Epithelium‐dependent potentiation of anaphylactic contractions by β‐endorphin in tracheae isolated from actively sensitized guinea‐pigs

1 It has been shown that opioid peptides modulate airway function. In the present study, the effect of β‐endorphin on antigen‐induced contractions of isolated tracheal rings from actively sensitized guinea‐pigs has been studied. 2 β‐Endorphin had a concentration‐dependent bimodal effect on anaphylactic contractions of the trachea. Low concentrations of β‐endorphin (10 −10 and 10 −8 m ) significantly potentiated anaphylactic contractions, whereas higher concentrations (10 −7 and 10 −6 m ) significantly suppressed anaphylactic contractions of guinea‐pig trachea. 3 β‐Endorphin in concentrations of 10 −8 m and 10 −7 m did not affect the responsiveness of the tracheal rings to histamine or leukotriene D 4 . This indicates that β‐endorphin does not influence the responsiveness of tracheal smooth muscle to anaphylactic mediators. 4 In the presence of the non‐selective opioid receptor antagonist naloxone, 10 −8 m β‐endorphin still potentiated the anaphylactic contractions of the trachea. In addition, an equimolar concentration of des‐Tyr 1 ‐β‐endorphin, a fragment of β‐endorphin without opioid‐like activity, also potentiated anaphylactic contractions. The potentiation of anaphylactic contraction by 10 −8 m β‐endorphin is not therefore mediated by classical opioid‐receptors. 5 In the presence of naloxone, 10 −7 m , β‐endorphin did not suppress anaphylactic contractions of the trachea. Thus, the suppression of anaphylactic contraction is mediated via a classical opioid‐receptor. 6 In epithelium‐denuded tracheae, both 10 −8 and 10 −7 m β‐endorphin suppressed the anaphylactic contractions, whereas 10 −8 and 10 −7 m des‐Tyr 1 ‐β‐endorphin did not affect anaphylactic contractions. It is concluded that the potentiation of the anaphylactic contraction in intact trachea is epithelium‐dependent whereas the suppression of the anaphylactic contraction is epithelium‐independent.