Response of plasma beta-endorphins to transcutaneous electrical nerve stimulation in healthy subjects

A study of 31 healthy volunteers was done to test the hypothesis that analgesia produced by low frequency/high intensity (LoF/Hil) transcutaneous electrical nerve stimulation (TENS) is mediated by release of beta-endorphin (beta-E). After randomization, Group 1 (n = 10) received no stimulation (placebo); Group 2 (n = 9) received 30 minutes of high frequency/low intensity (HiF/Lol) TENS; and Group 3 (n = 12) received 30 minutes of low frequency/high density (LoF/Hil) TENS. Blood pressure, pulse, plasma beta-E levels, and evoked potential response were measured before and after treatment. Mean plasma beta-E increased with treatment in Groups 2 and 3 and fell in Group 1, but the difference between the groups was not statistically significant. Sixty-seven percent of Groups 2 and 3 showed an increase in plasma beta-E levels compared with 30 percent in Group 1 (two-sample test of proportions, p less than .05). Evoked potential response, a measure of pain threshold, varied directly with plasma beta-E level independent of the type of treatment applied. This study did not demonstrate a difference between the effects of HiF/Lol versus Lof/Hil TENS on plasma beta-E in healthy subjects.