Role of Nitric Oxide in Optic Nerve Head Blood Flow Regulation During Isometric Exercise in Healthy Humans

Medical University of Vienna18 enrolled

Overview

Autoregulation is defined as the ability of a vascular bed to adapt its vascular resistance to changes in perfusion pressure. In the eye, several studies have reported that retinal blood flow is autoregulated over a wide range of ocular perfusion pressures. The investigators recently showed that nitric oxide (NO) is a key metabolite in the regulation of vascular tone in the eye and plays an important role in the blood flow autoregulation of the choroidal circulation. However, no data is yet available for the optic nerve head. Thus, the present study is designed to test the hypothesis that NO plays also a role in optic nerve head blood flow autoregulation. Therefore, subjects will perform squatting to increase systemic perfusion pressure during administration of either a nitric oxide synthase inhibitor (L-NMMA), an α-receptor agonist (phenylephrine) or placebo. Optic nerve head blood flow will be continuously measured during the procedure to investigate optic nerve head autoregulation.

Study Type

INTERVENTIONAL

Allocation

RANDOMIZED

Purpose

BASIC_SCIENCE

Masking

TRIPLE

Enrollment

Conditions

Healthy

Interventions

bolus 6mg/kg over 5 minutes followed by a continuous infusion of 60µg/kg/min over 15 minutes

PhenylephrineDRUG

1μg/kg/min, infusion period 20 minutes

Physiological saline solution (as placebo)DRUG

infusion period 20 minutes

Laser Doppler FlowmetryDEVICE

blood flow measurements at the temporal neuroretinal rim of the optic nerve head

Goldmann applanation tonometerDEVICE

intraocular pressure measurements

squattingOTHER

Subjects will perform squatting for 6 minutes while blood flow is measured

Eligibility

Sex: ALLMin age: 18 YearsMax age: 35 YearsHealthy volunteers:

Medical Language ↔ Plain English

Inclusion Criteria: * Men and women aged between 18 and 35 years, nonsmokers * Men and women will be included in equal parts * Normal findings in the medical history and physical examination unless the investigator considers an abnormality to be clinically irrelevant * Normal findings in the laboratory testings unless the investigator considers an abnormality to be clinically irrelevant * Normal ophthalmic findings, ametropia less than 3 diopters 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 (except intake of oral contraceptives) * Symptoms of a clinically relevant illness in the 3 weeks before the first study day * 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 * Pregnancy

Locations (1)

Department of Clinical Pharmacology, Medical University of Vienna

Vienna, Austria

Outcomes

Primary Outcomes

Optic nerve head pressure-flow relationship

Time frame: in total 6x on 3 study days

Data from ClinicalTrials.gov

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