Effect of Muscular Exercise by Bicycle Ergometer on Erythrocyte Purine Nucleotides

Summary

The effect of muscular exercise by bicycle ergometer on erythrocyte purine nucleotides was investigated in 6 athletes. Muscular exercise increased the concentration of inosine monophosphate from 5.9±1.1 to 7.3±1.3 nmol/ml in venous erythrocytes and from 5.7±1.0 to 6.8± 1.4 nmol/ml in arterial erythrocytes, respectively, while it decreased the concentrations of adenosine diphosphate and adenosine monophosphate from 189.3±42.7 to 141.2±26.9 and from 26.0±7.8 to 15.7±4.3 nmol/ml in venous erythrocytes and also decreased their concentrations from 195.1±51.0 to 141±29.2 and from 26.5±9.6 to 14.8±3.0 nmol/ml in arterial erythrocytes, respectively. The muscular exercise also increased the concentration of inorganic phosphate in venous plasma from 1.12±0.12 to 1.46±0.22 mmol/l, that of NH₃ in blood from 41.90±6.91 to 150.22±50.80 μmol/l, that of lactic acid in blood from 7.90±1.71 to 61.03±18.43 mg/dl and that of hypoxanthine in venous plasma from 1.32±0.36 to 18.14±4.87 μmol/l, respectively. Therefore, in vitro study was performed to investigate whether inorganic phosphate, NH₄Cl, lactic acid or hypoxanthine affects nucleotides in erythrocytes. After 2 hour-incubation, 2 mM inorganic phosphate increased the erythrocyte concentration of inosine monophosphate 1.6 fold but decreased the erythrocyte concentrations of adenosine monophosphate and adenosine diphosphate 0.72 and 0.89 fold, respectively, in the suspension (pH 7.35), as compared with 1 mM inorganic phosphate. However NH₄Cl, lactic acid or hypoxanthine did not affect erythrocyte purine nucleotides. These results indicate that inorganic phosphate released from working muscle may partly be responsible for the alteration of the concentration of purine nucleotides in erythrocytes. In addition, as the concentration of erythrocyte inosine monophosphate was not different between vein and artery after exercise, it is suggested that hypoxanthine was hardly transported via inosine monophosphate in erythrocytes from the peripheral veins in ischemic tissue to the central veins.

Key words

Exercise - Purine Nucleotide - Erythrocyte - Inorganic Phosphate - Hypoxanthine