CATECHOLAMINE-INDUCED MECHANICAL SENSITIZATION OF CUTANEOUS NOCICEPTORS IN THE RAT

C-Fiber mechanoheat (C-MH) nociceptors from the saphenous nerve were s tudied, in control rats and in rats that underwent surgical sympathect omy. Intradermal injection, alone, of either norepinephrine (NE) or th e calcium ionophore, A23187, did not affect mechanical threshold. The combination of A23187 and NE, however, significantly decreased mechani cal threshold. In the presence of the alpha(2)-adrenergic antagonist, yohimbine, or the cyclooxygenase inhibitor, indomethacin, C-MHs were n ot sensitized by the combination of NE + A23187. One week after surgic al sympathectomy, the number of C-MHs sensitized by NE + A23187 was si gnificantly reduced. In summary, NE appears to sensitize nociceptors i ndirectly. These data are compatible with the suggestion that a sympat hetic postganglionic neuron-dependent release of prostaglandins mediat es the sensitization. NE appears to act at an alpha(2)-adrenergic rece ptor, only in the presence of an increased intracellular Ca2+.