Effects of nicorandil on the rhythmic contractile response of isolated miniature pig coronary artery to 3,4-diaminopyridine: comparison with nitroglycerin.

Effects of 2 antianginal agents, nicorandil and nitroglycerin, on the rhythmic contraction induced by 3,4-diaminopyridine (DAP) were investigated in the isolated coronary artery of the miniature pig. Application of 10(-2) M 3,4-DAP elicited a sustained rhythmic contraction of the artery, lasting more than 3 hr. Nicorandil significantly reduced the peak tension of the contraction phase and the tension of the relaxation phase at concentrations of 10(-6) and 10(-5) M. The cycle length and the reappearance time of the rhythmic contraction were only significantly prolonged at a concentration of 10(-5) M. Finally a concentration of 10(-4) M led to the disappearance of rhythmic contraction. Nitroglycerin (10(-8) - 10(-4) M) significantly reduced the peak tension of the contraction phase and the tension during the relaxation phase in a concentration-dependent manner. At concentrations of 10(-6) to 10(-4) M, it also greatly prolonged the reappearance time of the rhythmic contraction, but the contraction was never eliminated even at the highest concentration (10(-4) M) of nitroglycerin used. The result indicates that nicorandil has an effect on the rhythmic contraction caused by 3,4-DAP through a mechanism somewhat different from nitroglycerin.