Effect of systemic adenosine on pain and secondary hyperalgesia associatedwith the heat/capsaicin sensitization model in healthy volunteers

Background and objectives: Adenosine is an endogenous compound that may hav e analgesic effects. Results from clinical trials are not consistent, howev er, and there is a need for large-scale, randomized, placebo-controlled stu dies to clarify the role of adenosine in the treatment of pain states, incl uding acute nociceptive pain and pain involving central sensitization. Methods: The analgesic and antihyperalgesic effect of systemic adenosine on the heat/capsaicin sensitization model of experimental pain was investigat ed in 25 healthy human volunteers. Sensitization was produced by heating th e skin to 45 degreesC for 5 minutes, followed by a 30-minute application of 0.075% capsaicin cream, and maintained by periodically reheating the sensi tized skin to 40 degreesC for 5 minutes at 40-minute intervals. Subjects re ceived intravenous adenosine 60 mug/kg/min or saline for 85 minutes. Areas of secondary hyperalgesia to von Frey hair and brush stimulation, heat-pain detection thresholds (HPDTs) in normal and sensitized skin, and painfulnes s of stimulation with 45 degreesC for 1 minute (LTS) in normal skin were qu antified before, during, and after study drug infusion. Results: Systemic adenosine had no effect on the area of secondary hyperalg esia to von Frey hair or brush stimulation, HPDT in normal or sensitized sk in, or painfulness of LTS in normal skin. Conclusion: We conclude that adenosine has no effect on acute nociceptive p ain induced by heat stimulation or on secondary hyperalgesia induced by hea t/capsaicin sensitization in healthy volunteers.