Distribution and characterization of the adrenoceptors in dog coronary arteries.

Effects of catecholamines were studied in vitro on different portions of the left coronary artery of the dog. Adrenaline, noradrenaline and isoprenaline produced dose-related contractions in the common portion of the coronary artery which were blocked by phenoxybenzamine. The proximal portions were relaxed by noradrenaline and isoprenaline, but contracted or relaxed by adrenaline following an initial transient contraction. The contraction was blocked by phenoxybenzamine and the relaxation was blocked by propranolol. Adrenaline, noradrenaline and isoprenaline caused only relaxations which were blocked by propranolol in the distal portion and in the small branches. In coronary, femoral and tracheal strips contracted previously by KCl with or without a phenoxybenzamine pretreatment, isoprenaline produced dose-dependent relaxations. The dose-response curves for isoprenaline were shifted to the right on treatment with practolol. The blocking effects of practolol were nearly ten times potent in the coronary artery in comparison with the femoral artery and the trachea. The results indicate that the common portion mainly possesses alpha-adrenoceptors, the proximal portion contains both alpha- and beta-adrenoceptors, and that beta-adrenoceptors dominate in the distal portion and small artery branches. It is also shown that the beta-adrenoceptors in the coronary vessels differ from the femoral and tracheal beta-adrenoceptors in pharmacological feature.