ABSTRACT
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 various vasodilators against noradrenaline- and endothelin-1-induced spasms in saphenous vein, internal mammary artery and gastroepiploic artery. In internal mammary and gastroepiploic arteries, the nitrovasodilators, sodium nitroprusside and glyceryl trinitrate, effectively reversed the spasms induced either with noradrenaline (for sodium nitroprusside; internal mammary artery: 101.07% +/- 1.63%; gastroepiploic artery: 94.10% +/- 2.07%) or endothelin-1 (for sodium nitroprusside; internal mammary artery: 97.67% +/- 4.94%; gastroepiploic artery: 90.69% +/- 2.61%). However, in saphenous vein contracted with endothelin-1, the responsiveness to nitrovasodilators was significantly blunted (for sodium nitroprusside: 52.33% +/- 5.19%) than that of rings contracted with noradrenaline (for sodium nitroprusside: 95.04% +/- 1.94%). Both arterial and venous grafts exhibited moderate beta-receptor function in response to isoproterenol. Isoproterenol was less effective in inhibiting the contractions of endothelin-1 in saphenous vein and gastroepiploic artery but not in internal mammary artery. On the other hand, nifedipine and papaverine were fully effective in reversing all the spasms in three of the graft materials. From these results, it can be deduced that saphenous vein is refractory against cyclic guanidine monophosphate (cGMP)-dependent and beta-receptor mediated relaxations when endothelin-1 was used as the spasmogenic agent. Internal mammary artery is the most responsive graft material to the vasodilators regardless of the nature of spasmogenic stimulus. Gastroepiploic artery exhibits functional similarity with internal mammary artery, with the exception of beta-receptor responsiveness.
