The guinea pig tracheobronchial spiral strip: responses to selected agonists

The guinea pig tracheal spiral strip is a useful preparation for studying bronchoconstrictor and bronchodilator compounds. Employing a simple and rapid modification of this technique, experiments were performed in vitro to quantitate the effects of selected bronchospastic agents on guinea pig tracheobronchial smooth muscle. Three sections of the main airways were prepared from each animal: an upper tracheal, a lower tracheal, and a bronchial segment. The dose-dependent contractile responses of the three tissue segments were determined for carbachol, acetylcholine, histamine, 5-hydroxytryptamine, and bradykinin. Differences were observed amongst the agonists in magnitudes of contraction, effective concentration ranges, and slopes of dose-response curves. ED25, ED50, and ED75 values were calculated from regression analysis of dose-response data. The relative order for these agents to produce maximum contractions was found to be carbachol congruent to acetylcholine greater than histamine greater than 5-hydroxytryptamine greater than bradykinin. Furthermore, it was found that there was no significant difference between the three tissue segments in their responses to the various agonists.