Mu-opioid receptors modulate non-cholinergic constrictor nerves in guinea-pig airways

A role of opioids as inhibitors of the non-adrenergic non-cholinergic (NANC) excitatory nerves has been studied in the guinea-pig bronchi using electrical field stimulation. Morphine and DAGO gave dose-dependent inhibition of NANC contraction, which was reversed by naloxone, whereas the cholinergic nerve and substance P responses were unaffected. [Met5]enkephalin and [Leu5]enkephalin weakly inhibited NANC contraction, whereas dynorphin-(1-13) had no effect. These results suggest that opiates inhibit NANC bronchoconstriction via mu-opioid receptors.