Abstract

Isolated vessel rings from the proximal and distal ends of the bovine anterior descending coronary artery were mounted in tissue baths for the measurement of isometric contraction. These rings were pre-exposed to phenoxybenzamine to block tissue catecholamine uptake and alpha adrenoceptors. They were then contracted with high potassium, and beta adrenergic agonist dose-relaxation response curves were obtained in the presence and absence of beta antagonists. The orders of agonist potency in the arterial rings were the same as that in spontaneously beating guinea pig atria: isoproterenol (ISO) greater than norepinephrine (NE) greater than fenoterol (FE) greater than salbutamol (SA) and differed from that in the guinea pig trachea: ISO greater than FE greater than SA greater than NE. Schild analysis yielded propranolol pA2 values in the coronary artery rings which did not differ between the four agonists studied or between the proximal and distal ends of the coronary artery. Similar results were obtained with practolol and butoxamine with the exception that in the case of butoxamine, a higher pA2 value was obtained against ISO in the distal ring preparations. The practolol and butoxamine pA2 values in the artery rings matched the respective--log KB values obtained in the guinea pig atria using NE as the agonist but were the reverse of those obtained in the guinea pig trachea using either FE or SA as the agonist. It is concluded that the proximal and distal ends of the bovine anterior descending coronary artery possess a homogeneous population of beta-1 adrenergic receptors.