['The endothelial ADP receptor P2Y(1) is responsible for a large part of the reactive hyperemia following cardiac ischemia. Tissue plasminogen activator (t-PA) increases during reactive hyperemia. We postulated that the release of t-PA during reactive hyperemia could be mitigated through blocking the coronary endothelial P2Y(1) receptor.', 't-PA was measured in peripheral arterial blood and locally in the venous blood from the coronary sinus in a porcine model. The stable ADP analogue 2-MeSADP (10(-5) M), alone or as co-infusion with a selective P2Y(1) receptor blocker, MRS2179 (10(-3) M) was locally delivered in the left anterior descending artery through the tip of a coronary angioplasty balloon. In separate pigs the coronary artery was occluded with the balloon for 10 min. During the first and tenth minute of coronary ischemia, 2.5 ml of MRS2179 (10(-3) M) was delivered distal to the occlusion in 8 pigs, 10 pigs were used as controls.', '2-MeSADP increased levels of t-PA in the coronary sinus, which could be significantly inhibited by co-infusion with MRS2179. During cardiac ischemia and reperfusion, t-PA increased significantly, an effect that could be significantly inhibited by MRS2179.'] Does the ADP receptor P2Y ( 1 ) mediate t-PA release in pigs during cardiac ischemia?