[Potentiating action of bi- and trivalent metal salts on the analgesic effect of morphine].

It has been found that the metal salts MnCl2, NiCl2, GdCl3 and LaCl3 in doses up to 30, 20, 5 and 10 micrograms, respectively, potentiate the analgesic effect of intracisternally injected morphine (2 micrograms per mouse). The ability of the metal salts to potentiate the affinity of opiate ligands to the appropriate receptors is effectuated via interaction of metal cation with the specific opiate receptor site. It is suggested that one of the possible mechanisms of the potentiating effect of some metal salts on the morphine-induced analgesia involves the enhancement of morphine affinity for mu-receptors in the brain.