Selective blockade of beta-adrenoceptors by 1-(p-allylphenoxy)-3-isopropylamino-2 propanol hydrochloride (h 64-52) in the anaesthetized dog.

1. The beta-adrenoceptor blocking properties of 1-(p-allylphenoxy)-3-isopropylamino-2-propanol hydrochloride (H 64/52) on the cardiovascular and bronchomotor responses to isoprenaline have been determined in the anaesthetized dog.2. H 64/52 selectively blocked the isoprenaline-induced increase in heart rate, contractile force and reduction in airway pressure in the same dose range.3. H 64/52 produced a minimal blockade of vascular beta-adrenoceptors which was apparent only when the isoprenaline-induced fall in diastolic pressure was considered. No significant vascular beta-adrenoceptor blockade with H 64/52 could be shown with the femoral arterial flow or hind-limb perfusion studies.4. These results further support the hypothesis that several different beta-adrenoceptor subtypes exist in the dog. The beta-adrenoceptors subserving cardiac stimulation and bronchodilation appear to be similar and both differ from the beta-adrenoceptor subserving vasodilatation.