Central neurogenic antiinflammatory action of alpha-MSH: modulation of peripheral inflammation induced by cytokines and other mediators of inflammation.

The neuropeptide alpha-melanocyte-stimulating hormone (alpha-MSH) has potent antipyretic and antiinflammatory properties. When administered systemically, the naturally occurring molecule and its COOH-terminal tripeptide sequence inhibit inflammation induced by peripherally applied irritants and intradermal injections of mediators of inflammation such as interleukin-1 (IL-1), interleukin-6 (IL-6), and tumor necrosis factor-alpha (TNF alpha). We recently found that alpha-MSH can act solely within the brain to inhibit inflammation caused by a general irritant applied to the skin. This activity appears to be shared with salicylate drugs and the combined observations suggest the existence of descending neurogenic antiinflammatory signals capable of modulating inflammation in peripheral tissues. To improve our knowledge of the scope of this action of the peptide, alpha-MSH was injected into the cerebral ventricles (i.c.v.) of mice that had received intradermal injections in the ear of mediators of inflammation: IL-1 beta, IL-8, leukotriene B4, and platelet-activating factor. The centrally administered peptide inhibited the actions of all of these proinflammatory agents as determined from comparisons with measures of ear edema over time in control animals; this indicates that the central peptide can alter inflammation induced in the periphery by major mediators of inflammation. In tests confined to IL-1 beta, central administration of alpha-MSH(11-13) was also effective. These findings support the concept of a descending neurogenic antiinflammatory influence promoted by an action of alpha-MSH within the brain, an inhibitory influence that is not restricted to modulation of just one or a limited set of the mediators of inflammation.