Abstract
This investigation compared the selectivity of the beta adrenergic receptor agonists, salbutamol and terbutaline, with the relative nonselectivity of isoproterenol on cardiac, vascular and bronchiolar responses in anesthetized dogs. Dose-response data were obtained and the geometric mean ED values and relative potency ratios were calculated. From these data, the relative order of agonist potency appears to be: isoproterenol > salbutamol > terbutaline. Whereas isoproterenol was a potent activator of all beta receptors, salbutamol and terbutaline were relatively more potent activators of pulmonary and vascular beta receptors than of cardiac beta receptors. For reducing histamine-induced bronchospasm salbutamol was ½ as potent and terbutaline was ⅙ as potent as isoprotenenol. For vascular responses salbutamol was 1/20 and terbutaline was 1/30 to 1/20 as active as isoproterenol. For cardiac rate and force, both salbutamol and terbutaline produced dose-response curves that were less steep than those for isoproterenol and that did not approach the same maximum level produced by isoproterenol. A comparison of the interactions of the three agents on the receptors studied suggests the existence of three different beta adrenergic receptor subtypes in the dog: one in cardiac, another in vascular and a third in bronchiolar muscle.
Footnotes
- Received May 24, 1973.
- Accepted January 4, 1974.
- © 1974 by The Williams & Wilkins Co.
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