Influence of phenylbutazone on eicosanoid levels in equine acute inflammatory exudate

In a two part cross-over experiment, acute inflammatory exudates were induced in 7 ponies by subcutaneous implantation of 3 sterile carrageenin-soaked polyester sponge strips. Treatment comprised a single therapeutic geenin-soaked polyester sponge strips. Treatment comprised a single therapeutic dose of 4.4 mg/kg phenylbutazone (PBZ) administered intravenously at the time of sponge implantation. Exudates were harvested at 6, 12 and 24 hours and examined for leukocyte and erythrocyte numbers using the improved Neubauer technique; for eicosanoids by radioimmunoassay and by high performance liquid chromatography for concentrations of PBZ and its principal metabolite oxyphenbutazone. Plasma PBZ and oxyphenbutazone levels were measured in treated animals at 6, 12 and 24 hours. The administration of PBZ produced, at 6 hours, highly significant (P less than 0.001) reductions in exudate levels of prostaglandin E2 (PGE2) and 6-keto-PGF1 alpha (the stable breakdown product of prostacyclin, PGI2). Significant (P less than 0.01) reductions in these eicosanoids were maintained in treated animals at 12 and 24 hours. Levels of thromboxane B2 (TXB2), the catabolite of TXA2, were reduced in treated animals at 6 and 12 hours but these changes were not significant. Leukocyte numbers were significantly (P less than 0.001) increased from 6-hour values at 12 and 24 hours in both control and PBZ-treated animals but differences between control and treated ponies were not significant. This is the first report in ponies of eicosanoid inhibition following the administration of a non-steroid anti-inflammatory drug (NSAID). It is proposed that the model of inflammation used in this study might provide a means of assessing the efficacy and duration of action of NSAIDs in the horse.