title: Characterization of the vascular thromboxane A2/prostaglandin endoperoxide receptor in rabbit aorta. Regulation by dexamethasone.
abstract: Recently, we have shown that dexamethasone treatment of rabbits specifically reduces vascular smooth muscle responsiveness to agonists that interact with the vascular thromboxane A2/prostaglandin H2 (TXA2/PGH2) receptor. One potential site at which dexamethasone can influence prostanoid-mediated vasoconstriction may be at the level of the vascular TXA2/PGH2 receptor. Therefore, we characterized the vascular TXA2/PGH2 receptor in rabbit aortic membranes and examined the influence of dexamethasone treatment on vascular TXA2/PGH2 receptor affinity and number. The binding of [125I][1S-(1 alpha,2 beta(5Z),3 alpha(1E,3R)4 alpha)]-7-[3-(3- hydroxy-4-(p-iodophenoxy)-1-butenyl)-7-oxabicyclo[2.2.1] heptan-2-yl]-5-heptanoic acid ([125I]BOP), a potent TXA2/PGH2 receptor agonist, to rabbit aortic membranes was saturable, displaceable, and dependent on protein concentration. Scatchard analysis of equilibrium binding data disclosed one class of high affinity binding sites with a Kd of 0.44 +/- 0.13 nM and a Bmax of 114.4 +/- 5.2 fmol/mg protein (n = 7). Removal of the endothelium before membrane preparation did not significantly alter the affinity or number of binding sites for [125I]BOP. Kinetic analysis of the rates of [125I]BOP association/dissociation yielded a Kd of 0.62 nM. The ability of various agonists at the TXA2/PGH2 receptor to displace [125I]BOP from vascular membranes correlated well with their contractile potencies in rabbit aortic rings. Moreover, stereospecific displacement of [125I]BOP binding in aortic membranes and inhibition of U46619-mediated aortic contractions were obtained with the stereoisomers L657925(-) and L657926(+). Collectively, these data suggest that this binding site represents the functionally relevant vascular TXA2/PGH2 receptor. In functional experiments, [127I]BOP induced concentration-dependent contractions of the rabbit aorta, which were reduced by 52% in vessels from dexamethasone-treated rabbits.(ABSTRACT TRUNCATED AT 250 WORDS)
authors: Department of Pharmacology, New York Medical College, Valhalla 10595.
authors: W C
authors: WC
authors: Sessa
authors: P V
authors: PV
authors: Halushka
authors: A
authors: A
authors: Okwu
authors: A
authors: A
authors: Nasjletti
mesh_terms: D000818:Animals; D001011:Aorta; D001665:Binding Sites; D001667:Binding, Competitive; D001643:Bridged Bicyclo Compounds / Q000378:metabolism; D019086:Bridged Bicyclo Compounds, Heterocyclic; D003907:Dexamethasone / Q000494:pharmacology*; D005231:Fatty Acids, Unsaturated / Q000378:metabolism; D066298:In Vitro Techniques; D008297:Male; D009119:Muscle Contraction; D009131:Muscle, Smooth, Vascular / Q000502:physiology*; D011817:Rabbits; D011982:Receptors, Prostaglandin / Q000032:analysis* / Q000187:drug effects; D017482:Receptors, Thromboxane; D013931:Thromboxanes / Q000032:analysis*
chemical_list: D001643:Bridged Bicyclo Compounds; D019086:Bridged Bicyclo Compounds, Heterocyclic; D005231:Fatty Acids, Unsaturated; D011982:Receptors, Prostaglandin; D017482:Receptors, Thromboxane; D013931:Thromboxanes; C061750:7-(3-(3-hydroxy-4-(4'-iodophenoxy)-1-butenyl)-7-oxabicyclo(2.2.1)heptan-2-yl)-5-heptenoic acid; D003907:Dexamethasone