The source of thromboxane and prostaglandins in experimental inflammation

1 Although cyclo‐oxygenase products have been detected at inflammatory sites the tissue of origin remains uncertain. 2 Inflammatory exudates were collected from rats 4, 6, 8, 12 or 24 h after subcutaneous implantation of carrageenin‐impregnated sponges. 3 Concentrations of the cyclo‐oxygenase products prostaglandin E2 (PGE2), 6‐oxo‐PGF1α and thromboxane B2 (TXB2) in inflammatory exudates and serum (obtained from blood clotted at 37° C) were measured by specific radioimmunoassays. 4 TXB2 concentrations in exudates increased to about 100 ng ml−1 at 8 h but decreased to less than 20 ng ml−1 after 24 h. PGE2 concentrations increased from 4–12 h and remained between 80 and 120 ng ml−1 from 12–24 h. 6‐oxo‐PGF1α had the same time course as that of PGE2 but concentrations were approximately one third of PGE2 values. 5 TXB2 concentrations in serum from thrombocytopaenic rats were less than 5% of control values. Thrombocytopaenia did not affect TXB2, PGE2 or 6‐oxo‐PGF1α concentrations or total leukocyte numbers in inflammatory exudates. 6 Methotrexate‐induced neutropaenia did not affect serum TXB2 concentrations but cyclo‐oxygenase products (including TXB2) in 6 h inflammatory exudates were reduced by 60–95%. 7 Colchicine (1.0 mg kg−1 s.c.) prevented leukocyte accumulation in sponge exudates and this was accompanied by a reduction in TXB2, PGE2 and 6‐oxo‐PGF1α concentrations at 6 h. 8 These results indicate that platelets are the source of TXB2 in clotting blood but do not contribute to cyclo‐oxygenase activity in experimental inflammation. The results also suggest that migrating leukocytes are the major source of thromboxane and to a lesser degree prostaglandins in acute 6 h inflammatory exudates.