['Intramuscular (i.m.) administration of the central analgesics fentanyl and dipyrone, and also mediators of pain such as L-glutamate, CCK, ATP, phenylephine and analgesic mediator adenosine, slightly penetrating in CNS, in the minimum effective dose (MED) cause the maximal analgesic effect in the tail flick test in rats. MED of dipyrone and fentanyl are decreased 50-220-fold after combined i.m. administration of each analgesic with L-glutamate, CCK, adenosine, ATP and phenylephrine in threshold, independently noneffective doses. The intragastric administration of lidocaine and also subdiaphragmatic vagotomy completely eliminate analgesic effects of the above mentioned combinations.'] Do [ Peripheral acting mediators pain and analgesia potentiate the central analgesic action of fentanyl and dipyrone ]?