Pinealectomy reduces hepatic and muscular glycogen content and attenuates aerobic power adaptability in trained rats

The current study emphasizes the crucial role of the pineal gland on the effects of chronic training in different tissues focusing on carbohydrate metabolism. We investigated the maximal oxygen uptake (aerobic power), muscle and liver glycogen content, and also the enzymes involved in the carbohydrate metabolism of rat adipose tissue. Pinealectomized and sham-operated adult male Wistar rats were distributed into four groups: pinealectomized (PINX) untrained, pinealectomized trained, control untrained and control trained. The maximal oxygen uptake capability was assayed before and after the training protocol by indirect open circuit calorimetry. The rats were killed after 8 wk of training. Blood samples were collected for glucose and insulin determinations. The glycogen content was assayed in the liver and muscle. Maximal activities of epididymal adipose tissue enzymes (hexokinase, pyruvate kinase, lactate dehydrogenase, citrate synthase and malic enzyme) as well as adipocyte size were determined. The exercise training in control animals promoted an increase in the aerobic power and in liver glycogen content but caused a reduction in the malic enzyme activity in adipose tissue. However, PINX trained animals, in contrast to trained controls, showed a decrease in the aerobic power and in liver and muscle glycogen content, as well as an increase in the activity of the adipocyte enzymes involved in carbohydrate metabolism. In conclusion, these data show that the pineal gland integrity is necessary for the homeostatic control of energy metabolism among adipose, muscle and hepatic tissues. The pinealectomized animals showed alterations in adaptive responses of the maximal oxygen uptake to training. Therefore, the pineal gland must be considered an influential participant in the complex adaptation to exercise and is involved in the improvement of endurance capacity.