Role of adenosine in exercise vasodilation in dog gracilis muscle

Theophylline, quinidine, and dipyridamole were used to evaluate the role of adenosine in exercise vasodilation in dog gracilis muscles perfused at low, constant flow. Theophylline, 10(-3) M in blood, blocked adenosine vasodilation completely, but did not alter the magnitude or rate of vasodilation aroused by brief tetani, or by 1 min of twitch contraction. Quinidine's effects were too nonspecific to interpret in terms of the adenosine hypothesis. Dipyridamole increased and prolonged vasodilation due to injected adenosine, but did not increase the magnitude of exercise vasodilation known to be submaximal. In about half the muscles tested, dipyridamole slowed recovery of resistance after contraction stopped. Bioassay data strongly suggest it did so by enhancing the contribution of a purine metabolite. Results are interpreted to mean that adenosine does not influence the rate or magnitude of exercise vasodilation, but may prolong recovery from heavy work at constant flow. The generality of results and interpretations is discussed.