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Exercise Levels Of Phenylethylamine May Damp Depression

Antidepressant effects of exercise appear to be due to heightened levels of phenylethylamine.

"Considering the structural and pharmacological analogy between amphetamines and phenylethylamine, it is conceivable that phenylethylamine plays a role in the commonly reported 'runners high', thought to be linked to cerebral â-endorphin activity," declares Dr Ellen Billet and colleagues at the Department of Life Sciences, Nottingham Trent University, Nottingham, England.

Researchers point out that there is a consensus that physical activity has antidepressant effects. "Indeed, doctors widely recommend exercise either as treatment for mild depression or as complementary treatment to drug and/or psychotherapy in cases of more severe depression."

Mode of action of the effect from exercise, however, remains unclear. Phenylethylamine is an endogenous neuro-amine that has been linked to the regulation of physical energy, mood, and attention. Monoamine oxidase B selectively metabolises phenylethylamine to phenylacetic acid. There is evidence that phenylethylamine and phenylacetic acid levels are very low in the biological fluids of depressed patients.

Studies on urinary excretion of phenylacetic acid have shown that about 60 percent of unipolar and bipolar patients have lower than normal levels. Administration of phenylethylamine or its precursor L-phenylalanine, in conjunction with selegiline, a selective monoamine oxidase B inhibitor, has been reported to alleviate depression and to produce improvements in mood. The effects are sustained and also apparent in some patients who are insensitive to conventional treatment.

In their study, Dr Billet and colleagues enrolled 20 healthy young men, average age 22, who performed four hours of moderate to hard exercise every week. They stopped exercise completely for a day and their urine samples were measured for phenylacetic acid levels.

On the following day, the men exercised on a treadmill at 70 percent of their maximal heart rate capacity, a level thought to be capable of changing mood. The men assessed the effect of the exercise on them and further urine sample was taken.

The results showed that, overall, phenylacetic acid increased by 77 percent after exercise. However, there were considerable variations-- between 14 and 572 percent higher than it had been the day before in 18 of the 20 men. Three men rated the exercise as hard, and the highest rises were seen in two of these men.

Dr Billet and colleagues said: "These results show substantial increases in urinary phenylacetic acid levels 24 hours after moderate to high intensity aerobic exercise. As phenylacetic acid reflects phenylethylamine levels and the latter has antidepressant effects, the antidepressant effects of exercise appear to be linked to increased phenylethylamine concentrations."

Researchers conclude that "many factors may mediate phenylacetic acid responses to exercise, possibly including perceived and/or actual exercise intensity. Determination of these factors remains the object of future inquiries."
British Journal of Sports Medicine 2001; 35: 342-3]

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