Effects of Different Vasodilators on Human Internal Mammary Artery in Vitro

Abstract

In coronary artery bypass grafting (CABG) surgery, arterial grafts have been used with increased frequency. They are expected to be superior to vein grafts because of their long-term patency. The arterial grafts that have been used include internal mammary artery (IMA), gastroepiploic artery, inferior epigastric artery and radial artery (He et al., 1997). However, the use of arterial grafts has brought up the question of hypoperfusion that may occur due to the small diameter of the arterial grafts, the spastic characteristic, or both (He et al., dy1995; He and Yang, 1995). Perioperative infarction, due to restriction of flow caused by spasm of the arterial grafts which was resistant to pretreatment with papaverine has been reported (Meldrum-Hanna and Ross, 1986) and the incidence of cardiac related deaths in patients with IMA grafts is significantly greater than in patients with saphenous vein grafts (Molenaar et al., 1988). Recent studies have also demonstrated that blood flow through arterial grafts may be inadequate for maximal exercise (Kawasuji et al., 1993) and hence causes a hypoperfusion syndrome (Loop and Thomas, 1993). The cause for arterial graft vasoconstriction is still unknown. Studies on the pharmacology of human IMA, as the most frequent used arterial graft, may provide an understanding of the mechanism of spasm and suggest a rational approach for its reversal. Vasodilator drugs may affect vascular tissues either directly by acting on smooth muscle cells or indirectly via endothelial cells. The present study was designed to investigate the direct vasorelaxant effects of nifedipine (NFD), a calcium channel blocker, isosorbide dinitrate (ISDN), a nitrovasodilator, isoproterenol (ISPT), a non-selective-, and BRL 37344, a β₃-selective-adrenoceptor agonist.