EFFECTS OF OXYGEN RADICALS ON NOCICEPTIVE AFFERENTS IN THE RAT SKIN IN-VITRO

On the premises of clinical studies, a possible contribution of oxygen radicals has been considered to the development of inflammatory pain and hyperalgesia. In a rat skin-saphenous nerve preparation using stan dard teased-fiber techniques (n = 57) hydrogen peroxide (1 mM, 10 mM a nd 50 mM) was applied in aqueous solution to cutaneous nerve endings o f unmyelinated nociceptive afferents. Superoxide anion and hydroxyl ra dical were secondarily generated as reaction products from pyrogallol (1 and 10 mM) and from Fe-EDTA (1 mM) in hydrogen peroxide, respective ly. None of these substances, except exceptionally, induced ongoing ac tivity nor nociceptor sensitization to heat and mechanical stimuli. If occasionally there was a weak excitatory effect, the fibers were left with a profound desensitization to adequate stimulation. The addition of hydrogen peroxide did not enhance sustained responses to solutions of high proton concentration (pH 6.1). Responses to combined inflamma tory mediators (bradykinin, serotonin, histamine and prostaglandin E(2 ), 10 mu M) were increased, on average, when hydrogen peroxide was add ed but this effect did just not reach significance. These findings sug gest that oxygen radicals do not play a major and specific role in noc iceptor sensitization.