Arachidonic acid metabolites in carrageenin‐induced equine inflammatory exudate

The presence of cyclooxygenase products of arachidonic acid metabolism in carrageenin‐induced inflammatory exudate was investigated in ponies using two models. In the first model, an inflammatory response was stimulated by injecting carrageenin into subcutaneously implanted polypropylene tissue cages and exudates were collected at five predetermined times between 3 and 48 h. In the second model, exudates were harvested at 6, 12 and 24 h from carrageenin‐impregnated polyester sponges which had also been inserted beneath the skin. Prostaglandin (PG) E 2 , thromboxane (TX) B 2 and the stable breakdown‐product of prostacyclin (PGI 2 ), 6‐keto‐PGF1α, in exudates were measured by radioimmunoassay (RIA); PGE 2 ‐like and PGF 2α ‐like activities were bioassayed following an acid‐lipid extraction technique which provided a recovery rate of 78%. Agreement between RIA and bioassay was within acceptable limits. In Model 1, using RIA, mean PGE 2 concentration reached 197 ng‐ml ‐1 at 12 h decreasing to < 12 ng‐ml ‐1 at 24 h. Mean TXB 2 and 6‐keto‐PGF1α levels were highest at 48 h (22.3 and 34.2 ng‐ml ‐1 , respectively) after considerable fluctuations and with wide standard errors prior to this time. In the sponge model, however, PGE 2 levels were surprisingly low for each group (mean 12.8 ng‐ml ‐1 at 12 h) and TXB 2 and 6‐keto‐PGF 1α were similarly lower (means of 3.3 and 8.1 ng‐ml ‐1 respectively at 12 h). Mean total leucocyte counts and total protein concentrations were increased in both models after carrageenin stimulus. PGF 2α was not detected in measurable quantities in any exudate. It is concluded that PGE 2 , TXB 2 and PGI 2 could be regarded as possible mediators of acute inflammatory reactions to carrageenin in ponies.