Mechanisms of Choroidal Blood Flow Changes During Dark/Light Transitions

Study Overview
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Brief Summary
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There is evidence from a variety of animal studies that choroidal blood flow is under neural control. By contrast, only little information is available from human studies. Recent results indicate that a light/dark transition is associated with a short lasting reduction in choroidal blood flow. We have shown that during unilateral dark/light transition both eyes react with choroidal vasoconstriction strongly indicating a neural mechanism. The present studies investigate this possibility by using pharmacological interventions. The pharmacological agents tested include a nitric oxide synthase inhibitor, an alpha-receptor agonist (as a control substance for the blood pressure increasing nitric oxide synthase inhibitor), a muscarinic receptor blocker, and a non-specific beta-blocker. These drugs were chosen on the basis of previous animal experiments, as the systems, which are specifically influenced by these substances, are likely involved in neural control of choroidal blood flow.

Official Title
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Mechanisms of Choroidal Blood Flow Changes During Dark/Light Transitions

Conditions
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Regional Blood Flow, Ocular Physiology

Intervention / Treatment
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* Drug: Phenylephrine
* Drug: NG-Monomethyl-L-Arginine
* Drug: Propanolol
* Drug: Atropine


Participation Criteria
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Eligibility Criteria
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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 < 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

Ages Eligible for Study
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Minimum Age: 19 Years
Maximum Age: 35 Years

Sexes Eligible for Study
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Male

Accepts Healthy Volunteers
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Accepts Healthy Volunteers

Study Plan
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How is the study designed?
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Design Details

Primary Purpose: Treatment
Allocation: Randomized
Intervention Model: Crossover Assignment
Masking: Double


Arms and Interventions

| Intervention/Treatment |
| --- |
|Drug: Phenylephrine|nan|
|Drug: NG-Monomethyl-L-Arginine|nan|
|Drug: Propanolol|nan|
|Drug: Atropine|nan|

What is the study measuring?
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Primary Outcome Measures

| Outcome Measure | Measure Description | Time Frame |
| --- | --- | --- |
| choroidal blood flow |  |  | 
| fundus pulsation amplitude |  |  | 

 Terms related to the study
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Keywords Provided by Centre Hospitalier Valida
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Choroidal blood flow, NO-synthase, light/dark transition