The significance of equol in relation to the oestrogenic responses in sheep ingesting clover with a high formononetin content

Abstract

Equol (7,4'-dihydroxyisoflavan), a metabolite in sheep of the dietary isoflavone formononetin, was found to be oestrogenic in mice. By subcutaneous administration it had about one-quarter of the activity of genistein. Equol (35–68 µg/100 ml) was found in the peripheral blood of sheep 4–24 hr after first feeding with red clover (Trifolium pratense) pellets, and represented 9–68% of the "free" and 23–72% of the conjugated "phyto-oestrogens" in the plasma. In ewes grazing red clover, equol was found in the plasma (50 µg/100 ml) and in the uterine tissue (46 µg/uterus) and represented in both instances more than 70% of the extracted "phyto-oestrogen". It is concluded that equol is probably of major importance in relation to the oestrogenic activity found in sheep ingesting clover with a high formononetin content. In guinea-pigs, equol (32–71 µg/100 ml) was found in plasma samples 4–16 hr (day 3) after feeding with red clover pellets. Another probable metabolite of formononetin, referred to as metabolite "A" and tentatively identified as demethylated angolensin (2,4-dihydroxyphenyl-p-hydroxyphenylethylketone), was also noted in the plasma of sheep and guinea-pigs after ingesting red clover.