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

Medical University of Vienna

Status: Completed

Conditions: Healthy

Treatments: Device: Goldmann applanation tonometer; Drug: Phenylephrine; Other: squatting; Drug: Physiological saline solution (as placebo); Device: Laser Doppler Flowmetry; Drug: NG-monomethyl-L-arginine (L-NMMA)

Study type: Interventional

Funder types: Other

Identifiers

NCT00806741

OPHT-300708

Details and patient eligibility

About

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.

Enrollment: 18 patients

Sex: All

Ages: 18 to 35 years old

Volunteers: Accepts Healthy Volunteers

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

Trial design

Primary purpose: Basic Science

Allocation: Randomized

Interventional model: Crossover Assignment

Masking: Triple Blind

---

18 participants in 3 patient groups, including a placebo group

1

Active Comparator group

Description:

NG-monomethyl-L-arginine (L-NMMA)

Treatment:

Device: Laser Doppler Flowmetry

Other: squatting

Drug: NG-monomethyl-L-arginine (L-NMMA)

Device: Goldmann applanation tonometer

2

Active Comparator group

Description:

Phenylephrine

Treatment:

Device: Laser Doppler Flowmetry

Other: squatting

Drug: Phenylephrine

Device: Goldmann applanation tonometer

3

Placebo Comparator group

Description:

Physiological saline solution

Treatment:

Device: Laser Doppler Flowmetry

Other: squatting

Drug: Physiological saline solution (as placebo)

Device: Goldmann applanation tonometer