title: Effect of nifedipine on choroidal blood flow regulation during isometric exercise.
abstract: OBJECTIVE
  To determine whether nifedipine, an L-type calcium channel blocker, alters choroidal blood flow (ChBF) regulation during isometric exercise in healthy subjects.
  
  
  METHODS
  The study was carried out in a randomized, placebo-controlled, double-masked, two-way crossover design. Fifteen healthy male subjects were randomly assigned to receive either placebo or nifedipine on two different study days. Subfoveal ChBF was measured with laser Doppler flowmetry while the study participants performed isometric exercise (squatting). This was performed before drug administration and during infusion of nifedipine and placebo, respectively. Mean arterial pressure (MAP) and intraocular pressure (IOP) were measured noninvasively, and ocular perfusion pressure (OPP) was calculated as &frac23; MAP-IOP.
  
  
  RESULTS
  MAP and OPP increased significantly during all squatting periods (P < 0.01). The increase in ChBF was less pronounced than the increase in OPP during isometric exercise. Nifedipine did not alter the OPP increase in response to isometric exercise, but it significantly augmented the exercise-induced increase in ChBF (P < 0.001 vs. placebo). Although ChBF increased by a maximum of 14.2% ± 9.2% during the squatting period when placebo was administered, the maximum increase during administration of nifedipine was 23.2% ± 7.2%.
  
  
  CONCLUSIONS
  In conclusion, the data of the present study suggest that nifedipine augments the ChBF response to an experimental increase in OPP. In addition, it confirms that the choroidal vasculature has a significant regulatory capacity over wide ranges of OPPs during isometric exercise. (ClinicalTrials.gov number, NCT00280462.).
authors.affiliation: Department of Clinical Pharmacology, Medical University of Vienna, Vienna, Austria.
authors.forename: Doreen
authors.initials: D
authors.lastname: Schmidl
authors.forename: Ana
authors.initials: A
authors.lastname: Prinz
authors.forename: Julia
authors.initials: J
authors.lastname: Kolodjaschna
authors.forename: Elzbieta
authors.initials: E
authors.lastname: Polska
authors.forename: Alexandra
authors.initials: A
authors.lastname: Luksch
authors.forename: Gabriele
authors.initials: G
authors.lastname: Fuchsjager-Mayrl
authors.forename: Gerhard
authors.initials: G
authors.lastname: Garhofer
authors.forename: Leopold
authors.initials: L
authors.lastname: Schmetterer
mesh_terms: D000328:Adult; D001783:Blood Flow Velocity; D001794:Blood Pressure / Q000502:physiology; D001824:Body Constitution; D002121:Calcium Channel Blockers / Q000008:administration & dosage*; D015220:Calcium Channels / Q000502:physiology*; D002829:Choroid / Q000098:blood supply*; D018592:Cross-Over Studies; D004311:Double-Blind Method; D004562:Electrocardiography; D015444:Exercise / Q000502:physiology*; D006801:Humans; D007262:Infusions, Intravenous; D007429:Intraocular Pressure / Q000502:physiology; D017078:Laser-Doppler Flowmetry; D008297:Male; D009543:Nifedipine / Q000008:administration & dosage*; D012039:Regional Blood Flow / Q000502:physiology
chemical_list: D002121:Calcium Channel Blockers; D015220:Calcium Channels; D009543:Nifedipine