Further evidence for a homogeneous population of beta-1-adrenoceptors in bovine coronary artery.

Isolated rings from the proximal and distal ends of the bovine epicardial anterior descending coronary artery and guinea pig tracheal rings were mounted in tissue baths for the measurement of isometric contraction and relaxation, and spontaneously beating rabbit atria were prepared for measurement of chronotropic response. All tissues were exposed to phenoxybenzamine to block tissue uptake of catecholamines and alpha adrenoceptors. The arterial and tracheal rings were contracted with 25 mM K+ in order to observe agonist-induced relaxation. Beta adrenergic agonist dose-response curves were obtained in all tissues in the presence and absence of the beta-2 selective antagonist, ICI 118,551. The orders of agonist potencies in the proximal and distal coronary arteries and the rabbit atria were the same: namely, isoproterenol (ISO) greater than norepinephrine (NE) much greater than procaterol. In contrast, that in the guinea pig trachea was procaterol greater than ISO greater than NE. Procaterol was a weak, partial agonist in the bovine coronary artery and rabbit atria and a potent, full agonist in the guinea pig trachea. The ICI 118,551 pA2 values in the proximal segment of the bovine coronary artery were the same against both NE and fenoterol, 7.38. In the distal segment, the values were 7.33 and 7.14, respectively. ICI 118,551 -log KB values in the rabbit atria, 6.81 and 6.83 for NE and ISO, respectively, were slightly below those in the coronary artery segments, whereas -log KB values in the guinea pig trachea were substantially higher, 8.19 and 8.81 for fenoterol and procaterol, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)