Evaluation of the 20-day pubertal female assay in Sprague-Dawley rats treated with DES, tamoxifen, testosterone, and flutamide

Impact of Physiologically Relevant Genistein Exposure at Different Time Windows on Puberty Onset and Neuroendocrine Function in Female Rats

SCOPE

Puberty timing, critical for adulthood wellbeing, is influenced by the environment, life-style, and diets. However, differential puberty-interfering effects of soy and soy isoflavone are observed in both epidemiological and toxicological studies. Additionally, their impact on neuroendocrine function at various pre-pubertal developmental windows is unclear.

METHODS AND RESULTS

This study investigates the effect of genistein, a typical soy isoflavone, at neonatal, lactational, and post-weaning stages on the time of vaginal opening and determines the levels of neuroendocrine factors in female rats using immunofluorescence, immunochemistry, and enzyme-linked immunosorbent assays. A physiologically relevant dosage (10 mg kg^-1 ) is used to resemble human exposure. The results show that genistein exposure at lactational stage significantly accelerates vaginal opening time, marginally increases hypothalamic gonadotropin-releasing hormone (GnRH) secretion, significantly enhances kisspeptin receptor expression, and markedly elevates blood levels of GnRH, luteinizing hormone, and follicle-stimulating hormone, while neonatal and post-weaning exposures do not induce significant alternations.

CONCLUSION

Lactational stage may be an important window for genistein to impact reproductive development and neuroendocrine regulations.

Cardiovascular Properties of the Androgen-Induced PCOS Model in Rats: The Role of Oxidative Stress

Polycystic ovary syndrome (PCOS) is a multifaced reproductive endocrinopathy affecting 6-20% of women of childbearing age. It was previously shown that women with PCOS have an increased risk of cardiovascular (CV) diseases. The aim of this study was to evaluate the cardiodynamic parameters of isolated rats' hearts, blood pressure levels, and histomorphological changes in the heart tissue following the androgen-induced PCOS model in rats and the role of oxidative stress in the development of these CV properties of PCOS. 21-day-old female rats (n = 12) were divided into control and PCOS groups. PCOS was induced by administration of testosterone enanthate (1 mg/kg BW, daily) during 35 days. During the autoregulation protocol (40-120 mmHg) on the Langendorff apparatus, ex vivo cardiodynamic parameters of retrogradely perfused hearts showed enhanced contractile function and increased lusitropic effects in the left ventricle (LV) in PCOS rats. Systolic and diastolic pressures in LV were elevated at all perfusion pressure values. Systemic arterial systolic blood pressure showed borderline elevation, while mean arterial blood pressure was significantly higher in PCOS rats. Histological evaluation of heart tissue depicted hypertrophic (8.3%) alterations in LV cardiomyocytes and increase (7.3%) in LV wall thickness. Oxidative stress parameters were altered in systemic circulation, coronary venous effluent (CVE), and heart tissue. Levels of superoxide dismutase and reduced glutathione were decreased in blood and heart tissue, while catalase activity was not altered. Degree of lipid peroxidation was increased in circulation as well as heart tissue. Increased levels of O₂⁻ in CVE indicated the cardiotoxic effects in the rat PCOS model. The mentioned alterations of oxidative stress parameters in the blood, CVE, and heart could be recommended as potential contributors underlying the development of CV risk in PCOS women.

Suppression of ovarian hormones in adolescent rats has no effect on anxiety-like behaviour or c-fos activation in the amygdala

In humans, sex differences in mood disorders emerge during adolescence, with prevalence rates being consistently higher in females than males. It has been hypothesised that exposure to endogenous ovarian hormones during adolescence enhances the susceptibility of females to mood disorders from this stage of life onwards. However, experimental evidence in favour of this hypothesis is lacking. In the present study, we examined the long-term effects of suppressing adolescent gonadal hormone levels in a group of female Lister-hooded rats via administration of a gonadotrophin-releasing hormone antagonist (Antide; administered on postnatal day [PND] 28 and 42) compared to control females and males (n = 14 per group). We predicted that, in adulthood, Antide-treated female rats would exhibit more male-like behaviour than control females in novel environments (elevated-plus maze, open field and light-dark box), in response to novel objects and novel social partners, and in an acoustic startle task. Progesterone and luteinising hormone assays (which were conducted on blood samples collected on PND 55/56 and 69/70) confirmed that the hypothalamic-pituitary-gonadal axis was temporarily suppressed by Antide treatment. In addition, Antide-treated females were found to exhibit a modest pubertal delay, as measured by vaginal opening, which was comparable in length to the pubertal delay that has been induced by adolescent exposure to alcohol or stress in previous studies of female rats. However, Antide-treated females did not substantially differ from control females on any of the behavioural tests, despite the evidence for predicted sex differences in some measures. Following the acoustic startle response task, all subjects were culled and perfused, and c-Fos staining was conducted in the medial and basolateral amygdala, with the results showing no significant differences in cell counts between the groups. These findings suggest that ovarian hormone exposure during adolescence does not have long-term effects on anxiety-related responses in female rats.

Effects of 5-Hydroxymethylfurfural on Pubertal Development of Female Wistar Rats

OBJECTIVE

5-Hydroxymethylfurfural (HMF) is formed when sugars are heated in the presence of amino acids. HMF is naturally present in many foods. To investigate the toxic effects of HMF on the reproductive system of peripubertal rats.

METHODS

In the study, 24 immature female Wistar rat were divided into three groups: control (CT) fed with no HMF; low dose fed with 750 mg/kg/day of HMF and high dose (HD) groups fed with 1500 mg/kg/day of HMF. All groups received these diets for three weeks from postnatal day (PND) 21. The vaginal opening (VO) was monitored daily and euthanasia occurred on PND 44. Gonadotropin, estradiol (E2), progesterone and anti-Müllerian hormone (AMH) concentrations were measured. Reproductive organ weights and ovarian follicle counts were compared.

RESULTS

The HD HMF group had earlier VO. Higher mean luteinising hormone (2.9±1.2 vs 1.3±0.3 mIU/mL) and mean E2 (34.7±8.8 vs 21.2±3.9 pg/mL) and lower mean AMH (2.7±0.5 vs 4.7±0.7 ng/mL) concentrations were found in the HD compared to the CT group. The HD group also had increased number of secondary atrophic follicles.

CONCLUSION

These results indicate that peripubertal exposure to HMF at HD result in precocious puberty and decreased AMH levels in female Wistar rats.

Effect of metformin and flutamide on insulin, lipogenic and androgen-estrogen signaling, and cardiometabolic risk in a PCOS-prone metabolic syndrome rodent model

Polycystic ovary syndrome (PCOS) is highly associated with cardiometabolic risk and the metabolic syndrome (MetS), predisposing women to increased risk of developing type 2 diabetes and cardiovascular disease. Metformin is commonly used to treat insulin resistance-glucose intolerance, and flutamide, an androgen receptor (AR) antagonist, is used to target hyperandrogenemia and dyslipidemia. Currently, the physiological mechanism of action of these treatments on androgen, lipidogenic, and insulin signaling pathways remains unclear in PCOS. The aim of this study was to investigate the effects and mechanisms of action of metformin and flutamide on plasma lipid-apolipoprotein (Apo)B-lipoprotein and insulin-glucose metabolism, and endocrine-reproductive indices in a PCOS-prone MetS rodent model. PCOS-prone rodents were treated with metformin (300 mg/kg body wt), flutamide (30 mg/kg body wt), or metformin + flutamide combination treatment for 6 wk. Metformin was shown to improve fasting insulin and HOMA-IR, whereas flutamide and combination treatment were shown to reduce plasma triglycerides, ApoB48, and ApoB100, and this was associated with decreased intestinal secretion of ApoB48/triglyceride. Flutamide and metformin were shown to reduce plasma androgen indices and to improve ovarian primary and preovulatory follicle frequency. Metformin treatment increased hepatic estrogen receptor (ER)α, and metformin-flutamide decreased intestinal AR and increased ERα mRNA expression. Metformin-flutamide treatment upregulated hepatic and intestinal insulin signaling, including insulin receptor, MAPK1, and AKT2. In conclusion, cardiometabolic risk factors, in particular ApoB-hypertriglyceridemia, are independently modulated via the AR, and understanding the contribution of AR and insulin-signaling pathways further may facilitate the development of targeted interventions in high-risk women with PCOS and MetS.

Disruptions in the reproductive system of female rats after prenatal lipopolysaccharide-induced immunological stress: role of sex steroids

Stress signals during fetal or early postnatal periods may disorganize reproductive axis development at different levels. This study was aimed to test the hypothesis that prenatal immunological stress induced by bacterial endotoxin, lipopolysaccharide (LPS), has impact on structure and function of the reproductive system in female offspring. Adult female Wistar rats were divided into two groups, a control group (n = 5) and a LPS group (n = 12). Rats were injected with LPS 50 μg/kg body or 0.9% saline intraperitoneally on the 12th day of pregnancy. After birth the female pups (n = 20 in each group) were divided into four groups: (group 1) 0.9% saline prenatally, sesame oil (vehicle) postnatally; (group 2) LPS prenatally, sesame oil postnatally; (group 3) LPS prenatally, fulvestrant postnatally; (group 4) LPS prenatally, flutamide postnatally. Pups were injected subcutaneously into the neck with fulvestrant (estrogen receptor antagonist), 1.5 mg/kg in sesame oil, from postnatal day (PND) 5 to PND14; or flutamide (androgen receptor antagonist), 20 mg/kg in sesame oil, from PND14 to PND30. Rats of the control group were injected with sesame oil during the same time period. Parameters were evaluated by ELISA (serum estradiol and testosterone) and ovarian histology. The main findings were: (1) prenatal stress during the critical period resulted in delayed vaginal opening, decreased body weight and serum concentrations of sex steroids, and significant disorders in ovarian development; (2) postnatal estradiol and testosterone antagonist treatments decreased follicular atresia through increasing the number of healthy follicles and restored endogenous steroid production. Lay summaryImmunological stress, caused by simulating infection through exposure to a bacterial toxin (LPS), during a critical period of fetal development in laboratory rats results in delayed reproductive maturity, decreased body weight and decreased secretion of sex steroids in female offspring, and abnormalities in the ovaries like those in polycystic ovarian syndrome. These prenatally toxin-induced sexual disorders in females could be corrected by estradiol/testosterone antagonists during the postnatal period.

Dexamethasone as endocrine disruptor; type I and type II (anti) oestrogenic actions on the ovary and uterus of adult Wistar rats (Rattus Novergicus)

Objective

Dexamethasone is a widely used glucocorticoid, which has been prescribed increasingly in recent years. The effects of Dexamethasone on the ovary and uterus was investigated in present study.

Methods

Twenty (20) adult female Wistar rats, weighing 130-170 g were assigned to four (4) groups of five (5) animals each. The rats in the control group received saline, while the rats in the experimental group was subjected to oral treatment of dexamethasone of 12 mg/kg, 10 mg/kg, and 7 mg/kg doses daily for a period of 10 days, respectively. The rats were slaughtered after 24 hours of the last administration, and the uterus and ovaries were harvested following abdominal incision. Histological and biochemical investigations were carried out and the results were analyzed using ANOVA with the Graph-Pad prism software package 6.

Results

There was a significant decrease in the activities of the carbohydrate metabolic enzymes of the uterus in the dexamethasone-treated groups compared to the control group (p<0.05). Vacuolation, atrophy, thick epithelium, enlarged cells, inactive interstitial glands and follicular cyst, characterized the histological observation in the dexamethasone-treated groups in a dose-dependent manner.

Conclusion

This present study revealed that high-dose dexamethasone causes multiple changes in the histological features of the ovary and uterus, exerting type I and type II anti-oestrogenic effects on the female reproductive compartment.

Permitted Daily Exposure of the Androgen Receptor Antagonist Flutamide

This report aims to determine the permitted daily exposure (PDE) of flutamide, an androgen receptor blocker, as directed by guideline EMA/CHMP/CVPM/SWP/169430/2012 that came into effect on June 2015. A literature review was conducted to identify toxicity studies of flutamide. Hazards and sensitive endpoints were determined. Based on the no adverse effect levels (NOAELs) and lowest observed adverse effect levels (LOAELs) reported from both reproductive, developmental, and 28-day toxicity studies the PDE was calculated. Most of the toxicity studies converge toward a NOAEL of 1 mg/kg/d that translates to a PDE of 0.1 mg/d. However, taking into consideration the worst case scenarios for additional safety a PDE of 0.025 mg/d (25 μg/d) was calculated based on a reported NOAEL of 0.25 mg/kg/d. A PDE of 0.05 mg/d (50 μg/d) was also calculated from reproductive/developmental toxicity studies, which is in close agreement with the PDE from the 28-day toxicity studies. Considering the lowest PDE of 0.025 mg/d, residual flutamide at this dose is unlikely to pose any risk to humans. Nonmonotonic dose response (NMDR) effects of flutamide were not supported by literature. Oral route of administration was considered.

Follicular Development and Secretion of Ovarian Hormones during the Juvenile and Adult Reproductive Lives of the Myelin Mutant taiep Rat: An Animal Model of Demyelinating Diseases

Infertility and reproductive problems have been reported in women with several neurological disorders, for example, demyelination. However, the physiology of such problems has remained unknown so far. The taiep rats are an animal neurological model that initially shows a hypomyelination followed by a progressive demyelination of the central nervous system. This animal has reproductive problems, and the aim of this work is to characterize the follicular development, secretion of ovarian hormones, and presence of noradrenaline in the ovaries of the female taiep rats in the juvenile and adult stages. The taiep rats have low body weight (approximately 19% less than that of SD rats), a delay of 4 days in the age of vaginal opening, and an irregularity in the estrous cycle by the absence or prolongation of some estral cycle stage. In the juvenile stage, we observed a decrease of approximately 44% in the total number of follicles with a 15% increase of atresia and an 80% decrease in the fluorescence intensity of catecholamines in the ovaries, with a 21% increment in plasma concentrations of testosterone. In the adult stage, we observed follicular cysts and a 50% decrease in fluorescence intensity of catecholamines in the ovaries, with changes in the secretion of ovarian hormones, an increase of 20 times in progesterone, and a decrement of a half in estradiol. The demyelination in taiep rats affects follicular development and steroidogenesis in the early stages of the animal's life, and this is maintained until adulthood.

Peri-pubertal high caffeine exposure increases ovarian estradiol production in immature rats

Chronic caffeine consumption exerts a negligible effect on the reproductive organs of normal adult females, but it is not known whether this is also true for children and adolescents. Here, we investigated the effects of high caffeine exposure on sexual maturation and ovarian estradiol production in immature female rats. Immature female SD rats were divided into controls and caffeine groups fed 120 and 180mg/kg/day for 4 or 8 weeks. There was a significant delay in vaginal opening in the caffeine-fed groups. In addition, serum estradiol levels were elevated in the caffeine-fed animals after 2 and 4 weeks of exposure. Estradiol secretion as well as aromatase expression also increased significantly in the ovarian cells in response to caffeine. These results demonstrate that peripubertal exposure to high caffeine increases estradiol production in the ovary; this may disturb the coordinated regulation of the hypothalamo-pituitary-ovarian axis, thereby interfering with sexual maturation.

Mammary Gland Evaluation in Juvenile Toxicity Studies: Temporal Developmental Patterns in the Male and Female Harlan Sprague-Dawley Rat

There are currently no reports describing mammary gland development in the Harlan Sprague-Dawley (HSD) rat, the current strain of choice for National Toxicology Program (NTP) testing. Our goals were to empower the NTP, contract labs, and other researchers in understanding and interpreting chemical effects in this rat strain. To delineate similarities/differences between the female and male mammary gland, data were compiled starting on embryonic day 15.5 through postnatal day 70. Mammary gland whole mounts, histology sections, and immunohistochemically stained tissues for estrogen, progesterone, and androgen receptors were evaluated in both sexes; qualitative and quantitative differences are highlighted using a comprehensive visual timeline. Research on endocrine disrupting chemicals in animal models has highlighted chemically induced mammary gland anomalies that may potentially impact human health. In order to investigate these effects within the HSD strain, 2,3,7,8-tetrachlorodibenzo-p-dioxin, diethylstilbestrol, or vehicle control was gavage dosed on gestation day 15 and 18 to demonstrate delayed, accelerated, and control mammary gland growth in offspring, respectively. We provide illustrations of normal and chemically altered mammary gland development in HSD male and female rats to help inform researchers unfamiliar with the tissue and may facilitate enhanced evaluation of both male and female mammary glands in juvenile toxicity studies.

Evaluation of the estrogenic activity of Indian medicinal plants in immature rats

Introduction:

The objective of the study was to evaluate the estrogenic activity of four Indian medicinal plants Saraca indica (Si), Symplocos racemosa (Sr), Cyperus rotundus (Cr), Terminalia arjuna (Ta), a marketed preparation of Si (Aśokāriṣṭa) and a combination of Si + Sr using an experimental model of estrogenicity.

Materials and Methods:

After approval of the institutional animal ethics committee, 22 day old female rats (n = 54) were randomly allocated to 9 groups – Group 1 and Group 2: Vehicle controls, Group 3: Ethinyl estradiol, Group 4: Si (270 mg/kg), Group 5: Sr (270 mg/kg), Group 6: Cr (540 mg/kg), Group 7: Ta (270 mg/kg), Group 8: Ashokarishta (4 ml/kg), Group 9: Si + Sr (135 mg/kg). Variables studied were: Body weight, uterine weight, relative uterine weight, presence of vaginal opening, histomorphology of the uterus and total uterine glycogen content. Parametric data were analyzed using one-way ANOVA and the categorical data were analyzed using Chi-square test.

Results:

All animals in the ethinyl estradiol group showed a significant change in all the variables. None of the individual test drugs, neither the marketed preparation produced change in any of the variables. The plant drug combination also did not produce a change in any of the variables studied except in histomorphology wherein it caused a slight increase in the height of the luminal epithelium of the uterus (P < 0.05 vs. Group 1).

Conclusion:

The plant drugs Si, Sr, Cr, Ta and Aśokāriṣṭa did not demonstrate estrogenic activity in the immature rat model. The plant drug combination Si + Sr showed questionable estrogenic activity which needs to be evaluated in further studies.

Determination of in vivo estrogenic potential of Di-isobutyl phthalate (DIBP) and Di-isononyl phthalate (DINP) in rats

Estrogenic potential of Di-isobutyl phthalate (DIBP) and Di-isononyl phthalate (DINP) was studied using two different test systems. Two different doses of DIBP (250 and 1250 mg/kg) and DINP (276 and 1380 mg/kg) were administered to immature female rats (20 days old) orally once daily for 3 and 20 days in uterotrophic and pubertal assay, respectively. The animals were sacrificed on day 4 and day 41 in case of 3-day uterotrophic and 20-day pubertal assay, respectively. The results indicated that non-significant alterations in uterine and ovarian wet weight were observed in both the DIBP- and DINP-treated groups while the uterus weight increased significantly (i.e., 4-6 times) in the Diethylstilbesterol (DES)-treated group in both the assays. In the present study, precocious vaginal opening occurred at 26 days of age in the DES-treated group with a mean body weight of 30.39 ± 1.08 g. However, no precocious vaginal opening was found in any of the DIBP- and DINP-treated groups. The results indicated that both the phthalate compounds were unable to induce elevation in the uterine weight in both the assays and unable to cause vaginal opening indicating non-estrogenic potential of both the phthalate compounds, i.e., DIBP and DINP in vivo.

Developmental variations in environmental influences including endocrine disruptors on pubertal timing and neuroendocrine control: Revision of human observations and mechanistic insight from rodents

Puberty presents remarkable individual differences in timing reaching over 5 years in humans. We put emphasis on the two edges of the age distribution of pubertal signs in humans and point to an extended distribution towards earliness for initial pubertal stages and towards lateness for final pubertal stages. Such distortion of distribution is a recent phenomenon. This suggests changing environmental influences including the possible role of nutrition, stress and endocrine disruptors. Our ability to assess neuroendocrine effects and mechanisms is very limited in humans. Using the rodent as a model, we examine the impact of environmental factors on the individual variations in pubertal timing and the possible underlying mechanisms. The capacity of environmental factors to shape functioning of the neuroendocrine system is thought to be maximal during fetal and early postnatal life and possibly less important when approaching the time of onset of puberty.

Differential Growth of the Reproductive Organs during the Peripubertal Period in Male Rats

In mammals, puberty is a process of acquiring reproductive competence, triggering by activation of hypothalamic kisspeptin (KiSS)-gonadotropin releasing hormone (GnRH) neuronal circuit. During peripubertal period, not only the external genitalia but the internal reproductive organs have to be matured in response to the hormonal signals from hypothalamic-pituitary-gonadal (H-P-G) axis. In the present study, we evaluated the maturation of male rat accessory sex organs during the peripubertal period using tissue weight measurement, histological analysis and RT-PCR assay. Male rats were sacrificed at 25, 30, 35, 40, 45, 50, and 70 postnatal days (PND). The rat accessory sex organs exhibited differential growth patterns compared to those of non-reproductive organs. The growth rate of the accessory sex organs were much higher than the those of non-reproductive organs. Also, the growth spurts occurred differentially even among the accessory sex organs; the order of prepubertal organ growth spurts is testis = epididymis > seminal vesicle = prostate. Histological study revealed that the presence of sperms in seminiferous tubules and epididymal ducts at day 50, indicating the puberty onset. The number of duct and the volume of duct in epididymis and prostate were inversely correlated during the experimental period. Our RT-PCR revealed that the levels of hypothalamic GnRH transcript were increased significantly on PND 40, suggesting the activation of hypothalamic GnRH pulse-generator before puberty onset. Studies on the peripubertal male accessory sex organs will provide useful references on the growth regulation mechanism which is differentially regulated during the period in andevrepogen-sensitive organs. The detailed references will render easier development of endocrine disruption assay.

Endocrine-disrupting chemicals: elucidating our understanding of their role in sex and gender-relevant end points

Endocrine-disrupting chemicals (EDCs) are diverse and pervasive and may have significant consequence for health, including reproductive development and expression of sex-/gender-sensitive parameters. This review chapter discusses what is known about common EDCs and their effects on reproductively relevant end points. It is proposed that one way that EDCs may exert such effects is by altering steroid levels (androgens or 17-estradiol, E₂) and/or intracellular E₂ receptors (ERs) in the hypothalamus and/or hippocampus. Basic research findings that demonstrate developmentally sensitive end points to androgens and E₂ are provided. Furthermore, an approach is suggested to examine differences in EDCs that diverge in their actions at ERs to elucidate their role in sex-/gender-sensitive parameters.

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.

Histologic Features of Prepubertal and Pubertal Reproductive Development in Female Sprague-Dawley Rats

In response to growing concerns that environmental chemicals may have adverse effects on human health by altering the endocrine system, the Endocrine Disruptor Screening Program (EDSP), under the auspices of the United States Environmental Protection Agency (U.S. EPA), recently instituted a Tier I battery of tests including a female pubertal assay. This assay requires dosing of female rats from postnatal day (PND) 22 through PND 42 (or 43), the period of pubertal development in the rat, to identify test articles that may have estrogenic or antiestrogenic effects, or may alter hormones or neurotransmitters. While certain landmarks in female rat reproductive development are published, little is published on the microscopic appearance of the female reproductive tract during prepubertal and pubertal development. In this study, reproductive tissues from three female Sprague-Dawley rats were collected each day from PND 20 through PND 50, such that tissues from a total of 93 rats were collected throughout the prepubertal and pubertal period. Tissues were formalin-fixed, trimmed, paraffin-embedded, sectioned at 5-µm thickness, and examined microscopically. The major histologic features of the female reproductive tract throughout this critical period were described in detail. This information will help pathologists interpret findings observed in female pubertal assays.

The influence of reproductive hormones on the torpor patterns of the marsupial Sminthopsis macroura: bet-hedging in an unpredictable environment

Seasonal cycles of reproduction are common in many mammals and these are combined with the necessary energy budgeting for thermoregulatory challenges. Many mammals meet the challenge of changing environmental temperatures in winter by using torpor, a controlled reduction in body temperature and metabolic rate. We aimed to determine the effects of photoperiod and reproductive hormones on the seasonal cycles of reproduction and torpor use in a marsupial that commences reproduction in winter, the stripe-faced dunnart, Sminthopsis macroura. Males and females were placed under LD 14:10 and natural reproductive hormones blocked by either flutamide (males) or mifepristone (females) or tamoxifen (females). Reproductive parameters, metabolic rate and torpor variables were determined. The same animals were then placed under LD 10:14 and given testosterone (males) or progesterone (females) or oestrogen (females). Reproductive parameters, metabolic rate and torpor variables were measured. Body mass and tail widths (fattening indicator) in males were significantly affected by testosterone, and the effects were reversed by hormone blockers. Reproductive parameters were unaffected. Resting metabolic rate and ability to use torpor were not affected by treatment in males, however torpor characteristics, especially torpor bout duration, were affected by presence of testosterone in males. In females, body mass was unaffected by hormone presence, although tail widths were affected. Disruption of reproductive cycles occurred with hormone blockers in females, however, resting metabolic rate was not affected, and only presence of progesterone affected torpor characteristics in females. Our results differ from those found for rodents, where presence of testosterone abolishes the use of torpor in males, and oestrogen inhibits torpor use in females. Our study suggests that, in this mammal, metabolic responses to the presence or absence of reproductive hormones differs between males and females, and there is no absolute endocrinologically-driven reproductive season demarcated from the torpor season.

Loss of Foxd3 results in decreased β-cell proliferation and glucose intolerance during pregnancy

A complete molecular understanding of β-cell mass expansion will be useful for the improvement of therapies to treat diabetic patients. During normal periods of metabolic challenges, such as pregnancy, β-cells proliferate, or self-renew, to meet the new physiological demands. The transcription factor Forkhead box D3 (Foxd3) is required for maintenance and self-renewal of several diverse progenitor cell lineages, and Foxd3 is expressed in the pancreatic primordium beginning at 10.5 d postcoitum, becoming localized predominantly to β-cells after birth. Here, we show that mice carrying a pancreas-specific deletion of Foxd3 have impaired glucose tolerance, decreased β-cell mass, decreased β-cell proliferation, and decreased β-cell size during pregnancy. In addition, several genes known to regulate proliferation, Foxm1, Skp2, Ezh2, Akt2, and Cdkn1a, are misregulated in islets isolated from these Foxd3 mutant mice. Together, these data place Foxd3 upstream of several pathways critical for β-cell mass expansion in vivo.

Gender-based differences in endocrine and reproductive toxicity

Basic differences in male versus female reproductive physiology lead to differentials in their respective susceptibilities to chemical insult as evidenced by a variety of observations. As individuals undergo maturation from prenatal sex differentiation through pubertal development, these susceptibilities become evident in each gender. Gender bias occurs in human populations for birth defects and for the acceleration of the onset of puberty. Data on gender bias in fetal origins of adult disease are more complex. Useful for understanding reproductive and developmental effects in animals are a range of standard methodological procedures including the multigeneration testing protocol and the National Toxicology Program (NTP) Reproductive Assessment by Continuous Breeding (RACB). Examples of gender-based differences seen in reproductive toxicology studies on animals include teratogenic effects, reproductive effects in adult males and females, and effects on pubertal development. It is clear that gender biases exist in the reproductive and developmental toxicity, and the biological bases for these differences need to be explored.

Lindane may modulate the female reproductive development through the interaction with ER-beta: an in vivo-in vitro approach

Lindane (gamma-HCH) is a persistent environmental pollutant that may act as endocrine disrupter, affecting the nervous, immune and reproductive system, possibly through endocrine-mediated mechanisms. Since both estrogen receptors (ER-alpha and -beta) have shown to be target for endocrine disruption, we investigated the role of gamma-HCH on the development of female reproductive system. For an in vivo evaluation of gamma-HCH effects during prenatal period, pregnant CD1 mice were treated p.o. on gestational days 9-16 with 15 mg/kg bw/day of gamma-HCH and vehicle. The in vivo findings in treated F1 pups - in the absence of signs of systemic toxicity - included increase in the absolute and relative and absolute uterus weight revealed on post-natal day 22, earlier vaginal patency and reduced diameters of primary oocytes at fully sexual maturity. No effects on steroid hormone metabolism (aromatase, testosterone catabolism) were observed. Thus, gamma-HCH elicited subtle effects on female reproductive development likely mediated by ER-beta-mediated pathway(s), without a concurrent impairment of steroid hormone metabolism. Furthermore, to verify whether the endocrine interference of gamma-HCH is attributable to stimulation of ER-beta-mediated pathway(s), its effect has been evaluated in vitro on a cell line, LNCaP, expressing only functional ER-beta. In vitro treatments revealed a concentration-related effect on LNCaP cell viability and proliferation. Significantly, the contemporary addition of a pure anti-estrogen, the ER antagonist ICI 182,780, completely reversed gamma-HCH effects indicating an ER-beta-mediated action. Our findings indicate that gamma-HCH may act as endocrine disruptor during the female reproductive system development and ER-beta as a potential target for this compound and other endocrine disrupting chemicals as well.

Hypothalamus region-specific global gene expression profiling in early stages of central endocrine disruption in rat neonates injected with estradiol benzoate or flutamide

To identify genes linked to early stages of disruption of brain sexual differentiation, hypothalamic region-specific microarray analyses were performed using a microdissection technique with neonatal rats exposed to endocrine-acting drugs. To validate the methodology, the expression fidelity of microarrays was first examined with two-round amplified antisense RNAs (aRNAs) from methacarn-fixed paraffin-embedded tissue (PET) in comparison with expression in unfixed frozen tissue (UFT). Decline of expression fidelity when compared with the 1x-amplified aRNAs from UFTs was found as a result of the preferential amplification of the 3' side of mRNAs in the second round in vitro transcription. However, expression patterns for the 2x-amplified aRNAs were mostly identical between methacarn-fixed PET and UFT, suggesting no obvious influence of methacarn fixation and subsequent paraffin embedding on expression levels. Next, in the main experiment, neonatal rats at birth were treated subcutaneously either with estradiol benzoate (EB; 10 microg/pup) or flutamide (FA; 250 microg/pup), and medial preoptic area (MPOA)-specific microarray analysis was performed 24 h later using 2x-amplified aRNAs from methacarn-fixed PET. Numbers of genes showing constitutively high expression in the MPOA predominated in males, implying a link with male-type growth supported by perinatal testosterone. Around 60% of genes showing sex differences in expression demonstrated altered levels after EB treatment in females, suggesting an involvement of genes necessary for brain sexual differentiation. When compared with EB, FA affected a rather small number of genes, but fluctuation was mostly observed in females, as with EB. Moreover, many selected genes common to EB and FA showed down-regulation in females with both drugs, suggesting a common mechanism for endocrine center disruption in females, at least at early stages of post-natal development.

Risk Assessment of Endocrine Disrupters: The Role of Toxicological Studies

Endocrine disrupters (ED) represent a good challenge for experimental toxicology. In order to deal with several critical points relevant to risk assessment: (a) ED may induce long-term effects upon exposure in susceptible developmental phases, including postnatal life up to puberty; thus, efforts are required to refine testing strategies, for example, by supporting the two-generation rodent study with a comprehensive in vitro/in vivo screening battery; (b) due to the regulatory role of endocrine homeostasis, mechanisms of endocrine disruption may impact on immune, neurobehavioral, and reproductive development, as well as on susceptibility to cancer; (c) the potential multiple exposure to ED with common targets through diet and/or living environment calls for the development of models to understand mechanisms of interactions and effects of mixtures; and (d) last but not least, ED may interact with a number of factors related to differential vulnerability of individuals or population subgroups, including the intake of nutrients or bioactive food components. Besides reducing the chance for noxious chemicals to enter our life, toxicological research on mechanisms may also lead to the definition of possible biomarkers of exposure, effect, and susceptibility that may be further exploited in human health surveillance.

Infantile 4-tert-octylphenol exposure transiently inhibits rat ovarian steroidogenesis and steroidogenic acute regulatory protein (StAR) expression

Phenolic compounds, such as 4-tert-octylphenol (OP), have been shown to interfere with rat ovarian steroidogenesis. However, little is known about steroidogenic effects of infantile OP exposure on immature ovary. The aim of the present study was to investigate the effects of infantile OP exposure on plasma FSH, LH, estradiol, and progesterone levels in 14-day-old female rats. The effect on ovarian steroidogenic acute regulatory protein (StAR) and FSH receptor (FSHr) expression was analyzed by Western blotting. Ex vivo analysis was carried out for follicular estradiol, progesterone, testosterone, and cAMP production. Sprague-Dawley rats were given OP (0, 10, 50, or 100 mg/kg) subcutaneously on postnatal days 6, 8, 10, and 12. On postnatal day 14, plasma FSH was decreased and progesterone increased significantly at a dose of 100 mg OP/kg. In addition, the highest OP dose advanced the time of vaginal opening in puberty. OP had no effect on infantile LH and estradiol levels or ovarian FSHr content. Ovarian StAR protein content and ex vivo hormone and cAMP production were decreased at all OP doses compared to controls. However, hormone levels recovered independent on FSH and even increased above the control level during a prolonged culture. On postnatal day 35, no statistically significant differences were seen between control and OP-exposed animals in plasma FSH, LH, estradiol, and progesterone levels, or in ovarian StAR protein content. The results indicate that the effect of OP on the infantile ovary is reversible, while more permanent effects in the hypothalamus and pituitary, as described earlier, are involved in the reduction of circulating FSH levels and premature vaginal opening.

Effects of in utero and lactational exposure to tamoxifen in SD rats

Pregnant CD (SD) IGS rats were given tamoxifen (TMX) orally at doses of 0.12, 0.6, or 3 microg/kg/day from gestational day 6 to postnatal day 21, and the effects of TMX exposure on all offspring were examined 10 weeks after birth; the reproductive performance of the offspring was also evaluated. Although the body weights of the dams treated with TMX remained normal from gestational day 6 until the day of autopsy (postnatal day 21), three dams in the 3 microg/kg/day group died during the pregnancy or partum periods. These deaths were regarded as the toxicological effects of TMX. No changes were detected in the reproductive parameters of all the TMX groups except for a decrease in the number of newborns/live newborns in the 3 microg/kg/day group. No abnormal clinical signs, body weight change, ano-genital distance, vaginal opening, or organ weight changes were detected in any of TMX groups, but the day of preputial separation was prolonged in the male offspring of all TMX groups and cleft phallus was detected in the female offspring of the 0.6 and 3 microg/kg/day groups. No abnormalities were detected in the reproductive performance of the male and female offspring.

Effects of tamoxifen, 17α-ethynylestradiol, flutamide, and methyltestosterone on plasma vitellogenin levels of male and female Japanese medaka (Oryzias latipes)

The effects of oral administration of tamoxifen, 17α-ethynylestradiol (EE2), flutamide, and methyltestosterone (MT), on plasma vitellogenin levels of male and female medaka were investigated. Medaka were fed diets containing different concentrations of these chemicals for 7 days, and these plasma vitellogenin levels were measured. Tamoxifen increased significantly the vitellogenin levels in male, but inhibited the normal vitellogenin induction in female in the high concentration groups. EE2 increased significantly vitellogenin levels in both sexes. Flutamide increased significantly the vitellogenin levels in female, but gave no effects on male. MT inhibited the normal vitellogenin induction in female, but increased slightly vitellogenin levels in male without a clear tendency. Administration of tamoxifen, EE2, flutamide, and MT showed the different pattern in vitellogenin levels in both sexes.

Use of the Laboratory Rat as a Model in Endocrine Disruptor Screening and Testing

The screening and testing program the US Environmental Protection Agency (EPA) is currently developing to detect endocrine-disrupting chemicals (EDCs) is described. EDCs have been shown to alter the following activities: hypothalamic-pituitary-gonadal (HPG) function; estrogen, androgen, and thyroid hormone synthesis; and androgen and estrogen receptor-mediated effects in mammals and other animals. The value and limitations of mammalian in vivo assays are described that involve the use of the laboratory rat, the EPA Endocrine Disruptor Screening and Testing Advisory Committee species of choice. The discussion includes the evaluation of high-priority chemicals positive in the Tier 1 Screening (T1S) battery, and of subsequent testing in the Tier 2 (T2) battery, with additional short-term screening assays proposed for use in T1.5 to eliminate any uncertainty about T1S results. Descriptions include the in vivo uterotropic assay, which detects estrogens and antiestrogens; the pubertal female assay, which assesses steroidogenesis, antithyroid activity, antiestrogenicity, and HPG function; and the Hershberger assay, which detects the weight of androgen-dependent tissues in castrate-immature-male rats (antiandrogens). Of the several alternative mammalian in vivo assays proposed, a short-term pubertal male rat assay appears most promising for inclusion in T1 or T1.5. An additional in utero-lactational screening protocol is being evaluated, but appears to be better suited for T1.5 or T2 due to the size, complexity, and duration of the assay. The adult intact male assay, also proposed as an alternative for T1, attempts to identify EDCs in a hormonal battery, but has limited value as a screen due to lack of sensitivity and specificity. For Tier 2 testing, the number of endocrine-sensitive endpoints and offspring (F1) examined in multigenerational tests must be thoughtfully expanded for EDCs on a mode-of-action-specific basis, with consideration given to tailoring T2 based on the results of T1S.

Chronic administration of anabolic steroids disrupts pubertal onset and estrous cyclicity in rats

Use of anabolic-androgenic steroids (AASs) is becoming increasingly popular among adolescent girls, yet the effects of AASs on female physiology and development are not well understood. The present study compared the effects of chronic exposure to three individual AASs, stanozolol (0.05-5 mg/kg), 17alpha-methyltestosterone (0.5-5 mg/kg), and methandrostenolone (0.5-5 mg/kg) on the onset of puberty and estrous cyclicity in the rat. Female rats received daily injections of AASs for 30 days (Postnatal Day [PN] 21-51). Rats receiving the highest dose of each of the AASs (5 mg/kg) displayed vaginal opening at a younger age than rats receiving the oil vehicle. The day of first vaginal estrus was delayed in rats receiving stanozolol (5 mg/kg) or 17alpha-methyltestosterone (0.5-5 mg/kg) but not in rats receiving methandrostenolone. At the highest dose (5 mg/kg), each of the AASs reduced the incidence of regular estrous cyclicity during the treatment period. Concurrent administration (on PN21-51) of the androgen receptor antagonist, flutamide (10 mg/kg, twice daily), reversed the effects of 17alpha-methyltestosterone (5 mg/kg) on vaginal opening. Flutamide administration also eliminated the effects of stanozolol (5 mg/kg) and 17alpha-methyltestosterone (5 mg/kg) on the day of first vaginal estrus. In contrast, rats receiving flutamide and methandrostenolone (5 mg/kg) exhibited first vaginal estrus earlier than controls. The present results indicate that chronic exposure to AASs during development has deleterious effects on the female neuroendocrine axis and that these effects appear be mediated via multiple mechanisms.

EFFECTS OF MATERNAL EXPOSURE TO DIETHYLSTILBESTROL ON THE DEVELOPMENT OF THE REPRODUCTIVE SYSTEM AND THYROID FUNCTION IN MALE AND FEMALE RAT OFFSPRING

Diethylstilbestrol (DES) was administered subcutaneously at 1.5 or 15 microg/kg/day (DES 1.5 group, DES 15 group) to pregnant SD rats daily on days 7-21 of gestation to investigate its effects on the development and functions of the reproductive system and thyroid gland in their offspring. Of the 11 pregnant rats in the DES 15 group, only one delivered a live pup. Rat pups in the DES 1.5 group were autopsied at 1, 3, or 6 weeks after birth. In the DES 1.5 group, the plasma T4 concentrations at all weeks of age at autopsy were significantly increased, the TSH concentration at 6 weeks of age was also significantly increased, and the height of thyroid follicular epithelial cells was increased at 3 weeks. The testosterone concentration in the DES 1.5 group at 6 weeks was significantly decreased and the plasma LH concentration was increased. The DES treatment increased the plasma FSH concentration in female pups at 3 weeks, increased the percentages of primary and secondary ovarian follicles, and decreased the percentage of primordial follicles, but did not influence the timing of the vaginal opening or the onset of the estrous cycle. These observations indicate that prenatally administered DES increases thyroid function, and has an inhibitory effect on testicular function and a promoting effect on female reproductive function.