We studied the effects of milrinone, an inhibitor of type 3 phosphodiesterase on vascular segments of coronary artery bypass grafts (approved by Ethics Committee of our Institution). Segments of internal thoracic artery and saphenous vein were taken from 12 patients undergoing coronary artery bypass surgery and segments of left coronary and radial arteries were obtained from five multiorgan donors. Vascular rings (3 mm in length) were suspended in organ bath chambers and isometric tension was recorded at 37°C. Milrinone (10^-9-10^-5 M) caused concentration-dependent relaxation in precontracted vascular rings that was of greater magnitude in saphenous vein (median effective concentration, EC₅₀ = 1.8 X 10^-8 M) and radial artery (EC₅₀ = 5.7 X 10^-8 M) than in coronary (EC₅₀ = 2.1 X 10^-7 M) and internal thoracic (EC₅₀ = 3.0 X 10^-7 M) arteries. Compared with other vasodilators, the order of potencies in terms of EC₅₀ was sodium nitroprusside ²le³ milrinone ²le³ papaverine. The results indicate that milrinone causes dilatation of human vascular segments used in the coronary bypass surgery and in human coronary artery. The data suggest the possible use of milrinone in the treatment of hypoperfusion caused by graft spasm.

This work was supported by the Ministerio de Sanidad and Generalitat Valenciana.