The effect of tachykinins on the conducting airways of the rat.

We studied the bronchial effects of intravenously administered tachykinins in inbred rats. Substance P and related tachykinins caused a dose-dependent bronchoconstriction. The bronchial reactivity to substance P differed significantly between different inbred rat strains. Substance K, eledoisin and kassinin were more potent than substance P in causing bronchoconstriction. This suggests a predominance in the bronchi of SP-E receptors. The bronchial effects of substance P and eledoisin were largely inhibited by atropine and slightly enhanced by hexamethonium. In addition to a direct effect on airway smooth muscle, tachykinins interfere with the cholinergic airway innervation of the rat at the ganglionic and postganglionic level.