Nitric oxide gas is important in regulating blood vessel dilation, and consequently, blood
flow. This gas is continuously produced by endothelial cells, which line the blood vessels.
This study will examine whether nitrite, a molecule that normally circulates in the blood
stream, can also dilate blood vessels. The results of this study may be valuable in
developing treatments for people with conditions associated with impaired endothelial
production of nitric oxide, including high blood pressure, high blood cholesterol, diabetes,
estrogen deficiency, and others.
Healthy, non-smoking normal volunteers 21 years of age or older may be eligible for this
study. People who lack the enzyme G6PD or cytochrome B5 in their red blood cells may not
participate. Absence of these enzymes can lead to episodes of sudden shortness of breath and
cyanosis (blueness of the skin due to lack of sufficient oxygen). Participants will undergo
the procedures described in study Parts A and B, as follows:
- Part A - After numbing the skin, small tubes are placed in the artery and vein at the
inside of the elbow of the dominant arm (right- or left-handed) and a small tube is
placed in a vein of the other arm. The tubes are used for infusing saline (salt water)
and for drawing blood samples. A pressure cuff is placed around the upper part of the
dominant arm, and a rubber band device called a strain gauge is also placed around the
arm to measure blood flow. When the cuff is inflated, blood flows into the arm,
stretching the strain gauge at a rate proportional to the flow. Grip-strength of the
dominant arm is measured with a dynamometer to determine maximum grip-strength. Then,
several measurements of blood flow, nitrite, hemoglobin, and handgrip are made before
and after administration of L-NMMA, a drug that blocks endothelial production of
- Part B - Part A testing is repeated, except that sodium nitrite dissolved in a saline
solution is infused into the artery of the forearm for a few minutes before and during
the hand-grip exercises. In addition, blood samples are drawn before and after each
handgrip exercise to measure methemoglobin, a substance that, at excessive levels, can
cause adverse side effects.
Nitric oxide (NO) is a soluble gas continuously synthesized by the endothelium and
contributes importantly to vasodilator tone of the coronary and systemic circulations by
activating guanylyl cyclase in vascular smooth muscle, causing relaxation. Although
regional synthesis of NO by the endothelium contributes to local vasodilator tone, we have
shown previously that NO may be transported in blood, and have biological effects at a
distance from the site of entry into the circulation. Thus, we found that NO may be
transported bound to heme iron in red blood cells and released at vascular sites of
deficient NO synthesis, restoring vasodilator tone. Another potential source of bioactive
NO is via nitrite, formed by the auto-oxidation of NO. This study is designed to determine
the contribution of nitrite transported in blood to forearm microvascular dilator tone in
healthy subjects at rest and during regional hypoxia associated with forearm exercise
stress, with measurements made before and after regional blockade of endothelial NO
synthesis. Findings in this study may be relevant to understanding the physiological
contribution and therapeutic potential of nitrite in the regulation of vasodilator tone in
diseases and conditions associated with regional endothelial dysfunction and reduced
endothelial NO bioactivity (e.g., hypertension, diabetes mellitus, hypercholesterolemia,
cigarette smoking, estrogen deficiency).
All volunteer subjects must be at least 21 years of age in good health and have provided
informed, written consent for participation in this study.
Subjects with a history or evidence of present or past hypertension (blood pressure
greater than 145/95 mmHg), hypercholesterolemia (LDL cholesterol greater than 130 mg/dL),
diabetes mellitus (fasting blood glucose greater than 130 mg/dL), smoking within two
years, cardiovascular disease, peripheral vascular disease, coagulopathy, or any other
disease predisposing to vasculitis or Raynaud's phenomenon.
All subjects will be tested for red blood cell G6PD deficiency; levels below the lower
limits of normal will result in exclusion from participation in the study.
Subjects with a known cytochrome B5 deficiency will not participate in this study.
Subjects with a history of reaction to a medication or other substance characterized by
dyspnea and cyanosis will not participate in this study.
Subjects with a baseline methemoglobin level greater than 1% will not receive nitrite
Lactating and pregnant females.
No volunteer subject will be allowed to take any medication (oral contraceptive agents are
allowed), vitamin supplements, herbal preparations, nutriceuticals or other 'alternative
therapies' for at least one month prior to study and will not be allowed to take aspirin
for one week prior to study.