Agonist-induced desensitization of beta-adrenoceptor function in humans. Subtype-selective reduction in beta 1- or beta 2-adrenoceptor-mediated physiological effects by xamoterol or procaterol.

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Abstract
We investigated the effects of beta 2- (procaterol 2 x 50 micrograms/day for 9 days) and beta 1- (xamoterol 2 x 200 mg/day for 14 days) adrenoceptor agonists on lymphocyte beta 2-adrenoceptor density and beta 1- and beta 2-adrenoceptor in vivo function (assessed as isoprenaline-infusion-evoked hemodynamic effects and exercise-induced tachycardia) in healthy volunteers. Procaterol decreased lymphocyte beta 2-adrenoceptor density and all beta 2-adrenoceptor-mediated in vivo effects but did not affect beta 1-adrenoceptor-mediated in vivo effects. In contrast, xamoterol neither affected lymphocyte beta 2-adrenoceptors nor beta 2-adrenoceptor-mediated in vivo effects but decreased beta 1-adrenoceptor-mediated in vivo effects. It is concluded that in humans, generally long-term application of beta 1- or beta 2-adrenoceptor agonists causes desensitization of beta-adrenoceptor function but in a beta-adrenoceptor subtype-selective fashion.