Prostaglandin E2, cyclic adenosine monophosphate and morphine analgesia.

Intravenous administration of prostaglandin E2 (PGE2) to mice results in a significant distribution of PGE2 into the brain and an elevation of cyclic adenosine monophosphate (cAMP) in the midhindbrain and corpus striatum. Neither acute morphine administration nor morphine tolerance alters this response. Morphine alone also elevates cAMP levels. Although these elevations are blocked by the narcotic antagonist, naloxone, they only occur at supra-analgesic doses. Therefore morphine analgesia does not correlate with either elevation of cAMP levels of antagonism of PGE2-induced elevations of cAMP.