Somnogenic muramyl peptides.

Sleep-promoting materials isolated from human urine and rabbit brain are muramyl peptides (MPs). The most active component of the urinary material is N-acetylglucosaminyl-1,6-anhydro-N-acetylmuramyl-Ala-Glu-diaminopimel yl-Ala; 1 pmol, infused into a lateral cerebral ventricle of rabbits, induced excess slow-wave sleep (SWS) for several hours. MP-induced sleep is normal in that it is similar to the deep sleep that follows sleep deprivation. Other biological actions of MPs (e.g., pyrogenicity and immunomodulatory activity) could be dissociated, but only in part, from somnogenic actions. Interleukin 1, a substance thought to mediate many MP activities, is somnogenic, and thus may be involved in MP-induced sleep. That MPs and other immunologically active substances can greatly enhance SWS suggests that some immunological mechanisms integrate sleep in their actions.