Exaggeration of blood pressure-related hypoalgesia and reduction of blood pressure with low frequency transcutaneous electrical nerve stimulation.

Reduced pain perception has been observed in hypertensive individuals and normotensive individuals at risk for high blood pressure and may involve increased endogenous opioid release or receptor sensitivity. The present study examined the issue by administering two subjectively similar but physiologically different forms of the pain-reducing procedure transcutaneous electrical nerve stimulation (TENS). Men varying in resting blood pressure and parental history of hypertension participated in three testing sessions during which was presented (a) high-frequency (100 Hz) TENS; (b) low-frequency (2 Hz) TENS, the type believed to elicit endogenous opioid activity; or (c) no-TENS stimulation. Measurements of blood pressure (BP) and other physiological variables were obtained during this period. Afterwards, two pain stimuli were presented: a series of electric shocks and 5 min of arm ischemia. There was a significant negative association between pain and resting systolic blood pressure (SBP), and pain and parental history of hypertension in the no-TENS and high-frequency TENS conditions that was significantly strengthened by administration of low-frequency TENS. As well, low-frequency TENS produced a modest but significant acute reduction in SBP, especially among those with higher resting levels. These results provide further evidence that opioid mechanisms are involved in blood pressure-related hypoalgesia and blood pressure regulation.