Inhibition of antigen-induced tone in isolated trachea.

The relaxing effect of the beta-adrenoceptor stimulating agent terbutaline was studied on the spirally cut trachea from actively ovalbumin-sensitized guinea pigs. Terbutaline counteracted the antigen-induced muscular tone more effectively when added 5 min before the addition of the antigen than when added at the peak effect. The reason for the improved efficacy of pretreatment with terbutaline might be terbutaline's synergistic effect on the release of spasmogens from the preparation and on the direct relaxing effect of the muscle.