Nitric oxide mediates the amplification by interleukin-1 beta of neurogenic vasodilatation in the rat skin.

Blood flow in the plantar hindpaw skin of anaesthetized rats was measured by laser Doppler flowmetry. Intraplantar injection of interleukin-1 beta (50 pg) significantly enhanced the hyperaemic response to intraplantar capsaicin (0.3 microgram). Pretreatment with a neurotoxic dose of capsaicin reduced the capsaicin-evoked hyperaemia and prevented the facilitatory effect of interleukin-1 beta. Blockade of nitric oxide formation by NG-nitro-L-arginine methyl ester failed to affect the capsaicin-evoked vasodilatation but abolished its amplification by interleukin-1 beta. These data indicate that the enhancement by interleukin-1 beta of the capsaicin-induced hyperaemia involves thin afferent nerve fibres and depends on nitric oxide as essential intermediate.