Uterine abnormalities in rats exposed neonatally to diethylstilbestrol, ethynylestradiol, or clomiphene citrate

Pre-clinical models to study abnormal uterine bleeding (AUB)

Abnormal Uterine Bleeding (AUB) is a common debilitating condition that significantly reduces quality of life of women across the reproductive age span. AUB creates significant morbidity, medical, social, and economic problems for women, their families, workplace, and health services. Despite the profoundly negative effects of AUB on public health, advancement in understanding the pathophysiology of AUB and the discovery of novel effective therapies is slow due to lack of reliable pre-clinical models. This review discusses currently available laboratory-based pre-clinical scientific models and how they are used to study AUB. Human and animal in vitro, ex vivo, and in vivo models will be described along with advantages and limitations of each method.

Endocrine-disrupting chemicals and uterine fibroids

Uterine fibroids are the most frequent gynecologic tumor, affecting 70% to 80% of women over their lifetime. Although these tumors are benign, they can cause significant morbidity and may require invasive treatments such as myomectomy and hysterectomy. Many risk factors for these tumors have been identified, including environmental exposures to endocrine-disrupting chemicals (EDCs) such as genistein and diethylstilbestrol. Uterine development may be a particularly sensitive window to environmental exposures, as some perinatal EDC exposures have been shown to increase tumorigenesis in both rodent models and human epidemiologic studies. The mechanisms by which EDC exposures may increase tumorigenesis are still being elucidated, but epigenetic reprogramming of the developing uterus is an emerging hypothesis. Given the remarkably high incidence of uterine fibroids and their significant impact on women's health, understanding more about how prenatal exposures to EDCs (and other environmental agents) may increase fibroid risk could be key to developing prevention and treatment strategies in the future.

The impact of neonatal exposure to 17alpha-ethynylestradiol on the development of kisspeptin neurons in female rats

Neonatal exposure to 17alpha-ethynylestradiol (EE) at relatively low doses leads to delayed effects characterized by the early onset of age-related anovulation. Kisspeptin neurons in the anteroventral periventricular nucleus (AVPV), located at the anterior hypothalamus, are proposed to play key roles in appearance of these delayed effects after maturation. To understand the initial changes, we investigated Kiss1 mRNA expression in the anterior and posterior hypothalamus before weaning in female rats that received neonatal exposure to EE at various doses (0.002-2000μg/kg). The level of Kiss1 mRNA in the anterior hypothalamus was decreased from 0.002μg/kg which did not induce delayed effects. In the posterior hypothalamus, Kiss1 mRNA expression did not differ among the groups except 2000μg/kg group. These results suggest that neonatal exposure to EE affects the development of kisspeptin neurons and kisspeptin neurons in the AVPV are highly susceptible to neonatal EE treatment.

Early indicators of delayed adverse effects in female reproductive organs in rats receiving neonatal exposure to 17alpha-ethynylestradiol

We previously reported that neonatal exposure to 17α-ethynylestradiol (EE) led to delayed adverse effects in which age-related anovulation after sexual maturation was accelerated. To identify early indicators of these adverse effects, female Wistar Hannover GALAS rats received a single EE injection (0, 0.02, 0.2, 2, 20, or 200 μg/kg) within 24 hr of birth. Histopathological changes in ovarian and uterine development were investigated from postnatal day (PND) 14 to 10 weeks of age. Immunohistochemical expression of estrogen receptor alpha (ERα) in the uterus, serum levels of sex-related hormones and gene expression in the hypothalamus were examined. Although neonatal exposure to EE did not affect body growth or ovarian development, serum FSH tended to decrease at doses ≥ 2 μg/kg, and Kiss1 mRNA level in the whole hypothalamus was significantly decreased in all EE-treated groups at PND14.The number of uterine glands at PND21 was suppressed at doses ≥ 20 μg/kg, and ERα expression in the uterine epithelium at estrus stage decreased in a dose-dependent manner at 10 weeks of age. These results demonstrated that the various identified changes that occurred before the appearance of delayed adverse effects could be candidate early indicators.

Assessment of estrogenic potential of di-n-butyl phthalate and butyl benzyl phthalate in vivo

Phthalate compounds are widely used industrial chemicals; when incorporated into polyvinyl chloride, they are not covalently bound and released into the surrounding media. Some of them have estrogenic potential in vitro but data on in vivo studies are scanty. For the 3-day uterotrophic assay, di- n-butyl phthalate (DBP;10 and 100 mg/kg), butyl benzyl phthalate (BBP; 20 and 200 mg/kg), and diethylstilbestrol (DES, 40 µg/kg, positive control) were administered orally to immature female rats for three consecutive days from postnatal day (PND) 21. For the 20-day pubertal onset assay, DBP (10 and 20 mg/kg), BBP (20 and 200 mg/kg), and DES (6 µg/kg) were administered orally from PND 21 daily for 20 days. In the uterotrophic assay, in groups treated with higher dose of DBP and BBP, the uterine wet weight significantly decreased in the higher dose, and there were minor variations in the ovary wet weight, while the wet weight of these organs increased significantly in DES-treated group. In the 20-day pubertal assay, the weight of uterus and ovary declined significantly and changes in vaginal weight were nonsignificant in DBP- and BBP-treated groups. However, in DES-treated group nonsignificant elevation in vagina weight was observed. All the DES-treated animals showed the vaginal opening (VO) on day 26.17 ± 0.16. However, VO was not observed in any of the animals in control, vehicle control, BBP-, and DBP-treated groups up to PND 42, except in one animal each in vehicle control and DBP (100 mg/kg)-treated groups. The data indicated that both DBP and BBP were unable to induce elevation in the uterine and ovarian weight. While DES treatment can accelerate the growth of uterus and ovary and alter the onset of puberty and estrous cyclicity in prepubertal rats. These suggest that these compounds may not have estrogenic potential in vivo.

Delayed effects of neonatal exposure to 17alpha-ethynylestradiol on the estrous cycle and uterine carcinogenesis in Wistar Hannover GALAS rats

We investigated the delayed effects of neonatal exposure to 17α-ethynylestradiol (EE) on the female reproductive tract using Wistar Hannover GALAS rats. Female pups received single injections of EE (0, 0.02, 0.2, 2, 20, or 200 μg/kg) within 24h after birth and estrous cyclicity was observed until 10 months of age. All animals were treated at 9 weeks of age with the uterine carcinogen, N-ethyl-N'-nitro-N-nitrosoguanidine. Although the vaginal opening was not affected, abnormal cycles were significantly increased from 0.2 μg/kg. Persistent estrus was prominent and the incidence increased age- and dose-dependently. Severity of atypical hyperplasia of the uterus tended to increase from 2 μg/kg. In these groups, serum progesterone level was lowered relative to estradiol level. In conclusion, estrous cyclicity was a sensitive indicator reflecting delayed effects on the female reproductive tract. Early onset of anovulation leading to prolonged estrogen exposure might be a risk factor for uterine carcinogenesis.

Mal-development of the penis and loss of fertility in male rats treated neonatally with female contraceptive 17alpha-ethinyl estradiol: a dose-response study and a comparative study with a known estrogenic teratogen diethylstilbestrol

The objectives of this study were to find a minimal dose of 17alpha-ethinyl estradiol (EE) that is detrimental to the developing penis and fertility and to compare estrogenic effects between EE and diethylstilbestrol (DES). Neonatal rats received EE at 10 ng (1 microg/kg), 100 ng, 1 microg, or 10 microg per pup on alternate days from postnatal days 1 to 11 (dose-response study) or received EE or DES at 100 ng per pup daily from postnatal days 1 to 6 (comparative study). Effects of EE were dose dependent, with > or = 100-ng dose inducing significant (p < 0.05) reductions in penile length, weight, and diameter. Additionally, the penis was malformed, characterized by underdeveloped os penis and accumulation of fat cells. Fertility was 0% in the > or = 1-microg groups, in contrast to 60% in the 100-ng group and 100% in the 10-ng and control groups. Animals treated with > or = 10 ng had significant reductions in the weight of bulbospongious muscle, testis, seminal vesicle, epididymal fat pad, and in epididymal sperm numbers. A comparison of EE and DES effects showed similar reductions in penile weight and length and the weight of bulbospongiosus muscle, testis, seminal vesicle, epididymis, and epididymal fat pad in both adolescent and adult rats. While 5/6 control males sired, only 1/6 in the EE group and 0/6 in the DES group sired. Hence, neonatal exposure to EE at 10 ng (environmentally relevant dose) adversely affects male reproductive organs. A dose ten times higher than this leads to permanently mal-developed penis and infertility. Furthermore, EE and DES exposures show similar level of toxicity to male reproductive organs.

Developmental exposure to diethylstilbestrol alters uterine gene expression that may be associated with uterine neoplasia later in life

Previously, we described a mouse model where the well-known reproductive carcinogen with estrogenic activity, diethylstilbestrol (DES), caused uterine adenocarcinoma following neonatal treatment. Tumor incidence was dose-dependent reaching >90% by 18 mo following neonatal treatment with 1000 microg/kg/d of DES. These tumors followed the initiation/promotion model of hormonal carcinogenesis with developmental exposure as initiator, and exposure to ovarian hormones at puberty as the promoter. To identify molecular pathways involved in DES-initiation events, uterine gene expression profiles were examined in prepubertal mice exposed to DES (1, 10, or 1000 microg/kg/d) on days 1-5 and compared to controls. Of more than 20 000 transcripts, approximately 3% were differentially expressed in at least one DES treatment group compared to controls; some transcripts demonstrated dose-responsiveness. Assessment of gene ontology annotation revealed alterations in genes associated with cell growth, differentiation, and adhesion. When expression profiles were compared to published studies of uteri from 5-d-old DES-treated mice, or adult mice treated with 17beta estradiol, similarities were seen suggesting persistent differential expression of estrogen responsive genes following developmental DES exposure. Moreover, several altered genes were identified in human uterine adenocarcinomas. Four altered genes [lactotransferrin (Ltf), transforming growth factor beta inducible (Tgfb1), cyclin D1 (Ccnd1), and secreted frizzled-related protein 4 (Sfrp4)], selected for real-time RT-PCR analysis, correlated well with the directionality of the microarray data. These data suggested altered gene expression profiles observed 2 wk after treatment ceased, were established at the time of developmental exposure and maybe related to the initiation events resulting in carcinogenesis.

Female sexual maturation and reproduction after prepubertal exposure to estrogens and endocrine disrupting chemicals: a review of rodent and human data

Natural hormones and some synthetic chemicals spread into our surrounding environment share the capacity to interact with hormone action and metabolism. Exposure to such compounds can cause a variety of developmental and reproductive detrimental abnormalities in wildlife species and, potentially, in human. Many experimental and epidemiological data have reported that exposure of the developing fetus or neonate to environmentally relevant concentrations of some among these endocrine disrupters induces morphological, biochemical and/or physiological disorders in brain and reproductive organs, by interfering with the hormone actions. The impact of such exposures on the hypothalamic-pituitary-gonadal axis and subsequent sexual maturation is the subject of the present review. We will highlight epidemiological human studies and the effects of early exposure during gestational, perinatal or postnatal life in female rodents.

Hsp90 and environmental impacts on epigenetic states: a model for the trans-generational effects of diethylstibesterol on uterine development and cancer

Hsp90 is a chaperone for over 100 'client proteins' in the cell, most of which are involved in signaling pathways. For example, Hsp90 maintains several nuclear hormone receptors, such as the estrogen receptor (ER), as agonist-receptive monomers in the cytoplasm. In the presence of agonist, Hsp90 dissociates and the receptors dimerize, enter the nucleus and ultimately activate transcription of the target genes. Increasing evidence suggests that Hsp90 also has a role in modifying the chromatin conformation of many genes. For example, Hsp90 has recently been shown to increase the activity of the histone H3 lysine-4 methyltransferase SMYD3, which activates the chromatin of target genes. Further evidence for chromatin-remodeling functions is that Hsp90 acts as a capacitor for morphological evolution by masking epigenetic variation. Release of the capacitor function of Hsp90, such as by environmental stress or by drugs that inhibit the ATP-binding activity of Hsp90, exposes previously hidden morphological phenotypes in the next generation and for several generations thereafter. The chromatin-modifying phenotypes of Hsp90 have striking similarities to the trans-generational effects of the ER agonist diethylstilbesterol (DES). Prenatal and perinatal exposure to DES increases the predisposition to uterine developmental abnormalities and cancer in the daughters and granddaughters of exposed pregnant mice. In this review, we propose that trans-generational epigenetic phenomena involving Hsp90 and DES are related and that chromatin-mediated WNT signaling modifications are required. This model suggests that inhibitors of Hsp90, WNT signaling and chromatin-remodeling enzymes might function as anticancer agents by interfering with epigenetic reprogramming and canalization in cancer stem cells.

Developmental effects of prenatal exposure to bisphenol a on the uterus of rat offspring

Exposure to estrogenic compounds during critical periods of fetal development could result in adverse effects on the development of reproductive organs that are not apparent until later in life. Bisphenol A (BPA), which is employed in the manufacture of a wide range of consumer products, is a prime candidate for endocrine disruption. We examined BPA to address the question of whether in utero exposure affects the uterus of the offspring and studied the expression and distribution of the estrogen receptors alpha (ERalpha) and beta (ERbeta), because estrogens influence the development, growth, and function of the uterus through both receptors. Gravid Sprague-Dawley dams were administered by gavage either 0.1 or 50 mg/kg per day BPA or 0.2 mg/kg per day 17alpha-ethinyl estradiol (EE2) as reference dose on gestation days 6 through 21. Female offspring were killed in estrus. Uterine morphologic changes as well as ERalpha and ERbeta distribution and expression were measured by immunohistochemistry and Western blot analysis. Striking morphologic changes were observed in the uterine epithelium of postpubertal offspring during estrus of the in utero BPA-treated animals (the thickness of the total epithelium was significantly reduced). ERalpha expression was increased in the 50-mg BPA and EE2-treated group. In contrast, we observed significantly decreased ERbeta expression in all BPA- and EE2-treated animals when compared with the control. In summary, these results clearly indicate that in utero exposure of rats to BPA promotes uterine disruption in offspring. We hypothesize that the uterine disruption could possibly be provoked by a dysregulation of ERalpha and ERbeta.

Epigenetic alteration by the chemical substances, food and environmental factors

Epigenetic alteration is one of the most important mechanisms for gene regulation; however, it is not changes in gene function with DNA sequence changes. Recently, epigenetics were studied in the wide ranging fields of research. In the present review, we introduce recent studies on epigenetic alteration, especially DNA methylation, by chemical exposure, food intake and environmental factors. In addition, we introduced our results on alteration of DNA methylation by transient exposure of neonatal mice to diethylstilbestrol. As these data suggest that chemical exposure, food intake and environmental factors are responsible for epigenetic alteration, we insist the necessity of the new risk assessment focusing on epigenetic alteration. (Reprod Med Biol 2004; 3: 115-121).

Lack of modifying effects of genistein on disruption of the reproductive system by perinatal dietary exposure to ethinylestradiol in rats

We previously found that effects of perinatal dietary exposure to ethinylestradiol (EE) on the rat reproductive system differ depending on the diet used, with a more pronounced estrogenic impact with a regular diet that includes soy-derived proteins than with a soy-free (SF) diet. The present study was performed to examine whether genistein (GEN), a soy-derived major phytoestrogen, acts synergistically with EE. Maternal rats were fed SF diet without chemical (control) or containing 0.5-ppm EE, 0.5-ppm EE + 100-ppm GEN, 0.5-ppm EE + 1250-ppm GEN, or 1250-ppm GEN, from gestational day 15 to postnatal day (PND) 11. EE reduced serum testosterone in males at PND 3, and affected the onset of puberty of both sexes and estrous cyclicity and reproductive system in females, irrespective of co-administration of GEN. GEN alone also affected estrous cyclicity and the reproductive system in females. However, no combination effects of GEN with EE were evident, suggesting no synergism between the two.

Estrogenicity of solid phase-extracted water samples from two municipal sewage treatment plant effluents and river Rhine water using the yeast estrogen screen

In the present study, the yeast estrogen screen (YES) was used to estimate the estrogenic potential of solid phase-extracted water samples from the effluents of two municipal sewage treatment plants (STPs 1 + 2) and from four lanes (left to right) of the river Rhine at Worms, Germany, i.e. downstream the STPs. Estrogenic activities of extracted water samples were expressed as 17beta-estradiol equivalents (E(2)-EQs). Estrogenic activity was detected in the effluents of both STPs with values of 0.242 +/- 0.038 nM (65.96 +/- 10.4 ng/l) and 0.125 +/- 0.026 nM E(2)-EQs (34.1 +/- 7.18 ng/l) at STP 1 and 2, respectively. In river Rhine water, estrogenic activity was lower, however, displaying significant differences between the left and right bank of the river (0.044 +/- 0.003 nM E(2)-EQs [11.97 +/- 0.7 ng/l] for lanes 1-3; 0.071 +/- 0.01 nM E(2)-EQs [19.42 +/- 2.8 ng/l] for lane 4). Chemical analysis of corresponding water samples resulted in a potential estrogenic response in the YES, expressed as E(2)-EQs for the known estrogens and phytoestrogens in the STP effluents with values up to 0.0662 nM E(2)-EQs (18.04 ng/l). In Rhine water from lane 4, however, total estrogenic activity of steroidal estrogens was equal to 0.014 nM E(2)-EQs (3.8 ng/l). Furthermore, total concentrations of flavonoids, fecal- and phytosteroids and resorcyclic lactones were about 1.2 microg/l at STP 1, 0.62 microg/l at STP 2 and 0.25 microg/l at the river Rhine, lane 4. Results indicate that estrogenic activity can clearly be measured in SPT effluents as well as in river Rhine water using the YES in combination with chemical analysis. Results from the bioassay, however, indicated a higher estrogenic potential (expressed as E(2)-EQs) than that obtained by chemical analysis.

Neonatal diethylstilbestrol exposure induces persistent elevation of c-fos expression and hypomethylation in its exon-4 in mouse uterus

Perinatal exposure to diethylstilbestrol (DES) induces reproductive tract cancers later in life in both humans and animals. Because there is no clear evidence that perinatal DES exposure induces gene mutation, we proposed that perinatal DES exposure causes epigenetic methylation changes that result in persistent alterations in gene expression, leading to tumorigenesis. The proto-oncogene c-fos is one of the immediately induced genes in uterine epithelium after estrogen simulation and a key player in uterine carcinogenesis. Here, we investigated c-fos expression in mice neonatally exposed to DES (2 microg/pup/day on postnatal days 1-5). The mRNA levels of c-fos in uteri of neonatal DES-treated mice were persistently 1.4-1.9-fold higher than that in the control mice from day 5 to day 60. Overall, the uterine c-fos expression level in the neonatal DES-exposed group was significantly higher than that in the control group. After examination of the methylation status of the c-fos gene, we found that the CpGs in promoter and intron-1 regions were completely unmethylated. In exon-4, from day 17 to day 60, the percentage of unmethylated CpGs was higher in neonatal DES-exposed mice uteri than that in control (42%, 51%, 47%, and 42% in DES-exposed mice vs 33%, 34%, 33%, and 21% in control mice at day 17, 21, 30, and 60, respectively). These results suggest that perinatal DES exposure may permanently alter gene expression and methylation, and the methylation modification may occur in either the promoter regions or other regulatory sites in the gene.

Neonatal exposure to p-tert-octylphenol causes abnormal expression of estrogen receptor alpha and subsequent alteration of cell proliferating activity in the developing Donryu rat uterus

In the present study, we investigated immunohistochemically the time-course alterations in estrogen receptor alpha (ER) expression and cell proliferating activity in the developing uteri of Donryu rats exposed neonatally to a high dose p-tert-octylphenol (OP), an endocrine disrupting chemical (EDC). OP-treatment (sc injections of 100 mg/kg, every other day from postnatal days 1 to 15) induced an early and enhanced ER expression in the luminal epithelium compared with age-matched controls from postnatal day (PND) 10, and increased proliferating cell nuclear antigen (PCNA) positive cells up to PND21. At PND28, ER expression in the luminal epithelium of the OP-treated group was decreased, in association with decline in the luminal epithelial areas. PND14, the second week of life, is coincident with the normal time for differentiation when the luminal epithelium invaginates into the stroma to form uterine glands. OP-treatment, however, delayed and inhibited gland-formation, and suppressed ER expression in the invaginated-luminal and glandular epithelium at this time. These results indicate that ER expression in these sites is strongly linked with cell proliferating activity. In stromal cells, ER was expressed from PND6 in both groups without any PCNA positive cells, but significantly lower values were noted in the OP-treated group up to PND10. Our immunohistochemical investigation did not reveal any abnormalities in expression of the proto-oncogene c-fos, mitotic inhibitor p21, or epidermal growth factor antigen, although the apoptotic index in the luminal epithelium was slightly increased in the OP-treated group. These results demonstrate neonatal effects of a high dose of OP, already detectable at PND10, with early and enhanced ER expression, resulting in increase of cell proliferative activity in the luminal epithelium, though expression in the glandular epithelium was suppressed in relation to inhibited gland-genesis. The present study thus suggests that neonatal exposure to high doses of EDCs with estrogenic activity can induce abnormal differentiation in the developing rat uteri via abnormal ER expression and subsequent alteration of cell proliferating activity.

Altered prostate growth and daily sperm production in male mice exposed prenatally to subclinical doses of 17alpha-ethinyl oestradiol

Approximately 2 million women in the USA and Europe continue taking oral contraceptives each year during undetected pregnancy due primarily to non-compliance and also to individual variation in sensitivity to hormones in the contraceptives. Prenatal exposure to oral contraceptives containing 17alpha-ethinyl oestradiol (EE) has generally not been associated with an increased incidence of externally observable malformations at birth. The purpose of this study was to assess effects on reproductive organs in adult male mice that had been exposed during gestation day 0 through 17 (equivalent to gestation week 16 in humans) to clinically relevant (approximately 0.5 microg/kg/day) and lower doses of EE. Doses used in this study ranged from 0.002 to 2 microg/kg/day. By 5 months of age, prostate weight was significantly (P < 0.05) higher than controls in most treatment groups of EE (0.02-2 microg/kg). Prostatic androgen receptor populations were significantly elevated only in the 0.02 microg/kg group, suggesting different mechanisms for the increase in prostate weight at different doses. Daily sperm production (DSP) and DSP per gramme of testis were reduced in all treatment groups during adolescence, but not later in adulthood. These findings are consistent with prior studies showing that prenatal exposure of mice to very low doses of a number of oestrogenic chemicals can alter the adult male reproductive system without causing gross external malformations.

Immature rat uterotrophic assay of bisphenol A

We used the immature rat uterotrophic assay to determine the estrogenicity of bisphenol A (BPA). We administered BPA (in sesame oil) to rats subcutaneously (sc; 0, 8, 40, and 160 mg/kg/day) or orally (0, 40, 160, and 800 mg/kg/day) for 3 days beginning on postnatal day (PND) 18; rats were sacrificed 24 hr after the last administration. Uterine wet, blotted, and relative weights increased in all groups given BPA sc. After oral administration, uterine relative weight increased in 160 and 800 mg/kg BPA groups, and wet and blotted weights increased in the 800 mg/kg BPA group. Plasma concentrations of BPA at 1 hr after the last administration were detected in all groups given BPA sc and in groups given 160 and 800 mg/kg BPA orally, with a dose-response effect. The study was then reproduced under the same conditions. After sc injections, uterine wet and blotted weights increased in the 40 and 160 mg/kg BPA groups, and relative weight increased in all groups given BPA sc. By contrast, uterine wet, blotted, and relative weights increased only in the 160 and 800 mg/kg oral BPA groups. Also, to examine time-course changes in uterine weight, we administered BPA (in sesame oil) sc from PND 18 to PND 20 for 3 days at doses of 0, 8, 40, and 160 mg/kg/day; uterine weights were then measured at 6, 12, 18, and 24 hr after the last administration. Uterine wet, blotted, and relative weights increased in all BPA groups at 6 and 24 hr and in 40 and 160 mg/kg BPA groups at 12 hr. By contrast, at 18 hr, uterine wet, blotted, and relative blotted weights increased in all BPA groups and relative wet weight increased in 40 and 160 mg/kg BPA groups. The percentage increases in uterine wet and relative weights of 40 and 160 mg/kg BPA groups at 6 hr were higher than those at 24 hr relative to the controls, but the coefficient of variation in these weights in the group given 8 mg/kg BPA at 24 hr was smaller than that at 6 hr. These findings demonstrate BPA-induced uterotrophy in the immature uterotrophic assay in rats administered 8 mg/kg/day sc and in rats given 160 mg/kg/day orally, and suggest that the autopsy at 24 hr after the last administration is suitable.

Irreversible effects of neonatal exposure to p-tert-octylphenol on the reproductive tract in female rats

It has been known for many years that administration of androgens or estrogens at critical periods of development in mammals causes severe long-term effects on the endocrine/genital systems. The environmental pollutant p-tert-octylphenol (OP) possesses a weak but clear estrogen agonist activity in in vitro and in vivo studies. In the present study, effects of neonatal exposure to OP on the reproductive tract of female rats were investigated. Newborn female pups were injected with 100 mg/kg OP subcutaneously within 24 h after birth. Administration was repeated every other day until postnatal day 15 (total of eight doses). Before weaning, serum follicle-stimulating hormone (FSH) and luteinizing hormone (LH) remained at low levels during OP exposure, although the serum FSH peak and the high LH level were obvious in the controls. Histologically, inhibition of uterine gland genesis was apparent. The day of vaginal opening was about 4 days earlier in OP-treated animals than in controls. Persistent estrus was consistently observed in OP-treated animals. Atrophic and polycystic ovaries without corpora lutea showed anovulation. In the endometrium, cell-proliferative activity and cell-death were increased and decreased, respectively, and expression of estrogen receptor alpha mRNA was apparent by in situ hybridization. Unexpectedly, endometrial hyperplasias appeared at 8 weeks of age. After ovariectomy, vaginal smears immediately became of castration type and the uterus was atrophied. These results suggested that neonatal exposure to a high dose of OP alters developmental hormonal secretion presumably due to a hypothalamo-pituitary-ovarian disorder, with accelerated vaginal opening, subsequent persistent estrus, and uterine endometrial hyperplasia. The changes in the uterus and vagina are ovary-dependent.

Environmental estrogens and reproductive health: a discussion of the human and environmental data

Estrogenic activity of certain xenobiotics is an established mechanism of toxicity that can impair reproductive function in adults of either sex, lead to irreversible abnormalities when administered during development, or cause cancer. The concern has been raised that exposure to ambient levels of estrogenic xenobiotics may be having widespread adverse effects on reproductive health of humans and wildlife. The purpose of this review is to evaluate (a) the nature of the evidence supporting this concern, and (b) the adequacy of toxicity screening to detect, and risk assessment procedures to establish safe levels for, agents acting by this mechanism. Observations such as adverse developmental effects after maternal exposure to therapeutic levels of the potent estrogen diethylstilbestrol or male fertility problems after exposure to high levels of the weak estrogen chlordecone clearly demonstrate that estrogenicity is active as a toxic mechanism in humans. High level exposures to estrogenic compounds have also been shown to affect specific wildlife populations. However, there is little direct evidence to indicate that exposures to ambient levels of estrogenic xenobiotics are affecting reproductive health. Reports of historical trends showing decreasing reproductive capacity (e.g., decreased sperm production over the last 50 years) are either inconsistent with other data or have significant methodologic inadequacies that hinder interpretation. More reliable historical trend data show an increase in breast cancer rate, but the most comprehensive epidemiology study to data failed to show an association between exposure to persistent, estrogenic organochlorine compounds and breast cancer. Clearly, more work needs to be done to characterize historical trends in humans and background incidence of abnormalities in wildlife populations, and to test hypotheses about ambient exposure to environmental contaminants and toxic effects, before conclusions can be reached about the extent or possible causes of adverse effects. It is unlikely that current lab animal testing protocols are failing to detect agents with estrogenic activity, as a wide array of estrogen-responsive endpoints are measured in standard testing batteries. Routine testing for aquatic and wildlife toxicity is more limited in this respect, and work should be done to assess the validity of applying mammalian toxicology data for submammalian hazard identification. Current risk assessment methods appear to be valid for estrogenic agents, although the database for evaluating this is limited. In conclusion, estrogenicity is an important mechanism of reproductive and developmental toxicity; however, there is little evidence at this point that low level exposures constitute a human or ecologic health risk. Given the potential consequences of an undetected risk, more research is needed to investigate associations between exposures and effects, both in people and animals, and a number of research questions are identified herein. The lack of evidence demonstrating widespread xenobiotic-induced estrogenic risk suggests that far-reaching policy decisions can await these research findings.

Growth of separated and recombined neonatal rat uterine luminal epithelium and stroma on extracellular matrix: effects of in vivo tamoxifen exposure

We have developed a system for serum-free culture of separated uterine epithelium and stroma from 11-day-old rats recombined on extracellular matrix extracted from Englebreth-Holm-Swarm tumors. Epithelium grew and, after 2 days in culture, developed into luminal epithelial spheres (LES) surrounding a fluid-filled lumen. Individual LES cells maintained epithelial cell characteristics such as basally located nuclei, apical microvilli (oriented toward the lumen), lateral membranes with interdigitations and desmosomes, secretory Golgi complexes, and abundant mitochondria and rough endoplasmic reticulum. Secretory vesicles were ubiquitous throughout the luminal fluid. Addition of 17 beta-estradiol to the growth medium increased the number and longevity of the LES. Prior exposure of uteri to tamoxifen via s.c. injection in vivo on postnatal Days 1 to 5 reduced or completely inhibited formation of LES in vitro. These effects occurred regardless of whether the stromal or epithelial component of the recombinant tissue was exposed to tamoxifen. These data suggest a directive property of neonatal stroma in culture resulting in the formation of highly secretory spherical epithelial structures completely enclosing a lumen. LES formation is responsive to both estrogen (positive response) and antiestrogen (negative response).

Long-term effects of postnatal exposure to diethylstilbestrol on uterine estrogen receptor and growth

Diethylstilbestrol (DES) treatment of female rats on postnatal days (PND) 1-5 reduces uterine growth, estrogen receptor (ER) level and gland number by PND 25, while daily DES treatment on PND 1-25 increases uterine growth 4-fold, further reduces ER level and completely suppresses gland formation. We now report the persistence of these effects in adults. By PND 60, uterine weight was 70% of controls in rats injected with DES on PND 1-5 but only 10% of controls in rats injected PND 1-10 or longer. In fact, uterine weights were the same on PND 10 and 60. Uterine gland numbers were reduced to 30% of controls in all DES-treated rats regardless of exposure length; however, luminal and glandular epithelial cell heights were reduced to less than 50 and 70%, respectively, of controls when DES was given on PND 1-25 but not when given on PND 1-5. Ovariectomy 7 days prior to sacrifice on PND 60 reduced uterine weight in controls by 67% and in rats injected with DES on PND 1-5 by 53%, but had no effect in rats injected with DES on PND 1-10. DES exposure at either PND 1-5 or 1-10 lowered ER levels by 35-50% at both 60 and 90 days. Treatment with a high dose of estradiol (E2) 1 week before sacrifice significantly down-regulated ER to the same concentration in all treatment groups at PND 60 and 90. Following E2 treatment, all groups also showed increased uterine weight at PND 60 and 90. These data show there is a short period of development (PND 5-10) in which further DES exposure indirectly inhibits uterine growth.

Growth of neonatal rat uterine luminal epithelium on extracellular matrix

We have developed a tissue culture system using an extract of basement membrane (extracellular matrix) which promotes the in vitro growth and development of uterine luminal epithelium from the 5-day-old rat. Uterine luminal epithelium, free of stroma, was obtained as short tubes by trypsinization of uterine segments followed by mechanical separation. Epithelial segments were grown in a serum-free medium on culture dishes coated with an extracellular matrix. After 2 days, rapid cell growth resulted in monolayer cultures, which subsequently formed organoid structures similar to differentiated uterine glands present in uterine tissue taken from older rats. Electron microscopy of cultures revealed columnar cells with basally located nuclei, apical microvilli, lateral membranes with interdigitations, desmosomes, and secretory Golgi complexes, all features found in functioning uterine epithelium in vivo. This model will allow the in vitro investigation of the development of uterine epithelium-specific functions free of the influence of stromal cell factors.

Transplacental estrogen responses in the fetal rat: increased uterine weight and ornithine decarboxylase activity

The synthetic estrogens, diethylstilbestrol (DES) and ethynylestradiol (EE2), are more potent than 17 beta-estradiol (E2) in inducing uterine weight gain in the neonatal rat, due to the binding of E2 to serum alpha-fetoprotein (AFP). However, all three hormones are equipotent in inducing neonatal uterine ornithine decarboxylase (ODC) activity. The present study assessed estrogen potency in fetal rats. Pregnant CD rats were injected sc daily on gestation days (GD) 16-20 with DES, EE2, or E2 in sesame oil. Both DES and EE2, but not E2, significantly increased uterine weight at birth, to more than twice that of controls. In addition, implants which continuously release E2 only slightly increased uterine weight at birth. Alternatively, dams were given a single estrogen injection on GD 20 and were sacrificed at various times after injection. Peak fetal uterine ODC activity occurred at 6-8 hours after maternal injection for all three estrogens. E2 had a relative potency about tenfold less than either DES or EE2 in stimulating fetal ODC activity, in contrast to equal potencies of the three estrogens in the postnatal rat uterus. Similar patterns were found following direct fetal injection with E2 or DES. In summary, these data demonstrate a transplacental induction of fetal uterine ODC activity and uterine weight gain by both DES and EE2. In addition, the lack of correlation between these endpoints in response to E2 suggests that they may be useful as selective indicators of potential toxicity of both natural and synthetic estrogens.