Adenosine reduces secondary hyperalgesia in two human models of cutaneous inflammatory pain

Secondary hyperalgesia is characterized by increased sensitivity to noxious mechanical stimuli in the area surrounding injured skin. The pathophysiolo gical mechanisms involve increased excitability of second-order neurons loc ated in the spinal cord, i.e., central sensitization. The mechanisms behind this phenomenon may be of importance in clinical pain, including neuropath ic pain. To study the effects of systemic infusion of the endogenous compou nd adenosine (ADO) on sensory function, a superficial cutaneous burn injury was induced by the 4-min topical application of mustard oil or by heat (47 degrees C for 7 min) during N ADO infusion (60 mu g.kg(-1).min(-1)). Healt hy human subjects (n = 10 for each model) were tested, using a blinded, pla cebo-controlled procedure. The area of secondary hyperalgesia, as well as t actile and thermal sensory function, was tested using psychophysical method s during and after treatments. ADO significantly reduced the area of second ary hyperalgesia in both models. The maximal reduction compared with placeb o was 58% +/- 20% (heat burn) and 39% +/- 13% (mustard oil burn). No other differences in sensory function were observed. The results are interpreted as an ADO-induced modulatory effect on the mechanisms of central sensitizat ion. Implications: We tested the effects of adenosine on the development of increased sensitivity in the skin surrounding a superficial skin injury in humans. A superficial skin burn was induced with a chemical irritant or he at. The results show that adenosine reduces the skin area with increased se nsitivity surrounding the injury.