Figure 20.

Blood flow responses to temporary reductions in blood flow and perfusion pressure to the rhythmically contracting forearm muscles (20 contractions/min at 20% of maximum) evoked by inflation of a balloon in the brachial artery. Under control conditions, downstream vasodilation as contractions continued caused a complete recovery of blood flow over 2–3 min. This recovery of flow was delayed and blunted by NOS inhibition with l-NMMA and further blunted by the adenosine antagonist aminophylline. While adenosine does not appear obligatory in the vasodilator responses to contractions under many circumstances, its role becomes more critical when blood flow to the contracting muscles is restricted.