RESUMO
BACKGROUND: Clinical studies have shown opioid-sparing effects of ß-adrenergic antagonists perioperatively and ß-blockers are being investigated for chronic musculoskeletal pain. However, the direct analgesic effects of ß-blockers have rarely been examined in healthy humans. METHODS: In a randomized, counter-balanced, double-blind, within-subject crossover design, we tested the effect of the lipophilic ß-blocker propranolol (0.035 mg/kg body weight i.v.) on heat pain sensitivity in 39 healthy males, compared with placebo. To test for peripheral versus central effects, the peripherally acting ß-blocker sotalol was also examined. Experimental stimuli were brief superficial noxious heat stimuli applied to the volar forearm. Non-painful cold stimuli were included to test for specificity. Sedation, mood and anxiety were assessed to investigate potential mechanisms underlying any analgesic effect. ß-blocker effects on blood pressure were incorporated into the analysis because of a known inverse relationship between pain sensitivity and systolic blood pressure. RESULTS: Propranolol significantly decreased perceived intensity of heat pain stimuli but only in participants with small propranolol-induced blood pressure decreases. Even in this group, the effect was small (4%). Propranolol did not influence perceived intensity of non-noxious stimuli and had no effect on sedation, anxiety or mood. Sotalol did not influence heat pain sensitivity. CONCLUSIONS: Propranolol decreased pain sensitivity but its analgesic effects were small and counteracted by blood pressure decreases. The analgesic effects were not mediated by peripheral ß-receptor blockade, sedation, mood or anxiety. The small effect indicates that the utility of ß-blockers for clinical pain must be related to factors that do not play a significant role for experimental pain.
