Roles of poly (ADP-ribose) polymerase 1 activation and cleavage in induction of multi-oocyte ovarian follicles in the mouse by 3-nitropropionic acid

3-nitropropionic acid (3-NPA) is known to be a mitochondrial toxin produced by plants and fungi, which may produce DNA damage in cells. However, studies of its reproductive toxicology are lacking. We know that poly(ADP-ribose) polymerase (PARP) plays an important role in a large variety of physiological processes and is involved in DNA repair pathways. The present study was therefore aimed at exploring the involvement of PARP-1 activation and cleavage after 3-NPA stimulation in female mice. We observed an increased number of atretic follicles and multi-oocyte follicles (MOFs) after treatment with 3-NPA and serum concentrations of 17β-oestradiol and progesterone were significantly reduced. Our results provide evidence that PARP-1 cleavage and activational signals are involved in pathological ovarian processes stimulated by 3-NPA. In addition, total superoxide dismutase, glutathione peroxidase and catalase activities were significantly increased, whereas succinate dehydrogenase was decreased in a dose-dependent manner. Results from our in vitro study similarly indicated that 3-NPA inhibited the proliferation of mouse granulosa cells and increased apoptosis in a dose-dependent manner. In summary, 3-NPA induces granulosa cell apoptosis, follicle atresia and MOFs in the ovaries of female mice and causes oxidative stress so as to disrupt endogenous hormonal systems, possibly acting through PARP-1 signalling.

Very low-dose (femtomolar) 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) disrupts steroidogenic enzyme mRNAs and steroid secretion by human luteinizing granulosa cells

2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) is the most toxic congener of the polyhalogenated aromatic hydrocarbons (PAH), which causes anatomical abnormalities and developmental defects, impairs ovulation and reduces fertility. TCDD's endocrine-disrupting effects are, in part, caused by a direct action at the ovary. Herein we investigated the in-vitro effects of environmentally relevant doses of TCDD on estradiol-17β (E2) production by human luteinizing granulosa cells (hLGC) obtained from women stimulated for in-vitro fertilization (IVF). TCDD at all concentrations tested (3.1fM, 3.1pM and 3.1nM) significantly decreased E2 secretion when assayed for by radioimmunoassay (RIA). Herein we confirm that TCDD alters E2 secretion by hLGC in a time-, not dose-dependent fashion and are the first to show decreases in E2 secretion with fM concentrations of TCDD. Using real-time quantitative PCR (RT-qPCR), the decreased E2 secretion correlates with a decrease in the mRNA expression levels two enzymes in the estrogen biosynthesis pathway: CYP11A1 and CYP19A1.

Low-dose gold nanoparticles exert subtle endocrine-modulating effects on the ovarian steroidogenic pathway ex vivo independent of oxidative stress

Gold nanoparticles (GNPs) have gained considerable attention for application in science and industry. However, the untoward effects of such particles on female fertility remain unclear. The objectives of this study were to (1) examine the effects of 10-nm GNPs on progesterone and estradiol-17β accumulation by rat ovaries ex vivo and (2) to identify the locus/loci whereby GNPs modulate steroidogenesis via multiple-reference gene quantitative real-time RT-PCR. Regression analyses indicated a positive relationship between both Star (p < 0.05, r(2) = 0.278) and Cyp11a1 (p < 0.001, r(2) = 0.366) expression and P4 accumulation upon exposure to 1.43 × 10(6) GNPs/mL. Additional analyses showed that E2 accumulation was positively associated with Hsd3b1 (p < 0.05, r(2) = 0.181) and Cyp17a1 (p < 0.01, r(2) = 0.301) expression upon exposure to 1.43 × 1(3) and 1.43 × 10(9) GNPs/mL, respectively. These results suggest a subtle treatment-dependent impact of low-dose GNPs on the relationship between progesterone or estradiol-17β and specific steroidogenic target genes, independent of oxidative stress or inhibin.

Histopathologic alterations associated with global gene expression due to chronic dietary TCDD exposure in juvenile zebrafish

The goal of this project was to investigate the effects and possible developmental disease implication of chronic dietary TCDD exposure on global gene expression anchored to histopathologic analysis in juvenile zebrafish by functional genomic, histopathologic and analytic chemistry methods. Specifically, juvenile zebrafish were fed Biodiet starter with TCDD added at 0, 0.1, 1, 10 and 100 ppb, and fish were sampled following 0, 7, 14, 28 and 42 d after initiation of the exposure. TCDD accumulated in a dose- and time-dependent manner and 100 ppb TCDD caused TCDD accumulation in female (15.49 ppb) and male (18.04 ppb) fish at 28 d post exposure. Dietary TCDD caused multiple lesions in liver, kidney, intestine and ovary of zebrafish and functional dysregulation such as depletion of glycogen in liver, retrobulbar edema, degeneration of nasal neurosensory epithelium, underdevelopment of intestine, and diminution in the fraction of ovarian follicles containing vitellogenic oocytes. Importantly, lesions in nasal epithelium and evidence of endocrine disruption based on alternatively spliced vasa transcripts are two novel and significant results of this study. Microarray gene expression analysis comparing vehicle control to dietary TCDD revealed dysregulated genes involved in pathways associated with cardiac necrosis/cell death, cardiac fibrosis, renal necrosis/cell death and liver necrosis/cell death. These baseline toxicological effects provide evidence for the potential mechanisms of developmental dysfunctions induced by TCDD and vasa as a biomarker for ovarian developmental disruption.

Engineered nanomaterials: an emerging class of novel endocrine disruptors

Over the past decade, engineered nanomaterials (ENMs) have garnered great attention for their potentially beneficial applications in medicine, industry, and consumer products due to their advantageous physicochemical properties and inherent size. However, studies have shown that these sophisticated molecules can initiate toxicity at the subcellular, cellular, and/or tissue/organ level in diverse experimental models. Investigators have also demonstrated that, upon exposure to ENMs, the physicochemical properties that are exploited for public benefit may mediate adverse endocrine-disrupting effects on several endpoints of mammalian reproductive physiology (e.g., steroidogenesis, spermatogenesis, pregnancy). Elucidating these complex interactions within reproductive cells and tissues will significantly advance our understanding of ENMs as an emerging class of novel endocrine disruptors and reproductive toxicants. Herein we reviewed the recent developments in reproductive nanotoxicology and identified the gaps in our knowledge that may serve as future research directions to foster continued advancement in this evolving field of study.

Gene expression and pathologic alterations in juvenile rainbow trout due to chronic dietary TCDD exposure

The goal of this project was to use functional genomic methods to identify molecular biomarkers as indicators of the impact of TCDD exposure in rainbow trout. Specifically, we investigated the effects of chronic dietary TCDD exposure on whole juvenile rainbow trout global gene expression associated with histopathological analysis. Juvenile rainbow trout were fed Biodiet starter with TCDD added at 0, 0.1, 1, 10 and 100 ppb (ngTCDD/g food), and fish were sampled from each group at 7, 14, 28 and 42 days after initiation of feeding. 100 ppb TCDD caused 100% mortality at 39 days. Fish fed with 100 ppb TCDD food had TCDD accumulation of 47.37 ppb (ngTCDD/g fish) in whole fish at 28 days. Histological analysis from TCDD-treated trout sampled from 28 and 42 days revealed that obvious lesions were found in skin, oropharynx, liver, gas bladder, intestine, pancreas, nose and kidney. In addition, TCDD caused anemia in peripheral blood, decreases in abdominal fat, increases of remodeling of fin rays, edema in pericardium and retrobulbar hemorrhage in the 100 ppb TCDD-treated rainbow trout compared to the control group at 28 days. Dose- and time-dependent global gene expression analyses were performed using the cGRASP 16,000 (16K) cDNA microarray. TCDD-responsive whole body transcripts identified in the microarray experiments have putative functions involved in various biological processes including growth, cell proliferation, metabolic process, and immune system processes. Nine microarray-identified genes were selected for QPCR validation. CYP1A3 and CYP1A1 were common up-regulated genes and HBB1 was a common down-regulated gene among each group based on microarray data, and their QPCR validations are consistent with microarray data for the 10 and 100 ppb TCDD treatment groups after 28 days exposure (p<0.05). In addition, in the 100 ppb group at 28 days, expression of complement component C3-1 and trypsin-1 precursor have a more than 10-fold induction from the microarray experiments, and their QPCR validations are consistent and showed significant induction in the 100 ppb group at 28 days (p<0.05). Overall, lesion in nasal epithelium is a novel and significant result in this study, and TCDD-responsive rainbow trout transcripts identified in the present study may lead to the development of new molecular biomarkers for assessing the potential impacts of environmental TCDD on rainbow trout populations.

Differential gene expression associated with dietary methylmercury (MeHg) exposure in rainbow trout (Oncorhynchus mykiss) and zebrafish (Danio rerio)

The objective of this study was to identify and evaluate conserved biomarkers that could be used in most species of teleost fish at most life-stages. We investigated the effects of sublethal methylmercury (MeHg) exposure on developing rainbow trout and zebrafish. Juvenile rainbow trout and young adult zebrafish were fed food with MeHg added at 0, 0.5, 5, and 50 ppm. Atomic absorption spectrometry was applied to measure whole body total Hg levels, and pathologic analysis was performed to identify MeHg-induced toxicity. Fish at 6 weeks were sampled from each group for microarray analysis using RNA from whole fish. MeHg-exposed trout and zebrafish did not show overt signs of toxicity or pathology, nor were significant differences seen in mortality, length, mass, or condition factor. The accumulation of MeHg in trout and zebrafish exhibited dose- and time-dependent patterns during 6 weeks, and zebrafish exhibited greater assimilation of total Hg than rainbow trout. The dysregulated genes in MeHg-treated fish have multiple functional annotations, such as iron ion homeostasis, glutathione transferase activity, regulation of muscle contraction, troponin I binding and calcium-dependent protein binding. Genes were selected as biomarker candidates based on their microarray data and their expression was evaluated by QPCR. Unfortunately, these genes are not good consistent biomarkers for both rainbow trout and zebrafish from QPCR evaluation using individual fish. Our conclusion is that biomarker analysis for aquatic toxicant assessment using fish needs to be based on tissue-, sex- and species-specific consideration.

Evaluation of ultrasonography for monitoring follicular growth in rhesus monkeys

The purpose of this study was to determine if the ovaries and uterus of rhesus monkeys could be visualized by ultrasonography and to detect changes associated with follicular growth and ovulation. Animals were examined during 15 menstrual cycles, for an average of nine consecutive days. Ultrasonic recordings were correlated with hormonal parameters (estradiol 17beta, E(2); luteinizing hormone, LH; and progesterone, P) and laparoscopic findings. The uterus and both ovaries were observed in more than 90% of the examinations. A dominant follicle (DF) was identified during all ovulatory cycles, on average 1 d preceding the E(2) peak. The maximal diameter of the DF ranged from 3 to 7 mm. Laparoscopic examinations to determine the site of the DF confirmed ultrasonic findings in 10 of 14 cycles (P < 0.1). There was no significant difference in the size of the dominant and contralateral ovaries; however, more follicles with a diameter of 2 to 7 mm were found on the dominant ovary (P < 0.05). Two animals stimulated with exogenous gonadotropins showed a linear increase in ovarian size for 6 d prior to oocyte recovery (P < 0.05), reflecting an increase in the number of developing follicles. Ultrasonography can be used to identify the DF during spontaneous cycles in rhesus monkeys and to monitor the response of monkeys to exogenous gonadotropins.

Effect of the IGF-1/PTEN/Akt/FoxO signaling pathway on the development and healing of water immersion and restraint stress-induced gastric ulcers in rats

Insulin-like growth factor 1 (IGF-1) and Akt [also known as protein kinase B (PKB)] proteins have been reported to exhibit gastroprotective effects by reducing water immersion and restraint stress (WRS)-induced gastric mucosal cellular apoptosis. To confirm whether the IGF-1/PTEN/Akt/FoxO signaling pathway is effective in protecting against gastric ulcers, our current study was conducted to examine the expression and localization of IGF-1, phosphatase and tensin homologue deleted on chromosome 10 (PTEN), Akt and O subfamily of forkhead box (FoxO) proteins, caspase-3 activity and the number of apoptotic cells in gastric mucosa of rats subjected to WRS. Our results demonstrated that WRS induced gastric ulcers by enhancing cell apoptosis in rat gastric mucosa. In addition, in normal rat gastric mucosa, PTEN, total Akt and FoxO1 were found mainly in the cell cytoplasm of fundic glands in the lamina propria close to the muscularis mucosa. In addition, strong staining of IGF-1, FoxO3a and FoxO4 in the gastric mucosa was primarily concentrated in the cell cytoplasm of the fundic glands in whole lamina propria. However, in rat gastric ulcers, IGF-1, total Akt, FoxO3a and FoxO4 were localized in proximity to the base of the ulcer margin and were also present in the granulation tissues of the gastric ulcers. Moreover, in the rat gastric ulcers, the mRNA transcript levels of IGF-1, PTEN, Akt-1, Akt-2, FoxO3 and FoxO4 were upregulated in the gastric ulcer margin, with a peak between Days 4 and 8 following 7 h of WRS. In conclusion, our results imply that the IGF-1/PTEN/Akt/FoxO signaling pathway plays a certain role(s) in the protection against ulceration through the regulation of cellular apoptosis as observed in the development and healing of rat gastric ulcers.

Current status of potential bisphenol toxicity in dentistry

Bisphenols are chemical components found in dental composites and sealants. Similar compounds also can be found in baby bottles, food can liners, and even drinking water. Bisphenols have gained attention recently because they, like other natural and synthetic compounds, including hormone-based drugs and soybean products, have the capacity to mimic the actions of the hormone estrogen in living cells and animals. Such estrogenic activity has been linked to a variety of health problems, including breast and prostate cancer, metabolic disorders, and reproductive dysfunction. In early 2010, the FDA issued a report stating that there are some concerns about the safety of bisphenols in food products and called for more research on bisphenol toxicity. At present, no regulatory or professional organization has expressed concern about health effects of bisphenols in dental materials.

Involvement of cell proliferation in the process of follicular atresia in the guinea pig

Cell morphology and proliferation was investigated in the atretic follicles during estrous cycles in the guinea pig. Ovarian samples on days 1, 4, 8, 12 and 16 of the estrous cycle in the guinea pig were taken in the morning for histologic staining with hematoxylin and eosin (HE), and immunohistochemical staining of the protein proliferating cell nuclear antigen (PCNA). The results indicated that the granulosa cells degenerated and eliminated first in atretic follicles, while the fibroblast-like cells appeared in the innermost layer of theca interna cells. When the fibroblast-like cells migrated to the antrum, they proliferated and formed a new tissue in peripheral to the zona pellucida of the oocyte. Our results also revealed that the orientation of the theca interna cell arrangement changed twice during the process of atresia, and the loose connective tissue in the antrum was critical for follicular atresia. Therefore, follicular atresia was not a simple process of cell death and elimination, but coexisted with cell proliferation. To our knowledge, we have for the first time confirmed cell proliferation and the presence of new tissue in atretic follicles in guinea pigs.

Gold nanoparticles enter rat ovarian granulosa cells and subcellular organelles, and alter in-vitro estrogen accumulation

Nanoparticle technology refers to research and technology developed at the atomic or molecular level for materials of approximately 1-100 nm in length. Through accidental or involuntary exposure, nanoparticles are potentially toxic to the body, including reproductive organs. Ovarian granulosa cells play a major role in maintaining ovarian function, health, and female fertility. Since these cells are involved in steroidogenesis, we wished to evaluate whether nanoparticles affected them after traversing their membranes. Cells were co-incubated with 10 nm gold particles for up to 24 h. Transmission electron micrographs were taken of GC treated with 10 nm gold particles in order to compare and contrast ultrastructural locations of nanoparticles with treatment. From micrograph comparisons of treated vs. untreated GC at various culture times, it appeared that some intracellular organelles involved in steroidogenesis were infiltrated and/or altered due to the presence of the nanogold particles. Medium samples were taken in order to determine estradiol-17beta (E2) accumulation/secretion by untreated vs. treated cells. GC incubated with 10 nm nanogold particles for 1, 3, or 5 h were found to accumulate significantly increased amounts of estrogen compared with untreated cells. Conversely, at 24 h there was a significant attenuation with respect to controls. The data presented here provide insight into the toxicologic effects gold nanoparticles elicit on ovarian granulosa cells.

Autoradiographic localization of aromatic hydrocarbon receptor (AHR) in rhesus monkey ovary

2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) is the most toxic congener of a large class of manmade pollutants that persist in the environment. TCDD exerts its toxic effects, in part, by binding to its receptor known as the aromatic hydrocarbon receptor (AHR). TCDD is estrogen modulatory and in some systems its receptor associates directly with estrogen receptors via co-activator molecules. TCDD inhibits steroid synthesis in human ovarian granulosa cells and AHR is found in these cells. We have previously shown that AHR is found in whole rhesus monkey ovary, but have yet to establish its location. In the present study, we set out to show that radiolabeled TCDD binds to monkey ovarian follicles and that this binding is receptor mediated. Ovaries from Macaca mulatta were sectioned on a cryostat at 10 micro m; and sections were incubated with either control vehicle, (3)H-TCDD, or (3)H-TCDD plus alpha-naphthoflavone (ANF), a known receptor-blocking agent. Here, we show for the first time specific binding of TCDD to the granulosa cells of antral follicles and other regions of the rhesus monkey ovary. Our data indicate a 60-fold increase in binding with (3)H-TCDD over that of control, and that this binding is reduced to the levels seen in controls with the addition of the competitive antagonist ANF. These findings support the hypothesis that TCDD directly affects primate ovarian function via the AHR.

Molecular targets of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) within the zebrafish ovary: insights into TCDD-induced endocrine disruption and reproductive toxicity

TCDD is a reproductive toxicant and endocrine disruptor, yet the mechanisms by which it causes these reproductive alterations are not fully understood. In order to provide additional insight into the molecular mechanisms that underlie TCDD's reproductive toxicity, we assessed TCDD-induced transcriptional changes in the ovary as they relate to previously described impacts on serum estradiol concentrations and altered follicular development in zebrafish. In silico computational approaches were used to correlate candidate regulatory motifs with observed changes in gene expression. Our data suggest that TCDD inhibits follicle maturation via attenuated gonadotropin responsiveness and/or depressed estradiol biosynthesis, and that interference of estrogen-regulated signal transduction may also contribute to TCDD's impacts on follicular development. TCDD may also alter ovarian function by disrupting various signaling pathways such as glucose and lipid metabolism, and regulation of transcription. Furthermore, events downstream from initial TCDD molecular-targets likely contribute to ovarian toxicity following chronic exposure to TCDD. Data presented here provide further insight into the mechanisms by which TCDD disrupts follicular development and reproduction in fish, and can be used to formulate new hypotheses regarding previously documented ovarian toxicity.

Short-Term Hormone Release from Adult Female Rat Hypothalamic and Pituitary Explants is not Altered by 2,3,7,8-Tetrachlorodibenzo-p-dioxin

2, 3, 7,8-Tetrachlorodibenzo-p-dioxin (TCDD) has adverse effects on reproduction, in part due to direct actions at the ovary. It is unclear whether effects are further mediated by glands that regulate ovarian function. We investigated whether effects of TCDD are mediated via the hypothalamic-pituitary axis. Hypothalamic and pituitary tissues were cultured in medium with and without TCDD. TCDD did not alter GnRH release from hypothalamic samples. It continued to be pulsatile with no differences in the average peak frequency, average peak amplitude, or baseline GnRH release. TCDD did not alter GnRH-induced release of gonadotropins from pituitary samples. There were no differences in average peak amplitude or baseline release. AhR, ARNT or ER alpha mRNA copy numbers in cultured pituitaries were not affected by TCDD. Our data suggest that TCDD effects on ovarian function are not mediated through the hypothalamic or pituitary release parameters tested in this study.

Regulation of FoxO1 transcription factor by nitric oxide and cyclic GMP in cultured rat granulosa cells

FoxO1 is a transcription factor implicated in a multitude of physiological processes including cell cycle progression, apoptosis and insulin signaling. Recent findings indicate that FoxO1 is a key regulator during the proliferation and maturation of granulosa cells. Over the past several years, it has become evident that nitric oxide (NO) and cGMP modulate ovarian function. There has been no information, however, about whether NO-cGMP affects FoxO1 expression or about the relationship between NO-cGMP and FoxO1. In the present study, we used immunoblot analysis to determine whether NO and cGMP affect FoxO1 expression in cultured granulosa cells. Our results clearly showed that FSH suppressed FoxO1 expression in a time-dependent manner, and that NO-cGMP stimulated FoxO1 expression in cultured granulosa cells. In addition, this stimulatory effects of NO and cGMP can be blocked by FSH in cultured granulosa cells. These findings demonstrate that NO and cGMP influence FoxO1 expression possibly through antagonizing the action of FSH in cultured granulosa cells. Results of both immunoblot analysis and immunohistochemistry also show that estradiol implantation do not affect the expression of FoxO1 in rat granulosa cells as gonadotrophins do, indicating that mechanism of estradiol on granulosa cells is different from gonadotrophins. Together, our experiments suggest that expression of FoxO1 in rat granulosa cells can be regulated by gonadotrophins and the NO/cGMP signaling pathway.

Inhibition of follicular development, vitellogenesis, and serum 17beta-estradiol concentrations in zebrafish following chronic, sublethal dietary exposure to 2,3,7,8-tetrachlorodibenzo-p-dioxin

The environmental toxicant 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) is a potent endocrine disruptor with the ability to affect several biologic processes, including reproduction. In fish, sublethal exposure to TCDD is known to modulate overall reproductive capacity, but impacts on follicular development and vitellogenesis are unknown. Here we show that chronic, dietary exposure to 0.08, 0.32, or 0.80 ng TCDD female(-1) day(-1) decreased egg production by more than 50% and that spawning success was reduced by as much as 96%. Serum estradiol concentrations were decreased more than twofold, accounting, in part, for observed decreases in serum vitellogenin concentrations by as much as 29%. Our data suggest that decreased egg production is likely the result of TCDD-mediated inhibition of the transition from pre-vitellogenic stage follicles to vitellogenic stage follicles, as well as the induction of follicular atresia. The majority of reproductive toxicity of TCDD is likely due to direct impacts on the ovary, yet histopathologic observations suggest liver toxicity could also contribute to observed impacts on vitellogenesis. Importantly, even when overall egg production is not significantly affected, our data show that subtle physiologic changes induced by TCDD can lead to altered gonadogenesis. This suggests that long-term exposure to very low concentrations of TCDD could greatly affect fecundity and reproductive success in fishes.

Accumulation, tissue distribution, and maternal transfer of dietary 2,3,7,8,-tetrachlorodibenzo-p-dioxin: impacts on reproductive success of zebrafish

TCDD (2,3,7,8-tetrachlorodibenzo-p-dioxin) is a reproductive toxicant and endocrine disruptor in nearly all vertebrates; however, the mechanisms by which TCDD alters the reproductive system is not well understood. The zebrafish provides a powerful vertebrate model system to investigate molecular mechanisms by which TCDD affects the reproductive system, but little is known regarding reproductive toxic response of zebrafish following chronic, sublethal exposure to TCDD. Here we investigate the accumulation of TCDD in selected tissues of adult female zebrafish and maternal transfer to offspring following dietary exposure to TCDD (0.08-2.16 ng TCDD/fish/day). TCDD accumulated in tissues of zebrafish in a dose- and time-dependent manner, except for brain. Chronic dietary exposure resulting in the accumulation of 1.1-36 ng/g fish did not induce an overt toxic response or suppress spawning activity. The ovosomatic index was impacted with an accumulation of as little as 0.6 ng/g fish, and 10% of the females showed signs of ovarian necrosis following accumulation of approximately 3 ng/g TCDD. Offspring health was impacted with an accumulation of as little as 1.1 ng/g female; thus the lowest observed effect level (LOEL) for reproductive toxicity in female zebrafish is approximately 0.6-1.1 ng/g fish. Maternal transfer resulted in the accumulation of 0.094-1.2 ng/g, TCDD, which was sufficient to induce the typical endpoints of larval TCDD toxicity, commonly referred to as blue sac syndrome. This study provides the necessary framework to utilize the zebrafish model system for further investigations into the molecular mechanisms by which TCDD exerts its reproductive toxic responses.

In utero and lactational exposure of Long-Evans rats to ammonium perchlorate (AP) disrupts ovarian follicle maturation

Ammonium perchlorate (AP) is a powerful oxidizer manufactured almost exclusively for the aerospace industry. AP salts are also used in airbags, flares, fertilizers, enamels and paints. As a result of widespread industrial use, AP has become a persistent environmental contaminant of drinking water in several U.S. states. AP ion disrupts the trapping of iodide as well as facilitates the discharge of unorganified iodide from the thyroid gland. Such disturbances in thyroid hormone concentrations during critical periods of development are then known to cause profound reproductive and developmental defects, since thyroid hormones modulate both follicular development and steroidogenesis and affect estrogen metabolism and receptor. This study was designed (1) to determine whether exposure to a low or high concentration of AP (LAP, HAP) exerts detrimental effects on follicle maturation in the Long-Evans hooded rat and (2) to determine whether the modulatory effects of AP can be ameliorated by levo-thyroxine sodium (T4) supplementation. Animals were treated via deionized drinking water on GD 7-21 with LAP (0.4 mg/kg/day) or HAP (4.0 mg/kg/day). Half of each group was also given T4 supplements via drinking water on GD 7-21. Female pups were sacrificed on postnatal days 24/25, and the ovaries were excised, fixed for histology and analyzed. The analysis included a count, measurement and classification of preantral and antral follicles in the greatest cross-sectional area of the ovary. The results indicated that treatment with the HAP significantly reduced the number of preantral follicles <50,000 microm2 and the total number of antral follicles in the <50,000, 50-100,000 and >100,000 microm2 size classes. In ovaries treated with the LAP, we observed no significant decrease in preantral follicles of any size class and only a significant reduction in the largest antral follicles. T4 only circumvented the effect on the number of small preantral and antral follicles; however, a significant diminution in the antral follicle number persisted in the mid-sized (HAP) and large (LAP, HAP)-sized classes. These data support the hypothesis that AP reduces the number of preantral and antral follicles in certain size classes in rats exposed during a critical period of development, and that T4 can attenuate the effects of AP on small preantral and antral follicles, but not on medium or large antral follicles. (T35ES007292 & ES08342.).

Effects of intrauterine growth retardation on development of the gastrointestinal tract in neonatal pigs

BACKGROUND

Intrauterine growth retardation (IUGR) is a common problem in human and other species and increases the risk of death of the fetus and newborn during the perinatal period.

OBJECTIVES

This study was conducted to examine the influences of intrauterine growth retardation (IUGR) on development of the gastrointestinal tract in newborn pigs.

METHODS

Ten animals from five litters were divided into five piglets with IUGR and five with normal birth-weight (NW). The IUGR category comprised animals with a birth weight 2 SD below the mean birth weight of the total population, while the NW category included animals with a birth weight within one SD of the mean birth weight in the total population. Animals were anesthetized and sampled within 2-4 h after birth and without suckling. The morphological changes of intestine and stomach of IUGR piglets were compared with NW ones. The expressions of IGF-I and receptors for growth hormone and insulin in intestinal mucosa were semiquantified using reverse transcription PCR.

RESULTS

The results of our study indicated that the weights of the stomach, small intestine and small intestinal mucosa were significantly lower in IUGR compared with NW piglets (p<0.01). In addition, the lengths of the small intestine and colon in IUGR pigs were also significantly less than those of NW (p<0.05). Furthermore, insulin-like growth factor-I (IGF-I) mRNA level in intestinal mucosa of IUGR piglets was increased significantly (p<0.05), and the expression mRNA levels of insulin receptor and growth hormone (GH) receptor in the mucosa in IUGR piglets showed a tendency to be lower (p=0.17 and p=0.11, respectively) than those of the NW animals.

CONCLUSION

We conclude from the data that IUGR affects intestinal growth and morphology and is in associated with altered gene expression of growth-related proteins. We speculate that the morphological change and associated altered endocrine homeostasis contribute to lower growth rates of pigs affected by IUGR.

Modulation of ovarian follicle maturation in Long-Evans rats exposed to polychlorinated biphenyls (PCBs) in-utero and lactationally

Polychlorinated biphenyls (PCBs) are ubiquitous man-made toxicants capable of endocrine disruption. Studies in several species have shown that exposure to PCBs and their hydroxylated metabolites reduces fecundity and decreases circulating concentrations of thyroid hormones, causing serious reproductive and developmental defects. Thyroid hormones modulate both follicular development and steroidogenesis, and affect estrogen metabolism and the regulation of estrogen receptor. This study was designed (1). to determine whether exposure to a commercially prepared PCB mixture (Aroclor 1016) exerts detrimental effects on follicle maturation in the Long-Evans hooded rat; and (2). to determine whether the modulatory effects of Aroclor can be attenuated by levo-thyroxine sodium (T(4)) supplementation. Animals were treated on gestation days 7-13 with a single daily intraperitoneal injection (2.5 mg/kg per day) of Aroclor. Half of the Aroclor-treated dams were also given T(4) supplements (2.89 microg/kg per day) via drinking water. Female pups were sacrificed on postnatal days 24/25, and the ovaries were excised, fixed for histology and analyzed. The analysis included a count, measurement and classification of healthy and atretic preantral and antral follicles in the greatest cross-sectional area. The results indicated that treatment with Aroclor significantly reduced the number of preantral follicles <50000 microm(2) and the total number of antral follicles in the 50-100000 and >100000 microm(2) size classes. T(4) circumvented the Aroclor effect on the number of preantral follicles <50000 microm(2); however, a significant reduction in the antral follicle number persisted in the 50-100000 and >100000 microm(2) size classes. In addition, we observed a significant increase in atresia in the Aroclor-treated ovaries in the antral <50000 microm(2) size class, which was not present in ovaries exposed to both Aroclor and T(4). These data support the hypothesis that Aroclor reduces the number of preantral and antral follicles of certain size classes in rats exposed during the critical period of development, and that supplementation with T(4) can attenuate the effects of Aroclor on small, but not medium or large antral follicles. Atresia of small, antral follicles may constitute one of the underlying mechanisms by which folliculogenesis is modulated by Aroclor 1016.

Estrous cycle-regulated expression of CYP1B1 mRNA in the rat ovary

CYP1B1, a member of the cytochrome p450 superfamily, is expressed constitutively in the steroidogenic tissues of mammals and is inducible by peptide hormones, cAMP and aromatic hydrocarbon receptor (AHR) ligands. The mechanism of induction of this cytochrome p450 is similar to that for CYP1A1, i.e. through the aromatic hydrocarbon receptor (AHR) signaling pathway. We have recently reported that CYP1B1, but not CYP1A1, is expressed in rat granulosa cells (GC) in the absence of any external stimulus. The induction of CYP1B1 mRNA in rat GC by 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) in vitro was followed by an increase in AHR and estrogen receptor (ER-beta) RNA levels. Estrous cycle-dependent expression of AHR, AHR-nuclear translocator (ARNT) and ER-mRNAs in the rat ovary was reported. We suggest that CYP1B1 may play a major role in the regulation of rat ovarian function/cycle but until now this has been unexplored experimentally. The present study was therefore aimed at examining the expression of CYP1A1, CYP1B1 and ER-mRNA in rat ovarian tissues throughout the estrous cycle to establish any correlation in the expressions of these mRNAs in rat ovary. Total RNA was extracted from the ovary and liver of cycling adult rats and the mRNAs were analyzed using relative RT-PCR with gene-specific primers for the target mRNA and for RPL 19 or S16 primers as an internal control. The results indicated that in the ovary, CYP1B1 mRNA increased significantly on the evening of proestrus and dramatically decreased on the morning of estrus, while ER-mRNA remained unaltered throughout the estrous cycle. CYP1A1 mRNA in the ovary and both CYP1A1 and CYP1B1 mRNAs in the liver were undetectable. That the sudden decrease of ovarian CYP1B1 mRNA on the morning of estrus was not an effect of the LH surge was verified in vitro using our short-term GC culture model. GC prepared from rats super-stimulated with equine chorionic gonadotropin (eCG) were cultured for 6 h with or without LH and TCDD. It was observed that both CYP1A1 and CYP1B1 mRNAs were induced by TCDD with no apparent effect of LH. It is suggested that the high level of CYP1B1 mRNA expression on the evening of proestrus in rat ovary might be involved in metabolism of estrogens to catecholestrogen (a known effect of CYP1B1), and that expression is unaffected in GC by LH.

2,3,7,8-Tetrachlorodibenzo-p-dioxin increases steady-state estrogen receptor-beta mRNA levels after CYP1A1 and CYP1B1 induction in rat granulosa cells in vitro

Previous in-vitro investigations of rat granulosa cells (GC) have shown that 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) inhibits estrogen secretion and FSH-induced aromatase activity. Although TCDD exerted no effect on basal aromatase enzyme activity, TCDD did reduce steady-state aromatase mRNA levels in GC using competitive RT-PCR. TCDD is hypothesized to induce these changes through aromatic hydrocarbon receptor(AHR)-mediated gene transcription and the modulation of the estrogen receptor (ER)-signaling pathway. In this study we show that rat GC express mRNA for AHR and the AHR nuclear translocator (ARNT) as well as biomarkers of TCDD action, CYP1A1 and CYP1B1 mRNA. Basal CYP1A1 and ER-alpha mRNAs were present only in trace amounts. By relative RT-PCR analysis we showed that CYP1A1 and CYP1B1 mRNA were induced significantly by TCDD at 6 h and that induction of CYP1A1 was maintained throughout the experiment. Using competitive RT-PCR, we observed no significant change in the mRNA levels of ARNT between control and TCDD-treated GC. Both AHR and ER-beta mRNA levels increased significantly at 48 h with TCDD compared with controls. Since ER-beta mRNA was not increased significantly until 48 h in culture, we suggest that in rat GC, the observed ER-beta mRNA increase by TCDD might be a result of CYP1A1/CYP1B1 catalyzed estrogen metabolism and aromatase mRNA inhibition via AHR.

Follicle selection in cyclic guinea pigs with active immunization against inhibin alpha-subunit

Experiments were conducted to elucidate the mechanisms of active immunization against inhibin on ovarian follicular development and selection in guinea pigs. Estrous cycle was synchronized in experimental guinea pigs by implanting progesterone containing tubes. Antibodies that bound 125I-labeled bovine inhibin were produced by all guinea pigs receiving the inhibin vaccine (recombinant ovine alpha-subunit in oil emulsion) without any effects on duration of the estrous cycle. Active immunization against inhibin increased the plasma concentrations of progesterone during the luteal phase and the plasma concentrations of estradiol but failed to increase the plasma concentration of follicle-stimulating hormone (FSH) during preovulatory period. The treatment also increased the number of corpora lutea (from 1.3+/-0.3 to 7.0+/-1.6 per each ovary), and preovulatory sized follicles (from 1.8+/-0.6 to 7.0+/-1.6 per each ovary), and follicles stained positively for inhibin alpha-subunit (from 2.3+/-0.5 to 6.3+/-1.3 per each ovary) significantly. The results indicate that active immunization against inhibin enhances ovulation rate by affecting the follicle selection and only dominant follicle can be stained for inhibin alpha-subunit in guinea pigs. This study is firstly to provide direct evidence that inhibins play important role in follicle selections in guinea pigs.

Lack of effect of beta-naphthoflavone on induction of Nramp genes in adult rainbow trout Oncorhynchus mykiss

Natural resistance-associated macrophage protein (Nramp) genes in rainbow trout, Oncorhynchus mykiss, were identified and characterized. The greatest mRNA level encoding these genes was in the developing ovary of rainbow trout. We evaluated the response of these genes to a certain aromatic hydrocarbon receptor (AHR) agonist. Adult rainbow trout were treated with beta-naphthoflavone (BNF) (50 and 100 mg/kg) for 48 h. Using reverse-transcriptase polymerase chain reaction with ovary and head kidney RNA and specific alpha and beta Nramp primers, a 400 bp Nramp-alpha- and a 400 bp Nramp-beta-specific cDNA were obtained. There were no changes in the alpha and beta Nramp mRNA levels in the ovary following BNF administration. CYP1A1 mRNA was increased in the ovary and kidney, suggesting the presence of AHR in rainbow trout ovary, while the AHR agonist produced no effect on Nramp mRNAs.

Demonstration of 2,3,7,8-tetrachlorodibenzo-p-dioxin attenuation of P450 steroidogenic enzyme mRNAs in rat granulosa cell in vitro by competitive reverse transcriptase-polymerase chain reaction assay

We investigated the effects of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), in prepubertal (PP) and adult (A) rat granulosa cells (GC) in vitro by examining the changes in estrogen secretion, aromatase enzyme activity and mRNAs for steroidogenic enzymes P450scc, 3beta-HSDI, P450arom; and for components of the AHR signaling pathway-CYP1A1, aromatic hydrocarbon receptor (AHR), and the AHR nuclear translocator protein (ARNT). In PP and A rat GC, TCDD (3.1 nM) reduced estrogen secretion at 48 h without altering aromatase enzyme activity. Addition of FSH (50 ng/ml) increased aromatase activity in GC with or without TCDD. FSH-induced aromatase activity was significantly reduced by TCDD (3.1 nM) at 48 h. Semi-quantitative RT-PCR showed a significant increase in CYP1A1 mRNA both at 24 and 48 h with TCAP, while a significant reduction in P450scc and P450arom mRNA was observed with competitive RT-PCR. All steroidogenic enzyme mRNAs were significantly lower in adults than in PP GC. We conclude that in rat GC, TCDD modulates the level of cytochrome P450 enzymes involved in the steroid biosynthetic cascade. This effect may be attributable to AHR interaction with dioxin-responsive elements present in the genes encoding these enzymes.

Minimal endocrine alterations in rodents after consumption of lake trout (Salvelinus namaycush)

Polychlorinated biphenyls (PCBs) and dioxins are known to cause disruptions in circulating hormone concentrations, which may influence fertility and normal fetal development. Structure activity relationships have been determined for individual congeners, but it is unclear what impacts occur due to exposure to complex mixtures of chemicals found in the environment. Most laboratory studies of PCB exposure have used commercial mixtures in high doses, which may not be representative of environmental concentrations of individual congeners, nor accurately represent complex interactions of multiple contaminants. The present study investigated endocrine alterations in rats associated with the consumption of lake trout collected from three specific locations in the Great Lakes. Composite fish samples were analyzed for PCBs, organochlorines, and mercury and ranged from 415 ppb to 1,275 ppb for individual contaminants. Fillet composites were fed to timed-pregnant Long-Evans rats as 30% of their diet. Concentrations of total thyroxine and estrogen were not significantly different in offspring of dosed dams from that of controls. However, aromatase activity was lowered in all dosed groups as compared with controls. This may represent a lowered expression of the CYP 19 gene in exposed rats or may be due to the presence of one or more substances in the contaminants that are capable of altering the affinity of the aromatase enzyme for its normal endogenous substrate. It is also possible that the number of maturing follicles in the lake trout-fed rats may be fewer than controls, which would result in an overall reduction in the enzyme activity. Data regarding the endocrine effects of environmental contaminant mixtures found in fish from the Great Lakes Basin are still controversial. Additionally, information is scarce with respect to the F1 generation of laboratory animals following environmental maternal exposures, therefore, we investigated the reproductive-endocrine alterations in rat offspring associated with the consumption of lake trout (Salvelinus namaycush) collected from three areas in the Great Lakes.

Estrous cycle-dependent changes in the expression of aromatic hydrocarbon receptor (AHR) and AHR-nuclear translocator (ARNT) mRNAs in the rat ovary and liver

The aromatic hydrocarbon receptor (AHR) and AHR nuclear translocator protein (ARNT) mediate the toxic effects of a wide variety of halogenated and polycyclic aromatic hydrocarbons. While it can be assumed that AHR has an endogenous function, its role in reproduction is currently undefined. The present study seeks to examine the regulation of AHR and ARNT mRNAs in liver and ovarian tissues across the rat estrous cycle. Message for hepatic AHR was increased significantly on the morning of proestrus, and decreased dramatically by the evening of proestrus; while hepatic ARNT mRNA was significantly decreased between diestrus and the morning of proestrus, and between the evening of proestrus and the morning of estrus. Ovarian AHR mRNA was unchanged from diestrus to proestrus, and was decreased on the evening of proestrus. Changes in the expression of ARNT mRNA mirrored changes in the liver. To assess interaction between the AHR- and estrogen-receptor (ER)-signaling pathways and to test the hypothesis that estrogen regulates AHR mRNA, 25-day-old female rats were injected with either 17beta-estradiol, the ER antagonist ICI 182 780, or with vehicle, and hepatic AHR mRNA was measured. Treatment with estrogen or the estrogen antagonist did not alter the abundance of AHR mRNA in the liver. These data suggest that while estrogen may not be the key regulator of AHR mRNA expression, a factor associated with the rat reproductive cycle may be important in regulating the expression of both the AHR and ARNT genes in the ovary and liver.

Secretion of ovarian inhibin and its physiologic roles in the regulation of follicle-stimulating hormone secretion during the estrous cycle of the female guinea pig

To characterize inhibin secretion during the estrous cycle in guinea pigs, the concentrations of plasma inhibin, estradiol, progesterone, and FSH were determined. A significant positive correlation was observed between inhibin and estradiol throughout the estrous cycle. Plasma inhibin and estradiol started to increase a few days before ovulation (Day 0 = day of estimated ovulation), and decreased after ovulation. These two hormones remained low during the luteal phase. The immunoreactivity of inhibin alpha, betaA, and betaB subunits was colocalized in the granulosa cells of one or two healthy large follicles in the ovary before ovulation. There was no positive reaction of inhibin alpha and beta subunits in the corpora lutea or other follicles. Ovariectomy resulted in an abrupt decrease in plasma inhibin and a significant increase in plasma FSH. Injection of anti-inhibin serum into adult female guinea pigs induced an elevation in plasma FSH in a dose-dependent manner. This report presents the first description of sequential changes in plasma inhibin and estradiol during the estrous cycle of guinea pigs. Results suggest that inhibin is secreted mainly by granulosa cells of a few healthy large follicles in the ovary and that it plays an important role in the regulation of FSH secretion during the estrous cycle in guinea pigs.

Dioxin perturbs, in a dose- and time-dependent fashion, steroid secretion, and induces apoptosis of human luteinized granulosa cells

Dioxin (2,3,7,8-tetrachlorodibenzo-p-dioxin; TCDD) is the most toxic congener of a large class of environmental pollutants. Several studies have shown that TCDD exposure reduced fecundity and ovulatory rate in rats and increased the incidence of endometriosis in monkeys. Recent work suggests that TCDD's endocrine-disrupting effects are, at least in part, caused by a direct action at the ovary. Although the factors involved in TCDD-induced toxicity are still under investigation, several studies have shown that TCDD induces programmed cell death, or apoptosis, in various tissues and may act in a similar fashion in the ovary. In the present study, we set out to evaluate the in vitro effects of TCDD on steroid secretion, specifically estradiol-17beta (E2) and progesterone, by human luteinized granulosa cells (LGC), and to further determine whether TCDD is capable of inducing apoptosis in this cell type. Human LGC were obtained from women participating in an in vitro fertilization program. Medium, with or without three different concentrations of TCDD and substrates [androstenedione (A4) or pregnenolone], was added to each culture. The media were collected at 4, 8, 12, 24, 36, and 48 h and were assayed by RIA. At 24 and 48 h, the LGC were fixed for assessment of DNA fragmentation via an in situ immunofluorescence technique. Transmission electron microscopy was also performed on LGC after 24 and 48 h with TCDD. TCDD, at all concentrations tested (3.1 pM, 3.1 nM, and 3.1 microM), significantly reduced E2 accumulation in the media at 8, 12, and 24 h, compared with controls. At 36 and 48 h, TCDD treatment (at 3.1 microM) caused a significant increase in E2, compared with controls. The effect of TCDD on E2 was abolished with the addition of A4. TCDD treatment did not alter progesterone accumulation. Apoptosis increased at 24 h with 3.1 microM TCDD, with no apparent effect at 3.1 nM. By 48 h, however, TCDD increased apoptosis in a dose-dependent manner. Transmission electron microscopy showed ultrastructural differences in LGC with 3.1 microM TCDD at 24 and 48 h. Collectively, the results of the present study suggest that TCDD perturbs E2 secretion by depletion of A4 precursor and increases apoptotic cell death of human LGC in a dose- and time-dependent fashion.

Reduced fertility in female mice lacking copper-zinc superoxide dismutase

Copper-zinc superoxide dismutase (CuZn-SOD) is believed to play a major role in the first line of antioxidant defense by catalyzing the dismutation of superoxide anion radicals to form hydrogen peroxide and molecular oxygen. Recent studies have shown that missense mutations in this gene contribute, evidently through a gain-of-function mechanism, to about 20% of familial amyotrophic lateral sclerosis. To define further the physiologic role of this enzyme, a model of mice deficient in this enzyme was generated using gene targeting technology. Mice lacking this enzyme were apparently healthy and displayed no increased sensitivity to hyperoxia. However, they exhibited a pronounced susceptibility to paraquat toxicity. Most surprisingly, female homozygous knock-out mice showed a markedly reduced fertility compared with that of wild-type and heterozygous knock-out mice. Further studies revealed that although these mice ovulated and conceived normally, they exhibited a marked increase in embryonic lethality. These data, for the first time, suggest a role of oxygen free radicals in causing abnormality of female reproduction in mammals.

Modulation of ovarian follicle maturation and effects on apoptotic cell death in Holtzman rats exposed to 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) in utero and lactationally

Recent reports have described the reproduction-modulating and endocrine-disrupting effects following exposure to toxic substances such as 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD). Herein, we set out (1) to determine whether TCDD exposure exerts detrimental effects on follicle maturation in the Holtzman rat ovary and (2) to determine whether the effects of TCDD are mediated in part via apoptotic cell death. In certain species, dioxin exposure is correlated with reduced fecundity, reduced ovulatory rate, an increased incidence of endometriosis, and various reproductive cancers. Although some of the effects of TCDD are mediated via the hypothalamic-pituitary axis, direct effects on the ovary have also been observed. In the present study, an oral dose of 1 microgram TCDD/kg maternal body weight was administered on Day 15 of gestation. Female pups were sacrificed on Postnatal Day 21/22, and the ovaries were excised, fixed for histologic analysis, and analyzed in a double-blind paradigm. The analysis included a count and measurement and classification of preantral and antral follicles throughout the entire ovary. The contralateral ovary from each animal was analyzed for DNA fragmentation indicative of apoptotic cell death. The results indicate that TCDD treatment significantly reduced the number of antral follicles in the size classes 50,000 to 74,999 microns2 and > 100,000 microns2. We also observed a reduction in the number of preantral follicles less than 50,000 microns2. No difference was observed in the degree of apoptotic cell death in antral (50,000 to > 100,000 microns2) and preantral follicles (50,000 microns2 to > 75,000 microns2) between TCDD-treated and control-treated tissues. These data support the hypothesis that TCDD results in a diminution in the number of antral and preantral follicles of certain size classes in animals exposed during critical periods of development, but that apoptosis does not appear to be the underlying mechanism in these particular follicles. This does not preclude apoptosis occurring in pools of smaller precursor follicles.

Alterations to the pituitary-gonadal axis in the peripubertal female rat exposed in utero and through lactation to 2,3,7,8-tetrachlorodibenzo-p-dioxin

The environmental pollutant 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD; dioxin) is a potent disrupter of vertebrate endocrine systems. It was shown previously that in utero and lactational (IUL) exposure to TCDD resulted in a reduction in serum estradiol concentrations; however, the mechanism for this remains unknown. In the current study, the effects of perinatal exposure to TCDD on the pituitary-ovarian axis were examined. Pregnant rats were given a single oral dose of 1 microg TCDD/kg or vehicle as control on gestation Day 15, and female pups were killed on postnatal Day 21. Pituitaries were assayed for gonadotropin beta-subunit mRNA; additional pituitaries were cultured for 4 h and the media were assayed for FSH. Gonadotropin receptor mRNAs from vehicle- and TCDD-exposed animals were compared, with some ovaries cultured and the media assayed for estrogen secretion. LH, FSH, progesterone, and androstenedione concentrations were determined in serum. IUL exposure to TCDD resulted in a significant reduction of pituitary FSHbeta mRNA. Although estrogen output was shown to be reduced, neither serum FSH nor LH concentration was increased significantly, and FSH secretion in vitro was not altered. Similarly, serum progesterone and androstenedione were not altered by TCDD exposure, while in vitro estrogen secretion was significantly reduced. These data suggest that TCDD did not act on serum gonadotropin concentrations. The reduction in the concentration of serum estrogen appears to result from direct or indirect actions on the ovary at some point following androstenedione production.

Estrogen receptor and aromatic hydrocarbon receptor in the primate ovary

We have previously shown by immunocytochemistry and autoradiography the presence of estrogen receptors (ER) in rhesus monkey ovary. Intense chromogen staining showed specific binding for ER in nuclei of germinal epithelium and granulosa cells of antral follicles; and radiolabeled ligand bound specifically to functional corpora lutea (CL). Although it is accepted that the germinal epithelium of the primate ovary contains ER, some controversy still persists regarding the intraovarian localization of this molecule. In addition, no data exist that localize the aromatic hydrocarbon (dioxin) receptor (AHR), which is known to modulate ER, to the primate ovary. In the present study, we show the presence of ER using Western blot analysis, and ER capable of binding DNA within intraovarian compartments in two species of the genusMacaca (rhesus macaque,Macaca mulatta and stumptail macaque,Macaca arctoides); extend these findings to human ovarian granulosa cells (GC) using Western blot, reverse transcription-polymerase chain reaction (RT-PCR), and gel mobility-shift analysis; and localize the AHR to intraovarian compartments of the macaque ovary by Western blots and gel-shift assays. These experiments strongly suggest that estrogens can exert effects on follicle development directly at the ovary, and provide the first direct evidence that AHR-mediated toxicity may be manifested at the ovary to induce possible antifertility effects.

Modulation of growth axis gene expression by in utero and lactational exposure to 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) in the weaning Holtzman rat

While thein utero and lactational effects of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) on both male and female reproductive systems appear to be severe, little is known about its effects on the developing growth axis. The objective of this study was to describe changes in growth axis gene expression that accompany exposure to TCDD duringin utero and lactational development. Pregnant Holtzman rats were administered 1 μg TCDD/kg maternal body weight or vehicle control on gestational day 15 by gavage. Using ribonuclease protection assays, we compared mRNA levels measured in 21-d-old female pups exposed to TCDD with levels measured in control animals for the following genes: somatostatin, growth hormone-releasing hormone (GHRH), hypothalamic and pituitary galanin (GAL), growth hormone (GH), and insulin-like growth factor-I (IGF-I). Serum GH concentrations measured by radio-immunoassay were significantly increased, although GH mRNA levels were unchanged from controls by TCDD exposure. Hypothalamic GAL mRNA was decreased in TCDD-treated animals, whereas pituitary GAL mRNA in TCDD-treated animals was not altered. GHRH mRNA was increased in hypothalami from TCDD-exposed animals. IGF-I mRNA in the liver was decreased to 67% of controls. These data indicate that the growth axis is sensitive to the effects of TCDD delivered during critical periods of development. The alterations observed in growth axis gene expression with exposure to TCDD add to the body of data demonstrating a potent effect of this compound on the fetal and neonatal endocrine system.

In utero and lactational exposure of female Holtzman rats to 2,3,7,8-tetrachlorodibenzo-p-dioxin: modulation of the estrogen signal

The environmental pollutant 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD; dioxin) induces severe reproductive defects in male rats when exposure occurs in utero and during lactation. Yet there is currently a paucity of information regarding the effects of this exposure paradigm in females. In the current study, we examine the effects of TCDD during fetal and perinatal development on the estrogen-signaling system in peripubertal female rats. Pregnant Holtzman rats were given 1 microgram/kg TCDD or vehicle control by gavage on gestational Day 15. Body weights were reduced, though not significantly, on postnatal Day 21. While ovarian and uterine wet weights were not increased by TCDD exposure, the percentage of body weight attributed to the ovary was increased significantly. Through use of ribonuclease protection and gel-shift assays, exposed females were compared with nonexposed counterparts for estrogen receptor (ER) mRNA and DNA-binding activity in the following tissues: hypothalamus, pituitary (mRNA only), uterus, and ovary. ER mRNA levels increased in the hypothalamus, uterus, and ovary, and decreased in the pituitary. The results of the DNA-binding assays paralleled the mRNA results in the uterus, while DNA-binding activity was decreased in the hypothalamus and was unchanged in ovarian protein extracts. Circulating concentrations of estrogen were significantly lower in TCDD-exposed rats than in controls. These data suggest that the decrease in serum estrogen may be a cause of the alterations in ER mRNA; the changes in ER DNA-binding activity may indicate alterations in either translation or posttranslational receptor processing. Overall, this study shows that TCDD may act systemically in this model, and these effects should not necessarily be characterized as antiestrogenic.

Effects of follicle-stimulating hormone administration on oestradiol-induced cystic ovaries in guinea pigs

A consistent defect in follicle-stimulating hormone (FSH) secretion is seen in humans with Polycystic Ovarian Syndrome (PCOS); therefore, we evaluated whether Metrodin (a highly purified urinary FSH) administration concurrent with cyst induction or following cyst induction inhibits estrogen-induced cyst development and augments ovarian follicular growth in an established guinea pig model. All animals in these studies received subcutaneous implants containing oestradiol-17 beta (E2)-filled Silastic capsules for a 48-hour period. Guinea pigs in study #1 were administered four 0.25 mL injections of FSH or placebo at twelve-hour intervals simultaneously with the E2 treatment; guinea pigs assigned to study #2 were administered four 0.25 mL injections of FSH or placebo at twelve-hour intervals following the induction of the cystic condition by E2. Exogenous FSH appears to negate cyst formation when superimposed upon the cyst-inducing agent (E2). Further, treatment with FSH augmented the number of mid-sized follicles in both paradigms. This study is the first to establish evidence of an anti-cystic effect of FSH in an animal model.

Neurotrophin-3 augments steroid secretion by hamster ovarian follicles in vitro

Innervation of the ovary is known to be affected by neurotrophic factors; mRNA for some of these molecules and their low-affinity receptors have been identified in ovarian follicular tissue. We attempted to determine whether neurotrophin (NT-3) exerts a non-neuronal impact on the ovary, affecting follicular estradiol secretion via a possible humoral action. Ovaries were excised from mature Golden Syrian Hamsters (Mesocricetus auratus) and large preovulatory follicles were removed by microdissection. Follicles were incubated for 72 hr in control medium, or medium containing 10 ng, 100 ng, or 1000 ng/ml NT-3. After culture, medium samples were assayed for estradiol content. NT-3 exerted dichotomous effects, depending on concentration: NT-3 augmented mean estradiol output two-fold at 100 ng/ml, while 1000 ng/ml NT-3 decreased estradiol secretion back to control levels. By 48-72 hr in culture, all groups exhibited a significant decline in mean estradiol secretion due presumably to diminished viability, independent of neurotrophin action. These data suggest a humoral role for NT-3 in estradiol secretion of preovulatory follicles in culture.

Elevated follicular fluid angiotensin II and pregnancy outcome

OBJECTIVE

To assess whether a relationship exists between follicular fluid (FF) angiotensin II (AII) concentration and pregnancy outcome or earlier fecundity parameters and whether correlations exist among FF AII concentrations and P, E2, T, androstenedione (A), or various ratios of these.

DESIGN

Retrospective study in which hormone concentrations in FF samples were measured.

SETTING

In vitro fertilization clinic-Assisted Reproductive Technology Program, Rush Medical Center.

PATIENTS

Twenty-six female patients underwent ovarian stimulation for IVF.

INTERVENTION

Leuprolide acetate was combined with hMG and FSH for ovarian stimulation.

MAIN OUTCOME MEASURE

Follicular fluid aspirates were collected and oocytes were recovered 34 to 36 hours after hCG injection. The patients proceeded to undergo IVF and ET. Follicular fluid hormones were measured using standard RIA. Angiotensin II and steroid hormone concentrations in FF were compared for pregnant versus nonpregnant women using the Student's t-test and rank-sum test. Pearson multiple-correlation analysis was performed to calculate correlation coefficients among AII concentrations and steroid concentrations in FF aspirates.

RESULTS

Mean FF concentration of AII was significantly lower in samples from women showing clinical pregnancies (112.2 +/- 13.9 pg/mL [107.3 +/- 13.3 pmol/L]) compared with samples from women who did not achieve pregnancy (217.1 +/- 23.8 pg/mL [207.5 +/- 22.7 pmol/L]) (mean +/- SE). A negative correlation was observed between FF concentrations of AII and P. Correlations of AII with E2, T, A, or with ratios of these did not show significance.

CONCLUSION

These data suggest that high AII concentration at time of oocyte recovery may indicate poor pregnancy outcome in women undergoing ovarian stimulation for IVF. These data corroborate previous results in animal models showing that AII predisposes follicles to undergo atresia-like conditions.

Role and site of estrogen action in follicular atresia

Subsequent to an initial understanding that estrogen was only stimulatory to folliculogenesis, we have come full circle to the present recognition that many actions of estrogen are inhibitory to follicular function. The development of this interpretation has frequently been associated with the controversial issue o f the likely site o f estrogen action, especially in primates, where much of the evidence has been amassed. The accumulated findings in a variety of species seem to demonstrate clearly that at least part of the atretogenic effect of estrogen is exerted directly on the ovary, apparently by interaction with the nuclear estrogen receptor. Recent observations include identification of messenger RNAs for the estrogen receptor and for creatine kinase in the macaque ovary, and a current focus is to localize messages within specific compartments of the ovary.

Induction by estradiol-17 beta of polycystic ovaries in the guinea pig

In the present study we wished to develop a model for polycystic ovarian syndrome (PCOS) using the guinea pig, because this animal's cycle, compared to other rodent models, more closely emulates that of humans. Four silastic capsules, either empty or containing cholesterol or estradiol-17 beta, were placed subcutaneously for 48 h on Day 10 or 12 of the cycle. Vaginal smears were taken daily. Cardiac blood was drawn at various intervals. At necropsy, trunk blood was collected and ovaries were excised and analyzed histologically. Cycle length was extended over that in controls in animals treated with estradiol-17 beta (E2) on Day 12 of the cycle. Treatment with E2 resulted in an increase in serum estrogen 2 h after capsule insertion. No changes were evident in progesterone or androstenedione concentrations with treatment. Animals treated with E2 and killed late (54 days after capsule removal) showed cysts grossly (group A), while occult cysts were present in E2-treated animals killed early (17 days; group B); no cysts were observed in control groups. Ovarian weight and size were increased in group A over controls. There was an increase in the fraction of atretic:total follicles < 500 mm in size in group A compared to group B as well as compared to controls. Since these results are similar to those seen in human PCOS, we conclude that the guinea pig may serve as an exceptional and unique model for the study of PCOS and may be applicable to humans.

In-vitro effects of angiotensin II on steroid production by hamster ovarian follicles and on ultrastructure of the theca interna

Angiotensin II (AII) is present in the mammalian ovary and has been correlated with atresia in follicles. Since the theca interna may be one site at which atresia is initiated, we wished to determine whether AII exerts an effect on theca interna from explanted ovarian follicles of hamsters. Hamsters were sacrified on the morning of proestrus, and ovaries were removed. Preovulatory follicles were excised from the ovaries, and cultured with one of the following components: medium alone (control); medium plus AII (1 x 10(-6) M); the AII-receptor antagonist [Sar1, Ile8] AII (1 x 10(-4) M); or AII plus antagonist. After 72 h, the follicles were processed for transmission electron microscopy (to determine quantities of theca interna organelles involved in the steroid synthetic pathway) or for protein determination (to normalize steroid production rates). The incubation medium was drawn off and analyzed by radioimmunoassay for progesterone, androstenedione, or estradiol-17 beta. There was a significant positive correlation (r = 0.92, P less than 0.01) between follicular androstenedione secretion and area comprising theca interna smooth endoplasmic reticulum. In the theca interna, AII induced a two-fold and 1.6-fold increase in lipid droplet number and area comprising smooth endoplasmic reticulum, respectively (P less than 0.05). Excess antagonist negated the increase in cell organelles and also reduced androstenedione secretion compared with AII alone (P less than 0.05). Most importantly, AII significantly augmented the ratio of androstenedione:estradiol-17 beta secretion by 44% over that of control. The ultrastructural changes observed in this study and the increase in the androstenedione:estradiol-17 beta production ratio are consistent with atresia-like changes in ovarian follicles.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of equine chorionic gonadotropin on reproductive performance in anestrous mink

The incidence of anestrous mink during the normal breeding season has been reported to be as high as 5%. We sought to induce estrus in these mink by using various doses of equine chorionic gonadotropin (eCG) and human chorionic gonadotropin (hCG). Seventy-five female mink maintained under standard ranch conditions failed to demonstrate estrus during the annual breeding season in March. These anestrous mink were randomly assigned to treatment groups. Treatments were given on March 16 and again on March 18. On these 2 d, mink were treated with equal doses of saline, 25, 50, or 100 IU of eCG, or 50 IU of eCG on March 16 and 50 of IU of eCG + 100 IU of hCG on March 18. Females were paired with males beginning on March 22. None of the saline-treated mink mated. In contrast, reproductive performance of the anestrous mink was significantly improved by treatment with eCG. This included proportion of mink breeding (47 to 100%), proportion giving birth (33 to 80%), and average litter size (2.6 to 4.0 kits per whelping female). Reproductive efficiency improved with increasing doses of eCG and was not further improved by addition of hCG. These results demonstrate that eCG has a potential application for treating anestrous mink during the breeding season.