Neonatal exposure to coumestrol, a phytoestrogen, does not alter spermatogenic potential in rats

Estrogenic Pastures: A Source of Endocrine Disruption in Sheep Reproduction

Phytoestrogens can impact on reproductive health due to their structural similarity to estradiol. Initially identified in sheep consuming estrogenic pasture, phytoestrogens are known to influence reproductive capacity in numerous species. Estrogenic pastures continue to persist in sheep production systems, yet there has been little headway in our understanding of the underlying mechanisms that link phytoestrogens with compromised reproduction in sheep. Here we review the known and postulated actions of phytoestrogens on reproduction, with particular focus on competitive binding with nuclear and non-nuclear estrogen receptors, modifications to the epigenome, and the downstream impacts on normal physiological function. The review examines the evidence that phytoestrogens cause reproductive dysfunction in both the sexes, and that outcomes depend on the developmental period when an individual is exposed to phytoestrogen.

Coumestrol Antagonizes Neuroendocrine Actions of Estrogen via the Estrogen Receptor α

The phytoestrogen coumestrol has estrogenic actions on peripheral reproductive tissues. Yet in the brain this compound has both estrogenic and anti-estrogenic effects. We used estrogen receptor α knockout mice (ERαKO) to determine whether coumestrol has estrogenic actions in mice and also if these effects are mediated by the classic ERα. Female wild-type (WT) and ERαKO mice were ovariectomized and treated with estradiol (E2), dietary coumestrol, both, or neither compound. Ten days later the animals were sacrificed, blood was collected, and brain tissues were perfused. Fixed brains were sectioned and immunocytochemistry was employed to quantify progesterone receptors (PR) in the medial preoptic (POA) and ventromedial nucleus of the hypothalamus (VMN). Plasma was assayed for luteinizing hormone (LH). Estrogen treatment induced PR immunoreactivity in both regions in brains of WT females. In ERαKO mice, lower levels of PR were induced. The stimulatory effects of E2 on PR were attenuated in the POA by cotreatment with coumestrol, and the same trend was noted in the VMN. WT ovariectomized females treated with E2 had low levels of LH, while LH was high in untreated females and even higher in ovariectomized females treated with coumestrol. ERαKO females in all treatment groups had high levels of LH. Taken together, the results show that coumestrol has anti-estrogenic actions in the brain and pituitary and that ERα mediates these effects.

Soy, phyto-oestrogens and male reproductive function: a review

There is growing interest in the possible health threat posed by the effects of endocrine disruptors on reproduction. Soy and soy-derived products contain isoflavones that mimic the actions of oestrogens and may exert adverse effects on male fertility. The purpose of this review was to examine the evidence regarding the potential detrimental effects of soy and phyto-oestrogens on male reproductive function and fertility in humans and animals. Overall, there are some indications that phyto-oestrogens, alone or in combination with other endocrine disruptors, may alter reproductive hormones, spermatogenesis, sperm capacitation and fertility. However, these results must be interpreted with care, as a result of the paucity of human studies and as numerous reports did not reveal any adverse effects on male reproductive physiology. Further investigation is needed before a firm conclusion can be drawn. In the meantime, caution would suggest that perinatal phyto-oestrogen exposure, such as that found in infants feeding on soy-based formula, should be avoided.

Effects of chronic exposure to soy meal containing diet or soy derived isoflavones supplement on semen production and reproductive system of male rabbits

Soy and derivative diets deliver large doses of isoflavones to human and animals throughout their lifespan, including gestation. Epidemiologic and experimental data suggest that the consumption of soybean containing foods may protect against cardiovascular disease and decrease breast, prostate and endometrial cancer risk. Based on animal and in vitro studies, however, concerns have been raised that consumption of isoflavones may cause potential adverse effects on the reproductive tract and behavior. The aim of this study was to investigate the effects of chronic consumption of a soy meal containing diet or soy isoflavones supplement on the morphology of reproductive organs, semen quality, age that males reached puberty, and sexual behavior of male rabbits. With this purpose, 16 female rabbits were randomly assigned to receive: (1) a soy- and alfalfa-free diet; (2) a soy- and alfalfa-free diet supplemented with 5mg/kg body wt./day of soy isoflavones; (3) a soy- and alfalfa-free diet supplemented with 20mg/kg body wt./day of soy isoflavones; (4) a diet containing 18% of soy meal, throughout the gestation and lactation. After weaning, male offspring received the same diet, which was given to the respective mother. The age that males reached puberty, semen characteristics and sexual behavior were evaluated in these animals. At 33 weeks of age, the reproductive organs were submitted to histological evaluation. Rabbits, which received large amounts of isoflavones (20mg/kg body wt./day) had a lesser food intake, body weight and semen volume. Spermatogenesis, morphology of male genital organs and sexual behavior did not differ significantly from the control group. We conclude that chronic dietary treatment with soy based diet or soy isoflavones have no adverse effects on the observed reproductive patterns of male rabbits.

Effects of phytoestrogens on testosterone secretion by Leydig cells from Biłgoraj ganders (Anser anser)

The aim of this study was to examine ganders at different stages of the reproductive season and the effect of: (1) diets with high phytoestrogen content and (2) in vitro phytoestrogen treatment on testosterone secretion by isolated Leydig cells. Thirty-six male Biłgoraj geese were fed control diets with low phytoestrogen content (containing grass meal) and diets with high phytoestrogens (containing alfalfa meal and soy). Testes were obtained from both groups of ganders at three different times of the breeding season: peak of reproductive activity (March), second half of reproductive activity (May) and beginning of photorefractoriness (July). Isolated Leydig cells were incubated with LH as well as genistein, daidzein, equol and coumestrol and the concentration of testosterone in the medium was determined by radioimmunoassay. The mean weight of testes from ganders in May and July decreased relative to their weights in March, but no significant differences among experimental groups were noted. No differences were observed in basal and LH-stimulated testosterone secretion by Leydig cells of ganders fed the control diets and the diets with higher phytoestrogen content. In July, LH did not stimulate testosterone secretion in either group. In vitro treatment with genistein, daidzein and equol (5 and 50 microM) inhibited basal and LH-stimulated testosterone production by Leydig cells from both groups. Coumestrol (5 and 50 microM) inhibited basal testosterone secretion only in March in the control group. Dietary exposure to phytoestrogens had a slight effect on in vitro testicular secretion in ganders. In vitro treatment with phytoestrogen inhibited testosterone production by Leydig cells. Genistein showed the strongest effect and coumestrol had the weakest influence on testicular secretion.

Reproductive toxicity assessment of chronic dietary exposure to soy isoflavones in male rats

Epidemiologic and experimental data suggest that consumption of diets that are rich in isoflavones may decrease cancer risk in the breast, prostate, and other tissues. Isoflavones such as genistein and daidzein are structurally similar to endogenous estrogens, and demonstrate both estrogenic and weak anti-estrogenic activities; these activities may underlie the impaired fertility and reproductive tract disorders reported in animals exposed to high doses of isoflavones. To identify possible effects of isoflavones on male fertility, we evaluated reproductive parameters in Wistar-Unilever rats receiving dietary exposure to PTI G-2535, a characterized mixture of soy-derived isoflavones containing 45% genistein, 23% daidzein, and 4% glycitein. Beginning at 10 weeks of age, rats received chronic dietary exposure to the soy isoflavone mixture (200 or 2000 mg/kg diet) for a minimum of 12 months. Controls received unsupplemented chow diet only for the same period. Dietary exposure to isoflavones induced no gross toxicity or alterations in body weight gain. Absolute and relative weights of the testis and epididymis in groups receiving high or low doses of isoflavones were comparable to those of controls, and histopathologic evaluations demonstrated that testicular morphology was similar in all study groups. Isoflavone exposure had no significant effects on spermatid count, sperm production, or sperm morphology in any group. These data suggest that the reproductive system of adult male rats is relatively insensitive to isoflavone toxicity at dose levels that demonstrate significant activity in cancer chemoprevention, and that male reproductive function is unlikely to be affected by long-term administration of isoflavones for cancer prevention or other purposes. The results of this study conducted in adult male rats differ from the significant alterations in reproductive parameters that have been reported in female rats receiving prenatal or juvenile exposure to isoflavones.

Testicular endocrine function in GH receptor gene disrupted mice

The consequences of disruption of GH receptor gene in GH receptor knockout mice on testicular function were evaluated. Adult male GH receptor knockout mice and their normal siblings were divided in to two subgroups and treated with either saline or ovine LH (0.3 microg/g BW) in saline. One hour after saline or LH administration, blood was obtained via heart puncture. Plasma IGF-I, LH, FSH, PRL, androstenedione, and testosterone levels were measured by RIAs. Testicular LH and PRL receptor numbers as well as pituitary LHbeta-subunit and testicular sulfated glycoprotein-2 mRNA levels were measured. Also, testicular morphometric analysis was performed. Unlike in normal, wild-type mice, the circulating IGF-I was undetectable in GH receptor knockout mice. The plasma PRL levels were (P<0.01) higher in GH receptor knockout mice than in their normal siblings. The basal LH secretion was similar in normal and GH receptor knockout mice. However, the circulating FSH levels were lower (P<0.001) in GH receptor gene disrupted mice. Administration of LH resulted in a significant (P<0.001) increase in plasma testosterone levels in both GH receptor knockout and normal mice. However, this testosterone response was attenuated (P < 0.01) in GH receptor knockout mice. Plasma androstenedione responses were similar in both GH receptor knockout and normal mice. Testicular LH and PRL receptor numbers were significantly decreased in GH receptor knockout mice. The results of the morphometric analysis of the testis revealed that the Leydig cell volume per testis was reduced in mice with GH receptor gene disruption. The steady-state of LHbeta-subunit and testicular sulfated glycoprotein-2 mRNA levels were not different in GH receptor knockout mice relative to their normal siblings. The present in vivo study demonstrates that in GH receptor knockout mice, LH action on the testis in terms of testosterone secretion is significantly attenuated and suggests that this is due to a decrease in the number of testicular LH receptors. The reduced number of PRL receptors may contribute to the diminished responsiveness of testicular steroidogenesis to LH by decreased ability to convert androstenedione to testosterone. These changes are most likely due to the absence of circulating IGF-I. These findings provide evidence that systemic IGF-I plays a major modulatory role in testicular endocrine function.

Reproductive actions of phytoestrogens

This chapter reviews the reproductive actions of phytoestrogens, comparing mechanisms of action, dose-response relationships, and human exposures. Although a wide range of biochemical actions have been reported for phytoestrogens, in vitro tests suggest that phytoestrogens may be more likely to act through receptor-mediated mechanisms than through enzyme inhibition. Epithelial cell proliferation in the reproductive tract and anestrus are well-documented actions of isoflavonoids in experimental studies of animals. However, thus far, soy-based diets have generally failed to produce epithelial proliferation in ovariectomized rats and monkeys or menopausal women, and clinical studies have produced mixed evidence for effects of soy isoflavones on the human menstrual cycle or post-menopausal gonadotropin secretion. There has been considerable interest in the use of phytoestrogens as oestrogen replacement therapy in menopausal women. Reported results of initial clinical trials have been mixed, and it is unclear whether isoflavones in presently advised doses can substantially reduce menopausal symptoms. Some recent trials with oral isoflavone supplements report reductions in hot flushes, vaginal dryness, and breast pain. There is also limited clinical evidence for protective actions of isoflavones in mammary cancer. Like other oestrogenic substances, the isoflavonoids are effective differentiating agents in rodent models of development. The consequences of these actions for humans is of interest due to the high concentrations of isoflavonoids in some infant formulae. Thus, it is likely that some humans may experience greater exposure to phytoestrogens in infancy than in any other lifestage. At the time of writing, no ill effects of such exposure have been reported.