The Use of Changes in Capillary Permeability in Mice to Distinguish Between Narcotic and Nonnarcotic Analgesics

An extension of the "squirming test" is described which makes the method specific for nonnarcotic analgesics. The intraperitoneal injection of acetic acid causes squirming and an increase in capillary permeability that is measured by direct estimation of plasma-bound dye (Pontamine Sky Blue) which has leaked into the peritoneal cavity. Nonnarcotic analgesics inhibit squirming and leakage of dye. Values for the oral ED50s for both effects are given for a number of typical compounds. Narcotic analgesics, in doses that produce analgesia, inhibit squirming but do not significantly affect leakage of dye. Drugs that stimulate the central nervous system and also inhibit squirming have no significant effect on leakage of dye over the range of doses which inhibit squirming. Corticosteroids do not significantly inhibit either squirming or leakage of dye.