Mechanism of coronary spasm was examined regarding endothelium-related relaxation and contraction produced by smooth muscle cells of spastic vessels isolated from Göttingen miniature pigs. In these pigs, coronary artery spasm was documented angiographically in vivo three months after endothelial denudation, and spastic and control segments of the coronary artery were suspended in organ chambers at their optimal length for generating tension. Applications of KCl (118 mM), acetylcholine(10(-9) to 10(-4) M), and PGF2 alpha (10(-8) to 3 X 10(-5) M) produced similar tension, at the respective doses, in both the spastic and control coronary arteries. During increasing concentrations of histamine (10(-8) to 3 X 10(-4) M; n = 14) and serotonin (10(-9) to 10(-5) M; n = 13), the maximum tension of the spastic vessel was 136 +/- 6 and 97 +/- 4%, respectively, of the tension produced by 118 mM KCl. That is significantly larger than seen in the control vessels: 98 +/- 4 and 74 +/- 4%, respectively. The ED50 to histamine and serotonin was also significantly less in the spastic vessels. After mechanical removal of the endothelium, the tension generated during the cumulative administration of histamine (n = 8) but not serotonin (n = 8) was larger in the spastic than the control vessels, thereby suggesting the presence of augmented responses of the smooth muscle to histamine in the spastic vessels. The increase in maximum tension after mechanical denudation was greater in the control than the spastic vessels in cases of histamine and serotonin.(ABSTRACT TRUNCATED AT 250 WORDS)