REACTIVITY OF ISOLATED TRACHEA, BRONCHUS AND LUNG STRIP OF CATS TO CARBACHOL, 5‐HYDROXYTRYPTAMINE AND HISTAMINE: EVIDENCE FOR THE EXISTENCE OF METHYSERGIDE‐SENSITIVE RECEPTORS

1 The reactivity was investigated of cat isolated tracheal chains, bronchial spirals and lung parenchymal strips to carbachol, 5-hydroxytryptamine (5-HT) and histamine. 2 Carbachol and 5-HT produced concentration-dependent contractions of all three tissues, responses to the former drug being selectively blocked by atropine and to the latter by methysergide. 3 Histamine failed to elicit a contractile response from the tracheal or bronchial muscle. However, it induced dose-related concentrations of the lung strips, that were selectively blocked by mepyramine. 4 It is concluded that lung parenchymal strips of cats possess mepyramine-sensitive histamine H1-receptors. Receptors for 5-HT, susceptible to methysergide, occur in the tracheobronchial smooth muscles as well as in lung strips of cats.