Production of prostacyclin in mice following intraperitoneal injection of acetic acid, phenylbenzoquinone and zymosan: Its role in the writhing response

Abstract

The magnitude and temporal production of PGI 2, PGE 2 and LTB 4 were measure in the mouse peritoneal cavity for a 15 min period following the intraperitoneal injection of either acetic acid, phenyl-p-benzoquinone (PBQ) or zymosan. For each algogenic substance, PGI 2 (assayed as the stable metabolite, 6-keto-PGE 1α) represented the major eicosanoid with lower levels of PGE 2 also detected. Zymosan induced the greatest 6-keto-PGF 1α production among the three algogenic agents, but only a weak writhing response was observed. LTB 4 was detected in the peritoneal lavage only after zymosan. The magnitude of eicosanoid production did not correlate with the writhing response induced by the algogenic agents, even though the inhibition of both 6-keto-PGF 1α and writhing by several peripheral analgesics was positively correlated. PGI 2, (100 ng), 6-keto-PGF 1α (1 μg) and PGE 2 (100 ng) did not induce writhing. However, only PGI 2 acted synergistically with acetic acid to produce writhing. Presumbly due to the short biological lifetime of PGI 2, this synergism was notes only when PGI 2 was administered after the acetic acid. These results suggest that PGI 2 acts to sensitize the animal for the writhing response.