Central pyrogenic activity of muramyl dipeptide.

Fever can be elicited in the rabbit by the intravenous administration of relatively large doses of a synthetic immunoadjuvant, N-acetylmuramyl-L-alanyl-D-isoglutamine, or muramyl dipeptide (MDP). This response could be mediated by endogenous pyrogen because MDP has been shown to induce their production both in vivo and in vitro. The results reported here show that intracisternal injection of minute amounts of MDP could elevate fever without activating the release of endogenous pyrogen in the plasma or in the cerebrospinal fluid. Moreover, indomethacin inhibited hyperthermia produced by intracerebroventricular administration of MDP. Therefore, our findings argue in favor of a direct effect of the glycopeptide on the thermoregulatory centers besides its indirect effect through the production of leukocytic pyrogen. This molecule apparently represents the minimal requirement for the pyrogenicity of bacterial peptidoglycan because administration, even by the intracerebral route, of a mixture of muramic acid and of its dipeptide moiety did not elicit fever.