The effect of diet on the metabolism in sheep of the tritiated isoflavones formononetin and biochanin A

Abstract

The metabolism of tritiated formononetin was studied in vivo and in vitro in the sheep and the metabolism of biochanin A studied in vitro.In vivo. Most of the formononetin was metabolized to equol and 81% of the administered radioactivity was excreted in the urine within 48 h, the main component being equol. Little or no daidzein was found in either rumen, plasma or urine samples. Some metabolites appeared on the TLC chromatograms in small amounts (never more than 10%); these were probably desmethylangolensin and O-methylequol, and their role in isoflavone metabolism is unknown.In vitro. The rate of metabolism of formononetin and biochanin A added to rumen samples from sheep varied with diet, being more rapid in samples from sheep fed on lucerne chaff or clover. Formononetin was converted to equol. Biochanin A was converted to genistein in rumen liquor from sheep fed on oaten chaff, but was further metabolized if the sheep had been fed on clover. A metabolite of RF 0.1 was observed which with a longer incubation time was converted to a non-volatile compound at RF 0.9.