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In 45 consecutive patients with chronic pain syndromes endorphins, fraction I of the cerebrospinal fluid and pain measures by means of electric stimulation via saline electrodes were investigated. In patients with high levels of fraction I (above median) pain threshold, PT and tolerance level, TL, in condition C (continuous stimulation increase) were found to be significantly higher than in patients with low levels of fraction I (below median). The results indicate that the endorphins are one of the physiological factors that contribute to the pain threshold and the tolerance level.
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Knorring et al. (1978) studied this question.
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