Involvement of TP and EP3 receptors in vasoconstrictor responses to isoprostanes in pulmonary vasculature

• Published in: The Journal of pharmacology and experimental therapeutics Vol. 301; no. 3; p. 1060
• Main Authors: Janssen, Luke J, Tazzeo, Tracy
• Format: Journal Article
• Language: English
• Published: United States 01-06-2002
• Subjects: Animals; Dinoprostone - analogs & derivatives; Dinoprostone - pharmacology; Dose-Response Relationship, Drug; In Vitro Techniques; Isoprostanes - pharmacology; Isoprostanes - physiology; Lung - blood supply; Lung - drug effects; Lung - physiology; Muscle, Smooth, Vascular - drug effects; Muscle, Smooth, Vascular - physiology; Pulmonary Artery - drug effects; Pulmonary Artery - physiology; Pulmonary Veins - drug effects; Pulmonary Veins - physiology; Receptors, Prostaglandin E - agonists; Receptors, Prostaglandin E - antagonists & inhibitors; Receptors, Prostaglandin E - physiology; Receptors, Prostaglandin E, EP3 Subtype; Receptors, Thromboxane - agonists; Receptors, Thromboxane - antagonists & inhibitors; Receptors, Thromboxane - physiology; Swine; Vasoconstriction - drug effects; Vasoconstriction - physiology; Vasoconstrictor Agents - pharmacology
• ISSN: 0022-3565
• DOI: 10.1124/jpet.301.3.1060

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.