title: Chronic hypertension increases susceptibility to acute IOP challenge in rats.
abstract: OBJECTIVE
  To consider the effect of chronic arterial hypertension on the susceptibility of the retina to acute IOP challenge.
  
  
  METHODS
  Anesthetized adult Long-Evans rats with normal (n = 5, receiving saline subcutaneously), chronic high blood pressure (BP) for 4 weeks (n = 15, Angiotensin II subcutaneously), and acute high BP for 1 hour (n = 10, Angiotensin II intravenously) underwent IOP elevation (10-120 mm Hg, 5 mm Hg steps each 3 minutes). During IOP elevation, retinal function and ocular blood flow were monitored with electroretinogram (ERG) and laser-Doppler flowmetry (LDF), respectively. Blood pressure was monitored via a femoral artery cannula. Electroretinogram and LDF responses are expressed as a percentage of baseline and compared between groups. The left ventricle and the aorta were dissected to assess the morphologic changes associated with chronic hypertension.
  
  
  RESULTS
  Four weeks of hypertension (systolic BP 192 ± 4 mm Hg) produced cardiac hypertrophy and thickened aortic arterial walls compared with controls (systolic BP 112 ± 3 mm Hg). Retinal function was unaltered with chronic hypertension compared with normotensive animals. During acute IOP elevation, ERG and LDF were reduced in a dose-dependent manner in all BP groups. Both chronic and acute hypertension made the ERG and LDF less susceptible to IOP elevation. However, the degree of resistance to IOP elevation was greater in acute hypertension compared with chronic hypertension (P < 0.05).
  
  
  CONCLUSIONS
  Acute BP elevation makes retinal function and blood flow less susceptible to IOP elevation. The reduced susceptibility afforded by improved ocular perfusion pressure is compromised after 4 weeks of chronic hypertension.
authors.affiliation: Department of Optometry & Vision Sciences, University of Melbourne, Parkville, Victoria, Australia.
authors.forename: Zheng
authors.initials: Z
authors.lastname: He
authors.affiliation: Department of Optometry & Vision Sciences, University of Melbourne, Parkville, Victoria, Australia.
authors.forename: Algis J
authors.initials: AJ
authors.lastname: Vingrys
authors.affiliation: School of Medicine (Optometry), Deakin University, Waurn Ponds, Victoria, Australia Department of Anatomy and Developmental Biology, Monash University, Clayton, Victoria, Australia.
authors.forename: James A
authors.initials: JA
authors.lastname: Armitage
authors.affiliation: Department of Optometry & Vision Sciences, University of Melbourne, Parkville, Victoria, Australia.
authors.forename: Christine T
authors.initials: CT
authors.lastname: Nguyen
authors.affiliation: Department of Optometry & Vision Sciences, University of Melbourne, Parkville, Victoria, Australia.
authors.forename: Bang V
authors.initials: BV
authors.lastname: Bui
mesh_terms: D000208:Acute Disease; D000704:Analysis of Variance; D000818:Animals; D001013:Aorta, Thoracic / Q000473:pathology; D006332:Cardiomegaly / Q000209:etiology / Q000473:pathology; D002908:Chronic Disease; D004596:Electroretinography; D006352:Heart Ventricles / Q000473:pathology; D006973:Hypertension / Q000150:complications* / Q000503:physiopathology; D007429:Intraocular Pressure / Q000502:physiology*; D017078:Laser-Doppler Flowmetry; D009798:Ocular Hypertension / Q000503:physiopathology*; D051381:Rats; D020318:Rats, Long-Evans; D012160:Retina / Q000503:physiopathology
keywords: IOP; chronic high blood pressure; electroretinogram; retinal blood flow