Adenosine increases the cutaneous heat pain threshold in healthy volunteers

Adenosine is an endogenously produced substance which in animal experiments exerts anti-nociceptive effects. In humans, algesic effects have been presented following exogenous adenosine administration. A recent study on anaesthetized patients, however, suggested an anti-nociceptive effect during i.v. adenosine. We have studied the pain-reducing effect in healthy volunteers using adenosine 50-80 micrograms.kg-1.min-1 (n = 10), morphine 0.1 mg.kg-1 (n = 5), adenosine 50 micrograms.kg-1.min-1 + morphine 0.1 mg.kg-1 (n = 6), and ketamine 0.1 mg.kg-1 (n = 5); all drugs given i.v., single-blind. Quantitative sensory tests (QST) revealed a significantly increased cutaneous heat pain threshold following adenosine. No effect was seen following ketamine or morphine. Suprathreshold heat pain perception was unchanged in all subjects. Furthermore, warm and cold perception thresholds were not influenced significantly by any drug. Adenosine, morphine and ketamine produced well-known side-effects but of a mild intensity not necessitating any treatment. The present results show that i.v. adenosine can provide a modest but selective increase of cutaneous heat pain thresholds, suggesting a pain-reducing capacity of adenosine in humans.