Sympathetic innervation of human tracheal and bronchial smooth muscle
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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 leftward shift in the noradrenaline inhibitory dose-response curve by the neuronal uptake blocker imipramine; 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 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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