Peripheral analgesia: mechanism of the analgesic action of aspirin-like drugs and opiate-antagonists.

1 Prostaglandins released by tissue injury sensitize nociceptors and produce hyperalgesia. 2 Aspirin-like drugs inhibit prostaglandins I2 and E2, synthesis, which explains their anti-algic effect. 3 The anti-algic effect of aspirin-like drugs in carrageenin-induced rat paw inflammation may involve a central component. 4 Prostaglandin E2-induced hyperalgesia, once established, is not relieved by systemically administered drugs. 5 Prostaglandin-induced hyperalgesia is possibly a cyclic adenosine, 3',5'-monophosphate C2+ dependent process. 6 Morphine, enkephalins, opiate antagonists and cyclic guanosine 3',5'-monophosphate have a peripheral analgesic effect in the prostaglandin hyperalgesia test. 7 Morphine may produce peripheral analgesia by inhibiting adenylatecyclase activity at the nociceptors.