The use of the writhing test in mice for screening different types of analgesics.

The prostaglandin synthesis inhibitors studied were highly potent analgesics against ATP and ACh-induced writhing, but slightly effective or ineffective against MgSO4-induced pain. Morphine also proved to be more effective against ATP and ACh than against MgSO4-induced writhing. ATP and ACh-induced writhing syndrome could be inhibited by the prostaglandin receptor antagonist- Sc-19220. However, Sc-19220 failed to inhibit writhing elicited by MgSO4. The concentration of malondialdehyde was significantly higher in the peritoneal fluid following intraperitoneal injection of ATP and ACh, but was unaltered when MgSO4 was applied as a challenge substance. These results suggest that the prostaglandin system might be involved in the ATP- and ACh- but not in MgSO4-induced pain reaction.