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

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Abstract
The reactivity was investigated of cat isolated tracheal chains, bronchial spirals and lung parenchymal strips to carbachol, 5‐hydroxytryptamine (5‐HT) and histamine. 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. Histamine failed to elicit a contractile response from the tracheal or bronchial muscle. However, it induced dose‐related contractions of the lung strips, that were selectively blocked by mepyramine. 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.