FLOW RELAXATION IS NOT ATP-MEDIATED IN THE RABBIT EAR ARTERY

ATP has been proposed to play a role in flow-induced dilation of blood vessels. Changes in flow would alter the concentration of ATP at lume nal endothelial P-2Y receptors, occupation of which results in dilatio n. We tested the hypothesis that the lumenal release of ATP close its receptors on the endothelium and the subsequent influence of flow rate on its concentration at such receptors acts as a flow sensing system. The effect of the selective P-2Y-purinoceptor antagonist reactive blu e 2 on relaxation of the isolated rabbit ear resistance artery to flow , ATP and ACh was studied. We found that reactive blue 2 (100 mu mol/L ) significantly inhibited ATP-induced relaxation, but had no effect on equivalent relaxation induced by intraluminal flow (10-40 mu I/min). It reduced ACh-induced relaxation to a less extent. These findings str ongly suggest that flow-induced relaxation of the rabbit ear resistanc e artery can occur without the mediation of locally released ATP.