Naloxone blocks endomorphin-1 but not endomorphin-2 induced inhibition of tachykinergic contractions of guinea-pig isolated bronchus.
The recently identified endogenous agonists on the mu-opioid-receptor (mu OR), endomorphin-1 (EM-1) and endomorphin-2 (EM-2), induce a concentration dependent inhibition of electrical field stimulation (EFS)-induced tachykinin-mediated contractions of the guinea-pig bronchus (ED50s < 10 nM for both compounds). Surprisingly, only endomorphin-1 effects could be blocked by naloxone (10 microM), whereas endomorphin-2 effects were not affected by specific antagonists for the mu-, kappa-, and delta-opioid-receptor.
Institute for Anatomy & Cell Biology, Justus-Liebig-University, Giessen, Germany. axel.fischer@anatomie.med.uni-giessen.de
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D000701:Analgesics, Opioid / Q000037:antagonists & inhibitors / Q000494:pharmacology; D000818:Animals; D001980:Bronchi / Q000187:drug effects / Q000502:physiology*; D002211:Capsaicin / Q000494:pharmacology; D004558:Electric Stimulation; D006168:Guinea Pigs; D066298:In Vitro Techniques; D008297:Male; D009119:Muscle Contraction / Q000187:drug effects*; D009270:Naloxone / Q000494:pharmacology*; D009271:Naltrexone / Q000031:analogs & derivatives / Q000494:pharmacology; D009292:Narcotic Antagonists / Q000494:pharmacology; D015288:Neurokinin A / Q000494:pharmacology; D009842:Oligopeptides / Q000037:antagonists & inhibitors* / Q000494:pharmacology; D017450:Receptors, Opioid, mu / Q000819:agonists / Q000502:physiology; D015320:Tachykinins / Q000494:pharmacology*
D000701:Analgesics, Opioid; D009292:Narcotic Antagonists; D009842:Oligopeptides; D017450:Receptors, Opioid, mu; D015320:Tachykinins; C105293:endomorphin 1; D009270:Naloxone; C051844:norbinaltorphimine; C105294:endomorphin 2; D009271:Naltrexone; D015288:Neurokinin A; D002211:Capsaicin