Greater vasopressin-induced vasoconstriction and inferior effects of nitrovasodilators and milrinone in the radial artery than in the internal thoracic artery

BACKGROUND: Vasopressin may be a potential cause of spasm in both the radial artery and the internal thoracic artery. This study compared the vasopressin-induced contraction and the effects of milrinone, nitroglycerin, and nitroprusside in vasopressin-induced contraction between the human radial artery and the internal thoracic artery to find effective antispastic methods for arterial grafts. METHODS: Concentration-contraction (normalized as force gram produced by each millimeter of the circumference tissue of the artery) curves for vasopressin with or without pretreatment of vasodilators and concentration-relaxation curves for the vasodilators listed were established in the human radial artery (n = 107) and internal thoracic artery (n = 122) segments. RESULTS: Vasopressin induced a greater contraction in the radial artery than in the internal thoracic artery (1.9 +/- 0.2 g/mm vs 0.6 +/- 0.1 g/mm, P < .001) with a higher sensitivity (lower EC(50): -9.28 +/- 0.11 vs -8.91 +/- 0.05 log(10)M, P = .006). Milrinone was less potent than nitroglycerin and nitroprusside with higher EC(50) (P < .05) in both the internal thoracic artery and radial artery. Pretreatment with milrinone and nitroprusside significantly inhibited vasopressin contraction in the internal thoracic artery but had little effect in the radial artery. Pretreatment with nitroglycerin did not significantly inhibit the maximum vasopressin contraction in either the internal thoracic artery or radial artery. CONCLUSION: The radial artery is more prone to develop spasm related to vasopressin than is the internal thoracic artery, and the effect of vasodilators in vasopressin-induced contraction is different in the radial artery from that in the internal thoracic artery. A more significant prophylactic antispastic effect of milrinone and nitroprusside is demonstrated in the internal thoracic artery than in the radial artery. Therefore, more intensive antispastic treatment is necessary in the radial artery than in the internal thoracic artery during coronary artery bypass grafting.