Linsidomine or SIN-1, a vasodilator of epicardial arteries, is the active metabolite of Molsidomine which is regularly used for intracoronary injection. Although its vasodilatory action has been demonstrated on the large coronary vessels, it is not known whether this molecule can vasodilate epicardial coronary arteries which have been vasoconstricted with acetylcholine. Twelve patients with left anterior descending artery (LAD) disease were studied. Intracoronary flow velocity was measured with a Doppler catheter (Millar) placed in the proximal segment of the LAD and the diameter of the artery was evaluated by quantitative angiography. After recording the basal haemodynamic parameters, 12 mg of papaverine were injected into the left main coronary artery. After regaining the basal state, three incremental doses of acetylcholine (5 x 10(-7), 1(-6) and 5 x 10(-6) M) were selectively injected into the LAD over a 3 minute period for each injection. Then, during continuous infusion of 5 x 10(-6) of acetylcholine, 1 mg of SIN-1 was injected in a bolus into the left coronary ostium. After the papaverine, the coronary flow velocity increased by 199 +/- 8% associated with a vasoconstrictive tendency in the proximal and distal segments of the LAD (NS). In response to acetylcholine a dose-dependent vasoconstriction vas observed attaining 50 +/- 21% at the last injection in the distal segment of the LAD (p < 0.001). After an initial increase in coronary flow velocity of 46 +/- 11% (p = 0.004) and of 26 +/- 11% (p < 0.05) after the first two doses of acetylcholine, it decreased after the final injection to close to basal values (NS).(ABSTRACT TRUNCATED AT 250 WORDS)