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 res ponses 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 acet ylcholine 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 trache a (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 hum an trachea, suggesting that these peptides can inhibit cholinergic, parasym pathetic neurotransmission to the airways via the activation of classical o pioid receptors. (C) 1999 Elsevier Science B.V. All rights reserved.