Oestrogenic activity and metabolism of certain isoflavones in sheep

Pure genistein, biochanin A, and formononetin when administered to ovariectomized ewes by intraruminal (i/r) infusion appear to have oestrogenic activities of the same order. Coumestrol given similarly has activity about 15 times as great. Genistein, biochanin A, and coumestrol appear to be considerably less active when given i/r than when injected intramuscularly (i/m), but formononetin is more active i/r than i/m. This may be related to the lower solubility of formononetin. Examination of the urinary phenols before and after treatment showed that almost all the administered isofiavone underwent metabolic degradation. Genistein and biochanin A appeared to be largely excreted as p-ethylphenol, but only about 5% of the formononetin was accounted for as detectable metabolites, of which a major one was equol.