We have assessed functional and structural evidence for sympathetic innervation of human tracheal and bronchial smooth muscles. In the bronchus, functional evidence for such innervation was shown by the following results: (a) a leftward shift in the noradrenaline inhibitory dose-response curve by the neuronal uptake blocker imipramine; (b) the inhibition of uptake of 3H-l-noradrenaline by the neuronal uptake blockers imipramine, cocaine and phenoxybenzamine; and the induced release of noradrenaline and its metabolites by tyramine and electrical field stimulation using nerve-specific parameters; and (c) selective inhibition of field-stimulated contractions by isoprenaline. Structural evidence was shown by the presence of small dense-cored vesicles containing nerve varicosities, occasionally in close proximity to morphologically characteristic cholinergic nerve-endings. This suggests the possibility of presynaptic modulation of acetylcholine release by noradrenaline.
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Acknowledgements.P art of this work was carried out while C.D. was a McLaughlin Fellow at the Royal Postgraduate School with support from the M. R. C. to Dr. C. T. Dollery. Supported by the Medical Research Council of Canada. The authors are recipients of Senior Research Fellowships from the Heart and Stroke Foundation of Ontario.
- Adrenergic nerves
- Airway smooth muscle
- Sympathetic innervation
- beta adrenoceptor