RADIOIMMUNOASSAY FOR QUANTITATIVE-ANALYSIS OF FORMONONETIN IN BLOOD-PLASMA AND RUMEN FLUID OF WETHERS FED RED-CLOVER

Formononetin concentration was determined by radioimmunoassay (RIA) in plasma and rumen fluid of wethers fed on red clover. The RIA utilized antisera raised against a formononetin-7-O-(carboxymethyl) ether hapt en. The tracer used was a H-3-labeled derivative of formononetin, and the detection limit of the assay was 0.7 pmol/assay of formononetin. T he reliability and reproducibility of the assay were demonstrated by i ntra- and inter-assay variations, which were 6.5% and 11.9%, respectiv ely. With this assay, the concentration of formononetin was determined in blood plasma and rumen fluid from wethers at different times after red clover feeding. The maximum levels in both plasma and rumen fluid were within 4 h after red clover intake. At this time, the rumen flui d level was about 3 times higher than the plasma level. These results show that (a) a powerful RIA has been developed for formononetin quant ification and (b) the biological half-lives of formononetin concentrat ion in blood plasma and rumen fluid of wethers after red clover feedin g were 8 and 2h, respectively, which suggests the potential activity o f formononetin besides its metabolites.