Sympathetic innervation of human tracheal and bronchial smooth muscle.

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.