Radioimmunoassay for plasma thromboxane B2.

Platelet activity may play a major role in the acute phase of atherosclerotic cardiovascular disease. To assess such activity, an assay for plasma thromboxane B2, a prostaglandin metabolite unique to platelets, is needed. The radioimmunoassay described here is based on a nonequilibrium incubation followed by a solid-phase second-antibody separation of bound from free thromboxane B2. No prior purification is required. Values for 22 normal subjects averaged 39.0 (SD 24.6) ng/L. The thromboxane B2 concentration of a plasma sample was 20.3 ng/L as compared with 37 micrograms/L in the corresponding serum. Plasma thromboxane B2 concentrations before and after ingestion of aspirin differed significantly (p less than 0.025). The biological half-life of intravenously injected [3H]thromboxane B2 in rabbits was 20 min. At the end of 2 h, 85% of the label was accounted for in urine, 7% in liver, and 5% in lung. Our assay is simple, reproducible, sensitive, and specific. It can be used to reflect acute events involving platelet aggregation.