Interrelation between the alpha- and beta-receptor activating actions of catecholamines in the tracheal muscle.

The action of adrenaline, noradrenaline and isoproterenol on the alpha-adrenergic receptor in the isolated tracheal muscle of guinea pigs was investigated by using a manometric procedure. An application of adrenaline or noradrenaline after the treatment with beta-adrenergic blocking agents caused a constriction of the tracheal muscle. The constrictive response could be inhibited by the pretreatment with dibenamine or tolazoline, but it could not be inhibited by the pretreatment with atropine. It is assumed that the constricting response is caused by an activation of the alpha-receptor. The relaxing effect of adrenaline and noradrenaline on the tracheal muscle was potentiated by the pretreatment of dibenamine. These facts suggest that the action on the alpha-receptor is suppressed by the pretreatment of dibenamine and the action on the beta-receptor predominate more than that on the alpha-receptor. The ratios of the alpha-receptor activating effect to the beta-receptor activating effect, which were produced by an application of adrenaline or noradrenaline, were about 10-15% both. The beta-receptor stimulating action of adrenaline was intensive about 10 times that of noradrenaline, and the alpha-receptor stimulating action was intensive about 1.8 times that of noradrenaline.