Lifespan Effects of Muscle-Specific Androgen Receptor Overexpression on Body Composition of Male and Female Rats

Androgenic actions of gonadal testosterone are thought to be a major mechanism promoting sex differences in body composition across the lifespan. However, this inference is based on studies of androgen receptor (AR) function in late adolescent or emerging adult rodents. Here we assess body composition and AR expression in skeletal muscle of rats at defined ages, comparing wild-type (WT) to transgenic human skeletal actin-driven AR overexpression (HSAAR) rats which overexpress AR in skeletal muscle. Male and female HSAAR and WT Sprague Dawley rats (N = 288) underwent dual-energy x-ray absorptiometry (DXA) scanning and tissue collection at postnatal day (PND) 1, 10, 21, 42, 70, 183, 243, and 365. Expected sex differences in body composition and muscle mass largely onset with puberty (PND-21), with no associated changes to skeletal muscle AR protein. In adulthood, HSAAR increased tibialis anterior (TA) and extensor digitorum longus mass in males, and reduced the expected gain in gonadal fat mass in both sexes. In WT rats, AR protein was reduced in soleus, but not TA, throughout life. Nonetheless, soleus AR protein expression was greater in male rats than female rats at all ages of sexual development, yet only at PND-70 in TA. Overall, despite muscle AR overexpression effects, results are inconsistent with major sex differences in body composition during sexual development being driven by changes in muscle AR, rather suggesting that changes in ligand promote sexual differentiation of body composition during pubertal timing. Nonetheless, increased skeletal muscle AR in adulthood can be sufficient to increase muscle mass in males, and reduce adipose in both sexes.

Effect of Sex and Cross-Sex Hormone Treatment on Renal Monocarboxylate-Transporter Expression in Rats

Proton- and sodium-dependent monocarboxylate transporters (MCTs/SMCTs) are determinants of renal clearance through the renal reabsorption of monocarboxylate substrates. Prior studies with intact females and males, ovariectomized females and castrated males have revealed the hormonal regulation of renal monocarboxylate-transporter expression, prompting investigation into the regulatory role of individual hormones. The aim of the present study is to evaluate the effect of exogenous sex and cross-sex hormones on renal MCT1, MCT4, CD147 and SMCT1 mRNA and membrane-bound protein expression. Ovariectomized (OVX) females and castrated (CST) male Sprague Dawley rats received estrogen and/or progesterone, testosterone, or a corresponding placebo treatment for 21 days prior to kidney collection. The quantitative measurement of mRNA and membrane-protein levels were conducted using qPCR and Western blot. Quantitative analysis revealed the combination estrogen/progesterone treatment reduced membrane MCT1 and 4 expression and increased SMCT1 expression, while testosterone administration increased MCT1 membrane-protein expression. Correlation analysis indicated that plasma 17β-estradiol was negatively correlated with MCT1 and MCT4 membrane expression, while testosterone was positively correlated. In contrast, SMCT1 membrane expression was positively correlated with 17β-estradiol and progesterone concentrations. MCT1, MCT4, CD147 and SMCT1 renal expression are significantly altered in response to female and male sex hormones following sex and cross-sex hormone treatment in OVX and CST rats. Further studies are needed to understand the complex role of sex hormones, sex hormone receptors and the impact of puberty on MCT/SMCT regulation.

Corticosteroid-binding Globulin (SERPINA6) Establishes Postpubertal Sex Differences in Rat Adrenal Development

Encoded by SerpinA6, plasma corticosteroid-binding globulin (CBG) transports glucocorticoids and regulates their access to cells. We determined how CBG influences plasma corticosterone and adrenal development in rats during the pubertal to adult transition using CRISPR/cas9 to disrupt SerpinA6 gene expression. In the absence of CBG, total plasma corticosterone levels were ∼80% lower in adult rats of both sexes, with a greater absolute reduction in females than in males. Notably, free corticosterone and adrenocorticotropic hormone were comparable between all groups. Between 30 and 90 days of age, wild-type female rats showed increases in adrenal weight and the size of the corticosterone-producing region, the zona fasciculata (zf), in tandem with increases in plasma CBG and corticosterone concentrations, whereas no such changes were observed in males. This sex difference was lost in rats without CBG, such that adrenal growth and zf expansion were similar between sexes. The sex-specific effects of CBG on adrenal morphology were accompanied by remarkable changes in gene expression: ∼40% of the adrenal transcriptome was altered in females lacking CBG, whereas almost no effect was seen in males. Over half of the adrenal genes that normally exhibit sexually dimorphic expression after puberty were similarly expressed in males and females without CBG, including those responsible for cholesterol biosynthesis and mobilization, steroidogenesis, and growth. Rat adrenal SerpinA6 transcript levels were very low or undetectable. Thus, sex differences in adrenal growth, morphology and gene expression profiles that emerge during puberty in rats are dependent on concomitant increases in plasma CBG produced by the liver.

Effects of Tartrazine on Some Sexual Maturation Parameters in Immature Female Wistar Rats

Over the past century, the average age for onset of puberty has declined. Several additives present in our food are thought to contribute significantly to this early puberty which is recognized to also affect people's health in later life. On this basis, the impact of 40-days unique oral administration of the food dye tartrazine (7.5, 27, and 47 mg/kg BW doses) was evaluated on some sexual maturation parameters on immature female Wistar rats. Vaginal opening was evaluated during the treatment period. At the end of the treatments, animals were sacrificed (estrus phase) and the relative weight of reproductive organs, pituitary gonadotrophin and sexual steroids level, cholesterol level in ovaries and folliculogenesis were evaluated. Compared to the control group, animals receiving tartrazine (47 mg/kg BW) showed significantly high percentage of early vaginal opening from day 45 of age, and an increase in the number of totals, primaries, secondaries, and antral follicles; a significant increase in serum estrogen, LH and in uterine epithelial thickness. Our findings suggest that tartrazine considerably disturbs the normal courses of puberty. These results could validate at least in part the global observations on increasingly precocious puberty in girls feeding increasingly with industrially processed foods.

Research-Relevant Conditions and Pathology of Laboratory Mice, Rats, Gerbils, Guinea Pigs, Hamsters, Naked Mole Rats, and Rabbits

Animals are valuable resources in biomedical research in investigations of biological processes, disease pathogenesis, therapeutic interventions, safety, toxicity, and carcinogenicity. Interpretation of data from animals requires knowledge not only of the processes or diseases (pathophysiology) under study but also recognition of spontaneous conditions and background lesions (pathology) that can influence or confound the study results. Species, strain/stock, sex, age, anatomy, physiology, spontaneous diseases (noninfectious and infectious), and neoplasia impact experimental results and interpretation as well as animal welfare. This review and the references selected aim to provide a pathology resource for researchers, pathologists, and veterinary personnel who strive to achieve research rigor and validity and must understand the spectrum of "normal" and expected conditions to accurately identify research-relevant experimental phenotypes as well as unusual illness, pathology, or other conditions that can compromise studies involving laboratory mice, rats, gerbils, guinea pigs, hamsters, naked mole rats, and rabbits.

The laboratory rat: Age and body weight matter

Animal experimentation helps us to understand human biology. Rodents and, in particular, rats are among the most common animals used in animal experiments. Reporting data on animal age, animal body weight, and animal postnatal developmental stages is not consistent, which can cause the failure to translate animal data to humans. This review summarizes age-related postnatal developmental stages in rats by addressing age-related changes in their body weights. The age and body weight of animals can affect drug metabolism, gene expression, metabolic parameters, and other dependent variables measured in animal studies. In addition, considering the age and the body weight of the animals is of particular importance in animal modeling of human diseases. Appropriate reporting of age, body weight, and the developmental stage of animals used in studies can improve animal to human translation.

Scientific and Regulatory Policy Committee Best Practices: Documentation of Sexual Maturity by Microscopic Evaluation in Nonclinical Safety Studies

The sexual maturity status of animals in nonclinical safety studies can have a significant impact on the microscopic assessment of the reproductive system, the interpretation of potential test article-related findings, and ultimately the assessment of potential risk to humans. However, the assessment and documentation of sexual maturity for animals in nonclinical safety studies is not conducted in a consistent manner across the pharmaceutical and chemical industries. The Scientific and Regulatory Policy Committee of the Society of Toxicologic Pathology convened an international working group of pathologists and nonclinical safety scientists with expertise in the reproductive system, pathology nomenclature, and Standard for Exchange of Nonclinical Data requirements. This article describes the best practices for documentation of the light microscopic assessment of sexual maturity in males and females for both rodent and nonrodent nonclinical safety studies. In addition, a review of the microscopic features of the immature, peripubertal, and mature male and female reproductive system and general considerations for study types and reporting are provided to aid the study pathologist tasked with documentation of sexual maturity.

In Utero and Lactational Exposure to an Environmentally Relevant Mixture of Brominated Flame Retardants Induces a Premature Development of the Mammary Glands

In utero and prepubertal development of the mammary glands occurs minimally in a hormone independent manner until puberty where maturation of the hypothalamic-pituitary-gonadal axis drives an extensive remodeling. Nevertheless, because the immature glands contain functional hormone receptors, they are especially vulnerable to the effects of endocrine disruptors, such as brominated flame retardants (BFRs). BFRs are widespread chemicals added to household objects to reduce their flammability, and to which humans are ubiquitously exposed. We previously reported that in utero and lactational exposure to BFRs resulted in an impaired mammary gland development in peripubertal animals. Here, we assessed whether BFR-induced disruption of mammary gland development could manifest earlier in life. Dams were exposed prior to mating until pups' weaning to a BFR mixture (0, 0.06, 20, or 60 mg/kg/day) formulated according to levels found in house dust. The mammary glands of female offspring were collected at weaning. Histo-morphological analyses showed that exposure to 0.06 mg/kg/day accelerates global epithelial development as demonstrated by a significant increase in total epithelial surface area, associated with a tendency to increase of the ductal area and thickness, and of lumen area. Significant increases of the Ki67 cell proliferation index and of the early apoptotic marker cleaved caspase-9 were also observed, as well as an upward trend in the number of thyroid hormone receptor α1 positive cells. These molecular, histologic, and morphometric changes are suggestive of accelerated pubertal development. Thus, our results suggest that exposure to an environmentally relevant mixture of BFRs induces precocious development of the mammary gland.

Melatonin on hypothyroidism and gonadal development in rats: a review

We evaluated the evidence in research on the effects of melatonin on hypothyroidism and gonadal development. According to the World Health Organization, thyroid disorders due to iodine deficiency affect about 740 million people worldwide. Hypothyroidism is a thyroid dysfunction characterized by hypometabolism of the gland, with reduced or physiologically normal T3 and T4 serum levels, and high TSH level. This disorder occurs mainly in adult women in the reproductive phase, with a prevalence of 2% among the world's female population, with profound repercussions on gestation and fetal formation. During the gestational period, the thyroid is initially stimulated by high concentrations of human chorionic gonadotrophin; thus, maintaining maternal euthyroidism during pregnancy and lactation is fundamental for fetal growth and development. Besides, the hormones produced by this gland are involved in the formation of various organs, such as the skin, brain and gonads. Hypothyroidism is associated with several menstrual abnormalities, anovulation and hyperprolactinemia, resulting in a high rate of abortions, premature births, placental rupture, and weight-related neonatal deficits. In addition, there are studies showing that hypothyroidism can affect ovarian morphology (number of ovarian follicles) and testicular morphology (changes in the testicular-lumen epithelium). Melatonin is a hormone known to modulate the estrous cycle and pregnancy, and studies show that the exogenous application of melatonin increased T4 levels in female rats and controlled the decrease in T3 serum levels, reverting the sigs of hypothyroidism.

Cypermethrin exposure during perinatal period affects fetal development and impairs reproductive functions of F1 female rats

Cypermethrin (CYP) is a ubiquitously present synthetic pyrethroid insecticide. It has endocrine disrupting activities which may adversely affect reproductive development and functions of offspring if exposed during critical developmental period. The present study was undertaken to delineate the effects of CYP exposure in pregnant female rats during perinatal period on the sexual maturation, hormonal regulation, reproductive development and fertility of F1 female offspring and its molecular mechanism of action. Pregnant rats (F0) were gavaged daily with 0, 1, 10, 25 mg/kg bw/day CYP and 10 μg/kg bw/day Diethylstilbestrol (DES; positive control) from gestation day (GD) 6 to postnatal day (PND) 21. The reproductive development and function parameters were evaluated at PND 45 and 75. Reduced body weight, delayed vaginal opening, and disrupted estrous cyclicity were observed at 25 mg/kg CYP dose. CYP exposure significantly affected the reproductive organ development and their functions at all doses. Significant alterations in ovarian and uterine histology such as luteinization, reduction of primordial follicular reserves, presence of multi-oocyte follicles and thin degenerative luminal and glandular uterine epithelium were observed at adulthood. Altered circulatory steroid hormone levels and expression of ovarian and uterine steroid hormone receptors were observed at PND 75 in the F1 female offspring. Expression of HOXA10 and α-SMA which are important for uterine integrity and functions, were found to be altered at PND 75. Increased pre-implantation loss (PIL%), post-implantation loss (POL%), and reduced litter size in F1 females when cohabitated with unexposed fertile male rats were observed. Overall, perinatal exposure of pregnant rats to CYP led to significant long lasting effects on the reproductive functions of F1 female offspring. The adverse effects were passed on to F2 generation via female germ line and posed developmental anomalies. The present finding necessitates additional molecular studies to understand its trans-generational mechanism of action via female germline.

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.

Disruptions in the female reproductive system on consumption of calcium carbide ripened fruit in mouse models

This study investigated for the first time the outcome of ingestion of calcium carbide-ripened fruit on some female reproductive parameters. A set of unripe mature bananas ripened with calcium carbide (CCRB) and another set ripened via non-artificial means (NARB) were fed orally to prepubertal female mice for three days using the uterotrophic assay procedure. A distilled water group and oestradiol group (10 mg/kg) were also assigned. Food intake, body weights, vaginal openings and cytology were analysed. Samples of blood, uteri, ovaries and cervices were additionally collected and analysed. Increased serum oestrogen level and uterus weight were detected in the CCRB and oestradiol treated groups. Histopathology showed increased numbers of myometrial cells, presence of secondary follicles and regressing corpus lutea as well as thickened cervix epithelia which were evidence of oestrogenic disruptions. This study has shown that consumption of fruits ripened with calcium carbide negatively alters the female reproductive physiology, accelerates puberty onset and increases serum oestrogen levels. Caution must therefore be exercised by fruit sellers in the use of calcium carbide and policies set in place for strict regulation of its use worldwide.

Soy Isoflavone Improved Female Sexual Dysfunction of Mice Via Endothelial Nitric Oxide Synthase Pathway

Introduction

Female sexual dysfunction (FSD) is a common endocrine disease that impairs the quality of life for many women. The existing therapy strategies still have many disadvantages. It is necessary to explore new pharmacologic treatments that are effective and safe.

Aim

The aim of this study was to explore the effects of soy isoflavone (SI) on FSD in mice and the underlying mechanisms.

Methods and Main Outcome Measures

Laser Doppler flowmetry was used to determine vaginal blood flow. Serum hormone levels and histologic changes of the vagina were analyzed by enzyme-linked immunosorbent assay (ELISA) and by hematoxylin and eosin (H&E) and Masson’s trichome staining. The mRNA and protein expression of endothelial nitric oxide synthase (eNOS) was then evaluated by quantitative real-time polymerase chain reaction and western blot assays.

Results

Vaginal blood flow was found to be remarkably lower in adult mice, and SI was shown to increase vaginal blood flow in a dose-dependent manner (P < .05). The results of ELISA and H&E and Masson’s trichome staining suggest that SI had a positive effect on FSD, as evidenced by the levels of hormones in serum and histologic changes of the vagina, which changed consistently. In addition, the level of eNOS was positively correlated with the concentration of SI, and eNOS inhibitor was able to reverse the improvement in sexual function induced by SI.

Conclusion

Our study demonstrated that SI could improve sexual function by upregulating the eNOS pathway. Therefore, SI might serve as a promising candidate for the treatment of sexual dysfunction.

Zhang J, Zhu Y, Pan L, et al. Soy Isoflavone Improved Female Sexual Dysfunction of Mice Via Endothelial Nitric Oxide Synthase Pathway. Sex Med 2019; 7:345–351.

Chronic gestational hypoxia accelerates ovarian aging and lowers ovarian reserve in next-generation adult rats

Chronic fetal hypoxia is a common complication observed in human pregnancy, impacting pregnancies across global contexts. Exposure to chronic intrauterine hypoxia has major short- and long-term consequences for offspring health. However, the impact of chronic gestational hypoxia on female reproductive system development is unknown. We aimed to understand the impact of exposure to chronic fetal hypoxia on the developing female reproductive system. Wistar rat dams underwent normoxia (21%) or hypoxia (13%) during pregnancy. Postnatally, all female offspring were maintained in normoxic conditions into early adulthood. Female rats exposed to chronic gestational hypoxia (13%) during their intrauterine development had decreased ovarian primordial follicular reserve compared to controls (P < 0.05). Adult females who had been exposed to chronic fetal hypoxia had significantly reduced somatic ovarian telomere length (P < 0.05) and reduced ovarian protein expression of KU70, a critical component of the DNA-activated protein kinase repair complex (P < 0.01). Gene expression of NADPH oxidase 2-mediated oxidative stress markers was increased (P < 0.05). Exposure to chronic hypoxia during fetal development leads to accelerated aging of the somatic ovary and decreased ovarian reserve in adulthood. Ovarian aging is highly sensitive to gestational hypoxia, with implications for future fertility in next-generation offspring of high-risk pregnancies.-Aiken, C. E., Tarry-Adkins, J. L., Spiroski, A.-M., Nuzzo, A. M., Ashmore, T. J., Rolfo, A., Sutherland, M. J., Camm, E. J., Giussani, D. A., Ozanne, S. E. Chronic gestational hypoxia accelerates ovarian aging and lowers ovarian reserve in next-generation adult rats.

Early life environment influences the trajectory of post-partum weight loss in adult female rats

RESEARCH QUESTION

The physiological processes of pregnancy and lactation require profound changes in maternal metabolism and energy balance. The timescale of metabolic reversion after pregnancy, in particular post-partum weight loss, is highly variable between individuals. Currently, mechanisms influencing post-partum metabolic recovery are not well understood. The hypothesis tested here is that, in common with other metabolic and obesity-related outcomes, capacity for post-partum weight loss is influenced by developmental programming.

DESIGN

Adult female Wistar rats exposed to a maternal low-protein diet in utero then weaned onto a control diet post-natally (recuperated group) were compared with controls. Adult females from both groups underwent pregnancy at 3 months of age. Weight changes and metabolic parameters during pregnancy and lactation were compared between control and recuperated groups, and also with non-pregnant littermates.

RESULTS

Pregnancy weight gain was not different between the control and recuperated groups, but post-partum recuperated animals remained significantly heavier than both post-partum control animals (P<0.05) and their non-pregnant recuperated littermates (P<0.05) at the end of lactation. Post-partum recuperated animals had more intra-abdominal fat mass (P<0.05) and higher serum triglyceride concentrations (P<0.01) than controls. Post-partum recuperated animals also had increased expression of IL6, NRF2 and ALOX12 (key regulators of inflammation and lipoxygenase activity) in the intra-abdominal adipose tissue compared with control groups.

CONCLUSIONS

Mothers who themselves have been exposed to adverse early life environments are likely to have slower metabolic recovery from pregnancy than controls. Failure to return to pre-pregnancy weight after delivery predisposes to persisting sequential inter-pregnancy weight gain, which can represent a significant metabolic burden across a life course involving several pregnancies.

n-butylparaben exposure during perinatal period impairs fertility of the F1 generation female rats

Parabens are a class of preservatives widely used in the majority of personal care products, cosmetics, medicines, and food products. However, current literature suggests its plausible role as an endocrine disruptor, hence the present study was undertaken to delineate the effects of n-butyl paraben on perinatally exposed F1 female rats. F₀ dams were exposed subcutaneously to n-butylparaben from gestation day 6 (GD 6) to postnatal day (PND) 21 with doses of 10, 100, and 1000 mg/kg Bw/day in corn oil. The F1 female rats were monitored for pubertal development and sexual maturation through PND 30, 45, and 75; which were subsequently subjected to fertility assessment at PND 75. Perinatal exposure to n-butylparaben resulted in- This study documents impaired steroidogenesis and folliculogenesis might be the prime reason for the reduced fertility of F1 female rats. Hence, our study suggests that health monitors need to counsel potential females planning for pregnancy to avoid exposure to parabens.

Myrianthus arboreus P. Beauv (Cecropiaceae) Extracts Accelerates Sexual Maturation, and Increases Fertility Index and Gestational Rate in Female Wistar Rats

Background: Despite the wide use of leaves of Myrianthus arboreus (Cecropiaceae) in several African countries including Cameroon as food and against amenorrhea and female infertility, it has never been tested for this purpose. Methods: Using immature female Wistar rats, the impact of M. arboreus on the sexual maturation parameters (vaginal opening, ovarian relative weight and follicle maturation, gonadotropins and ovarian hormones serum levels) and fertility index has been evaluated through a 30-day oral administration of aqueous and methanol extracts of leaves at the doses of 20, 110 and 200 g/kg/day. Results: Aqueous extract increased the ovarian relative weight (p < 0.001), progesterone (p < 0.001) and gonadotropins (p < 0.001) serum levels, and induced the maturation of ovarian follicles. The methanol extract additionally induced an early vaginal opening (p < 0.001), uterine growth (p < 0.01) and increased estradiol (p < 0.001) serum levels. The fertility index generally increased following treatments, while the gestation rate remained almost unaffected except at the highest tested dose of M. arboreus extracts where lowest values were observed. Conclusion: Globally, M. arboreus induced an early puberty onset and an increased fertility rate validating at least in part its traditional use for female infertility.

Reproductive outcomes in rat female offspring from male rats co-exposed to rosuvastatin and ascorbic acid during pre-puberty

Dyslipidemias are occurring earlier in different countries due to the increase of obesity, bad eating habits, and sedentary lifestyle. Rosuvastatin reduces serum cholesterol; however, several studies associated statin exposure with male reproduction impairment. Ascorbic acid (AA) is an antioxidant substance that plays a protective role in the male reproductive system. Male rats were randomly divided into 6 experimental groups (n = 10), which received saline solution 0.9%, 3 or 10 mg/kg/day of rosuvastatin, 150 mg/day of AA or 3 or 10 mg/kg/day of rosuvastatin associated with 150 mg/day of AA from post-natal day (PND) 23 until PND 53. On PND 100, males were mated with non-treated female rats to obtain the female pups. The day of vaginal opening and the first estrus were assessed in the offspring. Two sets of females were euthanized on the first estrus after PND 42 and PND 75 to evaluate the histology of reproductive organs and hormone levels. A third set was used for sexual behavior and fertility test around PND 75. Female offspring from males exposed or co-exposed to the higher dose of statin exhibited a lower number of corpora lutea during puberty. On sexual maturity, the experimental group from males that were exposed to 3 mg displayed lower uterine luminal epithelium area. Paternal exposure to rosuvastatin at pre-puberty diminished uterine luminal epithelium in female offspring suggesting epigenetic changes were initiated by statin. Ascorbic acid co-administered to pre-pubertal males was able to ameliorate the reproductive damage in rat female offspring in adulthood.

Species Comparison of Postnatal Development of the Female Reproductive System

The postnatal development of the female reproductive system in laboratory animals and humans is reviewed. To enable a meaningful species comparison of the developing female reproductive system, common definitions of developmental processes were established with a focus made on aspects that are similar across species. A species comparison of the key endocrine, morphologic, and functional (onset of ovarian cycles and ability to reproduce) features of postnatal development of the female reproductive system is provided for human, nonhuman primate, dog, rat, and also mouse, minipig, and rabbit where possible. Species differences in the timing and control of female sexual maturation are highlighted. Additionally, a species comparison of the type and timing of female reproductive ovarian cycles was compiled. Human development provided the frame of reference, and then other common laboratory species were compared. The comparison has inherent challenges because the processes involved and sequence of events can differ greatly across species. Broad strokes were taken to assign a particular average age to an event and are to be used with caution. Methods of evaluation of postnatal female reproductive development in laboratory animals are discussed. Lastly, control rodent data from one of the author's laboratory on vaginal opening, first estrus, estrous cyclicity, and the histopathology involved with the developing female rat and mouse are presented. The information provided in this review is intended to be a resource for the design and interpretation of juvenile animal toxicity testing and ultimately, the relevance of the data to characterize potential risks for women and girls. Birth Defects Research 110:163-189, 2018. © 2017 Wiley Periodicals, Inc.

Points to Consider in Designing and Conducting Juvenile Toxicology Studies

In support of a clinical trial in the pediatric population, available nonclinical and clinical data provide input on the study design and safety monitoring considerations. When the existing data are lacking to support the safety of the planned pediatric clinical trial, a juvenile animal toxicity study is likely required. Usually a single relevant species, preferably a rodent, is chosen as the species of choice, while a nonrodent species can be appropriate when scientifically justified. Juvenile toxicology studies, in general, are complicated both conceptually and logistically. Development in young animals is a continuous process with different organs maturing at different rates and time. Structural and functional maturational differences have been shown to affect drug safety. Key points to consider in conducting a juvenile toxicology study include a comparative development of the organ systems, differences in the pharmacokinetics/absorption, distribution, metabolism, excretion (PK/ADME) profiles of the drug between young animal and child, and logistical requirement in the juvenile study design. The purpose of this publication is to note pertinent points to consider when designing and conducting juvenile toxicology studies and to aid in future modifications and enhancements of these studies to enable a superior predictability of safety of medicines in the pediatric population.

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.

The Impact of Age on the Female Reproductive System

Evaluation of the female reproductive system in a general toxicity setting can be challenging for the toxicologic pathologist due to the cyclic nature of the estrous and menstrual cycles, timing of puberty and reproductive senescence, and species differences. Age in particular can have a significant impact on the histologic appearance of the female reproductive system and create challenges when trying to distinguish test article-related findings from normal developmental or senescent changes. This review describes the key physiologic and histologic features of immaturity, the transition through puberty, sexual maturity, and reproductive senescence in the female reproductive system, with an emphasis on practical applications for the toxicologic pathologist, and includes recommendations for distinguishing and documenting these developmental periods. Rats and cynomolgus monkeys are used as examples throughout with correlations to clinically observed end points to better aid the toxicologic pathologist in understanding how age may impact study interpretation.

Scientific and Regulatory Policy Committee Points to Consider Review: Inclusion of Reproductive and Pathology End Points for Assessment of Reproductive and Developmental Toxicity in Pharmaceutical Drug Development

Standard components of nonclinical toxicity testing for novel pharmaceuticals include clinical and anatomic pathology, as well as separate evaluation of effects on reproduction and development to inform clinical development and labeling. General study designs in regulatory guidances do not specifically mandate use of pathology or reproductive end points across all study types; thus, inclusion and use of these end points are variable. The Scientific and Regulatory Policy Committee of the Society of Toxicologic Pathology (STP) formed a Working Group to assess the current guidelines and practices on the use of reproductive, anatomic pathology, and clinical pathology end points in general, reproductive, and developmental toxicology studies. The Working Group constructed a survey sent to pathologists and reproductive toxicologists, and responses from participating organizations were collected through the STP for evaluation by the Working Group. The regulatory context, relevant survey results, and collective experience of the Working Group are discussed and provide the basis of each assessment by study type. Overall, the current practice of including specific end points on a case-by-case basis is considered appropriate. Points to consider are summarized for inclusion of reproductive end points in general toxicity studies and for the informed use of pathology end points in reproductive and developmental toxicity studies.

Juvenile Toxicology: Relevance and Challenges for Toxicologists and Pathologists

The Society of Toxicologic Pathology (STP) Education Committee and the STP Reproductive Special Interest Group held a North Carolina regional meeting entitled, "Juvenile Toxicology: Relevance and Challenges for Toxicologists and Pathologists" on March 13, 2015, at the National Institute of Environmental Health Sciences/National Toxicology Program in Research Triangle Park, North Carolina. The purpose of this regional meeting was to familiarize attendees with the topic of juvenile toxicity testing and discuss its relevance to clinical pediatric medicine, regulatory perspectives, challenges of appropriate study design confronted by toxicologists, and challenges of histopathologic examination and interpretation of juvenile tissues faced by pathologists. The 1-day meeting was a success with over 60 attendees representing industry, government, research organizations, and academia.

Scientific and Regulatory Policy Committee (SRPC) Points to Consider: Histopathology Evaluation of the Pubertal Development and Thyroid Function Assay (OPPTS 890.1450, OPPTS 890.1500) in Rats to Screen for Endocrine Disruptors

The U.S. Environmental Protection Agency Endocrine Disruptor Screening Program (EDSP) is a multitiered approach to determine the potential for environmental chemicals to alter the endocrine system. The Pubertal Development and Thyroid Function in Intact Juvenile/Peripubertal Female and Male Rats (OPPTS 890.1450, 890.1500) are 2 of the 9 EDSP tier 1 test Guidelines, which assess upstream mechanistic pathways along with downstream morphological end points including histological evaluation of the kidneys, thyroid, and select male/female reproductive tissues (ovaries, uterus, testes, and epididymides). These assays are part of a battery of in vivo and in vitro screens used for initial detection of test article endocrine activity. In this Points to Consider article, we describe tissue processing, evaluation, and nomenclature to aid in standardization of assay results across laboratories. Pubertal assay end points addressed include organ weights, estrous cyclicity, clinical pathology, hormonal assays, and histological evaluation. Potential treatment-related findings that may indicate endocrine disruption are reviewed. Additional tissues that may be useful in assessment of endocrine disruption (vagina, mammary glands, and liver) are discussed. This Points to Consider article is intended to provide information for evaluating peripubertal tissues within the context of individual assay end points, the overall pubertal assay, and tier I assays of the EDSP program.

Postnatal ovary development in the rat: morphologic study and correlation of morphology to neuroendocrine parameters

Histopathologic examination of the immature ovary is a required end point on juvenile toxicity studies and female pubertal and thyroid function assays. To aid in this evaluation and interpretation of the immature ovary, the characteristic histologic features of rat ovary through the developmental periods are described. These histologic features are correlated with published changes in neuroendocrine profiles as the hypothalamic-pituitary-gonadal axis matures. During the neonatal stage (postnatal day [PND] 0-7), ovarian follicle development is independent of pituitary gonadotropins (luteinizing hormone [LH] or follicle-stimulating hormone [FSH]), and follicles remain preantral. Antral development of "atypical" follicles occurs in the early infantile period (PND 8-14) when the ovary becomes responsive to pituitary gonadotropins. In the late infantile period (PND 15-20), the zona pellucida appears, the hilus forms, and antral follicles mature by losing their "atypical" appearance. The juvenile stage (PND 21-32) is the stage when atresia of medullary follicles occurs corresponding to a nadir in FSH levels. In the peripubertal period (PND 33-37), atresia subsides as FSH levels rebound, and LH begins its bimodal surge pattern leading to ovulation. This report will provide pathologists with baseline morphologic and endocrinologic information to aid in identification and interpretation of xenobiotic effects in the ovary of the prepubertal rat.

Nonproliferative and proliferative lesions of the rat and mouse female reproductive system

The INHAND (International Harmonization of Nomenclature and Diagnostic Criteria for Lesions in Rats and Mice) Project (www.toxpath.org/inhand.asp) is a joint initiative of the Societies of Toxicological Pathology from Europe (ESTP), Great Britain (BSTP), Japan (JSTP) and North America (STP) to develop an internationally accepted nomenclature for proliferative and nonproliferative lesions in laboratory animals. The purpose of this publication is to provide a standardized nomenclature for classifying microscopic lesions observed in the female reproductive tract of laboratory rats and mice, with color photomicrographs illustrating examples of some lesions. The standardized nomenclature presented in this document is also available electronically on the internet (http://www.goreni.org/). Sources of material included histopathology databases from government, academia, and industrial laboratories throughout the world. Content includes spontaneous and aging lesions as well as lesions induced by exposure to test materials. There is also a section on normal cyclical changes observed in the ovary, uterus, cervix and vagina to compare normal physiological changes with pathological lesions. A widely accepted and utilized international harmonization of nomenclature for female reproductive tract lesions in laboratory animals will decrease confusion among regulatory and scientific research organizations in different countries and provide a common language to increase and enrich international exchanges of information among toxicologists and pathologists.