Nutritional design for repletion of liver and muscle glycogen during endurance exercise without inhibiting lipolysis.

Abstract

The effects of fructose (F), a glycogen precursor, and arginine (A), a stimulator of insulin secretion, on glycogen stores in liver and skeletal muscle and lipolysis were studied in endurance exercising rats, in comparison with that of glucose (G) and A. The addition of citrate (C), which previously has been shown to stimulate liver and muscle glycogen repletion after exhaustive exercise, was also tested. Rats were meal-fed twice daily and underwent treadmill running 6 days a week for 3 weeks (experiment 1) or treadmill running for 3 days and the usual voluntary wheel running of 3 days a week for 5 weeks (experiment 2). On the final days of experiments, rats were given one of the following water solutions; a 3.3 g F + 0.5 g A per kg bw, a 3.3 g G + 0.5 g A per kg bw and water (experiment 1) and a 3.3 g F + 0.5 g A + 0.5 g C per kg bw (experiment 2), at the 1.5 h point during a 3 h treadmill running course at 26 and 32.5 m/min up a 7 degree incline, respectively. There was a significant reduction in liver and soleus muscle glycogen during the period of exercise. The administration of either F + A or G + A during exercise was useful in preventing the further depletion of liver and muscle glycogen stores. The administration of G + A significantly suppressed an increased adipose tissue lipolysis caused by exercise, when compared with that of either F + A or water (experiment 1). The addition of C to F + A appeared to spare more soleus and liver glycogen stores during exercise, when compared with G + A (experiment 2).