Terbutaline-induced desensitization of beta 2-adrenoceptor in vivo function in humans: attenuation by ketotifen.

Use of beta-adrenoceptor agonists in long-term treatment of patients with chronic asthma bronchiale or heart failure is of limited value because beta-adrenoceptor desensitization develops. The antiallergic drug ketotifen prevents beta-adrenoceptor agonist-induced desensitization of rat and human pulmonary and lymphocyte beta 2-adrenoceptors. In 10 healthy volunteers in a double-blind, placebo-controlled study, we investigated whether ketotifen also prevents beta-adrenoceptor agonist-induced desensitization of beta 1- and/or beta 2-adrenoceptor-mediated physiologic in vivo effects. beta 1-Adrenoceptor-mediated effects were isoprenaline (ISO) infusion-induced increase in systolic blood pressure (SBP) and bicycle exercise-induced increase in heart rate (HR); beta 2-adrenoceptor-mediated effects were ISO infusion-induced increase in plasma norepinephrine (NE) and decrease in diastolic blood pressure (DBP); ISO infusion-induced increase in HR was assessed as mixed beta 1- and beta 2-adrenoceptor-mediated effect. These parameters were assessed before and after a 14-day treatment with the beta 2-adrenoceptor agonist terbutaline (5 mg three times daily) with or without simultaneous administration of ketotifen (1 mg twice daily). Terbutaline desensitized all in vivo effects involving beta 2-adrenoceptors (ISO-induced decrease in DBP and increase in plasma NE and, to a minor extent, the mixed beta 1- and beta 2-adrenoceptor-mediated increase in HR), but did not affect beta 1-adrenoceptor-mediated in vivo effects; concomitant treatment of the volunteers with ketotifen markedly blunted terbutaline-induced desensitization of beta 2-adrenoceptor in vivo function. We conclude that ketotifen prevents, or at least attenuates, beta-adrenoceptor agonist-induced desensitization of beta 2-adrenoceptor in vivo function.(ABSTRACT TRUNCATED AT 250 WORDS)