Different effects of activated platelets in the right gastroepiploic and internal mammary arteries. Implications for coronary artery grafting.

The right gastroepiploic artery is increasingly utilized as an alternative coronary bypass conduit, although postoperative spasm can represent a problem. Platelet-vessel wall interactions are important determinants of graft function and patency. We studied the effects of activated platelets in porcine and human gastroepiploic and mammary arteries. Arterial rings were suspended in organ chambers for isometric tension recording. In the porcine and human gastroepiploic arteries with or without endothelium contracted with norepinephrine, activated platelets evoked only further and strong contraction. In contrast, in the porcine and human mammary arteries, endothelium-dependent relaxations to platelets mediated by nitric oxide were noted, particularly in rings preincubated with the thromboxane A2 receptor antagonist SQ-30741 and the 5-hydroxytryptamine (5HT2)-serotonergic receptor antagonist ketanserin. Although endothelium-dependent and endothelium-independent relaxation to bradykinin and the nitrovasodilator 3-morpholino sydnonimine were more pronounced in the gastroepiploic than in the mammary artery, norepinephrine, serotonin, and potassium chloride evoked much stronger contractions in the former than in the latter. Thus activated platelets induce pronounced contraction of the gastroepiploic artery that may contribute to postoperative spasm. The administration of antiplatelet drugs and vasodilators that prevent the effects of thromboxane A2 and serotonin may be beneficial for gastroepiploic graft function.