Oestrogenic activity and metabolism of certain isoflavones in sheep

Braden, A. W. H.; Hart, N. K.; Lamberton, J. A.

doi:10.1071/ar9670355

Cited by 110 publications

(55 citation statements)

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“…When present in forage legumes, their concentration is low relative to that of the isoflavones that are produced in some clovers, independently of stimuli. When coumestrol was given to ovarectomized ewes by intraruminal infusion, they displayed oestrogenic activity that was~15 times as great as the isoflavones, genistein, biochanin A, and formononetin [52]. Thus, relatively low concentrations of coumestans in the diet are sufficient to influence fertility.…”

Section: Oestrogenic Activitymentioning

confidence: 96%

Fertility of Herbivores Consuming Phytoestrogen-containing Medicago and Trifolium Species

Reed¹

2016

Agriculture

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Despite their unrivalled value in livestock systems, certain temperate, pasture, legume species and varieties may contain phytoestrogens which can lower flock/herd fertility. Such compounds, whose chemical structure and biological activity resembles that of estradiol-17α, include the isoflavones that have caused devastating effects (some of them permanent) on the fertility of many Australian sheep flocks. While the persistence of old 'oestrogenic' ecotypes of subterranean clover (Trifolium subterraneum) in pasture remains a risk, genetic improvement has been most effective in lowering isoflavone production in Trifolium species; infertility due to 'clover disease' has been greatly reduced. Coumestans, which can be produced in Medicago species responding to stress, remain a potential risk in cultivars susceptible to, for example, foliar diseases. In the field, coumestrol is often not detected in healthy vegetative Medicago species. Wide variation in its concentration is influenced by environmental factors and stage of growth. Biotic stress is the most studied environmental factor and, in lucerne/alfalfa (Medicago sativa), it is the major determinant of oestrogenicity. Concentrations up to 90 mg coumestrol/kg (all concentrations expressed as DM) have been recorded for lucerne damaged by aphids and up to 600 mg/kg for lucerne stressed by foliar disease(s). Other significant coumestans, e.g., 4'-methoxy-coumestrol, are usually present at the same time. Concentrations exceeding 2000 mg coumestrol/kg have been recorded in diseased, annual species of Medicago. Oestrogenicity of some Medicago species is also influenced by maturity and senescence. Studies in Israel, North America, Europe, New Zealand and Australia have confirmed that coumestans in lucerne, represent an acute or sub-acute loss of reproductive efficiency in herbivores, e.g., sheep, cattle, and possibly horses. When sufficiently exposed peri-conception, coumestrol, sometimes present in lucerne, be it as pasture, hay, silage, pellets, meal, and sprouts, is associated with what can be an insidious, asymptomatic, infertility syndrome. Most livestock research with oestrogenic lucerne has been conducted with sheep. Ewes may be at risk when the coumestrol concentration in their diet exceeds 25 mg/kg. In studies where lambing was compared for lucerne and a phytoestrogen-free treatment, the mean decrease in lambs born/ewe was 13%; ewes on lucerne, exhibited a lower frequency of multiple births.

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Section: Oestrogenic Activitymentioning

confidence: 96%

Fertility of Herbivores Consuming Phytoestrogen-containing Medicago and Trifolium Species

Reed¹

2016

Agriculture

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“…The structure-activity relationships of various estrogenic compounds have received some attention [9][10][11], but no exhaustive rules have yet been defined which can be used to explain the estrogenic potency of a particular compound. Up to now the only sure way to determine the estrogenic potency of a chemical is to test it in a biological system [12][13][14]. This is generally done by comparison to a reference compound.…”

Section: Introductionmentioning

confidence: 99%

Vitellogenin synthesis in cultured hepatocytes; an in vitro test for the estrogenic potency of chemicals

Pelissero

Flouriot

Foucher

et al. 1993

The Journal of Steroid Biochemistry and Molecular Biology

266

108

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Smnmary--We describe here an/n vitro technique to assess the estrogenic activity of chemicals. This technique is based on rainbow trout hepatocytes incubated in a basic medium free of any additional growth factors or estrogenic chemicals and uses the production of vitellogenin (VTG) as a marker for the estrogenic potency of the compounds tested. The system allows at least some of the metabolic transformations which are undertaken by the liver cells/n vivo and could therefore be used for xenobiotic compounds which exhibit estrogenic activities after liver metabolic transformation. A dose-response curve was always consistently obtained using estradiol-17fl (E2), with a mid point at around 100 nME 2 and a maximum response at around 1000nM. Established estrogens such as 17al ethynylestradiol (EE2) or diethylstilboestrol (DES) were also tested. EE 2 appeared to be equipotent with E2 and DES slightly less potent. E2 conjugates were, perhaps surprisingly, also very potent. Estradiol-3-sulfate was equipotent with E2 and estradiol-17fl-glucuronide approx. 10% as potent. Other steroids such as androgens and progesterone, though active in the bioassay, were 3 orders of magnitude less potent than E 2. Of the various steroids tested, only cortisol, at concentrations up to 50 #M, was completely inactive. Six different phytoestrogens were tested in the assay. All were weakly estrogenic, possessing approximately one thousanth the potency of E 2 (they were as potent as the androgens and progesterone). All six phytoestrogens, as well as the androgens and progesterone, were tested in the presence of tamoxifen. In all cases tamoxifen reduced the production of VTG significantly, demonstrating that the estrogenic action of all of these compounds was most likely mediated by the E 2 receptor. The potencies determined here may not reflect the situation/n vivo but can provide complementary results about the activity of chemicals which need an hepatic metabolization to be estrogenic. Hepatocyte cultures would profitably be developed in other species to sustain these results.

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“…Coumestrol is structurally similar to steroidal oestrogens and will induce increased teat length in wethers (Millington, Francis & McKeown, 1964), increased uterine weight in ovariectomized ewes (Braden, Hart & Lamberton, 1967), decreased ovulation rate (Smith, Jagusch, Brunswick & McGowan, 1980), inhibition of oestrous behaviour and altered pituitary morphology (Kelly, Adams & Lindsay, 1976 Coumestrol assay. The coumestrol content of lucerne pellets was assayed according to the method of Le Bars & Le Bars (1984).…”

Section: Introductionmentioning

confidence: 99%

Gonadotrophin release in ovariectomized ewes fed different amounts of coumestrol

Montgomery¹,

Martin²,

Bars³

et al. 1985

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Oestrogenic activity and metabolism of certain isoflavones in sheep

Cited by 110 publications

References 0 publications

Fertility of Herbivores Consuming Phytoestrogen-containing Medicago and Trifolium Species

Fertility of Herbivores Consuming Phytoestrogen-containing Medicago and Trifolium Species

Vitellogenin synthesis in cultured hepatocytes; an in vitro test for the estrogenic potency of chemicals

Gonadotrophin release in ovariectomized ewes fed different amounts of coumestrol

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