Effect of alpha-adrenoceptor stimulation of isolated canine, ferret and guinea pig airways.

Functional responses and subtypes of alpha-adrenoceptors in canine trachealis smooth muscle were investigated using the agonists; epinephrine, norepinephrine, SK&F 89748 (alpha 1-selective) and BHT-933 (alpha 2-selective) in the presence of a beta-adrenoceptor antagonist. Tissue contractility to these agonists was in the range of 16 to 46% of the maximum response to serotonin. SK&F 89748 was most effective in canine airways; however, the contractions could be abolished by methysergide. Neither precontraction of the airways by KCl nor degree of beta-adrenoceptor blockade increased the reactivity of SK&F 89748 in this tissue. Reactivity of ferret and guinea pig airways to norepinephrine in the presence of beta-adrenoceptor blockade was insignificant. Responses of guinea pig airways to tyramine was about 1,000-fold less than those observed for vascular smooth muscle. Taken together these data suggest that alpha-adrenoceptors do not have any significance in the pathogenesis of airway hyperreactivity in dog, ferret and guinea pig airways. Moreover, adrenoceptors in guinea pig airways appear to be hormonal beta-adrenoceptors.