Official Title: “Choroidal Blood Flow Regulation During Isometric Exercise: Effects of Ca2+-Channel Blockade”

Autoregulation is the ability of a vascular bed to maintain blood flow despite changes in perfusion pressure. For a long time it had been assumed that the choroid is a strictly passive vascular bed, which shows no autoregulation. However, recently several groups have identified some autoregulatory capacity of the human choroid. In the brain and the retina the mechanism behind autoregulation is most likely linked to changes in transmural pressure. In this model arterioles change their vascular tone depending on the pressure inside the vessel and outside the vessel. In the choroid, several observations argue against a direct involvement of arterioles. In a previous project we were able to identify that the nitric oxide (NO) - system as well as the endothelin system are involved in choroidal blood flow regulation during isometric exercise.

In the present study autoregulation of the choroid during isometric exercise will be investigated and the pressure/flow relationships will be observed in the absence or presence of a calcium antagonist - nifedipine.

Study Type: Interventional

Study Design: Treatment, Randomized, Double Blind (Subject, Investigator), Placebo Control, Crossover Assignment, Safety/Efficacy Study

Study Primary Completion Date: April 2006

Intervention(s) in this Clinical Trial

• Drug: Nifedipine (drug)
  • Nifedipine (Adalat®, Bayer, Leverkusen, Germany) dose: 15µg/kg bolus infusion over 5 minutes; 0.2 µg/(kg.min) maintenance dose infusion period 25 minutes
• Drug: L-Arginin (drug)
  • L-Arginin (Clinalfa AG, Läufelfingen, Switzerland) 30% sodium chlorid solution, dose: 1g/min over 30 minutes
• Drug: Placebo
  • Placebo

Arms, Groups and Cohorts in this Clinical Trial

• Active Comparator: 1
  • Nifedipine
• Active Comparator: 2
  • L-Arginin
• Placebo Comparator: 3
  • Placebo

Primary Measures

• Choroidal pressure-blood flow relationship
  • Time Frame: in total 3x 3 hours
    Safety Issue?: No

Inclusion Criteria:

• Men aged between 19 and 35 years, nonsmokers
• Body mass index between 15th and 85th percentile (Must et al. 1991)
• Normal findings in the medical history and physical examination unless the investigator considers an abnormality to be clinically irrelevant
• Normal laboratory values unless the investigator considers an abnormality to be clinically irrelevant
• Normal ophthalmic findings, ametropy more than 3 Dpt.

Exclusion Criteria:

• Regular use of medication, abuse of alcoholic beverages, participation in a clinical trial in the 3 weeks preceding the study
• Treatment in the previous 3 weeks with any drug
• Symptoms of a clinically relevant illness in the 3 weeks before the first study day
• History of hypersensitivity to the trial drug or to drugs with a similar chemical structure
• History or presence of gastrointestinal, liver or kidney disease, or other conditions known to interfere with, distribution, metabolism or excretion of study drugs
• Blood donation during the previous 3 weeks

Gender Eligibility for this Clinical Trial: Male

Minimum Age for this Clinical Trial: 19 Years

Maximum Age for this Clinical Trial: 35 Years

Are Healthy Volunteers Accepted for this Clinical Trial?: Accepts Healthy Volunteers

Lead Sponsor: Medical University of Vienna

Overall Clinical Trial Officials and Contacts

Gabriele Fuchsjäger-Mayrl, M.D. Principal Investigator Department of Clinical Pharmacology, Medical University of Vienna  

Information obtained from ClinicalTrials.gov on October 07, 2008

Link to the current ClinicalTrials.gov record. http://clinicaltrials.gov/show/NCT00280462

Study ID Number: OPHT-110705

ClinicalTrials.gov Identifier: NCT00280462

Health Authority: Austria: Federal Ministry for Health and Women