title: Retinal arteriolar responses to acute severe elevation in systemic blood pressure in cats: role of endothelium-derived factors.
abstract: The purpose of this study was to investigate the roles of endothelium-derived factors in the retinal arteriolar responses to acute severe elevation in systemic blood pressure (BP) in cats. Acute elevation of mean arterial BP by 60% for 5 min was achieved by inflating a balloon-tipped catheter in the descending aorta. The retinal arteriolar diameter, flow velocity, wall shear rate (WSR) and blood flow (RBF) changes during BP elevation were assessed with laser Doppler velocimetry 2 h after intravitreal injections of nitric oxide (NO) synthase inhibitor l-NAME, cyclooxygenase inhibitor indomethacin, endothelin-1 receptor antagonists (BQ-123 for type A and BQ-788 for type B), or Rho kinase inhibitor fasudil. BP elevation caused a marked increase in retinal arteriolar flow velocity and WSR with slight vasoconstriction, resulting in an increase in RBF. The increases in velocity, WSR and RBF, but not diameter, were correlated with the increase in ocular perfusion pressure. With l-NAME or indomethacin, the increase in RBF upon BP elevation was significantly attenuated due to enhanced retinal arteriolar vasoconstriction. In contrast, BQ-123 and fasudil potentiated the increased RBF. BQ-788 had no effect on arteriolar diameter and hemodynamics. Our data suggest that acute elevation of BP by 60% leads to an increase in RBF due to the release of NO and prostanoids probably through a shear stress-induced vasodilation mechanism. The release of endothelin-1 and Rho kinase activation help to limit RBF augmentation by counteracting the vasodilation. It appears that the retinal endothelium, by releasing vasoactive substances, contributes to RBF regulation during acute severe elevation of systemic blood pressure.
authors.affiliation: Department of Ophthalmology, Asahikawa Medical University, Midorigaoka Higashi 2-1-1-1, Asahikawa 078-8510, Japan.
authors.forename: Seigo
authors.initials: S
authors.lastname: Nakabayashi
authors.forename: Taiji
authors.initials: T
authors.lastname: Nagaoka
authors.forename: Tomofumi
authors.initials: T
authors.lastname: Tani
authors.forename: Kenji
authors.initials: K
authors.lastname: Sogawa
authors.forename: Travis W
authors.initials: TW
authors.lastname: Hein
authors.forename: Lih
authors.initials: L
authors.lastname: Kuo
authors.forename: Akitoshi
authors.initials: A
authors.lastname: Yoshida
mesh_terms: D000818:Animals; D000959:Antihypertensive Agents / Q000008:administration & dosage; D001160:Arterioles / Q000502:physiology; D001783:Blood Flow Velocity / Q000502:physiology; D001794:Blood Pressure / Q000502:physiology*; D002415:Cats; D016861:Cyclooxygenase Inhibitors / Q000008:administration & dosage; D019332:Endothelin-1 / Q000378:metabolism; D004730:Endothelium, Vascular / Q000502:physiology*; D004791:Enzyme Inhibitors / Q000008:administration & dosage; D005260:Female; D006339:Heart Rate / Q000502:physiology; D006973:Hypertension / Q000503:physiopathology*; D007429:Intraocular Pressure / Q000502:physiology; D058449:Intravitreal Injections; D017078:Laser-Doppler Flowmetry; D008297:Male; D019331:NG-Nitroarginine Methyl Ester / Q000008:administration & dosage; D009569:Nitric Oxide / Q000378:metabolism; D012161:Retinal Artery / Q000187:drug effects / Q000502:physiology*; D014665:Vasodilator Agents / Q000008:administration & dosage; D054460:rho-Associated Kinases / Q000378:metabolism
chemical_list: D000959:Antihypertensive Agents; D016861:Cyclooxygenase Inhibitors; D019332:Endothelin-1; D004791:Enzyme Inhibitors; D014665:Vasodilator Agents; D009569:Nitric Oxide; D054460:rho-Associated Kinases; D019331:NG-Nitroarginine Methyl Ester