Radioimmunoassay of thromboxane B2 in horse plasma.

A radioimmunoassay for thromboxane B2 (TXB2) in unextracted horse plasma was evaluated. Sensitivity of the assay was 14.0 (SD 5.6) pg ml-1 of plasma. Interassay and intra-assay variation were 21.3 per cent and 4.3 per cent, respectively. The percentage of tracer bound in unextracted plasma in the absence of TXB2 was often higher than that in buffer. Therefore standard curves were obtained using standards diluted in plasma from horses treated with aspirin or in charcoal treated TXB2-free plasma. Standard curves determined in plasma and buffer were parallel. This assay was used to determine the half-life of exogenous TXB2 in horses. The mean value of 20.7 minutes (n = 3) is similar to that determined in other species. Storage of plasma samples at -20 degrees C for four months was found to alter the TXB2 levels in an unpredictable manner. Mean recovery was 102.4 per cent (SD 44.1). Effect of variability in sample collection and handling was assessed, but no consistent source of artifactual generation of TXB2 was found.