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In Vitro Metabolism of Formononetin and Biochanin a in Bovine Rumen Fluid^1,2,3,

Texas A&M University Agricultural Research and Extension Center, Overton 75684

Abstract

The phyto-estrogens formononetin (7-hydroxy-4'methoxyisoflavone) and biochanin A (5-7-dihydroxy-4'-methoxyisoflavone) were independently incubated in vitro at 39°C in bovine rumen fluid from a fistulated steer receiving an alfalfa hay diet. Formononetin was incubated in studies 1 and 2, whereas biochanin A was incubated in study 3. The isoflavones were separated and quantified by high performance liquid chromatography. In study 1, formononetin concentration, 14.80 µg/ml at time 0, declined to 1.16 µg/ml by 12 h and to .76 µg/ml by 24 h. Daidzein (7,4-dihydroxyisoflavone), .18 µg/ml at time 0, peaked at 12.92 µg/ml at 6 h and decreased to 1.30 µg/ml by 24 h. Equol (7,4'-dihydroxyisoflavan), detected at 6 h, peaked at 16.94 µg/ml at 18 h and dropped to 12.64 µg/ml at 24 h. In incubation study 2, formononetin declined from 17.57 µg/ml at time 0 to 7.08 µg/ml by 6 h. Daidzein concentration was 1.75 µg/ml at time 0 and increased to 12.03 µg/ml by 6 h. Equol was detected at 3 h and increased to 2.32 µg/ml at 6 h. The half-lives were 4.3 for formononetin and 9.8 h for daidzein in this in vitro system. In study 3, biochanin A, 8.54 µg/ml at time 0, decreased to 0 µg/ml by 12 h in incubation 3, whereas genistein (5,7,4'-trihydroxyisoflavone), 3.17 µg/ml at 1 h, peaked at 7.35 µg/ml at 4 h and decreased to .32 µg/ml at 24 h. Equol was not detected in incubation study 3. The half-lives of biochanin A and genistein were 3.9 and 5.5 h, respectively. Bovine rumen fluid metabolism of formononetin yielded daidzein and equol, but the only identified product of biochanin A was genistein.

¹ Journal paper TA 22839, Texas Agric. Exp. Sta.

² This study was a contribution to Western Regional Project W-112, Reproductive Performance in Domestic Ruminants.

³ Mention of a trademark of a proprietary product does not constitute a guarantee or warranty of the product by The Texas Agric. Exp. Sta. and does not imply its approval to the exclusion of other products that also may be suitable.

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