Beta-adrenoceptor subtypes in human, rat, guinea pig, and rabbit atria

Selective beta-adrenoceptor agonists and antagonists were used to characterize the beta-adrenoceptor subtypes in human right atrium. The activity order of selective agonists for rat, guinea pig, and rabbit atrial inotropic and chronotropic responses was consistent with the hypothesis that only beta 1-adrenoceptors mediate these responses. In human right atrium, however, the beta 2-selective agonists fenoterol and salbutamol were relatively much more active. The beta 1-selective antagonist practolol preferentially antagonized the human atrial response to noradrenaline (beta 1-selective) as opposed to fenoterol (beta 2-selective), whereas the beta 2-selective antagonist ICI 118,551 preferentially antagonized the response to fenoterol. The data indicate that the response of human right atrium to beta-adrenoceptor agonists is mediated by a mixed beta 1-plus beta 2-adrenoceptor population. The implications of these results with respect to the therapeutic uses of beta-adrenoceptor agonists are discussed.