title: Involvement of TP and EP3 receptors in vasoconstrictor responses to isoprostanes in pulmonary vasculature.
abstract: Although isoprostanes generally act on smooth muscle via TXA(2)-selective prostanoid receptors (TPs), some suggest other prostanoid receptors or possibly even a novel isoprostane-selective receptor might be involved. We studied contractions to several isoprostanes in porcine pulmonary vasculature using organ bath techniques. 8-iso-prostaglandin E(2) (PGE(2)) was the most potent and efficacious of the isoprostanes, with a log EC(50) of -7.0 +/- 0.2 in the pulmonary artery and -6.8 +/- 0.2 in the pulmonary vein. The responses to all the isoprostanes were essentially completely blocked by the TP receptor antagonist ICI 192605 [4(Z)-6-[(2,4,5-cis)2-(2-chlorophenyl)-4-(2-hydroxyphenyl)1,3-dioxan-5-yl]hexenoic acid], and the equilibrium dissociation constants for ICI 192605 competing with U46619 or 8-iso-PGE(2) were both approximately 2 nM, indicating that isoprostane-evoked responses involve primarily TP receptors. Only 8-iso-PGE(2) was able to evoke substantial contractions in the presence of ICI 192605 and only in the pulmonary vein. The EC(50) of these ICI 192605-insensitive responses was -6.1 +/- 0.2. Using a variety of prostanoid agonists, we found the pulmonary vein lacked excitatory PGF(2alpha)-selective prostanoid receptor (FP) or PGD(2)-selective prostanoid receptor (DP) but expressed excitatory EP(3) receptors. The ICI 192605-insensitive responses to 8-iso-PGE(2) were unaffected by the EP(1) antagonist SC-19220 [8-chloro-debenz[b,f][1,4]oxazepine-10(11H)-carboxy-(2-acetyl) hydrazine; 10(-5) M] but were antagonized by the less selective DP/EP(1)/EP(2) antagonist AH6809 (6-isopropoxy-9-oxoxanthene-2-carboxylic acid; 10(-5) M) or by cyclopiazonic acid (10(-5) M; depletes the internal Ca(2+) store). Our data indicate that, whereas 8-iso-PGE(2) constricts pulmonary vasculature primarily through TP receptors, a substantial portion of this response is also directed through EP(3) receptors or possibly a novel isoprostane receptor.
authors.affiliation: Asthma Research Group, Department of Medicine, McMaster University, St. Joseph's Hospital, 50 Charlton Avenue East, Hamilton, Ontario, L8N 4A6, Canada. janssenl@mcmaster.ca
authors.forename: Luke J
authors.initials: LJ
authors.lastname: Janssen
authors.forename: Tracy
authors.initials: T
authors.lastname: Tazzeo
mesh_terms: D000818:Animals; D015232:Dinoprostone / Q000031:analogs & derivatives / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D066298:In Vitro Techniques; D028421:Isoprostanes / Q000494:pharmacology / Q000502:physiology*; D008168:Lung / Q000098:blood supply* / Q000187:drug effects / Q000502:physiology; D009131:Muscle, Smooth, Vascular / Q000187:drug effects / Q000502:physiology*; D011651:Pulmonary Artery / Q000187:drug effects / Q000502:physiology; D011667:Pulmonary Veins / Q000187:drug effects / Q000502:physiology; D018078:Receptors, Prostaglandin E / Q000819:agonists / Q000037:antagonists & inhibitors / Q000502:physiology*; D058308:Receptors, Prostaglandin E, EP3 Subtype; D017482:Receptors, Thromboxane / Q000819:agonists / Q000037:antagonists & inhibitors / Q000502:physiology*; D013552:Swine; D014661:Vasoconstriction / Q000187:drug effects / Q000502:physiology*; D014662:Vasoconstrictor Agents / Q000494:pharmacology
chemical_list: D028421:Isoprostanes; D018078:Receptors, Prostaglandin E; D058308:Receptors, Prostaglandin E, EP3 Subtype; D017482:Receptors, Thromboxane; D014662:Vasoconstrictor Agents; D015232:Dinoprostone; C011987:8-isoprostaglandin E2