Regionally different influence of contractile agonists on isolated rat airway segments

Rats are increasingly used to study airway inflammation and bronchial responsiveness. Relative little is known on the contribution of small airways in this animal model. We therefore compared the responsiveness to various inflammatory agents of isolated trachea, main bronchi (using classic organ bath) and isolated bronchioles (using small myograph) from Wistar and Fisher 344 rats. The largest contraction was elicited on all preparations by carbachol. Histamine elicited a (small) contraction only on bronchioles. The contractions elicited by serotonin, bradykinin, and the thromboxane A2-mimetic U-46619 were always relatively larger in bronchioles than in trachea and main bronchi. The sensitivities to carbachol and serotonin were smaller in bronchioles. The tachykinins substance P and neurokinin A elicited no substantial contraction on bronchioles or main bronchi. Trachea of Fisher 344 but not of Wistar rats showed a small contraction. No other differences were found between preparations from Wistar and Fisher 344 rats. It is concluded that rat trachea, main bronchi and small bronchioles show regional and strain-dependent variations in their responsiveness to contractile agents.