title: PGE2 maintains the tone of the guinea pig trachea through a balance between activation of contractile EP1 receptors and relaxant EP2 receptors.
abstract: OBJECTIVE
  The guinea pig trachea (GPT) is commonly used in airway pharmacology. The aim of this study was to define the expression and function of EP receptors for PGE(2) in GPT as there has been ambiguity concerning their role.
  
  
  METHODS
  Expression of mRNA for EP receptors and key enzymes in the PGE(2) pathway were assessed by real-time PCR using species-specific primers. Functional studies of GPT were performed in tissue organ baths.
  
  
  RESULTS
  Expression of mRNA for the four EP receptors was found in airway smooth muscle. PGE(2) displayed a bell-shaped concentration-response curve, where the initial contraction was inhibited by the EP(1) receptor antagonist ONO-8130 and the subsequent relaxation by the EP(2) receptor antagonist PF-04418948. Neither EP(3) (ONO-AE5-599) nor EP(4) (ONO-AE3-208) selective receptor antagonists affected the response to PGE(2). Expression of COX-2 was greater than COX-1 in GPT, and the spontaneous tone was most effectively abolished by selective COX-2 inhibitors. Furthermore, ONO-8130 and a specific PGE(2) antibody eliminated the spontaneous tone, whereas the EP(2) antagonist PF-04418948 increased it. Antagonists of other prostanoid receptors had no effect on basal tension. The relaxant EP(2) response to PGE(2) was maintained after long-term culture, whereas the contractile EP(1) response showed homologous desensitization to PGE(2), which was prevented by COX-inhibitors.
  
  
  CONCLUSIONS
  Endogenous PGE(2), synthesized predominantly by COX-2, maintains the spontaneous tone of GPT by a balance between contractile EP(1) receptors and relaxant EP(2) receptors. The model may be used to study interactions between EP receptors.
authors.affiliation: Unit for Experimental Asthma and Allergy Research, Centre for Allergy Research, The Institute of Environmental Medicine, Karolinska Institutet, Stockholm, Sweden.
authors.forename: J
authors.initials: J
authors.lastname: Säfholm
authors.forename: S-E
authors.initials: SE
authors.lastname: Dahlén
authors.forename: I
authors.initials: I
authors.lastname: Delin
authors.forename: K
authors.initials: K
authors.lastname: Maxey
authors.forename: K
authors.initials: K
authors.lastname: Stark
authors.forename: L-O
authors.initials: LO
authors.lastname: Cardell
authors.forename: M
authors.initials: M
authors.lastname: Adner
mesh_terms: D000818:Animals; D016861:Cyclooxygenase Inhibitors / Q000494:pharmacology; D015232:Dinoprostone / Q000494:pharmacology* / Q000502:physiology; D004305:Dose-Response Relationship, Drug; D006168:Guinea Pigs; D008297:Male; D009119:Muscle Contraction / Q000187:drug effects*; D009129:Muscle Tonus / Q000187:drug effects*; D009130:Muscle, Smooth / Q000187:drug effects*; D009924:Organ Culture Techniques; D012333:RNA, Messenger / Q000096:biosynthesis; D051381:Rats; D017207:Rats, Sprague-Dawley; D060888:Real-Time Polymerase Chain Reaction; D058306:Receptors, Prostaglandin E, EP1 Subtype / Q000096:biosynthesis*; D058307:Receptors, Prostaglandin E, EP2 Subtype / Q000096:biosynthesis*; D013045:Species Specificity; D014132:Trachea / Q000187:drug effects*
chemical_list: D016861:Cyclooxygenase Inhibitors; D012333:RNA, Messenger; D058306:Receptors, Prostaglandin E, EP1 Subtype; D058307:Receptors, Prostaglandin E, EP2 Subtype; D015232:Dinoprostone