Effects of Di-Isononyl Phthalate (DiNP) on Follicular Atresia in Zebrafish Ovary

Di-isononyl phthalate (DiNP) is a plasticizer reported to elicit hormone-like activity and disrupt metabolism and reproduction in fish and other vertebrates. In general, phthalates have been used at high concentrations beyond reported environmental levels to assess their adverse effects on fish gonadal physiology. The present study exposed adult female zebrafish to a wide range of DiNP concentrations [0.42 µg L^-1 (10^-9 M), 4.2 µg L^-1 (10^-8 M), and 42 µg L^-1 (10^-7 M)] for 21 days. We evaluated gene expression profiles related to apoptosis, autophagy, and oxidative stress; DNA fragmentation (TUNEL assay: terminal deoxynucleotidyl transferase dUTP nick end labeling) and caspase activity (CAS3) were also examined. Exposure to 0.42 and 4.2 µg L^-1 upregulated the genes coding for tnfa and baxa, sod1, prkaa1, respectively. CAS3 immunohistochemistry revealed a higher number of positive vitellogenic oocytes in ovaries exposed to 0.42 µg L^-1. Subsequently, we examined the relationship between CAS3 signaling and DNA fragmentation. Accordingly, DNA fragmentation was observed in vitellogenic follicles of fish exposed to 0.42 and 4.2 μg L^-1. Our results demonstrate that follicular atresia can occur after exposure to environmental levels of DiNP for 21 days, which may adversely affect the reproductive performance of female zebrafish in a non-monotonic manner.

Effects of varying dietary intoxication with lead on the performance and ovaries of laying hens

In this study, we explored the effect of dietary lead nitrate on zootechnical performance, egg quality, accumulation of ovarian plumbum (Pb), follicular atresia rate, and ovarian oxidative stress in laying hens. Furthermore, the nuclear factor erythroid 2-related factor 2 (Nrf2) signaling molecule was studied to reveal the molecular mechanism of the stress. A total of 512 Hy-Line Brown laying hens aged 40 wk were randomly allocated to 4 groups (with 8 pens per group and 16 hens per pen). The Pb concentrations used to treat the 4 groups were 3.20, 33.20, 63.20, and 93.20 mg/kg. The results revealed that dietary Pb exposure significantly linearly reduced the zootechnical performance (P < 0.01) but significantly linearly increased the feed conversion ratio (P < 0.01). The dietary Pb exposure significantly linearly reduced the Haugh units (P < 0.01), albumen height (P < 0.01), eggshell thickness (P < 0.01), and eggshell strength (P < 0.01). In addition, the dietary Pb exposure significantly enhanced the follicular atresia rate (P < 0.01). After dietary Pb exposure, superoxide dismutase (P < 0.01) and glutathione peroxidase (GSH-Px) (P < 0.01) activities and glutathione (P < 0.01) contents were significant decreased quadratically, and there were significant linear decreases in the activities of catalase (CAT) (P < 0.01) and glutathione reductase (GR) (P < 0.01), whereas malondialdehyde content was significantly linearly increased (P < 0.01). In addition, except for manganese superoxide dismutase, the gene expressions of copper-zinc superoxide dismutase (P < 0.01), CAT (P < 0.01), and GR (P < 0.01) were significant decreased linearly. In addition, there were significantly quadratic decreases in the mRNA expressions of GSH-Px (P < 0.01) and Nrf2 (P < 0.01). By way of contrast, the Kelch-like ECH-associated protein 1 (Keap1) gene expression was significantly linearly increased (P < 0.01). In conclusion, dietary Pb exposure could induce oxidative stress by impairing the Nrf2-Keap1 signal pathway in the ovaries of laying hens.

Doxorubicin obliterates mouse ovarian reserve through both primordial follicle atresia and overactivation

Ovarian toxicity and infertility are major side effects of cancer therapy in young female cancer patients. We and others have previously demonstrated that doxorubicin (DOX), one of the most widely used chemotherapeutic chemicals, has a dose-dependent toxicity on growing follicles. However, it is not fully understood if the primordial follicles are the direct or indirect target of DOX. Using both prepubertal and young adult female mouse models, we comprehensively investigated the effect of DOX on all developmental stages of follicles, determined the impact of DOX on primordial follicle survival, activation, and development, as well as compared the impact of age on DOX-induced ovarian toxicity. Twenty-one-day-old CD-1 female mice were intraperitoneally injected with PBS or clinically relevant dose of DOX at 10 mg/kg once. Results indicated that DOX primarily damaged granulosa cells in growing follicles and oocytes in primordial follicles and DOX-induced growing follicle apoptosis was associated with the primordial follicle overactivation. Using the 5-day-old female mice with a more uniform primordial follicle population, our data revealed that DOX also directly promoted primordial follicle death and the DNA damage-TAp63α-C-CASP3 pathway was involved in DOX-induced primordial follicle oocyte apoptosis. Compared to 21-day- and 8-week-old female mice that were treated with the same dose of DOX, the 5-day-old mice had the most severe primordial follicle loss as well as the least degree of primordial follicle overactivation. Taken together, these results demonstrate that DOX obliterates mouse ovarian reserve through both primordial follicle atresia and overactivation and the DOX-induced ovarian toxicity is age dependent.

Silica nanoparticle exposure inducing granulosa cell apoptosis and follicular atresia in female Balb/c mice

Given that the effects of ultrafine fractions (< 0.1 μm) on reproductive diseases are gaining attention, this study aimed to explore the influence of silica nanoparticle (SiNP)-induced female reproductive dysfunction. In this study, 80 female mice were randomly divided into four groups including a control group and three concentrations of SiNP groups (7, 21, 35 mg/kg). Mice were exposed to the vehicle control and silica nanoparticles by tracheal perfusion every 3 days a total of five times in 15 days. Then, half of the mice in each group were sacrificed on 15 and 30 days after the first dose, respectively. Our findings indicated that SiNPs can result in ovarian damage, cause an imbalance of sex hormones, increase the number of atretic and primary follicles, and induce oxidative stress and DNA strand breaks in ovary by day 15. The protein expressions of ATM, CHK-2, P53, E2F1, P73, BAX, Caspase-9, and Caspase-3 were significantly increased, while expressions of RAD51 were down-regulated after SiNP exposure by days 15. Estradiol increased, while progesterone increased in low dose and decreased in high dose after SiNP exposure by 15 days. However, these changes were recovered by 30 days. The results suggest that SiNPs can cause reversible damage to follicles in mice. SiNPs could primarily cause DNA damage and DNA damage response through oxidative stress, while DNA damage repair failure because of severe DNA damage activated the mitochondrial apoptosis pathway and therefore resulted in apoptosis of granulosa cell. In addition, the disorder of reproductive endocrine function caused by SiNPs could be another reason for SiNP-induced reproductive dysfunction in mice. These events in turn induce the follicles to undergo atresia.

The effect of DHEA on apoptosis and cohesin levels in oocytes in aged mice

Female fertility declines with age as the number of ovarian follicles decreases and aneuploidy increases. Degradation of the cohesin complex might be responsible for age-related aneuploidy. Dehydroepiandrosterone (DHEA) can improve the ovarian reserve and reduce the rate of aneuploidy, but the relationship between DHEA and cohesin levels in oocytes is still unknown. The aim of the current study was to evaluate the effect of the supplement DHEA on ovarian function, including the number of follicles and cohesin levels in oocytes. C57BL/6J mice at 3 weeks, 6 weeks, 12 weeks, 6 months, and 10 months of age were used to obtain a systematic view into follicle apoptosis and cohesin levels in oocytes. Nine-month-old C57BL/6J mice were administered saline (n = 5), 17β-estradiol (100 µg/kg per day, n = 5), or DHEA (5mg/Kg per day, n = 5). After 4 weeks, aged mice were weighed and sacrificed, and ovarian tissue samples were prepared. Anti-VASA staining and HE staining were used to count the number of follicles. Anti-γH2AX staining and TUNEL were used to measure follicle apoptosis and immunofluorescent staining was used to detect the levels of three oocyte cohesin subunits: REC8, SMC1β, and SMC3. Administration of the supplements 17β-estradiol and DHEA to aged mice increased the number of primordial and primary follicles and decreased the age-related apoptosis of follicles. Levels of the cohesin subunits REC8 and SMC1β declined with age, but DHEA and 17β-estradiol tended to delay that decline. The supplement DHEA increased the number of primordial and primary follicles in aged mice by inhibiting follicle apoptosis and tended to delay the decrease in cohesin levels in oocytes.

Intra-cellular mechanism of Anti-Müllerian hormone (AMH) in regulation of follicular development

Anti-Müllerian hormone (AMH) is a member of the transforming growth factor-β superfamily and plays a crucial role in testicular and ovarian functions. In clinical practice, AMH is used as a diagnostic and/or prognostic marker in women in association with ovulation induction and in various pathophysiological conditions. Despite widespread clinical use of AMH, our mechanistic understanding of AMH actions in regulating follicular development is limited. Using a mouse model, we in this study report that in vivo AMH treatment while stalls follicular development and inhibits ovulation, also prevents follicular atresia. We further show that these AMH actions are mediated through induction of two miRNAs, miR-181a and miR-181b, which regulate various aspects of FSH signaling and follicular growth, ultimately affecting downstream gene expression and folliculogenesis. We also report that in this mouse model AMH pre-treatment prior to superovulation improves oocyte yield. These studies, therefore, offer new mechanistic insight into AMH actions in folliculogenesis and point toward potential utilization of AMH as a therapeutic agent.

Resveratrol protects the ovary against chromium-toxicity by enhancing endogenous antioxidant enzymes and inhibiting metabolic clearance of estradiol

Resveratrol (RVT), a polyphenolic component in grapes and red wine, has been known for its cytoprotective actions against several diseases. However, beneficial effects of RVT against early exposure to endocrine disrupting chemicals (EDCs) have not been understood. EDCs are linked to several ovarian diseases such as premature ovarian failure, polycystic ovary syndrome, early menopause and infertility in women. Hexavalent chromium (CrVI) is a heavy metal EDC, and widely used in >50 industries. Environmental contamination with CrVI in the US is rapidly increasing, predisposing the human to several illnesses including cancers and still birth. Our lab has been involved in determining the molecular mechanism of CrVI-induced female infertility and intervention strategies to mitigate CrVI effects. Lactating mother rats were exposed to CrVI (50ppm potassium dichromate) from postpartum days 1-21 through drinking water with or without RVT (10mg/kg body wt., through oral gavage daily). During this time, F1 females received respective treatments through mother's milk. On postnatal day (PND) 25, blood and the ovary, kidney and liver were collected from the F1 females for analyses. CrVI increased atresia of follicles by increasing cytochrome C and cleaved caspase-3; decreasing antiapoptotic proteins; decreasing estradiol (E2) biosynthesis and enhancing metabolic clearance of E2, increasing oxidative stress and decreasing endogenous antioxidants. RVT mitigated the effects of CrVI by upregulating cell survival proteins and AOXs; and restored E2 levels by inhibiting hydroxylation, glucuronidation and sulphation of E2. This is the first study to report the protective effects of RVT against any toxicant in the ovary.

The let-7g microRNA promotes follicular granulosa cell apoptosis by targeting transforming growth factor-β type 1 receptor

The intronic microRNA let-7g controls cell differentiation and proliferation during angiogenesis and oncogenesis. Here, we demonstrate that let-7g regulates granulosa cell (GC) apoptosis and follicular atresia in the pig ovary. Bioinformatics analyses and luciferase reporter assays showed that transforming growth factor-β type 1 receptor (TGFBR1) is a let-7g target. Overexpression of let-7g induced apoptosis of porcine GCs in vitro and repressed the mRNA and protein levels of TGFBR1, as well as the level of phosphorylated SMAD3 (p-SMAD3) protein. RNA interference-mediated knockdown of TGFBR1 and inhibitor LY2157299-mediated blocking of TGFBR1 significantly increased the rate of apoptosis of GCs and Caspase-3 activity. In addition, treatment of porcine GCs with TGF-β1 reduced the level of let-7g and increased the levels of the TGFBR1 mRNA and proteins significantly. Overall, these results demonstrate that let-7g regulates the apoptosis of GCs in the pig ovary by targeting TGFBR1 and down-regulating the TGF-β signaling pathway.

Expression of PUMA in Follicular Granulosa Cells Regulated by FoxO1 Activation During Oxidative Stress

Many studies have demonstrated that oxidative stress-induced apoptosis is a main cause of follicular atresia. Reactive oxygen species (ROS)-induced granulosa cell (GC) apoptosis is regulated by a variety of signaling pathways involving numerous genes and transcription factors. In this study, we found expression of the p53-upregulated modulator of apoptosis (PUMA), a BH3-only Bcl-2 subfamily protein, in ovarian GCs during oxidative stress. By overexpression and knockdown of Forkhead box O1 (FoxO1), we found that FoxO1 regulates PUMA at the protein level. Moreover, as c-Jun N-terminal kinase (JNK) has been shown to activate FoxO1 by promoting its nuclear import, we used a JNK inhibitor to reduce FoxO1 activation and detected decreased PUMA messenger RNA expression and protein levels during oxidative stress. In addition, in vivo oxidative stress-induced upregulation of PUMA was found following injection of 3 nitropropionic acid in mice. In conclusion, oxidative stress increases PUMA expression regulated by FoxO1 in follicular GCs.

Reproductive biomarkers responses induced by xenoestrogens in the characid fish Astyanax fasciatus inhabiting a South American reservoir: an integrated field and laboratory approach

Field studies evaluating the effects of endocrine disruption chemicals (EDCs) on the fish reproduction are scarce worldwide. The goal of this study was to assess hepatic levels of vitellogenin (Vtg), zona radiata proteins (Zrp) and insulin-like growth factors (IGF-I and IGF-II), and relating them to reproductive endpoints in a wild fish population habiting a reservoir that receive domestic sewage, agricultural and industrial residues. Adult fish Astyanax fasciatus were sampled during the reproductive season in five sites from the Furnas Reservoir, Grande River, and Paraguay-Paraná basin. As a control to field data, fish were experimentally exposed via dietary intake, to oestradiol benzoate (OB) for 7 days. Fish from site with little anthropogenic interference showed hepatic levels of Vtg, Zrp and IGF-I and IGF-II similar to those from the non-treated experimental group. In sites located immediately downstream from the municipal wastewater discharges, the water total oestrogen was >120 ng/l, and male fish displayed increased Vtg and Zrp and decreased IGF-I levels similar to OB treated fish. In females, levels of Vtg, Zrp, IGF-I and IGF-II suggest an impairment of final oocyte maturation and spawning, as also detected by frequency of over-ripening, follicular atresia and fecundity. At the sites that receive agricultural and industrial residues, the water total oestrogen was <50 ng/l and females showed decreased Zrp and increased IGF-II levels associated to reduced diameter of vitellogenic follicles, indicating an inhibition of oocyte growth. Overall, the current study reports oestrogenic contamination impairing the reproduction of a wild fish from a hydroeletric reservoir and, the data contribute to improving the current knowledge on relationship between hepatic Vtg, Zrp and IGF-I and IGF-II, and reproductive endpoints in a teleost fish. In addition, our data point out novel reproductive biomarkers (IGF-I, IGF-II and over-ripening) to assessing xenoestrogenic contamination in freshwater ecosystems.

3-Nitropropionic acid induces ovarian oxidative stress and impairs follicle in mouse

Oxidative stress induces many serious reproductive diseases in female mammals and thus poses a serious threat to reproductive health. However, the relationship between reactive oxygen species (ROS)-induced oxidative stress and follicular development, oocyte and embryo quality is not clear. The aim of this study was to investigate the effect of ovarian oxidative stress on the health of follicle and oocyte development. Female ICR mice were dosed with 3-nitropropionic acid (3-NPA) at three different concentrations (6.25, 12.5 and 25 mg/kg) and saline (control) via continuous intraperitoneal injection for 7 days. The treatment with 12.5 mg/kg reduced the weight of mouse ovaries, and significantly increased ROS levels and the activities of antioxidant enzymes--total superoxide dismutase (T-SOD), glutathione peroxidase (GPx) and catalase (CAT)--in granulosa cells and ovarian tissues, but not in other tissues (brain, liver, kidney and spleen). The same treatment significantly increased the percentage of atretic large follicles, and reduced the number of large follicles, the number of ovulated oocytes, and the capacity for early embryonic development compared with controls. It also significantly decreased the ratio of Bcl-2 to Bax, while causing an increase in the mRNA expression of (SOD2, CAT and GP X) and ROS levels in granulosa cells. Collectively, these data indicate that 3-NPA induces granulosa cell apoptosis, large follicle atresia, and an increase of ROS levels in the ovary. Therefore, we have established an in vivo model of ovarian oxidative stress for studying the mechanism of resulting damage induced by free radicals and for the screening of novel antioxidants.

Pregnenolone co-treatment partially restores steroidogenesis, but does not prevent growth inhibition and increased atresia in mouse ovarian antral follicles treated with mono-hydroxy methoxychlor

Mono-hydroxy methoxychlor (mono-OH MXC) is a metabolite of the pesticide, methoxychlor (MXC). Although MXC is known to decrease antral follicle numbers, and increase follicle death in rodents, not much is known about the ovarian effects of mono-OH MXC. Previous studies indicate that mono-OH MXC inhibits mouse antral follicle growth, increases follicle death, and inhibits steroidogenesis in vitro. Further, previous studies indicate that CYP11A1 expression and production of progesterone (P4) may be the early targets of mono-OH MXC in the steroidogenic pathway. Thus, this study tested whether supplementing pregnenolone, the precursor of progesterone and the substrate for HSD3B, would prevent decreased steroidogenesis, inhibited follicle growth, and increased follicle atresia in mono-OH MXC-treated follicles. Mouse antral follicles were exposed to vehicle (dimethylsulfoxide), mono-OH MXC (10 μg/mL), pregnenolone (1 μg/mL), or mono-OH MXC and pregnenolone together for 96 h. Levels of P4, androstenedione (A), testosterone (T), estrone (E1), and 17β-estradiol (E2) in media were determined, and follicles were processed for histological evaluation of atresia. Pregnenolone treatment alone stimulated production of all steroid hormones except E2. Mono-OH MXC-treated follicles had decreased sex steroids, but when given pregnenolone, produced levels of P4, A, T, and E1 that were comparable to those in vehicle-treated follicles. Pregnenolone treatment did not prevent growth inhibition and increased atresia in mono-OH MXC-treated follicles. Collectively, these data support the idea that the most upstream effect of mono-OH MXC on steroidogenesis is by reducing the availability of pregnenolone, and that adding pregnenolone may not be sufficient to prevent inhibited follicle growth and survival.

Postnatal exposure to chromium through mother's milk accelerates follicular atresia in F1 offspring through increased oxidative stress and depletion of antioxidant enzymes

Hexavalent chromium, CrVI, is a heavy metal endocrine disruptor, known as a mutagen, teratogen, and a group A carcinogen. Environmental contamination with CrVI, including drinking water, has been increasing in more than 30 cities in the United States. CrVI is rapidly converted to CrIII intracellularly, and CrIII can cause DNA strand breaks and cancer or apoptosis through different mechanisms. Our previous study demonstrated that lactational exposure to chromium results in a delay or arrest in follicle development and a decrease in steroid hormone levels in F1 female rats, both of which are mitigated (partial inhibition) by vitamin C. The current study tested the hypothesis that lactational exposure to CrIII accelerates follicle atresia in F1 offspring by increasing reactive oxygen species (ROS) and decreasing cellular antioxidants. Results showed that lactational exposure to CrIII dose-dependently increased follicular atresia and decreased steroidogenesis in postnatal day 25, 45, and 65 rats. Vitamin C mitigated or inhibited the effects of CrIII at all doses. CrIII increased hydrogen peroxide and lipid hydroperoxide in plasma and ovary; decreased the antioxidant enzymes (AOXs) GPx1, GR, SOD, and catalase; and increased glutathione S-transferase in plasma and ovary. To understand the effects of CrVI on ROS and AOXs in granulosa (GC) and theca (TC) cell compartments in the ovary, ROS levels and mRNA expression of cytosolic and mitochondrial AOXs, such as SOD1, SOD2, catalase, GLRX1, GSTM1, GSTM2, GSTA4, GR, TXN1, TXN2, TXNRD2, and PRDX3, were studied in GCs and TCs and in a spontaneously immortalized granulosa cell line (SIGC). Overall, CrVI downregulated each of the AOXs; and vitamin C mitigated the effects of CrVI on these enzymes in GCs and SIGCs, but failed to mitigate CrVI effects on GSTM1, GSTM2, TXN1, and TXN2 in TCs. Thus, these data for the first time reveal that lactational exposure to CrIII accelerated follicular atresia and decreased steroidogenesis in F1 female offspring by altering the ratio of ROS and AOXs in the ovary. Vitamin C is able to protect the ovary from CrIII-induced oxidative stress and follicle atresia through protective effects on GCs rather than TCs.

Bisphenol A exposure during adulthood causes augmentation of follicular atresia and luteal regression by decreasing 17β-estradiol synthesis via downregulation of aromatase in rat ovary

BACKGROUND

Bisphenol A (BPA) has been detected in human body fluids, such as serum and ovarian follicular fluids. Several reports indicated that BPA exposure is associated with the occurrence of several female reproductive diseases resulting from the disruption of steroid hormone biosynthesis in the adult ovary.

OBJECTIVE

We hypothesized that long-term exposure to low concentrations of BPA disrupts 17β-estradiol (E2) production in granulosa cells via an alteration of steroidogenic proteins in ovarian cells.

METHODS

Adult female rats received BPA for 90 days by daily gavage at doses of 0, 0.001, or 0.1 mg/kg body weight. We determined serum levels of E2, testosterone (T), follicle-stimulating hormone (FSH), and luteinizing hormone (LH). We also analyzed the expressions of steroidogenic acute regulatory protein (StAR), P450 side-chain cleavage (P450scc), 3β-hydroxysteroid dehydrogenase isomerase (3β-HSD), and aromatase cytochrome P450 (P450arom) in the ovary.

RESULTS

Exposure to BPA significantly decreased E2 serum concentration, which was accompanied by augmented follicular atresia and luteal regression via increase of caspase-3-associated apoptosis in ovarian cells. After BPA exposure, P450arom and StAR protein levels were significantly decreased in granulosa cells and theca-interstitial (T-I) cells, respectively. However, P450scc and 3β-HSD protein levels remained unchanged. The increase in LH levels appeared to be associated with the decreased synthesis of T in T-I cells after BPA exposure via homeostatic positive feedback regulation.

CONCLUSIONS

BPA exposure during adulthood can disturb the maintenance of normal ovarian functions by reducing E2. The steroidogenic proteins StAR and P450arom appear to be targeted by BPA.

Nanosized TiO2-induced reproductive system dysfunction and its mechanism in female mice

Recent studies have demonstrated nanosized titanium dioxide (nano-TiO2)-induced fertility reduction and ovary injury in animals. To better understand how nano-TiO2 act in mice, female mice were exposed to 2.5, 5, and 10 mg/kg nano-TiO2 by intragastric administration for 90 consecutive days; the ovary injuries, fertility, hormone levels, and inflammation-related or follicular atresia-related cytokine expression were investigated. The results showed that nano-TiO2 was deposited in the ovary, resulting in significant reduction of body weight, relative weight of ovary and fertility, alterations of hematological and serum parameters and sex hormone levels, atretic follicle increases, inflammation, and necrosis. Furthermore, nano-TiO2 exposure resulted in marked increases of insulin-like growth factor-binding protein 2, epidermal growth factor, tumor necrosis factor-α, tissue plasminogen activator, interleukin-1β, interleukin -6, Fas, and FasL expression, and significant decreases of insulin-like growth factor-1, luteinizing hormone receptor, inhibin α, and growth differentiation factor 9 expression in mouse ovary. These findings implied that fertility reduction and ovary injury of mice following exposure to nano-TiO2 may be associated with alteration of inflammation-related or follicular atresia-related cytokine expressions, and humans should take great caution when handling nano-TiO2.

Prenatal androgen excess programs metabolic derangements in pubertal female rats

Owing to the heterogeneity in the clinical symptoms of polycystic ovary syndrome (PCOS), the early pathophysiological mechanisms of PCOS remain unclear. Clinical, experimental, and genetic evidence supports an interaction between genetic susceptibility and the influence of maternal environment in the pathogenesis of PCOS. To determine whether prenatal androgen exposure induced PCOS-related metabolic derangements during pubertal development, we administrated 5α-dihydrotestosterone (DHT) in pregnant rats and observed their female offspring from postnatal 4 to 8 weeks. The prenatally androgenized (PNA) rats exhibited more numerous total follicles, cystic follicles, and atretic follicles than the controls. Fasting glucose, insulin, leptin levels, and homeostatic model assessment for insulin resistance were elevated in the PNA rats at the age of 5-8 weeks. Following intraperitoneal glucose tolerance tests, glucose and insulin levels did not differ between two groups; however, the PNA rats showed significantly higher 30- and 60-min glucose levels than the controls after insulin stimulation during 5-8 weeks. In addition, prenatal DHT treatment significantly decreased insulin-stimulated phosphorylation of AKT in the skeletal muscles of 6-week-old PNA rats. The abundance of IR substrate 1 (IRS1) and IRS2 was decreased in the skeletal muscles and liver after stimulation with insulin in the PNA group, whereas phosphorylation of insulin-signaling proteins was unaltered in the adipose tissue. These findings validate the contribution of prenatal androgen excess to metabolic derangements in pubertal female rats, and the impaired insulin signaling through IRS and AKT may result in the peripheral insulin resistance during pubertal development.

Dioxin exposure reduces the steroidogenic capacity of mouse antral follicles mainly at the level of HSD17B1 without altering atresia

2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) is a potent ovarian toxicant. Previously, we demonstrated that in vitro TCDD (1nM) exposure decreases production/secretion of the sex steroid hormones progesterone (P4), androstenedione (A4), testosterone (T), and 17β-estradiol (E2) in mouse antral follicles. The purpose of this study was to determine the mechanism by which TCDD inhibits steroidogenesis. Specifically, we examined the effects of TCDD on the steroidogenic enzymes, atresia, and the aryl hydrocarbon receptor (AHR) protein. TCDD exposure for 48h increased levels of A4, without changing HSD3B1 protein, HSD17B1 protein, estrone (E1), T or E2 levels. Further, TCDD did not alter atresia ratings compared to vehicle at 48h. TCDD, however, did down regulate the AHR protein at 48h. TCDD exposure for 96h decreased transcript levels for Cyp11a1, Cyp17a1, Hsd17b1, and Cyp19a1, but increased Hsd3b1 transcript. TCDD exposure particularly lowered both Hsd17b1 transcript and HSD17B1 protein. However, TCDD exposure did not affect levels of E1 in the media nor atresia ratings at 96h. TCDD, however, decreased levels of the proapoptotic factor Bax. Collectively, these data suggest that TCDD exposure causes a major block in the steroidogenic enzyme conversion of A4 to T and E1 to E2 and that it regulates apoptotic pathways, favoring survival over death in antral follicles. Finally, the down-regulation of the AHR protein in TCDD exposed follicles persisted at 96h, indicating that the activation and proteasomal degradation of this receptor likely plays a central role in the impaired steroidogenic capacity and altered apoptotic pathway of exposed antral follicles.

Methoxychlor-induced ovarian follicle toxicity in mice: dose and exposure duration-dependent effects

BACKGROUND

Methoxychlor (MXC) is specifically known to target ovarian antral follicles, increasing atresia (death via apoptosis) in them. This is of concern because females are born with a finite pool of ovarian follicles. Only limited studies have explored the phenomenon of a reduced fertility threshold for effect based on the percentage of antral follicle atresia.

METHODS

In this article, we report on adult female CD-1 mice exposed intraperitoneally to various doses of MXC for 5, 10, 20, and 30 days. In the 20-day treatment, mice were dosed with either the vehicle or MXC at 64 or 96 mg/kg/day, whereas in the 30-day treatment, mice were dosed with vehicle or MXC at 48, 64, or 96 mg/kg/day. The mice that were dosed with MXC for 30 days were also mated with untreated males for a determination of overall fertility.

RESULTS

A significantly increased percentage (50%) of atretic antral follicles was observed only after 20 and 30 days of treatment. Specifically, mice treated with MXC64 for 20 and 30 days had an increased percentage of atretic antral follicles compared with vehicle-treated mice. Interestingly, mice dosed with MXC96 had an increased percentage of atretic antral follicles after 30 days, but not after 20 days of treatment compared with vehicle-treated mice. Overall fertility of the mice was not different compared with controls.

CONCLUSIONS

The results indicate that as much as a 50% increase in atretic antral follicles does not affect the immediate fertility of the mice.

A thrombospondin-mimetic peptide, ABT-898, suppresses angiogenesis and promotes follicular atresia in pre- and early-antral follicles in vivo

Using a novel in vitro angiogenesis assay, we previously showed that thrombospondin (TSP)-1 has antiangiogenic effects on rat follicles and induces apoptosis in granulosa cells in vitro. ABT-898 is an octapeptide mimetic of TSP-1 closely related to ABT-510. Here, we demonstrate the inhibitory effects of ABT-898 on follicular angiogenesis and its proapoptotic effect on granulosa cells. To investigate the potential of this peptide to inhibit follicular angiogenesis in vivo, marmoset monkeys were treated with 2.5 mg/kg ABT-898 twice daily throughout the follicular phase of the cycle. Although treatment did not block emergence of dominant follicles, angiogenesis was reduced in preantral and early-antral follicles. Furthermore, the incidence of atresia at these follicle stages was increased. To investigate whether treatment with ABT-898 would interfere with the timing or duration of the normal ovulatory rise in plasma progesterone, marmosets were treated with a depot formulation containing 25 mg ABT-898 at the start of the follicular phase, with a second injection after 2 wk. Despite active concentrations of peptide being maintained in the circulation, no apparent effects on the ovulatory cycle were observed. Taken together, these results indicate that ABT-898 is capable of having a dual effect by inhibiting follicular angiogenesis and promoting atresia of antral follicles in vivo but does not prevent ovulation or induce luteolysis, as has been observed with direct vascular endothelial growth factor inhibitors. These results suggest that ABT-898 could be a novel therapeutic to inhibit abnormal angiogenesis and induce atresia of accumulated follicles in polycystic ovary syndrome.

Endocrine disruption and ovarian morphometric responses in rats following exposure to tetradifon

We have investigated whether exposure to tetradifon causes ovary injuries, disrupts folliculogenesis in rat and whether ovary hormones (estrogen and progesterone) to be affected by this endocrine-active agent. Female rats were exposed orally to a dose of 28.9 mg/kg/day for 6 or 12 weeks. After sacrifice, ovary glands were examined for morphometric changes. The serums were used to determine levels of 17beta-estradiol and progesterone. Results showed no sign of toxicity. However, tetradifon promoted a significant increase in the percentage of atretic follicles in the 12-weeks treated rats. Number and the diameter of mature follicles (tertiary and preovulatory) were markedly diminished together with a reduction of the relative weight of ovaries. Compared with controls, the treated rats exhibited significant reduction in serum 17beta-estradiol and progesterone levels. These results suggest an endocrine disruption by tetradifon which may interfere with ovarian follicles development in rat.

Testosterone selectively increases primary follicles in ovarian cortex grafted onto embryonic chick membranes: relevance to polycystic ovaries

Histological studies have demonstrated that polycystic ovaries (PCO) contain increased numbers of preantral follicles with a specific increase in primary follicles. Polycystic ovary syndrome is associated with hyperandrogenism and pre- and postnatal androgenization of primates increases the pool of growing follicles producing changes resembling PCO. In vitro studies could test the hypothesis that androgens alter early folliculogenesis, but conventional culture techniques for small follicles are generally unsuitable in non-rodent species. Our objective was to develop and use a method to investigate the effects of testosterone on early folliculogenesis. We adapted an in ovo technique in which lamb cortical ovarian fragments were grafted onto the chorioallantoic membrane of fertilised chick eggs. Optimal experimental conditions for vascularisation and survival of tissue were determined and the model then used to investigate the effects of testosterone on follicle growth. Eggs were inoculated with testosterone at the time of implantation of the ovarian tissue, which was retrieved 5 days later. Tissue was sectioned and follicles staged and counted. There was no wholesale initiation of primordial follicle growth over the 5-day in ovo culture. Importantly, the proportion of primordial, primary and secondary follicles remained similar to those in unimplanted tissue. Testosterone increased the number of primary follicles by 50% compared with controls, an effect that was largely due to a reduction in atresia. In conclusion, incubation of ovarian cortex with testosterone reproduces the changes in early folliculogenesis reported in histological studies of PCO.

Histopathological effects of hexavalent chromium in the ovary of a fresh water fish, Channa punctatus (Bloch)

The histopathological effects of hexavalent chromium (Cr VI) in the ovary of a fresh water teleost, Channa punctatus were investigated. An exposure-dependent alteration in ovarian histology is reported. For both acute and chronic exposures to Cr (VI), the percentages of atretic oocytes were increased; this increase was more pronounced in the acute exposure group. A decrease in percentage of vitellogenic oocytes was observed in the chronic exposure group indicating impairment of vitellogenesis. The hepatocellular vacuolization and atrophy along with pyknotic nuclei in both acute and chronic chromium exposed fish liver supports the vitellogenic impairment. The observed alterations may be due to both direct cytotoxic effect of Cr (VI) on the ovary as well as mediation by overall systemic toxicity affecting other vital organs.

Effects of inhibition of vascular endothelial growth factor at time of selection on follicular angiogenesis, expansion, development and atresia in the marmoset

This study determined the effects of inhibiting vascular endothelial growth factor (VEGF) at follicle selection. Marmosets were given an injection of VEGF antagonist, the VEGF Trap on Day 5 of the follicular phase and ovaries were evaluated on Day 10 or 15. Ovaries from controls were assessed on Day 5 (time of selection), Day 10 (peri-ovulatory) and Day 15 (luteal phase). At Day 10, ovaries of four of the five controls contained dominant follicles, while one had ovulated. VEGF Trap-treated ovaries also contained large follicles on Day 10, but VEGF inhibition had suppressed endothelial cell proliferation, leading to reductions in the thecal vascularization and plasma estradiol relative to controls. By Day 15, ovaries of controls contained active corpora lutea whereas ovaries of four of the five treated animals still contained large antral follicles similar in size to pre-ovulatory follicles, and one had small, avascular corpora lutea. However, these follicles had a restricted vasculature, increased incidence of activated caspase-3 staining and morphological features indicating they would become degenerative non-functional cysts. These results show that after follicle selection, VEGF is essential for angiogenesis and the generation of healthy ovulatory follicles and corpora lutea, but fluid accumulation can still occur in selected follicles in the absence of VEGF.

Steroidogenic changes and steady state amount of messenger RNA encoding steroidogenic enzymes, gonadotropin receptors and cell-death signalling in the dominant ovarian follicle during estradiol-induced atresia in cattle

Changes in steroidogenic function and associated gene expression were characterized in dominant ovarian follicles (DF) of cattle where follicles were induced to become atretic by systemic administration of estradiol benzoate (EB). In experiment 1, follicular fluid (FF) steroid concentrations in the DF were measured at 12-hourly time points for 48 h in heifers treated with 1 mg EB i.m./500 kg body weight (EB; n=20) as compared with untreated controls (C; n=19). Treatment with EB promoted a transient reduction in circulating FSH, a rapid (12 h) and sustained reduction in FF estradiol, a rapid (12 h) but transient reduction in FF progesterone and a delayed (36 h) increase in FF testosterone concentrations. In experiment 2, whole follicular wall tissue was collected from DF of mature non-lactating cows allocated to a 0 h control group (0 HC: n=7), a 24h control group (24 HC; n=7) or an EB-treated group where tissue was collected 24 h after administration of 1 mg EB i.m./500 kg body weight (EB; n=8). As for experiment 1, EB promoted a transient reduction in circulating FSH, a pronounced reduction in FF estradiol and a smaller but significant reduction in FF progesterone concentrations. Semi-quantitative RT-PCR on follicular wall tissue revealed that the loss in estrogen activity at 24 h after EB was associated with two-fold reduction in aromatase mRNA, with an apparent acceleration in loss of 17alpha-hydroxylase mRNA. Expression of genes for gonadotropin receptors (LHR and FSHR) and a cell-death signalling pathway (Fas antigen and Fas ligand) were unchanged during the initial 24h of EB-induced atresia. These results suggest that EB initiates atresia in dominant ovarian follicles through a rapid suppression of follicular estradiol synthesis, an effect associated with down-regulation of the aromatase gene. A transient suppression in circulating FSH following administration of EB appears to have initiated these events, and it is suggested that subsequent processes involved in atresia follow this loss in estrogenic function.

Development of an animal model for ovotoxicity using 4-vinylcyclohexene: a case study

BACKGROUND

The occupational chemical 4-vinylcyclohexene (VCH) has been shown to cause destruction of small pre-antral follicles in ovaries of mice. Further, its monoepoxide metabolites, 1,2-VCH epoxide, 7,8-VCH epoxide, and the diepoxide, VCD, have been shown to cause pre-antral follicle loss in rats as well as mice. Chemicals that destroy small pre-antral follicles are of concern to women because exposure can result in premature ovarian failure (early menopause).

METHODS

Studies working with these chemicals over the past decade have determined a number of aspects of the mechanism(s) of small pre-antral destruction, and a variety of questions have been answered.

RESULTS

Specifically, it has been determined that the diepoxide (VCD) is the bioactive form and it directly targets the ovary in mice and rats. Mice are more susceptible to VCH than rats because they are capable of its metabolic bioactivation. Follicle destruction by VCD is selective for primordial and primary follicles. Mechanistic studies in rats have determined that VCD causes ovotoxicity by accelerating the natural process of atresia (apoptosis) and this requires repeated exposures. Pro-apoptotic signaling events in the Bcl-2 and mitogen activated protein kinase families have been shown to be selectively activated in fractions of small pre-antral follicles (targets for VCD). Finally, a whole ovarian culture system using neonatal mouse and rat ovaries has been developed to expand the potential for more in depth investigations into ovotoxicity caused by VCD.

CONCLUSIONS

This article provides an overview of the questions asked and the approaches taken in studying VCH and VCD to support these conclusions.

Influence of mycotoxin zearalenone and its derivatives (alpha and beta zearalenol) on apoptosis and proliferation of cultured granulosa cells from equine ovaries

BACKGROUND

The mycotoxin zearalenone (ZEA) and its derivatives, alpha and beta-zearalenol (alpha and beta-ZOL), synthesized by genera Fusarium, often occur as contaminants in cereal grains and animal feeds. The importance of ZEA on reproductive disorders is well known in domestic animals species, particularly in swine and cattle. In the horse, limited data are available to date on the influence of dietary exposure to ZEA on reproductive health and on its in vitro effects on reproductive cells. The aim of this study was to evaluate the effects of ZEA and its derivatives, alpha and beta-ZOL, on granulosa cells (GCs) from the ovaries of cycling mares.

METHODS

The cell proliferation was evaluated by using the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) test after 3 days exposure at different concentrations of ZEA and its derivatives (from 1 x 10-7 to 0.1 microM). The apoptosis induction was evaluated after 1 day exposure, by DNA analysis using flow cytometry.

RESULTS

An increase in cell proliferation with respect to the control was observed in the presence of ZEA at 1 x 10-3 and 1 x 10-4 microM and apoptosis was induced by all mycotoxins at different concentrations.

CONCLUSION

The simultaneous presence of apoptosis and proliferation in GC cultures treated with zearalenones could indicate that these mycotoxins could be effective in inducing follicular atresia. These effects of zearalenones may result from both direct interaction with oestrogen-receptors as well as interaction with the enzymes 3alpha (beta)-hydroxysteroid dehydrogenase (HSD), involved in the synthesis and metabolism of endogenous steroid hormones. These cellular disturbances, described for the first time in equine GCs cultured in vitro, could be hypothesized as referred to reproductive failures of unknown ethiology in the mare.

Reduced recruitment and survival of primordial and growing follicles in GH receptor-deficient mice

GH influences female fertility. The goal of the present study was to obtain more insight into the effect of loss of GH signalling, as observed in humans suffering from Laron syndrome, on ovarian function. Therefore, serial paraffin sections of ovaries of untreated and IGF-I-treated female GH receptor knock-out (GHR/GHBP-KO) mice were examined to determine the follicular reserve and the percentage of follicular atresia in each ovary. Our observations demonstrate that the amount of primordial follicles was significantly elevated in GHR/GHBP-KO mice, while the numbers of primary, preantral and antral follicles were lower compared with wild-type values. The reduced number of healthy growing follicles in GHR/GHBP-KO mice was accompanied by a significant increase in the percentage of atretic follicles. IGF-I treatment of GHR/GHBP-KO mice for 14 days resulted in a reduced number of primordial follicles, an increased number of healthy antral follicles, and a decreased percentage of atretic follicles. The results of the present study suggest that GH may play a role, either directly or indirectly, via for instance IGF-I, in the recruitment of primordial follicles into the growing pool. Furthermore, GH seems to protect antral follicles, directly or indirectly from undergoing atresia.

Hormonal induction of ovulation stimulates atresia of antral follicles in a vespertilionid bat, Scotophilus heathi

Scotophilus heathi is a seasonally monoestrous subtropical vespertilionid bat found at Varanasi, India. Although the antral follicles remain present in the ovaries of S. heathi from November till March, ovulation is delayed in this species until early March. In order to understand the mechanism of ovulation suppression during this period of delayed ovulation, the effects of human chorionic gonadotropin (hCG), pregnant mare's serum gonadotropin (PMSG), follicle stimulating hormone (FSH) and gonadotropin releasing hormone agonist (GnRH agonist) on ovarian morphology and steroid concentration were investigated. Hormonal treatments were given as a single i.p. dose 24 h after capture. The bats were sacrificed 48 h after the injection. Treatment with hCG, PMSG, FSH and GnRH agonist failed to induce ovulation in S. heathi, although these hormones produced a high degree of ovarian stimulation. The administration of hCG and PMSG induced ovarian enlargement, intense hyperemia, marked changes in the interstitial cells (ICs), development of several antral follicles and a varying degree of abnormalities in the oocytes of most of the antral follicles. In the bats treated with hCG, PMSG and GnRH agonist, androstenedione concentration increased significantly to extraordinarily high levels, whereas estradiol concentration decreased. Administration of FSH caused regression of ICs and pyknosis of granulosa cells in the majority of antral follicles. FSH did not enhance androstenedione concentration. The results of the present study suggest that the failure of hormonal treatments to induce ovulation during the period of delayed ovulation might be due to a seasonal desensitization of ovarian follicles in S. heathi. The hormonal treatment instead stimulated the ICs to produce a high level of androstenedione resulting in atretic changes of the antral follicles.

Methoxychlor Inhibits Growth and Induces Atresia of Antral Follicles through an Oxidative Stress Pathway

The mammalian ovary contains antral follicles, which are responsible for the synthesis and secretion of hormones that regulate estrous cyclicity and fertility. The organochlorine pesticide methoxychlor (MXC) causes atresia (follicle death via apoptosis) of antral follicles, but little is known about the mechanisms by which MXC does so. Oxidative stress is known to cause apoptosis in nonreproductive and reproductive tissues. Thus, we tested the hypothesis that MXC inhibits growth and induces atresia of antral follicles through an oxidative stress pathway. To test this hypothesis, antral follicles isolated from 39-day-old CD-1 mice were cultured with vehicle control (dimethylsulfoxide [DMSO]), MXC (1-100 microg/ml), or MXC + the antioxidant N-acetyl cysteine (NAC) (0.1-10 mM). During culture, growth was monitored daily. At the end of culture, follicles were processed for quantitative real-time polymerase chain reaction of Cu/Zn superoxide dismutase (SOD1), glutathione peroxidase (GPX), and catalase (CAT) mRNA expression or for histological evaluation of atresia. The results indicate that exposure to MXC (1-100 microg/ml) inhibited growth of follicles compared to DMSO controls and that NAC (1-10 mM) blocked the ability of MXC to inhibit growth. MXC induced follicular atresia, whereas NAC (1-10 mM) blocked the ability of MXC to induce atresia. In addition, MXC reduced the expression of SOD1, GPX, and CAT, whereas NAC reduced the effects of MXC on their expression. Collectively, these data indicate MXC causes slow growth and increased atresia by inducing oxidative stress.

Promotion of ovarian follicular development by injecting vascular endothelial growth factor (VEGF) and growth differentiation factor 9 (GDF-9) genes

Ovarian follicular development in mammals is the complex process including endocrine, paracrine and autocrine. There is the development of four basic stages of ovarian follicles, i.e. the primordial, primary, secondary and tertiary or Graafian follicles. There are few blood vessels in the cortical area where primordial and primary follicles are assembled. The development of these follicles is stimulated by oocytes derived factor including growth differentiation factor 9 (GDF-9) or bone morphogenetic protein 15 (BMP-15). Porcine GDF-9 complementary DNA (cDNA) cloned, and then injected its gene into the ovary in gilts. The injection of porcine GDF-9 gene resulted in an increase in the number of primary, secondary and tertiary follicles, concomitant with a decrease in the number of primordial follicles, indicating that exogenous GDF-9 can promote early folliculogenesis in the porcine ovary. On the other hand, the development of antral follicles is associated with increased density of blood vessels within the theca cell layers surrounding the follicles. A recent study reported that vascular endothelial growth factor (VEGF) play an important role in the process of thecal angiogenesis during follicular development. To investigate whether additional induction of thecal angiogenesis would support subsequent follicular development, miniature gilts were directly injected VEGF gene into the ovary. Injection of VEGF gene increased the levels of mRNA expression of VEGF 120 and VEGF 164 isoforms in the granulosa cells and VEGF protein contents in the follicular fluid. The number of preovulatory follicles and the capillary density in the theca interna increased significantly in the ovaries injected with VEGF gene compared with those treated with eCG alone, indicating that the regulation of thecal angiogenesis during follicular development is a very important factor in the development of ovulatory follicles. This technique may be an innovative technique for enhanced induction of follicular development in the ovary through gene and hormonal treatment, which may lead to prevention of infertility caused by ovarian dysfunction.

Bisphenol A in artificial indoor streams: II. Stress response and gonad histology in Gammarus fossarum (Amphipoda)

The effects of the world wide-distributed chemical bisphenol A (BPA) on the endocrine system of vertebrates have been demonstrated in several studies. Here, we report on the impact of BPA (0, 5, 50 and 500 microg/l nominally, deduced effective concentrations 0, 0.24, 2.4, and 24.1 microg/l, respectively, all at 15 degrees C) on the 70 kD stress protein family (hsp70), the 90 kD stress protein family (hsp90), and gonad histology of the crustacean Gammarus fossarum exposed in artificial indoor streams. The animals were exposed for a maximum of 103 days and samples were taken at the beginning and at days 34, 69 and 103 of the experiment. Exposure to BPA resulted in accelerated maturation of oocytes in females and in a decline in the number and size of early vitellogenic oocytes. The level of hsp90, which plays a pivotal role in vertebrate sex steroid signal transduction, was significantly reduced by BPA. In all five streams, measured parameters did not indicate any captivity stress for a period of 69 days. Beyond this time, the mortality rate and proteotoxic effects, the latter measured by hsp70 expression, were found to be elevated.

Impact of gonadotropin administration on folliculogenesis in prepubertal ob/ob mice

Female leptin deficient (ob/ob) mice exhibit abnormal ovarian folliculogenesis resulting in an impaired ability to reproduce. This effect may be related to the hypogonadotropic state of these animals, or leptin may directly modulate ovarian follicle development. In the present study we assessed whether exogenous gonadotropin administration would normalize folliculogenesis and induce ovulation in immature ob/ob animals. Eight 26-day-old ob/ob and eight control mice were injected sc with pregnant mare serum gonadotropin followed 48 h later with a sc injection of human chorionic gonadotropin. Animals were killed 24 h later. Gonadotropin (GTH) administration increased both ovarian and uterine weights in control mice, but this effect was attenuated in leptin deficient animals. The number of preantral follicles was greater in ob/ob mice than controls, but in GTH-treated animals the number of antral follicles was subnormal in the ovaries of leptin deficient animals. Ob/ob animals also failed to ovulate in response to GTH, and the protective actions of GTH against granulosa cell apoptosis and follicular atresia were attenuated in these animals. Interestingly, however, serum levels of estradiol and progesterone were higher in ob/ob mice than controls, regardless of whether or not the animals received GTH treatment. We conclude that the ovarian responsiveness to GTH is subnormal in leptin deficient animals suggesting that leptin may modulate the process of folliculogenesis by directly altering the sensitivity of the ovary to GTH.

Methoxychlor Directly Affects Ovarian Antral Follicle Growth and Atresia through Bcl-2- and Bax-Mediated Pathways

Methoxychlor (MXC) is an organochlorine pesticide and reproductive toxicant. While in vivo studies indicate that MXC exposure increases antral follicle atresia, in part by altering apoptotic regulators (Bcl-2 and Bax), they do not distinguish whether MXC does so via direct or indirect mechanisms. Therefore, we utilized an in vitro follicle culture system to test the hypothesis that MXC is directly toxic to antral follicles, and that overexpression of anti-apoptotic Bcl-2, or deletion of pro-apoptotic Bax, protects antral follicles from MXC-induced toxicity. Antral follicles were isolated from wild-type (WT), Bcl-2 overexpressing (Bcl-2 OE), or Bax deficient (BaxKO) mice, and exposed to dimethylsulfoxide (control) or MXC (1-100 microg/ml) for 96 h. Follicle diameters were measured every 24 h to assess growth. After 96 h, follicles were histologically evaluated for atresia or collected for quantitative PCR analysis of Bcl-2 and Bax mRNA levels. MXC (10-100 microg/ml) significantly inhibited antral follicle growth at 72 and 96 h, and increased atresia (100 microg/ml) compared to controls at 96 h. Furthermore, MXC increased Bax mRNA levels between 48-96 h and decreased Bcl-2 mRNA levels at 96 h. While MXC inhibited growth of WT antral follicles beginning at 72 h, it did not inhibit growth of Bcl-2 OE or BaxKO follicles until 96 h. MXC also increased atresia of small and large WT and BaxKO antral follicles over controls, but it did not increase atresia of large Bcl-2 OE antral follicles over controls. These data suggest that MXC directly inhibits follicle growth partly by Bcl-2 and Bax pathways, and increases atresia partly through Bcl-2 pathways.

Effects of Two Fungicides with Multiple Modes of Action on Reproductive Endocrine Function in the Fathead Minnow (Pimephales promelas)

Many chemicals that adversely affect reproduction and/or development do so through multiple pathways within the reproductive tract and hypothalamic-pituitary-gonadal axis. Notable in this regard are fungicides, such as prochloraz or fenarimol, which in mammals have the potential to impact endocrine function through inhibition of CYP enzymes involved in steroid metabolism, as well as through antagonism of the androgen receptor(s). The objective of our studies was to assess the effects of prochloraz and fenarimol on reproductive endocrine function in a model small fish species, the fathead minnow (Pimephales promelas), using both in vitro and in vivo assays. The two fungicides inhibited in vitro CYP19 aromatase activity in brain and ovarian homogenates from the fish, with prochloraz exhibiting a greater potency than fenarimol. Prochloraz and fenarimol also bound competitively to the cloned fathead minnow androgen receptor expressed in COS-1 cells. The two fungicides significantly reduced fecundity of the fish in a 21-day reproduction assay at water concentrations of 0.1 (prochloraz) and 1.0 (fenarimol) mg/l. The in vivo effects of prochloraz on plasma steroid (17beta-estradiol, testosterone, 11-ketotestosterone) and vitellogenin (an estrogen-responsive protein) concentrations, as well as on gonadal histopathology, were consistent with inhibition of steroidogenesis. Fenarimol also affected several aspects of endocrine function in vivo; however, the suite of observed effects did not reflect either aromatase inhibition or androgen receptor antagonism. These studies contribute to a better mechanistic understanding of the extrapolation of effects of endocrine-disrupting chemicals across vertebrate classes.

Histological and steroidogenic changes in dominant ovarian follicles during oestradiol-induced atresia in heifers

Histological and steroidogenic changes within dominant ovarian follicles (DFs) undergoing atresia following systemic administration of oestradiol benzoate (ODB) were characterized in beef heifers. At 5.6 ± 0.1 days after the onset of oestrus, heifers received 1 mg ODB i.m./500 kg body weight (ODB; n = 15) or served as controls (n = 15). Timing of treatment initiation was designated as hour (h) 0 on day (d) 0, and coincided with the presence of the DF of the first follicular wave (DF1). Within treatments, the DF1 was collected following ovariectomy in four animals at h 12, h 36 or after ultrasonic detection of a new wave (NW) of ovarian follicular development. In heifers of the NW groups (n = 7 per treatment), blood samples were collected at intervals of 20 min for 12 h beginning at h − 12, 0, 24 and 48 to characterize circulating LH patterns. Administration of ODB suppressed (P < 0.01) mean concentrations of LH at h 24 and h 48 by preventing (P < 0.05) the increase in LH pulse amplitude observed in controls, but had no effect on FSH. Follicular fluid (FF) concentrations of androgens and oestradiol were reduced at h 36 in the ODB-treated group. The diameter of the DF1 and the number of granulosa cell layers were also reduced in ODB-treated as compared with control heifers. Treatment differences were not observed in the proportion of apoptotic granulosa cells as assessed using the TUNEL assay method, and timing of a new wave of follicular development (d 4.6 ± 0.2) was similar (P > 0.1) among treatments. A prominent characteristic of oestradiol-induced atresia of the DF1 of the oestrous cycle in heifers was a loss in oestrogenic function associated with reduced LH support. However, the timing of new follicular development may be influenced by a factor(s) other than the status of the DF undergoing oestradiol-induced atresia.

Ultrasound image attributes of human ovarian dominant follicles during natural and oral contraceptive cycles

BACKGROUND

Computer-assisted analyses were used to examine ultrasound image attributes of human dominant ovarian follicles that developed during natural and oral contraceptive (OC) cycles. We hypothesized that image attributes of natural cycle follicles would quantitatively differ from those in OC cycles and that OC cycle follicles would possess image attributes indicative of atresia.

METHODS

Dominant ovarian follicles of 18 clinically normal women were compared using transvaginal ultrasonography for the 7 days before ovulation during a natural cycle (n = 9) or the 7 days before peak estradiol in women using OC (n = 11). Follicles were analyzed using region and line techniques designed to compare the image attributes numerical pixel value (NPV), pixel heterogeneity (PH) and area under the curve (AUC).

RESULTS

NPV was higher in OC cycle follicles with region analysis and tended to be higher with line analysis (p = 0.005 and p = 0.06, respectively). No differences were observed in two other image attributes (AUC and PH), measured with either technique, between natural and OC cycle follicles.

CONCLUSION

The increased NPV value of OC cycle follicles and lack of differences in PH and AUC values between natural cycle and OC cycle follicles did not support the hypothesis that OC cycle follicles would show ultrasonographically detectable signs of atresia. Image attributes observed in OC cycle follicles were not clearly indicative of atresia nor were they large enough to preclude preovulatory physiologic status in OC cycle follicles.

Differences between rats and mice in the involvement of the aryl hydrocarbon receptor in 4-vinylcyclohexene diepoxide-induced ovarian follicle loss

Repeated dosing with the occupational chemical 4-vinylcyclohexene diepoxide (VCD) selectively depletes small pre-antral follicles in the ovaries of rats and mice via apoptosis. The aryl hydrocarbon receptor (AhR) plays a role in mediating the effects of several xenobiotics. Therefore, this study was designed to investigate a potential role of the AhR in VCD-induced ovotoxicity. Female F344 rats, C57BL/6 mice, or AhR-deficient (-/-, AhRKO) mice were dosed daily (15 days) with vehicle, VCD (80 mg/kg, i.p.) and/or the AhR antagonist, alpha-naphthoflavone (ANF; 80 mg/kg, i.p.). Compared with controls, VCD caused a 60% reduction (P < 0.05) in primordial and primary follicles in mice and rats. Concurrent dosing with ANF protected against the VCD-induced follicle loss in rats, but not in mice. As with AhR-intact mice and rats, VCD induced a 70% loss (P < 0.05) of small pre-antral follicles in AhRKO mice. AhR mRNA expression was increased (P < 0.05) by VCD dosing in small pre-antral follicles isolated from ovaries of rats but not mice. AhR protein in rats was increased by VCD dosing in oocyte nuclei in primordial and primary follicles when measured by immunofluorescence and confocal microscopy. In rat small pre-antral follicles, apoptosis-associated caspase-3-like activity was increased (P < 0.05) by VCD treatment, decreased (P < 0.05) by ANF treatment, and unaffected by VCD plus ANF treatment. VCD had no effect on expression of GST Ya1 or GST Ya2 mRNA or CYP 1A1 protein in rats. Taken together, these findings demonstrate a difference between rats and mice in the potential involvement of AhR as related to VCD-induced ovotoxicity. Whereas, AhR appears to be involved in rats, no evidence for a similar role in mice was obtained. Overall, these findings point out that there can be mechanistic species differences in ovarian responses to xenobiotic chemicals.

Methoxychlor-Induced Atresia in the Mouse Involves Bcl-2 Family Members, but Not Gonadotropins or Estradiol1

Methoxychlor (MXC) is an organochlorine pesticide that increases the rate of ovarian atresia. To date, little is known about the mechanism by which MXC induces atresia. Because Bcl-2 (an antiapoptotic factor), Bax (a proapoptotic factor), gonadotropins, and estradiol are important regulators of atresia in the ovary, the purpose of this study was first to examine whether MXC-induced atresia occurred through alterations in Bcl-2 or Bax, and second, to examine the effect of MXC on gonadotropins, estradiol, and their receptors. CD-1 mice were dosed with 8-64 mg kg(-1) day(-1) MXC or vehicle (sesame oil). Ovaries were subjected to analysis of antral follicle numbers, Bcl-2, Bax, estrogen receptor, and follicle-stimulating hormone receptor levels. Blood was used to measure gonadotropins and estradiol. In some experiments, mice that overexpressed Bcl-2 or mice that were deficient in Bax were dosed with MXC or vehicle and their ovaries were analyzed for atresia. MXC caused a dose-dependent increase in the percentage of atretic antral follicles compared with controls at the 32 and 64 mg kg(-1) day(-1) doses of MXC. MXC treatment did not result in changes in Bcl-2 levels, but it did result in an increase in Bax levels in antral follicles. MXC treatment did not affect gonadotropin or estradiol levels, nor did it affect the levels of follicle-stimulating hormone or estrogen receptors. Mice that overexpressed Bcl-2 or mice that were deficient in Bax were protected from MXC-induced atresia. These data suggest that MXC induces atresia through direct effects on the Bax and Bcl-2 signaling pathways in the ovary.

Anovulation in the prevention of cytotoxic-induced follicular attrition and ovarian failure

BACKGROUND

Gonadal failure secondary to alkylating agents may be related to ovulatory status. The objective of this investigation was to evaluate whether anovulation protected ovarian follicles during treatment with cyclophosphamide.

METHODS

Four groups (n = 20 mature female Sprague-Dawley rats per group) were studied: control (group I), 5 mg/kg/day cyclophosphamide only (group II), 5 mg/kg/day cyclophosphamide and the combination of 50 micro g ethinyl estradiol/2 mg norgestrel (group III) and 5 mg/kg/day cyclophosphamide and 2.5 micro g leuprolide acetate daily (group IV). Animals were sacrificed after 4 weeks of treatment. Follicles were classified as medium (300-450 micro m) and large (>450 micro m) per section of ovary.

RESULTS

Group II developed a significantly greater number of medium and large follicles [15.1 +/- 6.1 and 4.9 +/- 1.9 (mean +/- SD), respectively] compared with group I [7.1 +/- 2.1 and 1.0 +/- 0.7 (mean +/- SD), respectively] (P </= 0.05). Groups III and IV developed a significantly greater number of medium follicles [13.2 +/- 2.5 and 10.8 +/- 2.3 (mean +/- SD), respectively) compared with group I (P < or = 0.05). There was a trend toward a greater number of large follicles in groups III and IV when they were compared with group I. There were no differences in medium follicles in groups II, III and IV. No differences were noted in the number of large follicles between groups III and IV (2.9 +/- 1.2 and 2.3 +/- 1.0, respectively).

CONCLUSIONS

These results suggest that in the rat model, cyclophosphamide exerts a stimulatory effect on the ovary resulting in the greater development of both medium and large follicles. Anovulation conferred no protection against cyclophosphamide-induced gonadal toxicity. These data suggest that in the rat model, cyclophosphamide may result in ovarian failure by enhancing recruitment of follicles regardless of ovulatory status or hormonal milieu.

Effects of pregnant mare serum gonadotropin (eCG) on follicle development and granulosa-cell apoptosis in the pig

The effect of eCG on follicular development and granulosa-cell apoptosis in sexually mature and immature gilts and on granulosa-cell apoptosis in vitro were studied. The sexually mature gilts were treated with eCG on Day 11 of the estrous cycle, and effects were analyzed at different times after treatment with untreated animals at corresponding stages of the cycle as controls. Apoptosis was determined by terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling (TUNEL), hematoxylin and eosin staining, and DNA ladder. The proportion of apoptotic cells in atretic follicles (39%) was significantly higher (P<0.01) than that in healthy follicles (9%). At 24h after eCG treatment in mature gilts, the total number of follicles visible on the ovarian surface (57 per ovary), the number of small (<3mm) follicles (31.5 per ovary) and the number of medium-sized (3-5mm) follicles (23 per ovary) were significantly higher (P<0.05) than those of control animals (28, 20 and 6.5 per ovary, respectively), and declined gradually thereafter to below the level of control animals. The number of large (>or=5mm) follicles began to show a marked increase at 72h after eCG (8.5 versus 2.5, P<0.05). At 24h after eCG treatment, the proportions of apoptotic cells in small (7.2%) and medium-sized follicles (7.4%) were markedly lower (P<0.01) than those in controls (21.5 and 21%, respectively) and increased gradually thereafter to approach the level in controls. The percentage of apoptotic cells in large follicles (10% at 24h post-eCG) did not change significantly. Before eCG treatment, there were markedly fewer follicles of all types on ovaries of immature gilts than of mature gilts (9 versus 25 per ovary) and the proportion of apoptotic cells in small and medium follicles was high (25 and 34%, respectively). After eCG treatment, the changes in follicle number and proportion of apoptotic cells in the immature gilts followed a similar pattern to that of the mature gilts. Equine chorion gonadotropin inhibited apoptosis of granulosa cells cultured either in vitro or in intact follicles in a dose-dependent manner. Thus, follicular atresia in the pig, as in other animals, was characterized by apoptosis of large numbers of granulosa cells, and eCG promoted follicular development by inhibition of granulosa-cell apoptosis.

Induction of apoptosis and ovarian cyst formation in the mouse ovary by dehydroepiandrosterone (DHEA)

Exogenous dehydroepiandrosterone (DHEA) produces ovarian cysts and atretic follicles in mice. We sought to test the hypothesis that the abnormal follicular development found after DHEA administration in mice results from aberrant ovarian apoptosis. DHEA was injected subcutaneouly for 15 days. Controls received an equivalent volume of vehicle. Follicle size was measured, and the proportion of ovarian follicles containing apoptotis was assessed by in situ end-labeling of DNA. DHEA resulted in a greater proportion of follicles with evidence of apoptosis (62.4% in the DHEA group [n = 789 follicles] vs. 53.0% in the vehicle group [n = 440 follicles]; p = 0.031). DHEA also produced larger follicles (mean diameter: 234.7um +/- 24.6um in the DHEA group vs. 204.6um +/- 11.4um in the vehicle group; p < 0.01). All of the DHEA-treated mice contained follicles > 500um while only one of the mice in the vehicle group contained a follicle > 500um in diameter (p < 0.001). We conclude that DHEA administration results in increased ovarian apoptosis and in larger follicle size, thereby producing a characteristic cystic and atretic appearance in the mouse ovary. This may be the mechanism by which androgens cause ovarian cyst formation.

Effect of endosulfan on ovarian compensatory hypertrophy in hemicastrated albino mice

Endosulfan, a chlorinated cyclodiene insecticide, was administered orally at 1.5, 3, 6, and 9 mg/kg per day to normal hemicastrated virgin mice for 15 consecutive days to examine the effect on ovarian function. Sham-operated and hemicastrated control mice were administered a similar volume of olive oil. The vaginal smear and body weight of the mice were recorded daily and mice were sacrificed on day 16. The remaining left ovary, uterus, kidney, adrenal, liver, thymus, and thyroid were removed and weighed. The left ovary from each animal was serially sectioned and stained for histologic studies. The hemicastrated control mice had a 40.5% increase in weight of the remaining left ovary and a significant increase in healthy and atretic follicles when compared with sham-operated controls. The remaining left ovaries of mice treated with 1.5mg endosulfan had a 37.2% increase in weight with no significant difference in ovarian weight and or in the healthy and atretic follicles when compared with hemicastrated olive oil-treated controls. However, treatment with 3, 6, and 9 mg endosulfan resulted in weight increases in the remaining left ovary of only 14.9, 7.4, and 0.8% and a significant decrease in healthy follicles with a concomitant increase in the number of atretic follicles compared to the olive oil-treated controls. There was no significant change in the number of estrous cycles or the duration of each phase of the estrous cycle with 1.5 and 3mg/kg per day endosulfan. However, there was a significant decrease in the number of estrous cycles, and the duration of estrus and metestrus with a concomitant significant increase in the duration of the diestrus phase with 6 and 9 mg/kg per day endosulfan treatment when compared with hemicastrated olive oil-treated controls. There were no significant change in body weight or the weights of the uterus, kidney, adrenal, liver, thymus, or thyroid after endosulfan treatment. These observations show that endosulfan treatment caused a significant decrease in compensatory ovarian hypertrophy. An increase in the number of atretic follicles and disruption of the estrous cycle may have been due to a direct effect on the ovary or to effects on the hypothalamo-hypophysial-ovarian axis.

Long-term effects of ovarian follicular depletion in rats by 4-vinylcyclohexene diepoxide

4-Vinylcyclohexene diepoxide (VCD) destroys preantral ovarian follicles in rats. Female 28-day Fisher 344 (F344) rats were dosed (30 days) with VCD (80 mg/kg per day, i.p.) or vehicle, and animals were evaluated for reproductive function at subsequent time points for up to 360 days. At each time point animals were killed, and ovaries and plasma collected. VCD reduced (P<0.05) the number of preantral follicles by day 30 relative to control. There were no ultrastructural differences in morphology between VCD-treated and control ovaries. Circulating FSH levels in VCD-treated animals were greater (days 120, 240, and 360, P<0.05) than in controls. Cyclicity was disrupted in the VCD-treated group by day 360. These results show that VCD-induced follicular destruction in rats is associated with a sequence of events (loss of preantral follicles, increased plasma FSH, and cyclic disruption) preceding premature ovarian senescence that is similar to events that occur during the onset of menopause in women.

Activation of mitogen-activated protein kinases and AP-1 transcription factor in ovotoxicity induced by 4-vinylcyclohexene diepoxide in rats

Previous studies have demonstrated that ovotoxicity induced in small preantral (primordial and primary) ovarian follicles by 4-vinylcyclohexene diepoxide (VCD) in rats is likely via acceleration of the normal process of atresia (apoptosis). This acceleration is associated with increased activities of caspase cascades, changes in subcellular distribution of Bcl-2 family members, and alteration of estrogen receptor-mediated signaling pathways. The present study was designed to investigate possible effects of VCD dosing on the mitogen-activated protein kinases (MAPK)/AP-1 signaling pathways in rat ovarian small follicles. Female F344 rats were given a single dose of VCD (80 mg/kg i.p., 1 day--a time when ovotoxicity has not been initiated) or dosed daily for 10 or 15 days (80 mg/kg i.p.; 10 days--a time when the earliest signs of impending follicular destruction is seen, 15 days--a time when significant ovotoxicity is underway). Four hours following the final dose, ovaries and livers were collected. Ovarian small (25-100 microm) and large (100-250 microm) preantral follicles were isolated, and cytosolic or nuclear extracts were prepared from follicles and livers for analyses. Activities of MAPKs, including extracellular signal-regulated kinase, c-Jun N-terminal protein kinase (JNK), and p38 kinase, were determined in follicular and liver cytosolic extracts, and AP-1 DNA binding activity was determined in follicular and liver nuclear extracts. Compared with control, a single dose of VCD caused a decrease in JNK activity and an increase of AP-1 binding activity in isolated small ovarian follicles. After repeated daily dosing with VCD for 10 or 15 days, JNK and p38 kinase activities in small ovarian follicles were increased (p38 kinase: 1.64 +/- 0.14 for 10 days, 1.48 +/- 0.11 for 15 days, VCD/control, P < 0.01; JNK: 1.44 +/- 0.11 for 10 days, 1.37 +/- 0.06 for 15 days, VCD/control, P < 0.01) and AP-1 binding activity in small ovarian follicles was decreased (10 days, 0.29 +/- 0.04; 15 days, 0.51 +/- 0.04, VCD/control, P < 0.01). VCD did not affect any of these measurements in large preantral follicles or liver. Phosphorylation status of c-Jun protein as measured by Western blotting was increased (1.22 +/- 0.1, VCD/control, P < 0.05) after the 15-day daily dosing with VCD, but total c-Jun protein levels were unaffected. Using antibodies against c-Jun or phospho-c-Jun for supershift DNA binding assay, c-Jun and phospho-c-Jun were identified in the AP-1-DNA binding complex, and the binding activity was reduced in tissues with increased phospho-c-Jun protein levels. Taken together, these data provide evidence that accelerated atretic signals induced by VCD is associated with MAPK/AP-1 signaling pathways and phosphorylation of c-Jun plays a significant role in transmitting the apoptotic signals.

Methoxychlor may cause ovarian follicular atresia and proliferation of the ovarian epithelium in the mouse

Methoxychlor (MXC) is currently used to protect agricultural products from insects. Previous studies show that MXC adversely affects the ovary, but the target cells were not revealed by those studies. Therefore, the purpose of this study was to test the hypothesis that MXC induces ovarian changes by adversely affecting the antral follicles and the ovarian surface epithelium in the mouse. To test this hypothesis, cycling female CD-1 mice (39 days) were dosed with MXC (8, 16, or 32 mg/kg/day), kepone (KPN, 8 mg/kg/day, positive control), or sesame oil (vehicle control) via intraperitoneal injection for 10 or 20 days. Estrous cyclicity was evaluated daily via vaginal lavage. After dosing, ovaries were collected for histological evaluation of follicle numbers, atresia, and surface epithelial height. The results indicate that at the 20-day time point, MXC (32 mg/kg) and KPN (8 mg/kg) increased the percentage of atretic antral follicles (n= 4-9,p<or= 0.001). MXC (32 mg/kg) also increased the height of the ovarian surface epithelium compared with controls (n= 7-10,p<or= 0.045), and KPN increased the percentage of days in estrus (n= 6-10,p<or= 0.0001). These data suggest that MXC and KPN increase antral follicle atresia, MXC increases surface epithelial height, and KPN affects vaginal cytology.

Reproductive toxicity and infertility effect of Ferula hornonis extracts in mice

The anti-fertility, anti-implantation, and ovarian histological alterations of the ethanolic extract of Ferula hormonis have been investigated in female mice. The intragastric application of 3 mg/kg per day of such extract for 6 weeks resulted in a significant reduction in female mice fertility. Furthermore, it caused a decrease in the number of mated females, the total number of implantations, and the number of viable fetuses. These changes were also associated with ovarian atrophy and a concomitant increase in the connective tissue. The ova showed degeneration while most of the ovarian follicles suffered follicular atresia.

17beta-estradiol affords protection against 4-vinylcyclohexene diepoxide-induced ovarian follicle loss in Fischer-344 rats

Repeated dosing with 4-vinylcyclohexene diepoxide (VCD) accelerates atresia via apoptosis in primordial and primary follicles in ovaries of rats. The mechanisms that control atresia and VCD-induced toxicity are unknown; however, they could involve 17beta-E2. Atresia slows as animals enter puberty, whereas circulating E2 levels increase with the the onset of cyclicity. This inverse relationship suggests that E2 may be involved in the control of atresia. Therefore, this study was designed to determine whether treatment of immature rats with E2 could protect follicles normally destroyed by VCD-induced apoptosis. Female F344 rats were treated daily with E2, ER analogs, and/or VCD for 15 d. VCD alone caused a 50% reduction in primordial and primary follicles. Coinjection of E2 (0.1 mg/kg) and VCD (80 mg/kg) selectively protected primary follicles from VCD-induced follicle loss. This protection was mimicked by an ER agonist, genistein (0.1 mg/kg), and prevented by an ER antagonist, 4-hydroxytamoxifen (2 mg/kg). VCD treatment increased caspase-3-like activity, whereas concurrent treatment with genistein and VCD restored caspase-3-like activity to control levels. VCD treatment had no effect on circulating E2 levels, uterine weight, or E2 binding to the ER, nor could it directly displace E2 from ERbeta. These observations support the idea that ER-mediated protection against VCD-induced follicle toxicity is obtained by reducing apoptosis in small preantral follicles, although VCD does not appear to directly interact with ER.

Alteration of activation, growth, and atresia of bovine preantral follicles by long-term treatment of cows with estradiol and recombinant bovine somatotropin

The hypothesis was that long-term treatment of cattle with estradiol (E(2)) and bovine somatotropin (bST) would alter the earliest stages of folliculogenesis. Nonlactating Holstein cows (n = 26) were treated in a 2 x 2 arrangement with E(2) (2 x 24 mg implants, 67.1 +/- 1.4 days) and bST (Posilac, 63.6 +/- 1.5 days). At Day 67 +/- 1.3, one ovary was removed for morphometric and immunohistochemical analysis. For each ovary, 388 +/- 38 microscopic fields (2 x 2 mm) were examined and follicles within each field were classified by histological stage. Fields that contained no follicles were classified as empty. Empty fields (n = 100 per ovary) were further classified as containing no evidence of follicles or containing atretic remnants of follicles. Approximately 30 4-microm sections per ovary were stained for proliferating cell nuclear antigen (PCNA), and 150 fields per ovary were evaluated. Additional sections (n = 10 per ovary) were assessed immunohistochemically for apoptosis, and fluorescence intensity was determined for each follicle. Treatment with bST significantly decreased percentage of empty fields containing atretic remnants. Treatment with E(2) induced activation of follicles as shown by a decrease in percentage of primordial follicles and an increase in percentage of primary follicles as determined by PCNA staining. At the primary follicle stage the combination of bST + E(2) decreased apoptosis as shown by decreased fluorescence intensity. Thus, E(2) induced activation of follicles, bST enhanced survival, and the combination lowered atresia.

Prolactin and lipopolysaccharide treatment increased apoptosis and atresia in rat ovarian follicles

Follicular atresia is associated with the presence of increased macrophages within the follicle. What is not known is whether, in the adult rat, macrophages are instrumental in inducing apoptosis and/or atresia or whether they are simply secondary to a hormonally mediated event. As prolactin is an immunoreactive hormone and stimulates the expression of monocyte chemoattractant, the present experiments compared the effects of prolactin treatment with that of an immune challenge with lipopolysaccharide (LPS) on the invasion of macrophages into the follicular and luteal compartments of the ovary and the occurrence of apoptosis/atresia in relation to macrophage invasion. Rats were treated for 3 days with either prolactin or LPS and ovaries obtained at pro-oestrus or oestrus. Prolactin and LPS increased the number of atretic vs. healthy follicles (P < 0.008, chi2) in pro-oestrus ovaries and increased the mean number of apoptotic cells and macrophages (P < 0.05 for some groups). Macrophages were typically observed in the thecal layer, apoptotic cells in the granulosa cell layer, although 84% follicles which had macrophages within the granulosa cell layer also contained relatively high numbers of apoptotic nuclei. Prolactin and LPS treatment in vivo reduced the progesterone response to follicle stimulating hormone (FSH) (P < 0.001) in cultures of ovarian dispersates but did not inhibit the response to forskolin. In contrast, prolactin or LPS added in vitro to the cultures inhibited the progesterone response to forskolin. Results show that both prolactin and LPS increase follicular apoptosis and atresia and reduce the progesterone response to FSH.

A mechanistic study of ovarian carcinogenesis induced by nitrofurazone using rasH2 mice

In order to clarify whether the ovarian tumors induced in a long-term carcinogenicity study of nitrofurazone (NF) in mice can be also produced in a short-term model using transgenic (Tg) mice carrying the human c-Ha-ras gene (rasH2 mice), the following 3 experiments were performed. In experiment 1, both rasH2 mice and their wild CB6F1 littermates carrying no c-Ha-ras gene (non-Tg mice) that were fed a diet containing 500 to 1,000 ppm NF for 7 weeks demonstrated ovarian atrophy characterized by decreased labeling indices (LIs) for proliferating cell nuclear antigen (PCNA) in granulosa cells. In experiment 2, increased numbers of atretic follicles and decreased PCNA LIs in granulosa cells were recognized in rasH2 mice given diets containing 250 or 500 ppm NF for 26 weeks, but no tumor induction was grossly observed. In experiment 3, similar ovarian atrophy was observed in association with increased serum luteinizing hormone (LH) levels in both rasH2 and non-Tg mice given diet containing 1,000 ppm NF for 11 days. These results indicate that long-term NF treatment induces ovarian tumors in mice, possibly by continuous stimulation with gonadotropins such as LH via a negative-feedback phenomenon secondary to ovarian atrophy (as the tumor-induction mechanism), although we could not completely rule out a genotoxic mechanism.