Existence of antiopiate systems as illustrated by MIF-1/Tyr-MIF-1

Evidence is presented that the small peptides MIF-1/Tyr-MIF-1 are part of an endogenous antiopiate system that may function to balance the opiate system. We review the biological activity, behavioral activity, and functional effects of this proposed opiate antagonist system. In addition, we suggest, based on antinociceptive mechanisms, that the individual components of the antiopiate system might function differently from naloxone.