The antinociceptive effects of prostaglandin antagonists in the rat

This study examined the antinociceptive effects of two prostaglandin antagonists, SC-25469 and SC-19220 in the rat. SC-25469 and SC-19220 inhibited acetic acid-induced writhing with ED 50 s of 6.9 and 6.8 mg/kg p.o., respectively. When compared to other analgesics, the rank order of potency in the writhing test was morphine > pentazocine = U-50,488 > SC-25469 = SC-19220 > ibuprofen > aspirin > acetaminophen. SC-25469 (150 and 300 mg/kg p.o.) and SC-19220 (50–300 mg/kg p.o.) also suppressed the behavioral response to s.c. injection of formalin, as did aspirin (50–150 mg/kg p.o.), ibuprofen (25–100 mg/kg p.o.) and acetaminophen (300 mg/kg p.o.). However, the suppression was not of the magnitude observed after administration of morphine (ED 50: 0.9 mg/kg s.c.), pentazocine (ED 50: 2.4 mg/kg s.c.) or U-50,488 (ED 50: 0.8 mg/kg s.c.). This study demonstrates the antinociceptive properties of prostaglandin antagonists in two distinct tests of nociception.