title: The selectivity of beta-adrenoceptor antagonists on cardiovascular and bronchodilator responses to isoprenaline in the anaesthetized dog.
abstract: 1 The actions of five beta-adrenoceptor antagonists, chosen because of reported differences in their selectivities, were compared using the positive chronotropic, vasodepressor and bronchodilator responses to isoprenaline in anesthetized dogs. 2 Propranolol was a potent antagonist of the isoprenaline responses in all three systems. 3 Practolol and acebutolol (M & B 17,803) blocked the positive chronotropic responses to isoprenaline to a greater extent than the vasodepressor or bronchodilator responses. 4 Butoxamine and alpha-methyl dichloroisoprenaline showed the opposite selectivity, blocking the vasodepressor and bronchodilator responses to isoprenaline to a greater extent than positive chronotropic responses. However, both drugs were considerably less potent than the other antagonists studied and their selectivities were less clear-cut than those of practolol or acebutolol. 5 All the antagonists lowered the resting heart rate and to a lesser extent the diastolic blood pressure. The effects of propranolol, practolol and acebutolol on heart rate probably result from cardiac beta-adrenoceptor blockade. With butoxamine and alpha-methyl dichloro isoprenaline, however, the effects on heart rate probably result from a direct cardiodepressant action. 6 The relevance of the results to the problem of the sub-classification of beta-adrenoceptors is discussed.
mesh_terms: D000319:Adrenergic beta-Antagonists / Q000494:pharmacology*; D000403:Airway Resistance / Q000187:drug effects; D000818:Animals; D001794:Blood Pressure / Q000187:drug effects; D001993:Bronchodilator Agents / Q000494:pharmacology*; D004285:Dogs; D004347:Drug Interactions; D005260:Female; D006339:Heart Rate / Q000187:drug effects; D006439:Hemodynamics / Q000187:drug effects*; D007545:Isoproterenol / Q000494:pharmacology*; D008297:Male
chemical_list: D000319:Adrenergic beta-Antagonists; D001993:Bronchodilator Agents; D007545:Isoproterenol