title: Ascorbate elevates perfusion pressure in the bovine extraocular long posterior ciliary artery: role of endothelium-derived hyperpolarizing factor (EDHF).
abstract: Ascorbate blocks agonist-induced, endothelium-derived hyperpolarizing factor (EDHF)-mediated vasodilatation in the bovine perfused ciliary artery and this is associated with a rise in perfusion pressure. We now report the origins of this ascorbate-induced rise in perfusion pressure. In segments of ciliary artery perfused at 2.5 ml/min, the addition of ascorbate (10-150 microM) enhanced U46619-induced perfusion pressure. Ascorbate produced no enhancement in the absence of U46619, suggesting that its effects resulted not from a constrictor action but through removal of a tonic vasodilator influence. Experiments revealed the endothelial source of this vasodilator influence, and EDHF, but not nitric oxide or prostanoids, appeared to be involved. The ascorbate-induced enhancement of vasoconstrictor tone was not seen in a static myograph or in segments perfused at low rates of flow, but was seen at flow rates of 2.5 ml(-1) and above. We conclude that ascorbate augments vasoconstrictor tone through inhibition of flow-induced EDHF activity.
authors.affiliation: Division of Neuroscience and Biomedical Systems, Institute of Biomedical and Life Sciences, West Medical Building, University of Glasgow, Glasgow G12 8QQ, Scotland, UK.
authors.forename: Alison
authors.initials: A
authors.lastname: Stirrat
authors.forename: Silvia
authors.initials: S
authors.lastname: Nelli
authors.forename: Alicia
authors.initials: A
authors.lastname: McGuckin
authors.forename: Vivian Wing Man
authors.initials: VW
authors.lastname: Ho
authors.forename: William S
authors.initials: WS
authors.lastname: Wilson
authors.forename: William
authors.initials: W
authors.lastname: Martin
mesh_terms: D019796:15-Hydroxy-11 alpha,9 alpha-(epoxymethano)prosta-5,13-dienoic Acid / Q000494:pharmacology; D000818:Animals; D001205:Ascorbic Acid / Q000494:pharmacology*; D001685:Biological Factors / Q000037:antagonists & inhibitors* / Q000378:metabolism; D002417:Cattle; D019842:Ciliary Arteries / Q000187:drug effects* / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D004730:Endothelium, Vascular / Q000187:drug effects / Q000378:metabolism; D051660:Intermediate-Conductance Calcium-Activated Potassium Channels / Q000187:drug effects / Q000378:metabolism; D010477:Perfusion; D026902:Potassium Channel Blockers / Q000494:pharmacology; D011312:Pressure; D011720:Pyrazoles / Q000494:pharmacology; D014662:Vasoconstrictor Agents / Q000494:pharmacology; D014664:Vasodilation
chemical_list: D001685:Biological Factors; D051660:Intermediate-Conductance Calcium-Activated Potassium Channels; D026902:Potassium Channel Blockers; D011720:Pyrazoles; C411671:TRAM 34; D014662:Vasoconstrictor Agents; C067410:endothelium-dependent hyperpolarization factor; D019796:15-Hydroxy-11 alpha,9 alpha-(epoxymethano)prosta-5,13-dienoic Acid; D001205:Ascorbic Acid