title: Role of cytosolic phospholipase A2 in the enhancement of alpha2-adrenoceptor-mediated vasoconstriction by the thromboxane-mimetic U46619 in the porcine isolated ear artery: comparison with vasopressin-enhanced responses.
abstract: Pre-contraction with the thromboxane-mimetic U46619 enhances the subsequent alpha(2)-adrenoceptor-mediated vasoconstriction in the porcine ear artery through an enhanced activation of ERK-MAP kinase. In this study we determined the role of cPLA(2) in this enhanced response, and determined whether vasopressin is also able to enhance alpha(2)-adrenoceptor-mediated vasoconstriction through the same pathway. The cPLA(2) inhibitors AACOCF3 (50 microM) and MAFP (50 microM) both inhibited the U46619-enhanced alpha(2)-adrenoceptor response, but had no effect on the direct alpha(2)-adrenoceptor response. AACOCF3 also inhibited the enhanced ERK activation associated with the enhanced alpha(2)-adrenoceptor-mediated vasoconstriction. Pre-contraction with arachidonic acid mimicked the effect of U46619 by enhancing the contractile response to the alpha(2)-adrenoceptor agonist UK14304 (1 microM) and enhancing the alpha(2)-adrenoceptor-mediated ERK activation. Pre-contraction with vasopressin also enhanced the contractile response to UK14304, but neither PD98059 (50 microM) nor AACOCF3 (50 microM) had any effect this vasopressin-enhanced response, indicating that neither the ERK pathway, nor cPLA(2) are involved in vasopressin-enhanced responses. The alpha(2)-adrenceptor-stimulated activation of ERK was also unaffected by pre-contraction with vasopressin. On the other hand, inhibition of PKCzeta inhibited the enhanced alpha(2)-adrenoceptor contraction after pre-contraction with both U46619 and vasopressin. This study demonstrates that alpha(2)-adrenoceptor-mediated vasoconstriction can be enhanced through two different pathways-one dependent upon the enhanced activation of ERK-MAP kinase through activation of cPLA(2), and the other through a different, ERK/cPLA(2)-independent pathway.
authors.affiliation: School of Biomedical Sciences, Medical School, University of Nottingham, Queen's Medical Centre, UK.
authors.forename: B
authors.initials: B
authors.lastname: Bhattacharya
authors.forename: R
authors.initials: R
authors.lastname: Williams
authors.forename: M L
authors.initials: ML
authors.lastname: Latif
authors.forename: R E
authors.initials: RE
authors.lastname: Roberts
mesh_terms: D019796:15-Hydroxy-11 alpha,9 alpha-(epoxymethano)prosta-5,13-dienoic Acid / Q000494:pharmacology*; D000818:Animals; D015153:Blotting, Western; D003600:Cytosol / Q000201:enzymology*; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005419:Flavonoids / Q000494:pharmacology; D010741:Phospholipases A / Q000037:antagonists & inhibitors / Q000378:metabolism*; D054467:Phospholipases A2; D018341:Receptors, Adrenergic, alpha-2 / Q000502:physiology*; D013552:Swine; D014662:Vasoconstrictor Agents / Q000494:pharmacology*; D014667:Vasopressins / Q000494:pharmacology
chemical_list: D004791:Enzyme Inhibitors; D005419:Flavonoids; D018341:Receptors, Adrenergic, alpha-2; D014662:Vasoconstrictor Agents; D014667:Vasopressins; D019796:15-Hydroxy-11 alpha,9 alpha-(epoxymethano)prosta-5,13-dienoic Acid; D010741:Phospholipases A; D054467:Phospholipases A2; C093973:2-(2-amino-3-methoxyphenyl)-4H-1-benzopyran-4-one