ANALGESIA BY DIRECT ANTAGONISM OF NOCICEPTOR SENSITIZATION INVOLVES THE ARGININE-NITRIC OXIDE-CGMP PATHWAY

We tested the hypothesis that activation of the nitric oxide (NO)-cGMP pathway is involved in the mechanism of two directly acting non-opiate peripheral analgesics, myrcene and dipyrone, using our modification of the Randall-Selitto test. The NO inhibitor, N(G)-monomethyl-L-arginine (50-mu-g/paw) and methylene blue (500-mu-g/paw) abolished the analgesic effect of dipyrone and myrcene. Dibutyryl cyclic adenosine monophosphate (DbcAMP) caused a dose-dependent hyperalgesia (20, 50 and 100-mu-g/paw). Only responses to low doses of DbcAMP were inhibited by the two analgesics. Pretreatment with MY5445 (50-mu-g/paw) resulted in potentiation of the effects of both analgesics. These results support our hypothesis that the sensitivity of nociceptors may be controlled by the balance between the levels of cAMP and cGMP. Stimulation of the NO-cGMP pathway is probably the common denominator for the mode of action of peripheral analgesics which block hyperalgesia directly.