[Vasoconstrictor responses of isolated pig coronary arteries]

In helical strips of pig coronary arteries, histamine, serotonin, acetylcholine and a stable analogue of thromboxane A2 (9, 11-epithio-11, 12-methano TXA2: s-TXA2) produced a dose-dependent contraction. The histamine-induced contraction was suppressed by treatment with chlorpheniramine, suggesting an involvement of H1 receptors. Contractile responses to serotonin were attenuated by not only ketanserin, an S2 antagonist, but also by cinanserin and methysergide. Relaxation induced by serotonin in preparations treated with high concentrations of ketanserin were inhibited by cinanserin and methysergide. Norepinephrine contracted coronary arteries treated with propranolol. Contractile responses to norepinephrine were reversed to relaxations by prazosin, which were abolished by treatment with yohimbine. Contractile responses to histamine were potentiated by treatment with low concentrations of serotonin or s-TXA2. Contractile responses to serotonin were also potentiated by low concentrations of histamine or s-TXA2. Removal of the endothelium from pig coronary arterial strips potentiated contractions induced by serotonin, histamine and norepinephrine. These results suggest that, in addition to damaged endothelium, integrating action of endogenous vasoconstrictors, including histamine, serotonin, TXA2 and norepinephrine, may play an important role in producing coronary vasospasm.