Effects of phosphate injection on metabolic and hormonal responses to exercise in fructose-injected rats

The purpose of the present study was to evaluate the effects of an intraperitoneal injection of sodium phosphate on the metabolic and hormonal responses to exercise. Fructose-injected rats were either injected with sodium phosphate (Na2HPO4) or NaCl, either in a fed or in a food-restricted state (24 h), and evaluated at rest or after a 30-min exercise period (26 m/min; 0% grade). Liver ATP, phosphate (Pi), and glycogen concentrations were, on the whole, significantly (p < 0.05) higher in Na2HPO4 than in NaCl groups. Exercise resulted in a significant (p < 0.01) decrease in liver ATP and glycogen levels in fed and food-restricted rats whether injected with NaCl or Na2HPO4. Exercise, after NaCl and Na2HPO4 injection, resulted in a significant (p < 0.01) increase in liver phosphate and Pi/ATP ratio, and in a decrease in glucose and an increase in glucagon levels in food-restricted rats only. The normal exercise-induced increase in plasma FFA, glycerol, and norepinephrine levels (p < 0.05), observed in both fed and food-restricted NaCl-injected rats, was abolished by the injection of phosphate. The data are in line with the new concept that in addition to blood glucose levels, the increase in liver Pi/ATP ratio could also contribute to the increase in glucagon response during exercise.