THE COMPARISON OF VASCULAR REACTIVITIES OF ARTERIAL AND VENOUS GRAFTSTO VASODILATORS - MANAGEMENT OF GRAFT SPASM

Graft spasm in the perioperative or postoperative period increases the risk of morbidity and mortality after coronary revascularization and hence necessitates urgent treatment. We have studied the effects of va rious vasodilators against noradrenaline- and endothelin-1-induced spa sms in saphenous vein, internal mammary artery and gastroepiploic arte ry. In internal mammary and gastroepiploic arteries, the nitrovasodila tors, sodium nitroprusside and glyceryl trinitrate, effectively revers ed the spasms induced either with noradrenaline (for sodium nitropruss ide; internal mammary artery: 101.07% +/- 1.63%; gastroepiploic artery : 94.10% +/- 2.07%) or endothelin-1 (for sodium nitroprusside; interna l mammary artery: 97.67% +/- 4.94%; gastroepiploic artery: 90.69% +/- 2.61%). However, in saphenous vein contracted with endothelin-1, the r esponsiveness to nitrovasodilators was significantly blunted (for sodi um nitroprusside: 52.33% +/- 5.19%) than that of rings contracted with noradrenaline (for sodium nitroprusside: 95.04% +/- 1.94%). Both arte rial and venous grafts exhibited moderate beta-receptor function in re sponse to isoproterenol, Isoproterenol was less effective in inhibitin g the contractions of endothelin-1 in saphenous vein and gastroepiploi c artery but not in internal mammary artery. On the other hand, nifedi pine and papaverine were fully effective in reversing all the spasms i n three of the graft materials. From these results, it can be deduced that saphenous vein is refractory against cyclic guanidine monophospha te (cGMP)-dependent and beta-receptor mediated relaxations when endoth elin-1 was used as the spasmogenic agent. Internal mammary artery is t he most responsive graft material to the vasodilators regardless of th e nature of spasmogenic stimulus. Gastroepiploic artery exhibits funct ional similarity with internal mammary artery, with the exception of b eta-receptor responsiveness.