Opioid inhibition of neurally mediated mucus secretion in human bronchi

Capsaicin, which induces release of neuropeptides such as substance P from sensory nerves, stimulated mucus secretion in surgically resected human bronchi in vitro. Pretreatment of the tissue with the opioid antagonist naloxone significantly enhanced secretion, possibly by blocking the inhibitory effect of opiate premedication before surgery. Capsaicin-induced mucus secretion was completely blocked by morphine, and this effect was reversed by naloxone. Thus, sensory nerve stimulation increases mucus secretion in human airways, which might contribute to the mucus hypersecretion seen after inhalation of irritants such as cigarette smoke. Secretion can be completely inhibited by opioid drugs, so they may represent a new therapeutic approach to airway hypersecretion in chronic bronchitis and asthma, in which axon reflex mechanisms have been implicated.