Human small airway smooth muscle responses in vitro; actions and interactions of methacholine, histamine and leukotriene C4.

The in vitro contractile responses to methacholine, histamine and leukotriene C4 (LTC4) were measured in human bronchiolar strips obtained after surgery. LTC4 was approximately 100 times more potent than both methacholine and histamine (mean pD2 values were 8.01, 6.18 and 5.87 respectively). All three agonists produced the same maximum contractile response (Tmax) and no difference was found in the time course of methacholine-, histamine- and LTC4-induced responses. When methacholine, histamine and LTC4 were applied in succession on one airway preparation, no interactions between these agonists were demonstrated for pD2. However, interactions were found concerning Tmax. The sensitivity (pD2) could be measured accurately and reproducibly and showed a relatively small within-patients variation (coefficients of variation 4-5%). In contrast, Tmax showed a considerable within-patients variation (coefficients of variation 47-91%), which limits its usefulness when small numbers of airway preparations are studied.