Effect of urapidil on beta-adrenoceptors of rat atria

The effects of the antihypertensive drug urapidil were studied on chronotropic responses to isoprenaline in rat isolated atria. Urapidil (1-30 microM) antagonized the responses to isoprenaline competitively, and the pA2 value was 6.05. Thus, in addition to its alpha 1-adrenoceptor blocking action for which the pA2 value is about 7, urapidil has beta-adrenoceptor blocking activity.