Naloxone blocks endomorphin-1 but not endomorphin-2 induced inhibition of tachykinergic contractions of guinea-pig isolated bronchus

摘要

The recently identified endogenous agonists on the μ-opioid-receptor (μOR), 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-ig bronchu (ED_50s < 10 nM for both compounds). Surprisingly, only endomorphin-1 effects could be blocked by naloxone (10μM), whereas endomorphin-2 effects were not affected by specific antagonists for the μ-, κ-, and δ-opioid-receptor.