Guanosine 3',5'-monophosphate: a central nervous system regulator of analgesia.

The dibutyryl derivative of guanosine 3',5'-monophosphate (cyclic GMP), administered centrally, totally abolishes response to noxious stimuli without depressing the central nervous system. Analgesic properties of the nucleotide are not reversed by naloxone. Microinjected intracerebrally into different sites, dibutyryl cyclic GMP does not mimic the action of morphine. Pharmacological effects of dibutyryl cyclic GMP suggest that endogenous cyclic GMP modulates an inhibitory pain pathway distinct from that on which morphine acts.