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... But quenched by ubiquitous hormone.

Melatonin -- secreted by the brain's pineal gland, but only at night -- has been called the chemical expression of darkness. For years, scientists have puzzled over the primary role of this hormone. New research now indicates that this brain secretion may have played an important evolutionary role by helping many of the world's life forms, from algae to humans, survive the potentially dangerous oxygen-rich environment in which they developed.

Of the many oxidants to which our cells are exposed, the most potent tend to be free radicals -- molecules or molecular fragments that contain an unpaired electron. And among free radicals, hydroxyl (OH) is the most damaging, observes Russel J. Reiter of the University of Texas Health Science Center at San Antonio. So, "if you have but one free radical to scavenge, make sure it's the hydroxyl radical," he says. Reiter and his co-workers have now demonstrated that melatonin does just that.

The researchers gave rats safrole, a carcinogen that damages DNA by generating hydroxyl and other oxygen-based free radicals. They found that rats treated with melatonin prior to the safrole sustained 41 to 99 percent less DNA damage than untreated rodents. The amount of damage depended on the amount of extra melatonin each rat received, they report in the June Cancer Letters.

The doses needed to protect the rats from safrole were small and nontoxic -- 0.2 to 0.4 milligram of melatonin per kilogram of body weight. Moreover, says Reiter, the team's subsequent research indicates that melatonin also fights the hydroxyl radical in another way: by neutralizing its precursor molecule.

These findings suggest that melatonin, which can cross all barriers to enter every cell, "is the best free-radical scavenger known," Reiter contends. As such, it might hold promise in treating a number of disorders involving free-radical damage, such as Parkinson's and Alzheimer's disease, he says.
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Title Annotation:brain secretion protects oxygen damage to tissues
Publication:Science News
Article Type:Brief Article
Date:Aug 14, 1993
Words:305
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