By Richard N. Podell, M.D.
Renewed interest in the neurotransmitter nitric oxide has researchers looking at its precursor, L-arginine, for treating certain kinds of heart disease. Once thought to be only a dangerous environmental pollutant and a poison, we now know nitric oxide is made in the body and it plays numerous roles including brain activity regulation and circulation control.
Administering nitric oxide for vasodilation has been a common practice for a long time but has only recently been understood. In World War I, doctors noticed that workers in ammunition factories who were packing shells with nitroglycerin had very low blood pressures. The observation eventually led to the development of a nitroglycerin pill for the rapid relief of angina–that is, exercise-induced chest pain caused by oxygen deficiency in the heart. In 1987 nitric oxide was determined to be the relaxant factor released by endothelial cells, explaining how nitroglycerin tablets help angina sufferers.
The body creates nitric oxide from the amino acid L-arginine, leading some to suggest arginine may also help those with angina. That said, people must understand the complexities of nitric oxide so they don’t cause harm by selfdosing with arginine. Whether to take arginine should be decided With a medical professional.
To test arginine’s potential, Polish physicians conducted a double-blind study involving 22 people with stable angina. Each subject took an exercise stress test, which was discontinued when changes on the electrocardiogram (EKG) indicated metabolic heart muscle strain. For three days half the group received placebo while the others took 1 g L-arginine twice daily. Participants then repeated the test.
Patients in the placebo group increased their exercise time by about one minute on the second test compared to the first (555 vs. 501 seconds). The arginine patients increased their time by nearly three minutes (from 531 to 700 seconds). After the sec- ond test, EKG abnormalities were significantly less in the arginine group, even though they exercised longer.
It appears that in the short term arginine improves the exercise capacity of patients a, with stable angina. How? Because nitric oxide, synthe- sized from L-arginine, helps arterial blood vessels relax, permitting improved blood flow to the heart.2 Defective nitric oxide metabolism may be one reason people with heart disease commonly have impaired blood-vessel relaxation.3
So should patients with angina ask for L-arginine? Not necessarily and not yet. The study showing benefit for angina patients needs to be duplicated and extended for longer treatment periods before we can confidently apply its results.
Appreciating the Oxidative Effect
Both inherent and supplemental nitric oxide have intricate actions in the body, which can sometimes complicate illness. For example, high natural or induced levels of nitric oxide potentially can cause damage by increasing free radical generation (oxidative stress)4 and by promoting inflammation. Nitric oxide molecules might be among those that stimulate oxidative stress in a heart attack, so elevated levels may worsen the prognosis for this condition. As a result, patients with congestive heart failure might respond better when their nitric oxide levels are lowered rather than raised.5
Clearly arginine and nitric oxide are not inert in human biochemistry. For one thing, their metabolism is intimately connected to the body’s oxidative-str