Sensitization of nociceptive C-fibers in zinc-deficient rats

A marked decrease in zinc concentration was observed in plasma (P < 0.001), hindpaw skin (P < 0.01), and dorsal skin (P < 0.01) in zinc-deficient rats (rats fed a zinc-deficient diet for 3 wk), compared with the control rats fed the same zinc-deficient diet supplemented with ZnCO3 (50 mg/kg diet). The threshold intensity needed to elicit vasodilatation in the hindpaw skin of the zinc-deficient rats on electrical stimulation of the saphenous nerve in a peripheral direction was markedly lower (P < 0.01) than that in the control rats. No difference was observed between control (n = 5) and zinc-deficient rats (n = 5) in the magnitude of the plasma extravasation evoked by either histamine or substance P. There was no difference between control and zinc-deficient rats in terms of the dose-response curve for release of histamine by substance P. Prostaglandin E2 (PGE2) concentration in the hindpaw skin of the zinc-deficient rats was nearly fourfold higher (P < 0.01) than that of the control rats, whereas no difference in the leukotriene B4 level in the hindpaw skin was observed between control and zinc-deficient rats. From the present study, it seems likely that an increased level of PGE2 in the vicinity of the nociceptive C-fiber terminals in the hindpaw skin of zinc-deficient rats may sensitize the terminals of the nociceptive C-fibers of the saphenous afferent nerve in the hindpaw and thus facilitate the production of antidromic vasodilatation.