Comparison of the effects of several selective B2-receptor agonists on bronchomotor function in vitro

Three selective B2-adrenergic stimulants were studied for their effect on the resting tone and on reversing acetylcholine (ACh)-induced bronchoconstriction in the intrapulmonary airways of rats in vitro. Neither 1-(3,5-dihydroxyphenyl)-2-[(1-[4-hydroxybenzyl]-ethyl)-amino]-ethanol-hydrobromide (Fenoterol) nor 2-tert-butylamino-1-(3,5-dihydroxyphenyl)-ethanol-sulphate (Terbutaline) had an effect on the resting tone. 4-Amino-3,5-dichlor-alpha-[(tert-butylamino)-methyl1-benzylalcohol-hydrochloride (NAB 365) caused a significant increase in the bronchial luminal diameter from control in the resting state at concentraions above 10(-5) g/ml. Only NAB 365 was effective in reversing ACh-induced bronchoconstriction in concentrations above 10(-6) g/ml. Terbutaline and Fenoterol reversed the ACh-induced bronchoconstriction only after the alpha-receptors had been blocked by phentolamine (10(-5)-10(-4)g/ml).