaustion but also from the central regulation of homeostasis. It is known that endogenous opiates are elevated during physical exercise and seem likely to be assigned a significant role in the integrated hormonal and metabolic response to exercise. It may also be possible that during exercise, the perception of fatigue is modulated by an increase of endogenous opioids. However, it has not been investigated yet how the opioid peptides contribute to exercise performance at the central nervous system level.Here with this study, it has been planned to see the effects of endogenous opioid peptides on exercise performance at central nervous system level. Rats which were treated with naloxone (50 µg in 10 µl physiologic saline solution) and naltrindole (50 µg in 10 µl physiologic saline solution) intracerebroventrically, were exercised till exhaustion. Time to exhaustion, blood glucose and lactate leves were determined. Naloxone and naltrindole has no effects on exhaustion time of exercised rats (p> 0,05); however naltrindole decreased blood glucose levels significantly (p< 0,05) after exhaustive exercise without any effects on blood lactate levels (p> 0,05).In conclusion, it has been suggested that the central endogenous opioid peptides have no effect on exercise performance. Delta opioid receptors, however, might have a role in regulation of glucose metabolism during the exhaustive exercise.