Adenosine release into venous plasma during free flow exercise.

We measured adenosine release into venous plasma as an index of interstitial adenosine concentration during free flow exercise hyperemia. Isolated, blood-perfused dog calf muscles were stimulated at 6 Hz for 10 min at free flow. Plasma samples were collected before, during, and after the exercise period for analysis of plasma adenosine concentration [( ADO]) by HPLC. Adenosine release (Rado) was calculated as plasma flow times venous-arterial [ADO] difference. Rado (nmole/min/100 g) went from -0.1 +/- 0.1 at rest to 6.6 +/- 4.6 during 6-Hz exercise. Isoproterenol infusion, which caused an increase in blood flow equivalent to 6-Hz exercise, did not result in increased Rado. Infusion of the 5'-nucleotidase inhibitor, alpha, beta, methylene adenosine 5'-diphosphate (AOPCP) did not prevent the increase in Rado during exercise. These results support the hypothesis that interstitial adenosine concentration increases during sustained free flow twitch exercise and that this results in increased release of adenosine into venous plasma.