Vasorelaxant properties of isolated human internal mammary arteries and saphenous veins: comparative effects of milrinone and sodium nitroprusside.

Summary Internal mammary arteries (IMA) and saphenous veins (SV) are vessels currently used in human coronary artery bypass surgery. In addition to late complications, the vessels may develop spasm perioperatively. We studied isolated IMA and SV from patients undergoing coronary artery bypass graft to reproduce in vitro the phenomenon of vasospasm. Vascular rings were constricted with phenylephrine in a classic organ bath. The effects of two vasodilator agents, milrinone and sodium nitroprusside (SNP), on phenylephrine precontracted vessels and as a pretreatment to reverse or prevent the contraction, respectively, were studied. When added to a precontracted vessel, milrinone had the same vasorelaxant effect as SNP in artery rings (EC50: 7.4 × 10-7 ± 0.8 × 10-7 vs. 5.9 × 10-7 ± 0.8 × 10-7M, milrinone vs. SNP). In veins, milrinone was less effective in relaxing the rings than SNP (EC50: 15 × 10-7 ± 3 × 10-7 vs. 1.5 × 10-7 ± 0.1 × 10-7M, milrinone vs. SNP, p