The biology and physiology of the male as well as female reproductive system is hormonally regulated. Abnormalities in the dynamics of hormone production, metabolism and elimination, as well as their binding to certain target tissues, has been associated with pathophysiological conditions of the reproductive system. Although oestrogens are known to be one of the major hormone groups in regulating the reproductive function and the fertilization process, the cellular and biochemical mechanism or mechanism(s) via which oestrogens induce their effects are still not fully defined. Moreover, in a modern environment we are also exposed to a wide battery of environmental agents which are structurally similar to oestrogens, and termed 'environmental oestrogens'. Because environmental oestrogens have been shown to mimic some of the effects of oestradiol, it has been postulated that these exogenous chemicals may influence or interfere with the oestrogen-dependent reproductive processes, and may be associated with beneficial as well as deleterious effects on the reproductive system. In this regard, two classes of environmental oestrogens have been widely studied, i.e. phyto-oestrogens (plant-derived dietary oestrogens) and xeno-oestrogens (industrial chemicals, including polychlorinated biphenyls, DDT, TCDD, dioxins, etc.). The main focus of this review is to provide an overview on the cellular and biochemical mechanism(s) by which xeno-oestrogens and phyto-oestrogens influence the oestrogen-dependent reproductive functions and induce their deleterious or protective effects on the reproductive system.

Leukaemia inhibitory factor (LIF) is an essential factor for embryo implantation. Factors generated by the oviduct cells (epithelial cells and fibroblasts) create the microenvironment for fertilization and first embryo stage development. Hence, it is feasible that the oviduct cells also synthesize LIF to promote and condition the embryo for implantation in the uterus. In the present study, we investigated whether cultured bovine oviduct epithelial cells and fibroblasts synthesize LIF. LIF production was measured in the conditioned medium of oviduct epithelial cells and fibroblasts, using LIF enzyme-linked immunosorbent assay. Moreover, expression of LIF mRNA was confirmed by LIF reverse transcriptase-polymerase chain reaction in extracts of RNA from oviduct epithelial/fibroblast cells. Quantitatively similar amounts of LIF were detected in the culture medium of epithelial cells and fibroblasts. In cells cultured for 1-7 days, the levels of LIF in the medium increased in a time-dependent manner. As compared to untreated cells, treatment of cells with 17β-oestradiol (1-100 ng/ ml), but not progesterone (1-100 ng/ml) and insulin (20 ng/ml), increased the levels of LIF in a concentrationdependent manner (P Ͻ 0.05). Similarly, tumour necrosis factor-α (100 ng/ml) significantly induced the levels of LIF. The effects of 17β-oestradiol (50 ng/ml) on LIF synthesis were enhanced and not blocked in the presence of tamoxifen (1 µg/ml), an oestrogen receptor antagonist, suggesting that the stimulatory effects of 17β-oestradiol on LIF synthesis are not receptor-mediated. In conclusion 17β-oestradiol, but not progesterone, induces LIF synthesis by bovine oviduct epithelial cells and fibroblasts and this may play an important role in the biology of early embryo development. However, the exact pathophysiological role of LIF within the oviduct needs to be further investigated.

In bovine oviduct cells 17beta-oestradiol can induce the synthesis of leukaemia inhibitory factor (LIF), a glycoprotein essential for embryo implantation. Therefore substances which are structurally similar to 17beta-oestradiol and possess oestrogenic activity may also modulate LIF synthesis and influence the reproductive process. We used primary cultures of bovine and human oviduct cells (epithelial cells:fibroblasts 1:1) to compare the effects of 17beta-oestradiol, phyto-oestrogens (genistein, biochanin A, daidzein, formononetin, and equol) and xeno-oestrogens [polychlorinated biphenyls (PCB): trichlorobiphenyl, 4-hydroxy-trichlorobiphenyl and 4-hydroxy-dichlorobiphenyl] on LIF synthesis. Immunoreactive LIF-enzyme-linked immunosorbent assay was used to determine the concentration of LIF in the culture medium. Similar to 17beta-oestradiol, genistein (0.02-2 micromol/l) induced LIF synthesis in bovine oviduct cells in a concentration-dependent manner. Equol, biochanin A and daidzein (2 micromol/l), 4-hydroxy-trichlorobiphenyl and 4-hydroxy-dichlorobiphenyl (0.01-10 micromol/l) but not formononetin (2 micromol/l) also induced LIF synthesis in bovine cells. Phyto-oestrogens and xeno-oestrogens also induced LIF synthesis in human oviduct cells (P < 0.05). The stimulatory effects of PCB, phyto-oestrogens and 17beta-oestradiol were blocked by ICI 182,780 (1 micromol/l). Moreover, 17beta-oestradiol, 4-hydroxy-trichlorobiphenyl, 4-hydroxy-dichlorobiphenyl, genistein, tamoxifen and ICI 182,780 displaced [(3)H]17beta-oestradiol from cytosolic oestrogen receptors in bovine oviduct cells. These results suggest that phyto-oestrogens and PCB mimic the effects of oestradiol in inducing LIF synthesis by bovine and human oviduct cells and that these stimulatory effects are oestrogen receptor-mediated. Environmental oestrogens act as endocrine modulators/disrupters and may induce deleterious effects on the reproductive process by influencing LIF synthesis in a non-cyclic fashion leading to tubal infertility.

Endothelin-1 (ET-1), a vasoconstrictor and mitogenic peptide that plays an important role within the endocrine/reproductive system, is synthesized by oviduct cells and regulates tubal contractility. Because 17beta-estradiol (estradiol) regulates oviduct function by influencing the synthesis of autocrine/paracrine factors, estradiol may also regulate ET-1 synthesis. Furthermore, environmental estrogens (EEs; phytoestrogens and xenoestrogens), which structurally resemble estradiol and possess estrogenic activity, may mimic the effects of estradiol on ET-1 synthesis and may influence the reproductive system. Using cultures of bovine oviduct cells (epithelial cells:fibroblasts, 1:1), we investigated and compared the modulatory effects of estradiol, phytoestrogens, and xenoestrogens on ET-1 synthesis and determined whether these effects were estrogen receptor (ER) mediated. A quantitative ELISA for ET-1 in the culture medium revealed that 17beta-estradiol inhibits ET-1 synthesis in a concentration-dependent manner (4-400 nmol/L). In contrast to estradiol, ET-1 synthesis was induced in cell cultures treated with xenoestrogens in the following order of potency (0.1 micromol/L): 4-hydroxy-trichlorobiphenyl > 4-hydroxy-dichlorobiphenyl > trichlorobiphenyl. The stimulatory effects of xenoestrogens on ET-1 production were mimicked by the phytoestrogens biochanin-A and genistein but not by formononetin, equol, and daidzein. The oviduct cells expressed both ERs (alpha and beta), but the modulatory effects of estradiol, but not EEs, on ET-1 synthesis were blocked by ICI-182 780 (1 microM), a pure ER antagonist. Our results provide evidence that estradiol inhibits ET-1 synthesis in oviduct cells via an ER-dependent mechanism, whereas, EEs induce ET-1 synthesis via an ER-independent mechanism. The contrasting effects of EEs on ET-1 synthesis suggests that EEs may act as endocrine modulators/disruptors and may have deleterious effects on the reproductive system by adversely influencing the biology and physiology of the oviduct.

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