Arachidonic acid metabolites in carrageenin-induced equine inflammatory exudate

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Abstract
The presence of cyclooxygenase products of arachidonic acid metabolism in carrageenan-induced inflammatory exudate was investigated in ponies using 2 models. In the 1st, an inflammatory response was stimulated by injecting carrageenan into s.c. implanted polypropylene tissue cages and exudates were collected at 5 predetermined times between 3 and 48 h. In the 2nd model, exudates were harvested at 6, 12 and 24 h from carrageenan-impreganted polyester sponges which had also been inserted beneath the skin. Prostaglandin (PG) E2, thromboxane (TX) B2 and the stable breakdown-product of prostacyclin (PGI2), 6-keto-PGF1.alpha., in exudates were measured by radioimmunoassay (RIA); PGE2-like and PGF2.alpha.-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 PGE2 concentration reached 197 ng/ml at 12 h decreasing to < 12 ng/ml at 24 h. Mean TXB2 and 6-keto-PGF1.alpha. levels were highest at 48 h (22.3 and 34.2 ng/ml, respectively) after considerable fluctuations and with wide standard errors prior to this time. In the sponge model, PGE2 levels were surprisingly low for each group (mean 12.8 ng/ml at 12 h) and TXB2 and 6-keto-PGF1.alpha. were similarly lower (means of 3.3 and 8.1 ng/ml, respectively, at 12 h). Mean total leukocyte counts and total protein concentrations were increased in both models after carrageenan stimulus. PGF2.alpha. was not detected in measurable quantities in any exudate. PGE2, TXB2 and PGI2 could be regarded as possible mediators of acute inflammatory reactions to carrageenan in ponies.