NEW YORK (Reuters Health) - Veterans with Gulf War syndrome appear to have subtle damage to the involuntary part of the nervous system, likely caused by low-level exposure to the chemical warfare agent sarin, according to a new study.

The findings tie together past research in both animals and humans on the syndrome, and neatly explain its symptoms, Dr. Robert Haley of the University of Texas Southwestern Medical Center in Dallas told Reuters Health. "This study is sort of the missing link," he said.

The parasympathetic nervous system works in balance with the sympathetic nervous system to control many body functions, from heart rate and blood pressure to digestion. While the sympathetic nervous system kicks in during emergencies, activating the "fight or flight" response, the parasympathetic nervous system is active during rest, digestion and other restorative activities.

During sleep, activity of the parasympathetic nervous system increases. But in Gulf War vets with the syndrome it does not activate properly, Haley and his colleagues report in the American Journal of Medicine.

Haley's team followed 19 healthy vets and 22 with Gulf War syndrome over a 24-hour period, measuring several indicators of nervous system function. While the healthy vets showed a normal increase in parasympathetic activity during sleep, resulting in a decline in heart rate, the ill vets did not. Sick vets' nighttime heart rates were, on average, eight beats per minute faster than those without the syndrome.

Symptoms of Gulf War syndrome include chronic diarrhea, night sweats, unrefreshing sleep, fatigue and sexual dysfunction, all of which could be caused by inadequate parasympathetic nervous system activation, Haley explained.

People with diabetes who have this type of nerve damage develop a similar constellation of symptoms, he added.

Studies in animals by Haley and his colleagues have shown that low-level sarin exposure injures the parasympathetic nervous system. Many vets were exposed to the nerve gas at low levels during the first Gulf War, the Department of Defense has confirmed, generally by Allied destruction of chemical weapons depots and ammo dumps.

Studies of the vets themselves have found that those with lower levels of paraoxonase, an enzyme that detoxifies sarin and similar nerve poisons, are much more likely to have Gulf War syndrome than those with high levels of the protective enzyme. And imaging studies of the brains of sick vets have shown areas of nerve damage within the basal ganglia, which control parasympathetic nervous system activity.

"The study clearly indicates consistent abnormal nighttime cardiac regulation in veterans who are ill," Dr. Philippe van de Borne of Erasme Hospital in Brussels, Belgium, writes in an accompanying editorial.

Haley and his colleagues are now working on a study to confirm the findings in a random sampling of Gulf War veterans.

SOURCE: American Journal of Medicine, October 1, 2004.

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