Modulation of acetylcholine release from parasympathetic nerves innervating guinea-pig and human trachea by endomorphin-1 and-2

Endomorphin-1 and -2 (mu-opioid receptor agonists) produced a concentration-dependent and naloxone-sensitive inhibition of cholinergic contractile responses in guinea-pig trachea (at 10 mu M, 46.1 +/- 8.0% and 33.8 +/- 8.6%, respectively). Endomorphin-1 and -2 also inhibited electrically-evoked acetylcholine release from cholinergic nerves innervating guinea-pig (at 0.1 mu M, 41.8 +/- 10.9%; at 1 mu M 60.1 +/- 6.3%, respectively) and human trachea (at 10 mu M, 76.2 +/- 18.1%, and 77.7 +/- 14.3%, respectively). Naloxone prevented the inhibition by endomorphin-1 and -2 in both guinea-pig and human trachea, suggesting that these peptides can inhibit cholinergic, parasympathetic neurotransmission to the airways via the activation of classical opioid receptors. (C) 1999 Elsevier Science B.V. All rights reserved.