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.

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Key information

Conditions

Ocular Physiology Regional Blood Flow

Age range

19 year–35 year

Sex eligibility

Male

Study type

Interventional

Phase

Not applicable

Primary location

Department of Clinical Pharmacology

Vienna, 1090, Austria

Who can participate

Healthy volunteers accepted: Yes

Only the study team can determine whether someone qualifies for participation.

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

Treatment and study plan

Nifedipine (drug)

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

L-Arginin (drug)

Drug

L-Arginin (Clinalfa AG, Läufelfingen, Switzerland) 30% sodium chlorid solution, dose: 1g/min over 30 minutes

Placebo

Drug

Placebo

Primary outcomes

Choroidal pressure-blood flow relationship

Time frame: in total 3x 3 hours

Sponsors and collaborators

Lead sponsor

Medical University of Vienna

Other

Registry information

Important dates

Study start: 2005
Primary completion: 2006
Study completion: 2006
First posted: Jan 23, 2006
Registry last updated: Jul 9, 2008

OpenTrials presents study information sourced from ClinicalTrials.gov. The official registry record should be consulted for the latest information.

View the official ClinicalTrials.gov record (opens in a new tab)

This listing is for discovery and informational purposes only. It is not medical advice, does not guarantee that a study is recruiting, and does not determine eligibility. Contact the study team and a qualified healthcare professional when considering participation.

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Completed