Nitric Oxide and the Autonomic Nervous System

Study Overview
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Brief Summary
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The amount of blood flowing to the different parts of the body is regulated by the autonomic (automatic) nerves and by local factors produced by the blood vessels. Nitric oxide (NO) is one of the most important of these metabolic factors. If the production of NO is slowed or stopped the amount of blood to the different parts of the body is decreased. There is increasing knowledge that NO mechanisms are impaired in a number of medical conditions. NO function is reduced in patients with risk factors for atherosclerosis (hardening of the arteries) such as hypercholesterolemia (patients with high cholesterol), or diabetes mellitus, and is also impaired in smokers. This NO deficiency is believed to contribute to the greater cardiovascular risk that marks these patient populations. This study is designed to examine if endothelial nitric oxide is an important control mechanism of blood pressure under normal conditions, and if impairment of nitric oxide contributes to hypertension.

Official Title
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Cardiovascular Regulation: Autonomic/Metabolic Mechanisms PO1 HL56693, Project 4: Cardiovascular Regulation: Autonomic/Metabolic Mechanisms

Conditions
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Hypertension, Pure Autonomic Failure

Intervention / Treatment
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* Drug: L-NMMA
* Drug: Trimethaphan


Participation Criteria
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Eligibility Criteria
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Inclusion Criteria: Adult subjects. 18 to 85 years. Non-smokers or long term smokers for specific aim 6. Drug-free. Long term hypertension in specific substudy 3, patients with autonomic failure in specific aims 4 and 5, diabetes mellitus in specific aim 5. Exclusion Criteria: Being on any medication other than antihypertensives (for hypertensives), autonomic medications (for autonomic failure [AF] patients), insulin or other treatment for diabetes (for diabetic patients). Having pulmonary, renal, hematopoietic, hepatic and/or cardiac disease.

Ages Eligible for Study
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Minimum Age: 18 Years
Maximum Age: 85 Years

Sexes Eligible for Study
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All

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

Allocation: Non-Randomized
Intervention Model: Parallel Assignment
Masking: Single


Arms and Interventions

| Participant Group/Arm | Intervention/Treatment |
| --- | --- |
| Experimental: Autonomic Failure Patients<br>To compare the effects of NO inhibition during intact and transient pharmacological blockade of the autonomic nervous system in Patients with Autonomic Failure. | Drug: L-NMMA<br>* IV infusion of 125, 250 and 500 mcg/Kg/min for 15 minutes each dose. The main outcome is the maximal increase in blood pressure produced at the end of the infusions or a maximal systolic blood pressure of 160 mm Hg. It could be achieved after the first dose or the third.<br>Drug: Trimethaphan<br>* IV infusion for the duration of the study at 4-6 mg/min depending on autonomic blockade. This is only to produce transient pharmacological blockade of the autonomic nervous system in order to allow the full expression of the inhibition of nitric oxide synthase. There is no direct outcome associated with this intervention.<br>|
| Experimental: Controls and hypertensives<br>To compare the effects of NO inhibition during intact and transient pharmacological blockade of the autonomic nervous system in normal volunteers and hypertensive subjects. | Drug: L-NMMA<br>* IV infusion of 125, 250 and 500 mcg/Kg/min for 15 minutes each dose. The main outcome is the maximal increase in blood pressure produced at the end of the infusions or a maximal systolic blood pressure of 160 mm Hg. It could be achieved after the first dose or the third.<br>Drug: Trimethaphan<br>* IV infusion for the duration of the study at 4-6 mg/min depending on autonomic blockade. This is only to produce transient pharmacological blockade of the autonomic nervous system in order to allow the full expression of the inhibition of nitric oxide synthase. There is no direct outcome associated with this intervention.<br>|

What is the study measuring?
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Primary Outcome Measures

| Outcome Measure | Measure Description | Time Frame |
| --- | --- | --- |
| Change in Systolic Blood Pressure | L-NMMA (nitric oxide synthase inhibitor) was infused intravenously at different doses for 15 minutes each, after blocking the autonomic nervous system with trimethaphan. The change in systolic blood pressure at the end of the highest tolerated dose is the main outcome. Trimethaphan infused intravenously was used to produce transient blockade of the autonomic nervous system to allow for a full response to nitric oxide inhibition (in the absence of the baroreflex. | At the end of the highest tolerated dose of IV infusion of L-NMMA | 
| Systolic Blood Pressure in Response to Systemic Nitric Oxide Inhibition | Systolic blood pressure at the highest tolerated dose of IV infusion of L-NMMA during autonomic nervous system blockade with trimethaphan. Trimethaphan, infused intravenously was used to produce transient blockade of the autonomic nervous system to allow for a full response to nitric oxide inhibition (in the absence of the baroreflex. | End of 15 minutes of infusion of L-NMMA at the highest tolerated dose | 

 Terms related to the study
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Keywords Provided by Centre Hospitalier Valida
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Autonomic Nervous System, Endothelial Nitric Oxide, L-NMMA, Trimethaphan, Nitric Oxide Inhibition