Mammary Gland Tumor Promotion in F1 Generation Offspring from Male and Female Rats Exposed to Soy Isoflavones for a Lifetime

The effect of dietary isoflavones in the form of NOVASOY (NS) was investigated on methylnitrosourea-initiated mammary gland cancer in F1 generation female Sprague Dawley rats from parents who had undergone lifetime exposure to variable levels of dietary NS. In comparison to NS-free dietary groups, lifetime exposure of F1 rats to 40 and 1000 mg/kg diets of NS reduced tumor latency, but did not significantly affect tumor incidence, tumor size, or tumor multiplicity. A significantly lower tumor multiplicity was, however, observed in rats fed the soy-based, NS-free diet compared to the casein-based, NS-free diet. An evaluation of a dose-response relationship pointed towards a biphasic effect, with a trend showing lower tumor incidence, lower tumor multiplicity, and lower tumor size in rats fed 1000 mg/kg diet NS compared to 40 mg/kg diet NS; however, the data failed to achieve statistical significance. Histologically, tumor type significantly differed according to the administered basal diet variety and NS dose. Our data and that of others provide conflicting evidence for chemopreventive effects of soy isoflavones on mammary gland tumor induction. We suggest standardization of interlaboratory experimental approaches for establishing low dose-response relationships for soy and its isoflavones to aid in risk assessment.

AReview of the Animal Models Used to Investigate the Health Benefits of Soy Isoflavones

This review considers the recent literature in which animal models were used to investigate the purported health benefits of soy isoflavones. The main conclusions are that our animal models demonstrate minimal effects in breast, prostate, and colon cancer prevention, and that, while some cancers may respond to isoflavones, it would appear that isoflavones do not prevent further development once cancer has become established. Regarding cardiovascular health, the lipid-lowering effects of isoflavones have been established, but their efficacy may be less than original research purported. However, it may be considered a bonus of habitual soy consumption that blood cholesterol levels would be reduced somewhat. With respect to osteoporosis and menopausal symptoms, animal models do not show any consistent benefit of isoflavones in preventing osteoporosis, and calcium fortification or the use of prescribed medications are likely much better approaches to combat bone loss. However, our animal models of osteoporosis and menopausal symptoms may not be entirely representative of the human situation. Perhaps the benefit of isoflavones in cognitive skills and in delaying Alzheimer's disease is an area where they can be of some advantage. However, this field is very recent and requires much more research in both humans and animal models before any definitive benefit can be propounded. On the other hand, isoflavones in moderation are probably not dangerous, as few studies have indicated adverse effects. However, large doses have been shown to increase apoptosis and cell degeneration, and in some cancer regimes, once the cancer has progressed beyond the hormone-dependent stage, high doses of isoflavones may be contraindicated. The prospect of mega-dosing from isoflavone supplements opens a new chapter in the risk assessment of isoflavone consumption.

Effects of Postnatal Exposure to a Mixture of Polychlorinated Biphenyls, p,p′-dichlorodiphenyltrichloroethane, and p-p′-dichlorodiphenyldichloroethene in Prepubertal and Adult Female Sprague-Dawley Rats

The postnatal period is a critical phase of development and a time during which humans are exposed to higher levels of persistent organic pollutants (POPs), than during subsequent periods of life. There is a paucity of information describing effects of postnatal exposure to environmentally relevant mixtures of POPs, such as polychlorinated biphenyls (PCBs), p,p′-dichlorodiphenyltrichloroethane (DDT), and p,p′-dichlorodiphenyldichloroethene (DDE). To provide data useful for the risk assessment of postnatal exposure to POPs, mixtures containing 19 PCBs, DDT, and DDE were prepared according to their concentrations previously measured in the milk of Canadian women, and dose-response effects were tested on the proliferation of MCF7-E3 cells in vitro, and in vivo experiments. Female neonates were exposed by gavage at postnatal days (PNDs) 1, 5, 10, 15, and 20 with dosages equivalent to 10, 100, and 1000 times the estimated human exposure level over the first 24 days of life. The MCF7-E3 cells showed a 227% increase in the AlamarBlue proliferation index, suggesting estrogen-like properties of the mixture, but this was not confirmed in vivo, given the absence of uterotrophic effects at PND21. An increase (511%) in hepatic ethoxyresorufin- o-deethylase activity at the dose 100 × was the most sensitive endpoint among those measured at PND21 (organ weight, mammary gland and ovarian morphometry, hepatic enzyme inductions, serum thyroxine and pituitary hormones). In liver samples from older female rats (previously involved in a mammary tumor study [Desaulniers et al., Toxicol. Sci. 75:468–480, 2001]), hepatic metabolism of 14C-estradiol-17 β (E2) at PND55 to PND62 was significantly higher in the 1000 × compared to the control group, but hepatic detoxification enzyme activities had already returned to control values. The production of hepatic 2-hydroxy-E2 decreased, whereas that of estrone increased with age. In conclusion, the smallest dose of the mixture to induce significant effects was 100×, and mixture-induced changes in the hepatic metabolism of estrogens might be a sensitive indicator of persistent effects.

A 28-day Gavage Toxicity Study in Fischer 344 Rats with 3-methylfuran

3-Methylfuran is produced in foods during food processing and preservation techniques that involve heat treatment such as cooking, jarring, canning, and pasteurization. Currently, there are no studies available on the toxicity of 3-methylfuran. We conducted a 28-day gavage toxicity study (7 days per week) using doses of 0.0, 0.1, 0.3, 1.5, 3.0, 6.0, 12.0, and 25.0 mg/kg bw/day in order to determine the dose range needed to establish a no observed adverse effect level and to better characterize nonneoplastic effects including those affecting hematology, clinical biochemistry, gross morphology, and histopathology. Histological changes of the liver were noted in all treated animals and gross changes were noted beginning at 3.0 mg/kg bw/kg. Alterations in the activity of serum enzymes indicative of effects on the liver were observed, including increases in levels of alanine transaminase and alkaline phosphatase at the highest dose. There was a significant increase in serum thyroxine (T4) and triiodothyronine (T3), which was not accompanied by histological changes in the thyroid. For the most part, statistically significant changes were seen only at the highest dose for hematology and at the 2 highest doses for clinical chemistry parameters. In contrast, mild histological lesions in the liver were observed even at the lowest dose of 0.1 mg/kg bw/day.

Hexabromocyclododecane concentrations in Canadian human fetal liver and placental tissues

Detectable concentrations of the flame retardant hexabromocyclododecane (HBCD) have been reported in human tissues worldwide, but investigations to determine fetal exposure to this brominated flame retardant are lacking. This study was undertaken to determine the concentrations of α-, β- and γ-HBCD in human tissues (fetal liver and placenta) from Canada. Tissue samples were collected over a thirteen year period following elective pregnancy terminations in Montreal, Quebec, Canada. Samples were extracted using homogenisation with solvent, cleaned up using adsorption chromatography and analysis was performed with liquid chromatography-tandem mass spectrometry. Total HBCD concentrations ranged from below the limit of detection (<LOD; <1 ng g(-1)) to 4500 ng g(-1) lipid in fetal livers and <LOD (<1 ng g(-1)) to 5600 ng g(-1) lipid in placental tissue. No clear temporal trend was established in liver samples, nor was a significant relationship observed between fetal age and ΣHBCD concentrations. Temporal differences, however, were noted in placental tissues before and after 2005. HBCD concentrations in liver:placental paired tissue samples did not show a correlation. HBCD was found in placental tissues from Canadian women and results indicate that HBCD was present, at measurable concentrations, in developing fetuses from as early as 6.5 weeks.

Biomonitoring of human fetal exposure to environmental chemicals in early pregnancy

The first trimester of human fetal life, a period of extremely rapid development of physiological systems, represents the most rapid growth phase in human life. Interference in the establishment of organ systems may result in abnormal development that may be manifest immediately or programmed for later abnormal function. Exposure to environmental chemicals may be affecting development at these early stages, and yet there is limited knowledge of the quantities and identities of the chemicals to which the fetus is exposed during early pregnancy. Clearly, opportunities for assessing fetal chemical exposure directly are extremely limited. Hence, this review describes indirect means of assessing fetal exposure in early pregnancy to chemicals that are considered disrupters of development. Consideration is given to such matrices as maternal hair, fingernails, urine, saliva, sweat, breast milk, amniotic fluid and blood, and fetal matrices such as cord blood, cord tissue, meconium, placenta, and fetal liver. More than 150 articles that presented data from chemical analysis of human maternal and fetal tissues and fluids were reviewed. Priority was given to articles where chemical analysis was conducted in more than one matrix. Where correlations between maternal and fetal matrices were determined, these articles were included and are highlighted, as these may provide the basis for future investigations of early fetal exposure. The determination of fetal chemical exposure, at the time of rapid human growth and development, will greatly assist regulatory agencies in risk assessments and establishment of advisories for risk management concerning environmental chemicals.

Effects of oral exposure to arsenobetaine during pregnancy and lactation in Sprague-Dawley rats

Arsenobetaine (ASB) is the major form of arsenic (As) in seafood sources such as molluscs and fish. Limited data demonstrated that ASB toxicity in mammals is minimal; however, data on possible reproductive effects are lacking. This study investigated the tissue distribution and developmental effects of ASB during pregnancy, early postnatal life, and development to adulthood. Pregnant rats were randomly assigned to 3 cohorts and gavaged daily from gestational day 8 (GD8) with ASB in deionized water at 0, 0.1, 1, or 10 mg/kg body weight (bw)/d. Cohort 1 dams were sacrificed on GD20 (n = 6 per dose group), cohort 2 dams and pups were sacrificed on postnatal day 13 (PND13; n = 4 dams per dose group), and cohort 3 pups (n = 2 dams per dose group) were sacrificed on PND90. Residue analysis detected significant levels of ASB in livers of cohort 1 dams and lower levels in cohort 1 GD20 fetuses, as well as in cohort 2 male and female offspring, indicating placental transfer from the maternal circulation in utero. Trace amounts of ASB in dams' milk were found only in the 10-mg/kg bw/d dose cohort 2 (PND13), demonstrating that lactational transfer was limited. ASB levels in liver varied during pregnancy, lactation, and postweaning, with levels falling rapidly as these physiological states progress. Although transfer of ASB through the placenta to the fetuses and to a limited extent through milk was confirmed, ASB exposure during pregnancy and lactation appeared to produce no teratogenic or deleterious effects on reproductive development.

Bisphenol A in human placental and fetal liver tissues collected from Greater Montreal area (Quebec) during 1998-2008

In this study, the presence of bisphenol A (BPA) in human placental and fetal liver samples collected from 1998 to 2008 was investigated to provide a more detailed analysis of the transfer of BPA across the placenta and fetal exposure to BPA. The average concentrations in placental samples were 12.6 ng g(-1) for free BPA, 17.2 ng g(-1) for BPA-glu, and 30.2 ng g(-1) for total BPA. The highest concentrations in placental samples were 165 ng g(-1) for free BPA, 178 ng g(-1) for BPA-glu, and 280 ng g(-1) for total BPA. Samples with higher levels of BPA-glu had higher levels of free BPA in general. Fetal age was observed to have a significant effect on BPA-glu levels in placental samples, but not on free or total BPA. The percentages of free BPA relative to total BPA for the placental samples varied considerably from 4.2% to 100%, suggesting that the ability of maternal liver and/or the placenta to conjugate BPA is highly variable during early to mid-gestation. The average concentrations in fetal liver samples were 9.02 ng g(-1) for free BPA, 19.1 ng g(-1) for BPA-glu, and 25.8 ng g(-1) for total BPA. The highest concentrations in fetal liver samples were 37.7 ng g(-1) for free BPA, 93.9 ng g(-1) for BPA-glu, and 123 ng g(-1) for total BPA. The percentages of free BPA level relative to total BPA for all fetal liver samples varied from 12.4% to 99.1%, indicating extensive variability in the ability of the human feto-placental unit to glucuronidate BPA.

Natural selection in the water: freshwater invasion and adaptation by water colour in the Amazonian pufferfish

Natural selection and ecological adaptation are ultimately responsible for much of the origin of biodiversity. Yet, the identification of divergent natural selection has been hindered by the spatial complexity of natural systems, the difficulty in identifying genes under selection and their relationship to environment, and the confounding genomic effects of time. Here, we employed genome scans, population genetics and sequence-based phylogeographic methods to identify divergent natural selection on population boundaries in a freshwater invader, the Amazonian pufferfish, Colomesus asellus. We sampled extensively across markedly different hydrochemical settings in the Amazon Basin and use 'water colour' to test for ecological isolation. We distinguish the relative contribution of natural selection across hydrochemical gradients from biogeographic history in the origin and maintenance of population boundaries within a single species and across a complex ecosystem. We show that spatially distinct population structure generated by multiple forces (i.e. water colour and vicariant biogeographic history) can be identified if the confounding effects of genetic drift have not accumulated between selective populations. Our findings have repercussions for studies aimed at identifying engines of biodiversity and assessing their temporal progression in understudied and ecologically complex tropical ecosystems.

Distribution of isoflavones in samples of serum, liver and mammary glands of rats or pigs fed dietary isoflavones

BACKGROUND/AIMS

There has been great interest in the potential beneficial and adverse health effects of dietary isoflavones. Determination of tissue concentrations of isoflavone metabolites provides an insight into the potential bioactivity of dietary isoflavones. However, data on the distribution of isoflavones in animal models fed dietary isoflavones are limited. In this study, additional data on the distribution of isoflavones in serum and/or tissues of rats and pigs fed dietary isoflavones were generated.

METHODS

Rats (male and female) were fed a casein control diet (containing no isoflavones) and an isoflavone-supplemented diet (containing an alcohol-washed soy protein isolate plus NOVASOY, providing a total of 1,047 mg/kg of total isoflavones). Female pigs were fed a control diet (without soy) containing 17.5 mg/kg of isoflavones, a soy diet containing 582.8 mg/kg of isoflavones or a soy diet supplemented with a daily dose of 2.3 g (equivalent to 42.0 and 14.5 mg/kg of body weight at the onset and end of treatment, respectively) of crystalline genistein. The concentrations of isoflavones in serum and tissues (liver and mammary gland) and in tissues (liver and mammary gland) of pigs were determined via a sensitive and rapid method using liquid chromatography/mass spectrometry.

RESULTS

Rats fed the control diet containing no isoflavones had nondetectable levels of isoflavone metabolites in serum, liver and mammary gland samples. Rats fed the isoflavone-supplemented diet had the greatest levels of equol, followed by genistein, daidzein and glycitein, respectively, in their serum, livers and mammary glands. The concentrations of total isoflavones (daidzein, equol and genistein plus glycitein) in serum were significantly (p < 0.05) greater in male rats vs. female rats, but the reverse was true in the case of livers. Concentrations of daidzein, equol, genistein and glycitein were lowest (p < 0.05) in the livers of pigs fed the control diet, and in the mammary glands of female pigs there was only an effect of feeding soy plus genistein on the concentrations of daidzein and equol (p <0.05).

CONCLUSIONS

The current data therefore show gender as well as species differences in the tissue distribution of isoflavones.

Evolution of steroid-5alpha-reductases and comparison of their function with 5beta-reductase

Steroid-5alpha-reductases (SRD5alpha) and steroid-5beta-reductase (SRD5beta) represent a convergence in evolution: they share similar biological functions, but do not have a common ancestor. In vertebrates, SRD5alpha and SRD5beta are involved in C-19 and C-21 steroid biosynthesis, bile acid biosynthesis and erythropoiesis. We compare and contrast the history, evolution, tissue distribution, enzyme characteristics and biological functions of SRD5alpha and SRD5beta and suggest possible future directions for research efforts. Both, the unique and overlapping roles that SRD5alpha and SRD5beta play in steroid hormone metabolism, are indicated. We also present the phylogeny of the SRD5alpha. The main SRD5alpha subfamilies obtained include, not only the well-known SRD5alpha type 1, type 2 and type 3, but also the synaptic glycoprotein (GPSN2)/trans-2,3-enoly-CoA reductase group. Phylogenetic analysis indicated that a eukaryotic ancestor likely underwent duplication events to generate these three subfamilies (type 1/2, type 3 and GPSN2 ancestors); both SRD5alpha type 1/2 and GPSN2 subfamilies may have evolved by ancient duplication events at the early stage of vertebrate and chordate evolution.

Fadrozole and finasteride exposures modulate sex steroid- and thyroid hormone-related gene expression in Silurana (Xenopus) tropicalis early larval development

Steroidogenic enzymes and their steroid products play critical roles during gonadal differentiation in amphibians; however their roles during embryogenesis remain unclear. The objective of this study was to investigate the expression and activity of aromatase (cyp19; estrogen synthase) and 5 beta-reductase (srd5 beta; 5 beta-dihydrotestosterone synthase) during amphibian embryogenesis. Expression and activity profiles of cyp19 and srd5 beta were first established during Silurana (Xenopus) tropicalis embryogenesis from Nieuwkoop-Faber (NF) stage 2 (2-cell stage; 1h post-fertilization) to NF stage 46 (beginning of feeding; 72 h post-fertilization). Exposures to fadrozole (an aromatase inhibitor; 0.5, 1.0 and 2.0 microM) and finasteride (a putative 5-reductase inhibitor; 25, 50 and 100 microM) were designed to assess the consequences of inhibiting these enzymes on gene expression in early amphibian larval development. Exposed embryos showed changes in both enzyme activities and sex steroid- and thyroid hormone-related gene expression. Fadrozole treatment inhibited cyp19 activity and increased androgen receptor and thyroid hormone receptor (alpha and beta) mRNAs. Finasteride treatment inhibited srd5 beta (activity and mRNA), decreased cyp19 mRNA and activity levels and increased estrogen receptor alpha mRNA. Both treatments altered the expression of deiodinases (thyroid hormone metabolizing enzymes). We conclude that cyp19 and srd5 beta are active in early embryogenesis and larval development in Silurana tropicalis and their inhibition affected transcription of genes associated with the thyroid and reproductive axes.

Low levels of the herbicide atrazine alter sex ratios and reduce metamorphic success in Rana pipiens tadpoles raised in outdoor mesocosms

BACKGROUND

There are conflicting reports regarding the effects of atrazine (ATZ) on amphibian development. Therefore, further studies are needed to examine the potential mechanisms of action of ATZ in amphibians.

OBJECTIVES

Our aim in this study was to determine whether low concentrations of ATZ affect gonadal development and metamorphosis in the Northern leopard frog, Rana pipiens.

METHODS

Tadpoles were exposed in outdoor mesocosms to nominal concentrations of 0.1 and 1.8 microg/L of formulated ATZ from Gosner stage 27 (G27) to metamorphic climax (G42). Exposure to 17alpha-ethinylestradiol (EE2; 1.5 microg/L) provided a positive control for induction of testicular oocytes in males. Endocrine-related gene expression and gonadal histopathology were examined at G42 and in a subset of premetamorphic G34 tadpoles that failed to metamorphose.

RESULTS

Gonadal gross morphology revealed that the 1.8-microg/L ATZ treatment produced 20% more females compared with the control. Histologic analysis revealed that 22% of EE2-treated males had testicular oocytes, whereas none were observed in any animals from the control or either ATZ groups. ATZ increased brain estrogen receptor alpha mRNA to 2.5 times that of the control at premetamorphosis and altered liver levels of 5beta-reductase activity at metamorphosis. In contrast, brain aromatase mRNA level and activity did not change. ATZ treatments significantly reduced metamorphic success (number of animals reaching metamorphosis) without affecting body weight, snout-vent length, or age at metamorphosis. Gene expression analysis indicated that ATZ decreased the expression of deiodinase type 3 in the tail at premetamorphosis.

CONCLUSIONS

Our study indicates that exposure to low concentrations of ATZ in experimental mesocosms alters gonadal differentiation and metamorphosis in developing R. pipiens.

The aromatase inhibitor fadrozole and the 5-reductase inhibitor finasteride affect gonadal differentiation and gene expression in the frog Silurana tropicalis

Aromatase (cyp19) and the 5alpha- and 5beta-reductases (srd5alpha and srd5beta) are important enzymes for vertebrate sexual development. We investigated the effects of inhibition of cyp19 by fadrozole (FAD), and srd5alpha and srd5beta by finasteride (FIN) during anuran larval development. Chronic exposures of Silurana (Xenopus) tropicalis from Nieuwkoop-Faber stage 12 until stage 60 were performed using either 2 microM FAD or 25 microM FIN. Histological analysis of exposed metamorphic frogs revealed that both treatments induced intersex individuals (presence of testicular oocytes). FAD treatment resulted in 55% male, 30% female and 15% intersex, while FIN treatment produced 27% male, 53% female and 20% intersex. Real-time RT-PCR analysis of hepatic sex steroid- and thyroid hormone-related gene expression demonstrated that FAD-induced intersex animals had higher srd5alpha1, srd5alpha2 and eralpha mRNA levels than control and FAD males. In contrast, FIN-induced intersex had low srd5alpha1, srd5alpha2, srd5beta and dio3 and high dio2 mRNA levels. FIN-treated males exhibited high trbeta, dio2 and a lower dio3 mRNA levels. We conclude that chemically induced intersex animals display different gene expression profiles than non-exposed animals and that, although morphologically similar, intersex animals produced by different chemicals have different endocrine pathophysiologies.

Oral p-tert-octylphenol exposures induce minimal toxic or estrogenic effects in adult female Sprague-Dawley rats

Contamination of the environment with endocrine-disrupting chemicals (EDC) has raised concerns about potential health hazards for humans and wildlife. Human and wildlife exposure to one such ubiquitous chemical, p-tert-octylphenol (OP), are likely, due to its persistence in the environment and its presence in food, water, and items of daily use. OP is reported to bind to the estrogen receptor (ER) and alter expression of estrogen-responsive genes. Detrimental effects of OP exposures on the reproductive system have been observed in most, but not all, in vivo experiments. This study examined estrogenic effects of oral exposures of adult female rats to OP. In vitro, OP bound weakly to human ER and a co-activator protein, and accelerated proliferation of MCF-7 cells. Adult Sprague-Dawley rats were given OP by gavage daily for 35 d (25, 50, or 125 mg/kg/d). Body and organ weights and ovarian follicle populations were not significantly altered in OP-exposed adult rats, despite detectable levels of OP in reproductive organs. The estrous cycle of rats was slightly altered, but there were no significant estrogen-like changes in histomorphology or gene expression of the uterus. Prepubertal rats given 125 or 250 mg/kg OP by gavage for 3 d had reduced body weight compared to vehicle-exposed rats but failed to show any uterotrophic response, although 17alpha-ethinyl estradiol (EE, 10 microg/kg/d, ip) induced a threefold increase in uterine weight. Overall, results suggest that toxicity will occur before estrogenic effects with oral exposures to OP. Relevant environmental exposures likely pose little risk for estrogenic effects.

Effect of glycosidation of isoflavones on their bioavailability and pharmacokinetics in aged male rats

There are limited reports on the bioavailability and pharmacokinetics of isoflavones in elderly humans and aged animals. The present study was conducted to assess the effect of glycosidation of isoflavones on their bioavailability and pharmacokinetics in aged (20 month old) male Fischer-344 (F-344) rats. The F-344 rat, developed by the National Institute on Aging, is an inbred rat model that is commonly used for aging studies and resembles many features of aging humans. Three sources of isoflavones; Novasoy (a commercial supplement), a mixture of synthetic aglycons (daidzein, genistein and glycitein), and a mixture of synthetic glucosides (daidzin, genistin, and glycitin) were tested. Following administration, blood samples were collected at different times (0-48 h post-oral gavage and 0-8 h post-IV dosing). Plasma isoflavones and 7-hydroxy-3-(4'-hydroxyphenyl)-chroman (a metabolite of daidzein) were measured by LC/MS. The extent of absorption was determined by comparing the area under the curve (AUC) of the plasma-concentration time curve after intravenous (IV) administration with that following oral administration. The extent of bioavailability was then calculated as: %bioabailability = (AUC(or)/AUC(IV))x(Dose(IV)/Dose(or))x100. Bioavailabilities for genistein were significantly (p = 0.013) higher for the aglycon (35 +/- 9%) compared with the glucoside forms (11 +/- 3%). In contrast, the bioavailabilities for glycitein were significantly (p = 0.011) higher in Novasoy (27 +/- 13%) and the glucoside form (21 +/- 10%) compared with the aglycon (8 +/- 3%). No significant differences in the bioavailability of daidzein were observed in aged rats dosed with aglycon, glucoside or Novasoy. However, aged rats were able to produce equol as early as 8 h post-dosing. In summary, the source of isoflavones had significant effects on genistein and glycitein bioavailability in aged male rats.

Persistent organic pollutant residues in human fetal liver and placenta from Greater Montreal, Quebec: a longitudinal study from 1998 through 2006

BACKGROUND

There is general concern that persistent organic pollutants (POPs) found in the environment, wildlife, food, water, house dust, human tissues, and fluids may alter normal human physiologic activities (e.g., fetal development, immune and endocrine systems). Although the levels of some POPs [polychlorinated biphenyls (PCBs) and organochlorine pesticides (OCs)] in these matrices have decreased after their ban, others [polybrominated diphenyl ethers (PBDEs)] have increased in recent years.

OBJECTIVE

To determine the longitudinal trend of specific POPs in human fetal tissues for risk assessment purposes.

METHODS

We analyzed early to mid-gestation fetal liver (n = 52) and placental (n = 60) tissues, obtained after elective abortions during 1998-2006, for selected PBDEs, PCBs, and OCs using gas chromatography-mass spectroscopy.

RESULTS

Total PBDEs in fetal liver increased over time (mean +/- SE: 1998, 284.4 +/- 229.8 ng/g lipid; 2006, 1,607.7 +/- 605.9; p < 0.03), whereas placental levels were generally lower, with no clear trend. Low levels of PCBs and OCs varied yearly, with no evident trend. The major analytes in 1998 were OCs (liver, 49%; placenta, 71%), whereas the major analytes in 2006 were PBDEs (liver, 89%; placenta, 98%). The 1998-2006 tissue PBDE congener profile is similar to that of DE-71, a commercial primarily pentabrominated diphenyl ether mixture manufactured in North America.

CONCLUSIONS

Although commercial production of penta- and octa-brominated diphenyl ethers in North America was halted in 2004, their concentrations in fetal liver and placenta are now greater than the tissue burdens for the analyzed OCs and PCBs. Our findings also demonstrate that PBDEs accumulate within the fetal compartment at a very early stage in gestation.

Soy isoflavones modulate azoxymethane-induced rat colon carcinogenesis exposed pre- and postnatally and inhibit growth of DLD-1 human colon adenocarcinoma cells by increasing the expression of estrogen receptor-beta

We studied the effects of lifetime exposure to dietary soy isoflavones in an azoxymethane (AOM)-induced rat colon cancer model. Male pups born to Sprague-Dawley rats exposed (including during pregnancy and lactation) to soy isoflavones at either no (0 mg = control), low (40 mg), or high (1000 mg) doses/kg diet were weaned and continued receiving their respective parental diets until the end of the study. Weaned rats received 2 subcutaneous injections (15 mg/kg body weight) of AOM 1 wk apart. After 26 wk, rats were killed and the coordinates of colon aberrant crypt foci (ACF) and tumors were determined. Expression of estrogen receptor (ER)-beta was assessed in rat colon tumors and in DLD-1 human colon adenocarcinoma cells exposed to soy isoflavones. Compared with the control, soy isoflavones did not affect incidences or multiplicities of colon ACF or tumors. Low-dose soy isoflavones decreased tumor burden and size compared with the control (P < 0.05). Expression of ERbeta increased in colon tumors of soy isoflavone-treated groups compared with the control. Soy isoflavones dose-dependently arrested the growth of DLD-1 cells and at subcytotoxic levels increased the expression of ERbeta. Our results suggest that pre- and postnatal exposure to dietary soy isoflavones suppresses the growth of colon tumors in male rats. The overexpression of ERbeta in both rat colon tumors and DLD-1 cells caused by soy isoflavones suggests that ERbeta is a critical mediator in mitigating its cancer-preventive effects.

Effects of chronic exposure to octylphenol on the male rat reproductive system

p-tert-Octylphenol (OP) is a degradation product of alkylphenol ethoxylates. OP is an endocrine disruptor known to bind to the estrogen receptor; however, effects on males are controversial. The objective of this study was to evaluate the effects of chronic exposure to OP on male reproduction. Adult Sprague-Dawley rats were administered OP for 60 d, representing 1.5 cycles of spermatogenesis. Experimental groups included a vehicle control, and three doses of OP (25, 50, or 125 mg/kg body weight [bw]) administered daily by gavage. There was a significant decrease in body weight in the 125-mg/kg group after 60 d of treatment. Both testicular and epididymal weights and histology were not altered by treatment with OP at any of the doses administered. There were no marked differences in cauda epididymal sperm counts at any doses; however, total percent sperm motility was significantly lower in rats exposed to the intermediate dose (50 mg/kg bw). There was an increase in percent static sperm cells in all OP-treated groups, with the intermediate dose (50 mg/kg) displaying a significantly higher proportion of static cells relative to untreated controls. Caput epididymal sperm motility was unaltered by OP treatment. Gene expression profiles of testes from control and high-dose-exposed rats indicate that 14 genes were modulated by at least twofold, although these changes were not statistically significant. Taken together, results from this study indicate that OP treatment of adult rats does not appear to exert major effects on male reproductive endpoints at relevant environmental exposure doses.

Toxicokinetics of p-tert-octylphenol in male and female Sprague-Dawley rats after intravenous, oral, or subcutaneous exposures

This study was undertaken to characterize the toxicokinetics of p-tert-octylphenol (OP), a weak estrogenic compound, in male and female rats. Male and female Sprague-Dawley rats were given a single dose of OP either by oral gavage (50, 125 or 250 mg/kg), by intravenous (iv) injection (2, 4, or 8 mg/kg), or by subcutaneous (sc) injection (125 mg/kg). In a repeated dosing experiment, rats were given OP (oral) daily (25, 50, or 125 mg/kg) for 35 d (female) or 60 d (male). Blood and tissue samples were collected and analyzed for OP content using gas chromatography with detection by mass spectrometry. Blood OP concentrations were generally higher in female than male rats following a single oral or sc administration but were similar following a single iv injection. Tissue OP concentrations were also higher in female than male rats following oral exposure, consistent with the faster metabolism of OP observed in male rat liver microsomes. After subchronic administration, blood OP concentrations were higher at the end of exposure for female (33 d) (2.26-fold, not significant) and male (57 d) (3.47-fold) rats than single dosing but there was no change in the tissue OP concentrations. Gender differences in tissue OP concentrations may contribute, in part, to gender differences in the toxicity of OP in rats. The fact that OP was found in all reproductive tissues confirms its potential for direct endocrine-like effects.

Organotin speciation and tissue distribution in rat dams, fetuses, and neonates following oral administration of tributyltin chloride

Tributyltin (TBT) is a biocide that contaminates human foodstuffs, especially shellfish. TBT is an endocrine disrupter, producing imposex in several marine gastropods. Previous studies showed that oral dosing of rat dams with TBT chloride leads to abnormal fetal and postnatal development. In this study, the tissue distribution and speciation of organotins in tissues were examined in dams, fetuses, and neonates following dosing of rat dams commencing on gestational day (GD) 8 by oral gavage with TBT in olive oil at 0, 0.25, 2.5, or 10 mg/kg body weight (BW)/d. Dams' body weights were significantly reduced by the 10-mg/kg BW/d TBT treatment. At GD20, there were no significant effects of any TBT treatment on pup weights, litter size, sex ratio, or tissue weights. However, at postnatal day (PND) 6 and 12, neonatal pup weights were reduced by the 10-mg/kg BW/d TBT treatment but tissue weights were unaffected, except for the liver weight of female pups, which was reduced by the 10-mg/kg BW/d TBT treatment. Tissues harvested on GD20 and PND6 and PND12 were extracted for determination of organotins by gas chromatography-atomic emission detection (GC-AED). In most tissues, TBT and its metabolite dibutyltin (DBT) were evident but monobutyltin (MBT) was rarely measured above the detection limit. The livers and brains of fetuses contained TBT and DBT at levels that were approximately 50% of the equivalent tissues in the dams. Furthermore, these tissues appeared to preferentially absorb/retain organotins, since the concentrations were greater than were found for the total loading in whole pups. The placenta also contained relatively large quantities of TBT and DBT. Postnatally, the TBT levels in pups decreased markedly, a probable consequence of the extremely low levels of organotins in rat milk. However, DBT levels in pups livers and brains were maintained, probably due to metabolism of TBT to DBT. Similarly, while dams' spleens contained significant quantities of organotins, the pups' spleens contained smaller quantities, and these decreased rapidly between PND6 and PND12. These results show that organotins cross the placenta and accumulate in fetal tissues but that during lactation, the pups would receive minimal organotins through the milk and during this period, the levels of TBT in pups' tissues decreases rapidly. Consequently, fetuses would be at greater risk of the adverse effects of TBT, but due to the lack of transfer through milk, the risk would be reduced during the lactational period.

An investigation of the effects of methylmercury in rats fed different dietary fats and proteins: Testicular steroidogenic enzymes and serum testosterone levels

Methylmercury (MeHg) is a testicular toxicant causing reduced steroidogenic enzyme activity, reduced serum testosterone (T) and abnormal spermatogenesis in mammals and fowl. It is also known that certain diets can alter androgen metabolism in rats. Previously we have shown that diets used in the current study impact circulating androgen levels and testicular steroidogenic enzyme activities in Sprague Dawley rats in the absence of MeHg. In the present study, we have investigated the impact of imposing an environmental contaminant (MeHg) commonly found in marine mammals and fish onto the rats' dietary intake of different proteins and lipids in order to determine if the different diets could modify MeHg toxicity in rats. Therefore, we examined the effects of MeHg on testicular steroidogenic enzymes and serum testosterone in rats fed diets containing either different protein sources (casein, fishmeal, whey) or different lipid sources (soybean oil, docosahexaenoic acid (DHA), seal oil, fish oil, lard). Male rats 42-45 days of age (18 per group) were assigned to different experimental diets for 28 days after which 6 rats in each group were gavaged daily with 0, 1 or 3 mg/kg body weight (BW)/day MeHg chloride in 5 mM Na(2)CO(3) solution for 14 days while being maintained on their diets. On the 43rd day of dosing, rats were sacrificed and blood plasma and testes frozen (-80 degrees C) until analysis. Microsomal steroidogenic enzyme activities (3beta-HSD, 17-OHase, C-17, 20-lyase, 17beta-HSD) were measured radiometrically. Serum testosterone was determined using ELISA kits. Testis weights were not affected by MeHg. MeHg at 3 mg/kg BW/day caused a reduction (>50%) in the activity of C-17, 20-lyase in all three protein diets and similar reductions in 17-OHase activity were seen in the casein and whey protein fed rats. At 3 mg/kg BW/day, MeHg reduced 17-OHase activity in the DHA diet but had no effect on 3beta-HSD activity and no inhibitory effects on 17beta-HSD activity. MeHg (3 mg/kg BW/day) caused significant reductions in serum T in the whey, soybean oil and fish oil groups. Interestingly, fishmeal protein but not fish oil offered some protection with respect to maintaining steroidogenic enzyme activities and serum T levels in rats dosed with MeHg. In conclusion, these studies show that different lipid diets can alter the toxic effects of MeHg on male rat steroidogenesis in terms of serum testosterone and steroidogenic enzyme activities.

Consumption of soy protein isolate modulates the phosphorylation status of hepatic ATPase/ATP synthase beta protein and increases ATPase activity in rats

ATPase/ATP synthase plays important roles in the regulation of carbohydrate, protein, and lipid metabolism through modulating energy homeostasis. The purpose of this study was to examine the effects of feeding soy proteins and isoflavones (ISF) on the enzymatic activity and protein modification of hepatic mitochondrial ATPase/ATP synthase. In Expt. 1, Sprague-Dawley rats aged 50 d were fed diets containing either 20% casein or 20% alcohol-washed soy protein isolate (SPI) with or without supplemental ISF (770.7 micromol/kg diet) for 70 d. In Expt. 2, weanling Sprague-Dawley rats were fed diets containing 20% casein with or without added ISF (154.1 micromol/kg diet) or 20% SPI for 90 d. Hepatic mitochondrial ATPase activity was significantly higher in the rats fed SPI than in those fed casein. Addition of ISF to SPI eliminated the action of SPI. ATPase/ATP synthase beta protein contents in the liver were unchanged; however, its patterns measured by 2-dimensional Western blot were different among dietary groups. The rats fed SPI or SPI plus ISF had 3 more major protein spots with the same molecular weights (80 kDa and 55 kDa) as those presented in the rats fed casein but with different isoelectric points. Pretreatment of hepatic mitochondrial proteins from the rats fed casein with alkaline phosphatase produced the same ATPase/ATP synthase beta patterns as observed in the SPI-fed rats and significantly elevated the ATPase activity. These results suggest that consumption of soy proteins increases hepatic ATPase activity, which might be a consequence of increased dephosphorylation or decreased phosphorylation of the mitochondrial ATPase/ATP synthase beta protein.

Tissue-specific regulation of acetyl-CoA carboxylase gene expression by dietary soya protein isolate in rats

We have recently reported that intake of soya protein isolate (SPI) inhibited the DNA-binding activities of hepatic thyroid hormone receptor (TR). The genes for acetyl-CoA carboxylase (ACC), a rate-limiting enzyme in fatty acid synthesis, contain the thyroid hormone response element in their promoters and are regulated by TR. The present study has examined the effect oflong-term feeding of SPI and soya isoflavones (ISF) on the gene expression and protein phosphorylation of different ACC isoforms in different tissues and plasma triacylglycerol (TAG) levels in rats. Sprague-Dawley female rats were fed diets containing 20% casein or alcohol-washed SPI with or without supplemental ISF for 70, 190 and 310d. SPI intake significantly reduced plasma TAG concentrations compared with casein, whereas supplemental ISF had no effect. Hepatic ACCα and ACCβ mRNA abundance and protein content were markedly lowerin the rats fed SPI than in those fed casein. The protein contents of ACCα in the kidneyand ACCβ, the predominant isoform in the heart and kidney, were unchanged by dietary SPI.The ratios of phospho-ACCα/ACCα and phospho-ACCβ/ACCβ were not differentamong dietary groups in all tissues measured. The present study demonstrates that ingestion ofSPI decreases plasma TAG level and down-regulates ACCα and ACCβ gene expression in the liver but not in the heart and kidney. The results indicate that the effect of SPI is tissue-specific and that alteration of ACC gene expression rather than phosphorylation status may play a major role in the regulation of ACC activities by soya proteins.

Dietary soy protein isolate modifies hepatic retinoic acid receptor-beta proteins and inhibits their DNA binding activity in rats

Retinoic acid receptors (RAR) belong to the same nuclear receptor superfamily as thyroid hormone receptors (TR) that were previously shown to be modulated by dietary soy protein isolate (SPI). This study has examined the effect of dietary SPI and isoflavones (ISF) on hepatic RAR gene expression and DNA binding activity. In Expt. 1, Sprague-Dawley rats were fed diets containing 20% casein or 20% alcohol-washed SPI in the absence or presence of increasing amounts of ISF (5-1250 mg/kg diet) for 70, 190, or 310 d. In Expt. 2, weanling Sprague-Dawley rats were fed diets containing 20% casein with or without supplemental ISF (50 mg/kg diet) or increasing amounts of alcohol-washed SPI (5, 10, and 20%) for 90 d. Intake of soy proteins significantly elevated hepatic RARbeta2 protein content dose-dependently compared with a casein diet, whereas supplemental ISF had no consistent effect. Neither RARbeta protein in the other tissues measured nor the other RAR (RARalpha and RARgamma) in the liver were affected by dietary SPI, indicating a tissue and isoform-specific effect of SPI. RARbeta2 mRNA abundances were not different between dietary groups except that its expression was markedly suppressed in male rats fed SPI for 310 d. DNA binding activity of nuclear RARbeta was significantly attenuated and the isoelectric points of RARbeta2 were shifted by dietary SPI. Overall, these results show for the first time, to our knowledge, that dietary soy proteins affect hepatic RARbeta2 protein content and RARbeta DNA binding activity, which may contribute to the suppression of retinoid-induced hypertriglyceridemia by SPI as reported.

Region-specific expression of androgen and growth factor pathway genes in the rat epididymis and the effects of dual 5alpha-reductase inhibition

Dihydrotestosterone (DHT) is the primary androgen acting in the epididymis, the site of sperm maturation. Previously, we showed that the treatment of male rats with PNU157706, an inhibitor that acts on both isoforms of 5alpha-reductase to prevent DHT formation, has effects on the expression of genes implicated in processes that create the optimal luminal microenvironment required for sperm maturation, and on sperm maturation itself. However, signaling pathways involved in regulating or mediating DHT actions in the epididymis remain largely unknown. The goals of this study were to determine the expression profiles of potential signaling systems in the epididymis and assess their DHT-dependence using two different dual 5alpha-reductase inhibitors. Rats were untreated or gavaged with vehicle, 10 mg/kg per day PNU157706 or 32 mg/kg per day FK143 for 28 days and epididymal gene expression was analyzed. Gene array analysis revealed analogous effects of FK143 on overall epididymal gene expression when compared with previous PNU157706 studies. Quantitative RT-PCR analysis of the expression of the 5alpha-reductase isozymes, androgen receptor, and members of the IGF, FGF, TGF, and VEGF families revealed novel region-specific expression profiles in the epididymis that were differentially affected by 5alpha-reductase inhibition; the two inhibitors had parallel effects. Specifically, in proximal regions, 5alpha-reductase 1, androgen receptor, and TGF-beta1 expression increased after treatment, while in distal regions expression of IGF-I, IGFBP-5, IGFBP-6, and FGF-10 decreased. These results provide insight into epididymal signaling mechanisms and indicate potential candidates acting either upstream or downstream of DHT to regulate and/or mediate its actions in the epididymis.

A review of the animal models used to investigate the health benefits of soy isoflavones

This review considers the recent literature in which animal models were used to investigate the purported health benefits of soy isoflavones. The main conclusions are that our animal models demonstrate minimal effects in breast, prostate, and colon cancer prevention, and that, while some cancers may respond to isoflavones, it would appear that isoflavones do not prevent further development once cancer has become established. Regarding cardiovascular health, the lipid-lowering effects of isoflavones have been established, but their efficacy may be less than original research purported. However, it may be considered a bonus of habitual soy consumption that blood cholesterol levels would be reduced somewhat. With respect to osteoporosis and menopausal symptoms, animal models do not show any consistent benefit of isoflavones in preventing osteoporosis, and calcium fortification or the use of prescribed medications are likely much better approaches to combat bone loss. However, our animal models of osteoporosis and menopausal symptoms may not be entirely representative of the human situation. Perhaps the benefit of isoflavones in cognitive skills and in delaying Alzheimer's disease is an area where they can be of some advantage. However, this field is very recent and requires much more research in both humans and animal models before any definitive benefit can be propounded. On the other hand, isoflavones in moderation are probably not dangerous, as few studies have indicated adverse effects. However, large doses have been shown to increase apoptosis and cell degeneration, and in some cancer regimes, once the cancer has progressed beyond the hormone-dependent stage, high doses of isoflavones may be contraindicated. The prospect of mega-dosing from isoflavone supplements opens a new chapter in the risk assessment of isoflavone consumption.

Effects of ciprofibrate on testicular and adrenal steroidogenic enzymes in the rat

Testicular and adrenal steroidogenic enzymes were measured radiometrically following oral dosing of rats with ciprofibrate (2-[4-(2,2-dichlorocyclopropyl) phenoxyl]-2-methylpropinoic acid), a peroxisome proliferator. Six-week-old male Fisher 344 rats were fed a diet containing ciprofibrate (0.025%, w/w) for 3, 7, 14, 28, 56, 84, 112 or 140 days leading to a daily ciprofibrate intake of approximately 15 mg/kg body weight/day. Ciprofibrate caused a marked inhibition of testicular 3beta-hydroxysteroid dehydrogenase-isomerase (3beta-HSD) activity that was significant after 3 days and subsequently decreased to 40% of control level. Ciprofibrate treatment also reduced 17beta-hydroxysteroid dehydrogenase (17beta-HSD) activity to a lesser extent but had no effect on 17-hydroxylase (17-OHase) activity. Immunoblot analyses indicated that ciprofibrate treatment did not alter enzyme protein levels and semi-quantitative RT-PCR analysis also revealed no significant changes in testicular 3beta-HSD mRNA levels. Furthermore, in addition to the enzyme-specific effect of ciprofibrate on 3beta-HSD in the testes, a tissue-specific effect was also evident, since no significant effects of ciprofibrate were seen on the activities of 3beta-HSD or 21-OHase in the adrenal glands from the same animals.

Mammary gland tumor promotion in F1 generation offspring from male and female rats exposed to soy isoflavones for a lifetime

The effect of dietary isoflavones in the form of NOVASOY (NS) was investigated on methylnitrosourea-initiated mammary gland cancer in F1 generation female Sprague Dawley rats from parents who had undergone lifetime exposure to variable levels of dietary NS. In comparison to NS-free dietary groups, lifetime exposure of F1 rats to 40 and 1000 mg/kg diets of NS reduced tumor latency, but did not significantly affect tumor incidence, tumor size, or tumor multiplicity. A significantly lower tumor multiplicity was, however, observed in rats fed the soy-based, NS-free diet compared to the casein-based, NS-free diet. An evaluation of a dose-response relationship pointed towards a biphasic effect, with a trend showing lower tumor incidence, lower tumor multiplicity, and lower tumor size in rats fed 1000 mg/kg diet NS compared to 40 mg/kg diet NS; however, the data failed to achieve statistical significance. Histologically, tumor type significantly differed according to the administered basal diet variety and NS dose. Our data and that of others provide conflicting evidence for chemopreventive effects of soy isoflavones on mammary gland tumor induction. We suggest standardization of interlaboratory experimental approaches for establishing low dose-response relationships for soy and its isoflavones to aid in risk assessment.

Increased serum and testicular androgen levels in F1 rats with lifetime exposure to soy isoflavones

The consequences of dietary soy isoflavones on serum and testicular androgen levels were examined in F1 male rats from a multigeneration study investigating the effects of diets varying in isoflavone content. Rats were fed either a soy-free casein based diet (AIN93G) or a diet in which alcohol-washed soy protein replaced casein as the protein source and to which increasing amounts of Novasoy, a commercially available isoflavone supplement were added. Analysis of these diets showed that the isoflavone content in each diet was 0 (diet 1; casein based control), 31.7 (diet 2; alcohol-washed soy-based diet control), 36.1 (diet 3), 74.5 (diet 4), 235.6 (diet 5) and 1046.6 (diet 6) mg total isoflavones/kg pelleted diet. The levels of isoflavones in diet 1 would represent a daily intake level of 0 mg isoflavones, diets 2 and 3 estimate a low soy-containing human diet (e.g. North American), diet 4 would correspond to Asian diets (e.g. Japanese) or adult humans taking isoflavone supplements, diet 5 approximates the isoflavone intake by babies fed soy based infant formula and diet 6 approximates fivefold the intake levels by babies or 10-fold the intake levels of adults consuming high isoflavone containing diets. Serum testosterone (T) from F1 male rats sacrificed on postnatal days (PND) 28, 70, 120, 240 and 360 were low at PND 28 (0.4 ng/ml), increased approximately five to sixfold at PND 70 (2.5-3.0 ng/ml) and thereafter declined to a steady state level of approximately 1 ng/ml by PND 120. However, rats on diets 5 and 6 demonstrated altered serum testosterone profiles such that at days 120, testosterone levels remained significantly elevated at approximately 3 ng/ml (P < 0.05). Serum dihydrotestosterone levels exhibited similar profiles and the levels in PND 120 rats on diet 5 or 6 were also significantly elevated (two to threefold, P < 0.05). The intra-testicular testosterone concentration in rats on diet 5 was also elevated at PND 120 compared with diet 1 (P < 0.05). These findings show that F1 male rats continuously exposed to a mixture of dietary soy isoflavones from conception onwards exhibit altered serum and testicular androgen profiles.

Altered testicular microsomal steroidogenic enzyme activities in rats with lifetime exposure to soy isoflavones

Androgen production in the testis is carried out by the Leydig cells, which convert cholesterol into androgens. Previously, isoflavones have been shown to affect serum androgen levels and steroidogenic enzyme activities. In this study, the effects of lifelong exposure to dietary soy isoflavones on testicular microsomal steroidogenic enzyme activities were examined in the rat. F1 male rats were obtained from a multi-generational study where the parental generation was fed diets containing alcohol-washed soy protein supplemented with increasing amounts of Novasoy, a commercially available isoflavone supplement. A control group was maintained on a soy-free casein protein-based diet (AIN93G). The diets were designed to approximate human consumption levels and ranged from 0 to 1046.6 mg isoflavones/kg pelleted feed, encompassing exposures representative of North American and Asian diets as well as infant fed soy-based formula. Activities of testicular 3beta-hydroxysteroid dehydrogenase (3beta-HSD), P450c17 (CYP17), 17beta-hydroxysteroid dehydrogenase (17beta-HSD) were assayed on post natal day (PND) 28, 70, 120, 240 and 360 while 5alpha-reducatase was assayed on PND 28. At PND 28, 3beta-HSD activity was elevated by approximately 50% in rats receiving 1046.6 mg total isoflavones/kg feed compared to those on the casein only diet. A similar increase in activity was observed for CYP17 in rats receiving 235.6 mg total isoflavones/kg feed, a level representative of infant exposure through formula, compared to those receiving 0mg isoflavones from the casein diet. These results demonstrate that rats fed a mixture of dietary soy isoflavones showed significantly altered enzyme activity profiles during development at PND 28 as a result of early exposure to isoflavones at levels obtainable by humans.

Suppression of aromatase activity in vitro by PCBs 28 and 105 and Aroclor 1221

The effects of polychlorinated biphenyls (PCBs) on human cytochrome P450 aromatase activity in vitro were investigated using a commercially available microsomal fraction obtained from baculovirus infected insects that had been transfected with the human CYP19 gene and cytochrome P450 reductase. The assay measured the conversion of tritiated testosterone to estradiol in Tris buffer at pH 7.4. When aroclors, commercial preparations of PCBs, were added to aromatase assays at a 10 microM concentration, Aroclor 1221 caused a reduction in the aromatase activity, whereas other aroclors (1016, 1232, 1242, 1248, 1254, 1260, 5432, 5442 and 5460) were without effect. Further investigation of the effect of Aroclor 1221 on aromatase activity showed that the inhibition was dose dependent. When a reconstituted mixture (RM) of PCBs that represented the congeneric content of human milk was investigated, no inhibition of aromatase activity at the maximum treatment of 15.0 microM was observed. None of the congeners present in the reconstituted mixture, except PCB 28 and 105, affected P450 arom activity. PCB 28 showed a statistically significant inhibition of aromatase activity (P<0.05) at 1.5 and 15 microM and a significant inhibition of aromatase activity by PCB 105 was also observed, but only at 15 microM. In three separate kinetic analyses the Km(app) for aromatase was 64, 89 and 69 nM (mean 74 nM). In addition, PCB 28 resulted in an increase in the Km(app) without a significant effect on Vmax(app), suggesting competitive inhibition by this congener. This conclusion was supported by slope (Km(app)/Vmax(app) versus [inhibitor]) and intercept (1/Vmax(app) versus [inhibitor]) replots. The slope replots gave Ki(app) values for PCB 28 of 0.9, 1.3 and 2.0 microM (mean 1.4 microM), whereas intercept replots were almost horizontal. Thus, PCB 28 is a competitive inhibitor of aromatase with a Ki(app) value approximately 20-fold the Km(app) value. Based on these studies, we conclude that most PCBs are not inhibitors of aromatase activity in vitro. However, as being inhibitors of aromatase activity, Aroclor 1221, PCB 28 and PCB 105 would remain a priority for further study as possible endocrine disrupters.

Effects of PNU157706, a dual 5alpha-reductase inhibitor, on gene expression in the rat epididymis

The epididymis is the site of sperm maturation and storage. 5alpha-Reductases (types 1 and 2) are key enzymes in this tissue because they convert testosterone to dihydrotestosterone (DHT), the main androgen regulating epididymal functions. Examining the consequences of inhibiting DHT formation is likely to provide important information regarding the regulation of epididymal functions, yet few inhibitor studies have focused on this tissue. To understand better DHT-mediated regulation of epididymal gene expression, we employed a dual 5alpha-reductase inhibitor and cDNA microarrays to examine the effects of 5alpha-reductase inhibition on gene expression in the initial segment, caput, corpus, and cauda epididymidis. Inhibition of epididymal 5alpha-reductase activity by PNU157706 was confirmed by in vitro enzyme assays. Rats were treated with 0, 0.1, 1.0 or 10 mg/kg per day PNU157706 for 28 days. The weights of DHT-dependent tissues, including the epididymis, were decreased following treatment. The effect of treatment on gene expression was dose-dependent and highly segment-specific. The initial segment responded uniquely in that a similar number of genes increased and decreased in expression compared with the other segments where the majority of affected genes decreased in expression. Some of the more dramatically affected genes were involved in signal transduction as well as fatty acid and lipid metabolism, regulation of ion and fluid transport, luminal acidification, oxidative defense and protein processing and degradation. These are essential processes contributing to the formation of an optimal luminal microenvironment required for proper sperm maturation. These results provide a novel insight into the DHT-dependent mechanisms that control epididymal functions.

Dietary soy protein isolate and isoflavones modulate hepatic thyroid hormone receptors in rats

Thyroid hormone receptors (TRs) are regulators of many genes involved in cholesterol and lipid metabolism. The purpose of this study was to examine the effect of soy protein isolate (SPI) and isoflavones on hepatic TRs in rats. In Expt. 1, Sprague-Dawley rats were fed diets containing either casein or alcohol-washed SPI with or without isoflavone supplementation (5-1250 mg/kg diet) for 70, 190, and 310 d. The offspring (F1) were fed the same diets as their parents (F0). In Expt. 2, Sprague-Dawley rats were fed diets containing casein or casein plus isoflavones (50-400 mg/kg diet) for 120 d. The mRNA and protein contents of the hepatic TRs were measured by semiquantitative RT-PCR and Western blot, respectively. TRalpha1, TRalpha2, and TRbeta2 contents were not affected by SPI. However, the content of the 52-kDa TRbeta1 protein, the major isoform present in the liver, was markedly increased by dietary SPI in both sexes of F0 and F1 compared with casein. The supplemental isoflavones had no effect on TRbeta1, whereas the high doses of isoflavones (250 and 1250 mg/kg diet) reduced the hepatic TRalpha1 protein content in F1 male rats on d 28. SPI had no effect on total T3 and T4 levels. However, higher dose of supplemental isoflavones markedly increased T4 level in female rats. Overall, this study demonstrates for the first time that SPI upregulates hepatic TRbeta1 expression, and that isoflavones reduce the hepatic TRalpha1 level in young male rats. The SPI-induced TRbeta1 may play a role in mediating the hypocholesterolemic and lipid-lowering actions of soy protein.

Oral (gavage), in utero and postnatal exposure of Sprague-Dawley rats to low doses of tributyltin chloride. Part 1: Toxicology, histopathology and clinical chemistry

Tributyltin (TBT) is a biocide that contaminates foods, especially shellfish. TBT is an endocrine disrupter in several marine species and is neurotoxic and immunotoxic in mammals. We have examined the effects of exposure to low doses of tributyltin chloride (TBTC) from day 8 of gestation until adulthood. Pregnant rats were gavaged daily with 0, 0.025, 0.25 or 2.5 mg TBTC/kg body weight from day 8 of gestation until weaning. Stomach contents of suckling pups contained undetectable levels of TBT and dibutyltin (DBT) levels were detectable only in the highest TBTC dose used, indicating negligible lactational transfer to pups. Post weaning, pups were gavaged daily with the same dose of TBTC administered to their mothers and sacrificed on post-natal days (PND) 30 (males and females), 60 (females) and 90 (males). TBTC had no effects on dams' body weights, food consumption, litter size, sex ratio or survival of pups to weaning. However, all doses of TBTC significantly affected parameters of the growth profile of the pups (mean body weights, average slope, curvature) and the ratio of weekly food consumption to weekly body weight gain indicated enhanced food conversion to body mass in females but a decreased conversion in males. Liver, spleen and thymus weights were also affected by TBTC. In male pups dosed at 2.5 mg/kg/day, reduced serum thyroxine levels were evident, indicating that the thyroid is a target for TBTC toxicity. No histopathological lesions were seen in the liver but elevated serum alanine aminotransferase, gamma-glutamyl transferase and amylase indicated hepatotoxicity. Significant decreases in liver weights in female pups exposed to 0.025 mg/kg/day TBTC were observed at PND 60. Decreases in spleen and thymus weights also pointed towards toxic effects of TBTC on the immune system. The 0.025 mg/kg/day TBTC should have been a no affect dose and yet this dose caused significant effects on growth profiles, decreased liver weights and elevated serum GGT levels in females.

Effects of in utero tributyltin chloride exposure in the rat on pregnancy outcome

Tributyltin, an organotin, is ubiquitous in the environment. The consumption of contaminated marine species leads to human dietary exposure to this compound. Tributyltin is an endocrine disruptor in many wildlife species and inhibits aromatase in mammalian placental and granulosa-like tumor cell lines. We investigated the effects of tributyltin chloride exposure on pregnancy outcome in the Sprague-Dawley rat. Timed pregnant rats were gavaged either with vehicle (olive oil) or tributyltin chloride (0.25, 2.5, 10, or 20 mg/kg) from days 0-19 or 8-19 of gestation. On gestational day 20, dams were sacrificed, and pregnancy outcome was determined. Tributyltin and its metabolites (dibutyltin, monobutyltin) were measured in maternal blood by gas chromatography. Both tributyltin and dibutyltin were present in maternal blood at approximately equal concentrations, whereas monobutyltin contributed minimally to total organotins. Organotin concentrations increased in a dose-dependent pattern in dams, independent of the window of exposure. Tributyltin chloride administration significantly reduced maternal weight gain only at the highest dose (20 mg/kg); a significant increase in post-implantation loss and decreased litter sizes, in addition to decreased fetal weights, was observed in this group. Tributyltin chloride exposure did not result in external malformations, nor was there a change in sex ratios. However, exposure to 0.25, 2.5, or 10 mg/kg tributyltin chloride from gestation days (GD) 0-19 resulted in a significant increase in normalized anogenital distances in male fetuses; exposure from days 8-19 had no effect. There was a dramatic increase in the incidence of low weight (< or =0.75 of the mean) fetuses after exposure to 20 mg/kg tributyltin chloride. Delayed ossification of the fetal skeleton was observed after in utero exposure to either 10 mg/kg or 20 mg/kg tributyltin chloride. Serum thyroxine and triiodothyronine levels were reduced significantly in dams exposed to 10 and 20 mg/kg tributyltin chloride throughout gestation; in dams treated with tributyltin from GD 8-19, serum thyroxine concentrations, but not triiodothyronine, were significantly decreased at both the 2.5 and 10 mg/kg exposures. Thus, maternal thyroid hormone homeostasis may be important in mediating the developmental toxicity of organotins.

Inhibition of rat testis microsomal 3beta-hydroxysteroid dehydrogenase activity by tributyltin

In this study, we have examined the effects of a range of organotin compounds (mono-, di-, tributyltin, mono-, di-, trioctyltin) on the activities of rat testis microsomal 3beta-hydroxysteroid dehydrogenase (3beta-HSD), 17-hydroxylase (17-OHase) and 17beta-hydroxysteroid dehydrogenase (17beta-HSD). 17-OHase activity was inhibited by more than 50% compared with the control rate by 59 microM tributyltin (TBT) but other organotin compounds showed no inhibition. 17beta-HSD activity was unaffected by all organotins tested. 3beta-HSD was inhibited by monooctyltin (81 microM) and by TBT at all concentrations tested in a dose-dependent manner, with almost complete loss of activity at TBT concentrations of 12 microM. The mechanism of inhibition of 3beta-HSD was investigated in kinetic analysis with 0-12 microM TBT. Three rat testis microsomal preparations were incubated with dehydroepiandrosterone as the steroid substrate ranging from 1 to 10,000 nM. Tributyltin was primarily a competitive inhibitor of 3beta-HSD activity, causing an increase in the value of the K(m(app)). However, the mechanism was not entirely competitive as while there was an increase in K(m(app)), a decrease in the V(max(app)) was also observed with increasing concentrations of TBT. Slope and intercept replots demonstrated that the K(i)((app)) from slope replots was around 2.7 microM whereas the K(i)((app)) value from intercept replots was around 30 microM. When compared with the K(m(app)) for 3beta-HSD of around 0.42 microM, TBT could be an effective inhibitor of this enzyme.

Gestational exposure to persistent organic pollutants: maternal liver residues, pregnancy outcome, and effects on hepatic gene expression profiles in the dam and fetus

Dietary exposure of Inuit people to a mixture of pesticides and polychlorinated biphenyls, or persistent organic pollutants (POPs), during pregnancy is a public health concern. We examined the consequences of administering the mixture of 28 POPs found in the Inuit diet (at doses representing 10-1000 times dietary levels) by gavage to pregnant Sprague-Dawley rats either during gestation days 0-19 or 8-19. The levels of individual components of the POPs mixture in the maternal liver were measured by high-resolution mass spectrometry. On gestation day 20, dams were sacrificed and pregnancy outcome determined. RNA isolated from maternal and fetal livers was 32P-labeled for gene expression profiling. The concentrations of individual POPs were increased in maternal livers of dams gavaged with the 1000x POPs mixture by 10- to 500-fold. While exposure to POPs had no significant effects on pregnancy outcome, dramatic changes were observed in the gene expression profiles of both the maternal and fetal livers. The gene expression profiles of maternal and fetal female and male liver were distinct with respect to the numbers of transcripts detected, the genes expressed exclusively in control or POPs-exposed livers, and those for which expression was up- or downregulated. While different genes were affected in each group, the overall consequence of POPs exposure on hepatic gene expression profiles was to decrease both the numbers of genes expressed and the relative intensity of expression. Thus, in utero exposure to POPs alters hepatic gene expression in the dam and the fetus; these changes may have functional implications.

Effects of Aroclors and individual PCB congeners on activation of the human androgen receptor in vitro

To investigate possible interactions between the human androgen receptor and PCBs in vitro, we have used a previously characterized human androgen receptor reporter gene assay in which PC-3 LUC(AR+) cells respond to 5alpha-dihydrotestosterone (DHT, 50 pM) with enhanced luciferase activity. The effects of Aroclors, commercial mixtures of PCBs, or polychlorinated terphenyls (PCTs) (0, 0.1, 1.0, and 10.0 microM) on luciferase activity in PC-3 LUC(AR+) cells were determined after exposure for 18 h in the presence and absence of DHT (50 pM). In the absence of DHT, none of the Aroclors induced luciferase activity but, in the presence of DHT (50 pM), Aroclors 1016, 1221, 1232, 1242, 1248, 1254, 1260, 5432, and 5442 acted antagonistically at concentrations that did not affect cell viability. Aroclor 5460 was without effect. Similarly, when PCBs found as human milk contaminants were assessed as individual congeners (each at 1 microM, where no cytotoxic effects were observed), none activated luciferase expression in the absence of DHT but PCBs 49, 66, 74, 105, and 118 completely antagonized the stimulation by DHT (50 pM) and PCBs 138, 153, and 156 were less effective antagonists, reducing the DHT stimulation by about 50%. Thus, 30% (by weight) of the PCBs in human milk are androgen antagonists (PCBs 66, 74, 105, and 118) and a further 25% are partial antagonists (PCBs 138, 153, and 156). A proportionally representative mixture of PCBs that contaminate human milk also caused the DHT-mediated activation of luciferase activity in PC-3 LUC(AR+) cells to be reduced by more than 50%.

Interaction between tris(4-chlorophenyl)methanol and the human androgen receptor in vitro

The interaction between tris(4-chlorophenyl)methanol (TCPM), an environmental contaminant of uncertain origin, and the human androgen receptor was examined in vitro using a previously characterized human androgen receptor reporter gene assay in which PC-3 LUC(AR+) cells respond to 5alpha-dihydrotestosterone (DHT) with enhanced luciferase activity. In two preliminary studies, TCPM (1 microM) had no effect on androgen receptor activation in the absence of DHT (50 pM), but DHT-mediated activation of the androgen receptor was decreased more than 90% by TCPM at 1 microM. This was not due to an effect of TCPM on cell viability since, with TCPM concentrations of 0.1 and 1.0 microM, cell viability was 111 and 102%, respectively, but at 10 microM TCPM, cell viability was reduced to 60% compared with controls. For kinetic studies of the effects of TCPM on androgen receptor activation, DHT was added at 0, 5, 25, 50, 75, 100, 250 and 500 pM and the TCPM concentrations used were 0, 1, 10, 100, 300 and 1000 nM. This range incorporated the levels of TCPM in human adipose tissue, where concentrations up to 55 nM (20 ng/g lipid) have been measured. TCPM increased the value of the K(m(app)) of the androgen receptor for DHT 4-6-fold with little or no effect on the V(max(app)). Slope and intercept replots revealed that TCPM inhibited the DHT-mediated activation of the androgen receptor in a competitive manner with K(i(app)) values of 0.26, 0.26 and 0.20 microM compared with respective K(m(app)) values of 9.8, 3.1 and 3.9 pM. Thus, TCPM is a competitive antagonist of human androgen receptor activation and the value of the K(i(app)) indicates that TCPM would be approximately 10-50 times more potent as an inhibitor than the previously identified androgen receptor antagonists p,p'-DDE and vinclozilin and also, the K(i(app)) values (200-260 nM) are very close to the concentration of TCPM found in the adipose tissue of some humans (55 nM).

Effect of organotins on human aromatase activity in vitro

The interaction between the human aromatase enzyme and some organotins was investigated. Tributyltin (TBT) at 12 and 59 microM and dibutyltin at 74 microM inhibited aromatase activity in vitro but monobutyltin and tri-, di- and monooctyltins were without effect. In four separate kinetic studies of aromatase, the K(m(app)) for testosterone was 0.24, 0.21, 0.16 and 0.24 microM. TBT inhibited aromatase activity by causing the K(m(app)) to be increased without affecting the V(max), indicative of competitive inhibition. Slope and intercept replots confirmed the effect of aromatase on the K(m(app)). Slope replots from three separate kinetic studies provided Ki values for TBT of 64.5, 40.9 and 37.3 microM. Consequently, TBT is a competitive inhibitor of human aromatase with a Ki approximately 300-fold the K(m(app)) value.

The mammalian testis accumulates lower levels of organochlorine chemicals compared with other tissues

Tissues were obtained from three separate experiments in order to quantify the tissue distribution of organochlorine chemicals that are thought to be potential reproductive toxicants in males: 1) Sprague Dawley rats received 1 microCi of 14C-Aldrin or 14C-Dieldrin (20.6 microCi/micromole) i.p. once a week for three weeks. One week and four weeks after the last injection, tissues were harvested and stored at -80 degrees C. Tissue 14C levels were quantified by scintillation spectrometry. 2) Cis- or trans-nonachlor (0, 0.25, 2.5, 25 mg/kg body weight) were administered daily in corn oil to male rats by gavage for 28 days. Tissues were harvested and frozen at -80 degrees C on the 29th day. Organochlorine residues were extracted and quantified by gas chromatography with electron capture detection. 3) Technical grade toxaphene (0, 0.1, 0.4 or 0.8 mg/kg body weight) was ingested daily by female cynomolgus monkeys of reproductive age for 18 months prior to being mated with control males. Dosing continued during pregnancy and lactation. Their infants received toxaphene via breast milk, and upon weaning, they ingested the same dose as their mothers for 48 to 49 weeks until, at 77 to 80 weeks of age, tissues were harvested and stored at -80 degrees C. Organochlorine residues were extracted and quantified as previously stated. In all three experiments, organochlorine residues in the testis were lower than in most of the other reproductive tract and nonreproductive tract tissues we examined. For example, testicular aldrin and dieldrin levels were <5% the epididymal content; testicular cis- and trans-nonachlor were <25% the epididymal content and, testicular toxaphene levels were <15% of the epididymal content. The reasons for the low degree of accumulation by the testis in comparison with other tissues are unknown. However, the lower testicular content may afford germ cells some protection from the potentially toxic effects of these chemicals.

Influence of season and low-level oestradiol immunoneutralization on episodic LH and testosterone secretion and testicular steroidogenic enzymes and steroidogenic acute regulatory protein in the adult ram

The regulation of LH-dependent and -independent increases in testosterone secretion by key proteins in the testes of adult rams was investigated. Serial blood samples were collected from groups of four control and passively immunized (oestradiol antiserum for 3 weeks) rams and the animals were gonadectomized in either the non-breeding season (April) or the breeding season (September). LH pulse frequency and basal (interpulse) concentrations were several times greater (P < 0.01) in the breeding season than in the non-breeding season. Neither of these parameters nor LH pulse amplitude were affected by oestradiol immunization. Parameters of testosterone episodic secretion and response to an injection (i.v.) of 15 micrograms NIH-LH-S25 were also greater (P < 0.05) in the breeding season and, with the exception of pulse frequency, in immunized rams versus controls. Substrate utilization established that testosterone biosynthesis was predominantly via the 5-ene pathway. Increases in blood testosterone concentration in the breeding season were associated with a fivefold higher (P < 0.01) activity of cytochrome P450 17alpha-hydroxylase/C-17,20 lyase (P450(17alpha)) and a 65% higher (P < 0.05) relative amount of mRNA for cytochrome P450 cholesterol side-chain cleavage enzyme complex (P450scc) in the testis. Of the steroidogenic enzyme activities examined, only that for 17beta-hydroxysteroid dehydrogenase (17beta-HSD) tended to be increased by oestradiol immunization. Blood concentrations of cholesterol lipoproteins and expression of the testicular low density lipoprotein receptor were not affected by season or immunization. The amount of steroidogenic acute regulatory protein (StAR) mRNA was 65% higher (P < 0.01) in the breeding season and 20% higher (P < 0.01) in immunized rams versus controls. These results indicate that greater LH stimulation may increase testosterone biosynthesis in the breeding season by increasing StAR mRNA (and presumably delivery of cholesterol to P450scc) and the activity of P450(17alpha), and possibly that of P450scc (activity not measured). More moderate increases in StAR mRNA and 17beta-HSD activity may explain, in part, the increases in testosterone secretion with oestradiol immunization.

Influence of season and low-level oestradiol immunoneutralization on episodic LH and testosterone secretion and testicular steroidogenic enzymes and steroidogenic acute regulatory protein in the adult ram

The regulation of LH-dependent and -independent increases in testosterone secretion by key proteins in the testes of adult rams was investigated. Serial blood samples were collected from groups of four control and passively immunized (oestradiol antiserum for 3 weeks) rams and the animals were gonadectomized in either the non-breeding season (April) or the breeding season (September). LH pulse frequency and basal (interpulse) concentrations were several times greater (P < 0.01) in the breeding season than in the non-breeding season. Neither of these parameters nor LH pulse amplitude were affected by oestradiol immunization. Parameters of testosterone episodic secretion and response to an injection (i.v.) of 15 micrograms NIH-LH-S25 were also greater (P < 0.05) in the breeding season and, with the exception of pulse frequency, in immunized rams versus controls. Substrate utilization established that testosterone biosynthesis was predominantly via the 5-ene pathway. Increases in blood testosterone concentration in the breeding season were associated with a fivefold higher (P < 0.01) activity of cytochrome P450 17alpha-hydroxylase/C-17,20 lyase (P450(17alpha)) and a 65% higher (P < 0.05) relative amount of mRNA for cytochrome P450 cholesterol side-chain cleavage enzyme complex (P450scc) in the testis. Of the steroidogenic enzyme activities examined, only that for 17beta-hydroxysteroid dehydrogenase (17beta-HSD) tended to be increased by oestradiol immunization. Blood concentrations of cholesterol lipoproteins and expression of the testicular low density lipoprotein receptor were not affected by season or immunization. The amount of steroidogenic acute regulatory protein (StAR) mRNA was 65% higher (P < 0.01) in the breeding season and 20% higher (P < 0.01) in immunized rams versus controls. These results indicate that greater LH stimulation may increase testosterone biosynthesis in the breeding season by increasing StAR mRNA (and presumably delivery of cholesterol to P450scc) and the activity of P450(17alpha), and possibly that of P450scc (activity not measured). More moderate increases in StAR mRNA and 17beta-HSD activity may explain, in part, the increases in testosterone secretion with oestradiol immunization.

Examination of selected food additives and organochlorine food contaminants for androgenic activity in vitro

In order to produce a reporter gene assay for androgenic chemicals, a constitutive expression vector coding for the human androgen receptor and a reporter construct containing the firefly luciferase coding sequence under transcriptional control of the androgen responsive MMTV promoter were cotransfected into the androgen-insensitive human PC-3 prostate carcinoma cell line and stable transfectants selected. One colony of transfectants, PC-3 LUCAR+, was characterized further. 5alpha-Dihydrotestosterone (DHT) enhanced luciferase activity in a linear fashion for up to 3 days of culture. The Kd for DHT activation was within the range of 25.0-60.0 pM (r2 values >0.95). Flutamide competitively inhibited DHT activation (mean Ki value of 0.89 microM). Progesterone, estradiol, dexamethasone, and hydrocortisone were weak agonists (100-fold less effective than DHT) and diethylstilbestrol was without effect. The effects of organochlorine food contaminants (0, 0.1, 1.0, and 10.0 microM) on luciferase activity in PC-3 LUCAR+ cells were determined after exposure to the chemical for 18 h in the presence and absence of DHT (50 pM). 1,1-dichloro-2,2-bis(p-chlorophenyl)-ethylene (p,p'-DDE) induced luciferase activity in the absence of DHT (100 microM p,p'-DDE equivalent to 50 pM DHT), but in the presence of DHT (50 pM), p,p'-DDE acted antagonistically. 2,3,7,8-Tetrachlorodibenzo-p-dioxin, kepone, butylated hydroxyanisole, and butylated hydroxytoluene all partially inhibited activation by DHT (50 pM) but alone had little or no effect. Toxaphene at 10 microM induced luciferase activity in the absence of DHT but decreased cell viability. Alpha- and delta-Hexachlorocyclohexanes (HCH) at 10 microM antagonized the DHT effect, but beta-HCH and gamma-HCH mirex, photomirex, oxychlordane, cis- and trans-nonachlor were without effect. Thus, of the chemicals tested, some interact with the human androgen receptor in vitro as agonists, others as antagonists, and some as partial agonists/antagonists.

Effects of in utero and lactational exposure to 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) on serum androgens and steroidogenic enzyme activities in the male rat reproductive tract

2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) has been shown to impair reproductive function of males in animal models, possibly due to a reduction in serum androgen levels. Thus, TCDD may alter the testosterone biosynthetic pathway in the testis or the conversion of testosterone to 5alpha-dihydrotestosterone (DHT) in androgen target tissues. Pregnant Sprague Dawley rats were gavaged with TCDD (0, 0.2 or 1.0 microg/kg) on day 15 of gestation only. TCDD caused a reduction in the body weight gain of the dams in both dose groups and a significant reduction in litter size in the higher dose group. Litters delivered normally and TCDD exposed male offspring grew at the same rate as controls. Males were sacrificed at 15, 30, 45, 60, 90 and 120 d of age. Steroidogenic enzyme activities were determined in testicular microsomes and androgen target tissue nuclear fractions. Serum androgens were measured by radioimmunoassay (RIA). At 30 d of age, rats exposed to 1.0 microg/kg TCDD exhibited lower 17-hydroxylase activity (P < 0.05) and lower caput-corpus epididymal weights (P < 0.05). At 45 d of age, the same treatment resulted in testicular 3beta-HSD, 17beta-HSD and 5alpha-reductase activities that were significantly greater (P < 0.05) but, conversely, serum androgens were one quarter the values evident in controls (P < 0.05). At the other ages, no differences were observed in serum androgens and, with the exception of lower 17beta-HSD activity at 90 d of age (P < 0.05), no other differences in testicular steroidogenic enzyme activities were found. 5Alpha-reductase activities in the androgen target tissues were also unchanged. Histological examination of testes showed that the spermatogenic profile was identical to controls at all ages.

Concentrations of energy substrates in oviduct fluid in unilaterally ovariectomised pigs

Nichol et al (1992, Journal of Reproduction and Fertility, 96, 699-707) identified a pre- to post-ovulatory decrease (approx 1 mM) in the amount of glucose in pig oviduct fluid. The present studies investigated whether the decrease was due to metabolism by embryos and/or oviduct tissues, and also whether there was a local influence of the ovary on the oviduct fluid content of energy substrates. Unilaterally ovariectomised pigs were used, in which, through compensation, oviducts that contained twice the normal number of embryos could be compared with oviducts which contained no embryos. Following unilateral ovariectomy and after two oestrous cycles of normal duration, surgery was performed 88 hours after the beginning of standing heat to obtain oviduct fluid samples, just before embryonic entry into the uterus. Luminal fluid samples from the ampulla and ampullary-isthmic junction from oviducts with and without an adjacent ovary were assayed for glucose, pyruvate and lactate concentrations. No significant differences were found between the glucose, pyruvate and lactate concentrations in fluids from the ampulla or ampullary-isthmic junction from oviducts containing embryos compared with absence of embryos (P > 0.05). Therefore, the post-ovulatory decrease was not due to the presence of embryos or to a local effect of the ipsilateral ovary. Consequently, pig oviduct fluid concentrations of glucose, lactate and pyruvate are seemingly regulated by systemic mechanisms.

Luteal and placental characteristics of carnivore gestation: expression of genes for luteotrophic receptors and steroidogenic enzymes

Experiments were carried out to investigate the abundance of mRNA for luteotrophic receptors and steroidogenic elements in the ovaries and corpora lutea of mink during the embryonic diapause, peri-implantation and postimplantation pregnancy. The second aim was to determine whether the mink placenta synthesized progesterone. Homologous cDNA probes for the mink LH and prolactin receptors were generated by the polymerase chain reaction. Heterologous cDNA probes for steroidogenic acute regulatory protein (StAR), cytochrome P450 side chain cleavage (P450scc) and 3 beta-hydroxysteroid dehydrogenase-delta 4-delta 5 isomerase (3 beta HSD) were also used. The abundance of mRNA encoding the prolactin receptor was low during the period of embryonic diapause and increased concurrent with circulating progesterone. The abundance of LH receptor message reached peak values during the peri-implantation period followed by maintenance of a steady-state after implantation. The abundance of StAR and P450scc messages appeared not to vary during gestation, while that for 3 beta HSD was correlated with changes in circulating progesterone. There was no evidence of 3 beta HSD activity or transcripts in the placenta. These results indicate that prolactin and LH are necessary for activation of the corpus luteum during the period of embryonic diapause, and for its maintenance during postimplantation gestation. The mink placenta does not synthesize progesterone.