Endotoxin-induced production of thromboxane and prostacyclin by equine peritoneal macrophages

Equine peritoneal macrophages were isolated and cultured in vitro to assess their ability to produce thromboxane (TxA2) and prostacyclin (PGI2) in response to endotoxin. Peritoneal macrophages (2.5 x 10(6)/ml) were incubated in tissue culture media, containing 1) no additive (nonstimulated control), 2) endotoxin (0.5 to 100 ng/ml) or 3) the calcium ionophore, A23187 (0.95 microM) for two and six h. Concentrations of the stable metabolites of TxA2 and PGI2 thromboxane B2 (TxB2) and 6-keto-prostaglandin F1 alpha (6-keto-PGF1 alpha), in the incubation media were determined by radioimmunoassay. The concentrations of both metabolites increased from two to six h incubation. Endotoxin increased the production of TxA2 and PGI2 over the nonstimulated control values at both two and six h and endotoxin-induced concentrations of 6-keto-PGF1 alpha were higher at six than at two h. The response of macrophages to A23187 was similar to endotoxin. Mean eicosanoid concentrations did not differ among the range of endotoxin concentrations at either time; however there was significant curvilinear regression between endotoxin concentration and TxB2 at both times, and between endotoxin and 6-keto-PGF1 alpha at two h. The results indicate that equine macrophages may be a significant source of TxA2 and PGI2 during endotoxemia.