Anxiety and pain: epinephrine-induced hyperalgesia and attentional influences

The role of peripheral epinephrine in the influence of anxiety on pain was investigated by intravenously infusing epinephrine and placebo in three increasing doses. The effect of epinephrine was measured within subjects on several subjective and autonomic measures: subjective pain, skin conductance response, heart rate response due to electrical stimulation, threshold for heat pain and threshold for pressure pain. Heat pain threshold was measured both on normal skin and on skin sensitized with capsaicin, since there is evidence that effects of sympathetic stimulation are only to be found in damaged or sensitized skin. Epinephrine caused a slight increase in subjective pain due to electrical stimulation and a decrease in heat pain threshold, which was larger on capsaicin-treated than on normal skin. However, heart rate response due to electrical stimulation and pressure pain threshold were not significantly influenced, while skin conductance response was even inhibited by epinephrine. Attentional focus, which was manipulated within electrical stimulation, seemed to have a much stronger influence on pain responses than pharmacological manipulation, independent of epinephrine. It may be speculated that, although evidence was found for effects of epinephrine on pain, they may be overruled by effects of attention.