Responses of dog large coronary arteries to constrictor and dilator substances: Implications for the cause and treatment of variant angina pectoris

Abstract

Canine circumflex coronary artery ring segments were mounted in organ baths and contracted by ergonovine (ergometrine), serotonin, phenylephrine, norepinephrine (in the presence of propranolol), potassium (K+) and a thromboxane A2 mimetic, U46619. Ergometrine was classified as a serotonin agonist since concentration-response curves were competitively inhibited by methysergide but not by alpha-adrenoceptor antagonists. Arteries precontracted to 80% of maximum were relaxed by verapamil, nifedipine and glyceryl trinitrate. However, nifedipine was 100-fold more potent against K+ than either serotonin- or phenylephrine-contracted vessels. Verapamil showed some selectivity for K+ and serotonin con..