title: Increased expression of cyclooxygenase-2 mediates enhanced contraction to endothelin ETA receptor stimulation in endothelial nitric oxide synthase knockout mice.
abstract: The aim of this study was to determine whether prolonged loss of NO activity, in endothelial NO synthase knockout (eNOS(-/-)) mice, influences endothelin (ET) ETA receptor-mediated smooth muscle contraction and, if so, to define the underlying mechanism(s). In isolated endothelium-denuded abdominal aortas, contractions to the selective ETA receptor agonist ET-1(1-31) were significantly increased in aortas from eNOS(-/-) compared with wild-type (WT) mice. In contrast, contractions to the alpha1-adrenergic agonist phenylephrine or the thromboxane (TX) A2 analog U-46619 were similar between eNOS(-/-) and WT mice. Immunofluorescent and Western blot analysis demonstrated that the aortic expression of ETA receptors was decreased in eNOS(-/-) compared with WT mice. Contractions evoked by ET-1(1-31), but not phenylephrine, were reduced by inhibition of cyclooxygenase-2 (COX-2) (indomethacin or celecoxib) or of TXA2/prostaglandin H2 receptors (SQ-29548). After COX inhibition, contractions to ET-1(1-31) were no longer increased and were actually decreased in eNOS(-/-) compared with WT aortas. Western blot analysis revealed that endothelium-denuded abdominal aortas express COX-2, but not COX-1, and that expression of COX-2 was significantly increased in eNOS(-/-) compared with WT mice. Contractions to the COX substrate arachidonic acid were also increased in eNOS(-/-) aortas. Furthermore, ET-1(1-31) but not phenylephrine stimulated production of the TXA2 metabolite TXB2, which was increased in eNOS(-/-) compared with WT aortas. Therefore, COX-2 plays a crucial and selective role in ETA-mediated smooth muscle contraction. Furthermore, COX-2 expression is increased in eNOS(-/-) mice, which overcomes a reduced expression of ETA receptors and enables a selective increase in contraction to ETA receptor stimulation.
authors.affiliation: Davis Heart & Lung Research Institute, The Ohio State University, Columbus, OH 43210, USA. zhou-4@medctr.osu.edu
authors.forename: Yingbi
authors.initials: Y
authors.lastname: Zhou
authors.forename: Srabani
authors.initials: S
authors.lastname: Mitra
authors.forename: Saradhadevi
authors.initials: S
authors.lastname: Varadharaj
authors.forename: Narasimham
authors.initials: N
authors.lastname: Parinandi
authors.forename: Jay L
authors.initials: JL
authors.lastname: Zweier
authors.forename: Nicholas A
authors.initials: NA
authors.lastname: Flavahan
mesh_terms: D000818:Animals; D001012:Aorta, Abdominal / Q000378:metabolism / Q000502:physiology*; D016718:Arachidonic Acid / Q000494:pharmacology; D051546:Cyclooxygenase 2 / Q000378:metabolism*; D066298:In Vitro Techniques; D051379:Mice; D018345:Mice, Knockout; D009131:Muscle, Smooth, Vascular / Q000378:metabolism / Q000502:physiology; D052250:Nitric Oxide Synthase Type III / Q000172:deficiency*; D044022:Receptor, Endothelin A / Q000378:metabolism / Q000502:physiology*; D013929:Thromboxane B2 / Q000378:metabolism; D014661:Vasoconstriction / Q000187:drug effects / Q000502:physiology*
chemical_list: D044022:Receptor, Endothelin A; D016718:Arachidonic Acid; D013929:Thromboxane B2; D052250:Nitric Oxide Synthase Type III; D051546:Cyclooxygenase 2