title: Role of adenosine in the control of choroidal blood flow during changes in ocular perfusion pressure.
abstract: OBJECTIVE
  The purpose of the present study was to investigate whether the nucleoside adenosine is involved in the regulatory processes of choroidal blood flow (ChBF) during an experimental decrease in ocular perfusion pressure (OPP).
  
  
  METHODS
  In this randomized, double-masked, placebo-controlled, two-way crossover study, 14 subjects received either intravenous adenosine or placebo on two different study days. The suction cup method was used for a stepwise increase in intraocular pressure (IOP). Subfoveal ChBF was measured by laser Doppler flowmetry. Mean arterial pressure (MAP) and IOP were measured noninvasively. Ocular perfusion pressure was calculated as OPP = 2/3MAP - IOP.
  
  
  RESULTS
  Adenosine increased ChBF significantly versus placebo before application of the suction cup (P < 0.05). When the suction cup was applied, a significant decrease in OPP was observed. This effect was comparable on all study days. The decrease in OPP was paralleled by a significant decrease in ChBF (maximum between -43% and -52%) which was less pronounced than the decrease in OPP (maximum between -62% and -64%). Neither placebo nor adenosine influenced the ChBF increase during suction cup-induced changes in OPP.
  
  
  CONCLUSIONS
  The data of the present study confirm that the human choroid shows some regulatory capacity during a decrease in OPP. Adenosine influences basal vascular tone in the choroid but is not involved in the regulatory mechanisms during an increase in IOP. (ClinicalTrials.gov number, NCT00712764.).
authors.affiliation: Department of Clinical Pharmacology, Medical University of Vienna, Vienna, Austria.
authors.forename: Doreen
authors.initials: D
authors.lastname: Schmidl
authors.forename: Guenther
authors.initials: G
authors.lastname: Weigert
authors.forename: Guido T
authors.initials: GT
authors.lastname: Dorner
authors.forename: Hemma
authors.initials: H
authors.lastname: Resch
authors.forename: Julia
authors.initials: J
authors.lastname: Kolodjaschna
authors.forename: Michael
authors.initials: M
authors.lastname: Wolzt
authors.forename: Gerhard
authors.initials: G
authors.lastname: Garhofer
authors.forename: Leopold
authors.initials: L
authors.lastname: Schmetterer
mesh_terms: D000241:Adenosine / Q000008:administration & dosage*; D000328:Adult; D002829:Choroid / Q000098:blood supply* / Q000502:physiology; D018592:Cross-Over Studies; D006706:Homeostasis / Q000187:drug effects / Q000502:physiology; D006801:Humans; D007275:Injections, Intravenous; D007429:Intraocular Pressure / Q000502:physiology*; D008297:Male; D010919:Placebos; D012039:Regional Blood Flow / Q000187:drug effects* / Q000502:physiology; D013396:Suction / Q000379:methods; D014655:Vascular Resistance / Q000187:drug effects / Q000502:physiology; D014665:Vasodilator Agents / Q000008:administration & dosage*; D055815:Young Adult
chemical_list: D010919:Placebos; D014665:Vasodilator Agents; D000241:Adenosine