Zinc reduces the hyperalgesia and upregulation of NGF and IL-1 beta produced by peripheral inflammation in the rat.

The effect of systemic zinc administration on the inflammatory hyperalgesia induced by intraplantar injections of either complete Freund's adjuvant (CFA) or bacterial endotoxin/lipopolysaccharide (LPS) in a hindpaw of adult rats was investigated. CFA injection resulted in mechanical and thermal hyperalgesia and an elevation in the levels of interleukin-1 beta (IL-1 beta) and nerve growth factor (NGF) in the ipsilateral hindpaw. Zinc treatment (20 nmole) significantly reduced sensitivity in the early phase of the inflammation and diminished the increase in the levels of IL-1 beta and NGF without affecting paw swelling. Intraplantar LPS injection also produced mechanical hyperalgesia and this too was reduced by zinc administration in a dose-dependent fashion (0.1-20 nmoles). Our results indicate that zinc has an analgesic action during early inflammation and that this may be the consequence of reducing levels of the inflammatory cytokine IL-beta and the growth factor NGF.