The inhibitory innervation of the guinea-pig trachea: a study of its adrenergic and non-adrenergic components

(1) Inhibitory responses to field stimulation have been determined in strip preparations from the thoracic, middle and cervical regions of the trachea and in the tracheal tube preparation. (2) The adrenergic neurone blocking drug guanethidine was found to cause a partial reduction of the amplitudes of the responses in all preparations. (3) The guanethidine-resistant inhibitory responses were resistant to pentolinium but were abolished by tetrodotoxin. The data favours the existence of non-adrenergic inhibitory intramural nerves in the guinea-pig trachea. (4) Inhibitory responses have been determined in the presence and absence of guanethidine at frequencies ranging from 2 to 60 Hz. This has enabled the combined responses to stimulation of both adrenergic and non-adrenergic nerves to be compared with the response to stimulation of non-adrenergic nerves alone at each frequency and in each preparation. (5) The contribution of each innervation to the combined inhibitory response was frequency dependent. The adrenergic innervation was more effective at lower frequencies and the non-adrenergic innervation more effective at higher frequencies. (6) The relative contribution of the two innervations to the combined inhibitory response was similar in the three regions of the trachea examined. (7) The occurrence of a hyoscine-resistant contraction in tracheal preparations is discussed. Its origin is considered.