25th anniversary of the Berlin workshop on developmental toxicology: DevTox database update, challenges in risk assessment of developmental neurotoxicity and alternative methodologies in bone development and growth

25 years after the first Berlin Workshop on Developmental Toxicity this 10th Berlin Workshop aimed to bring together international experts from authorities, academia and industry to consider scientific, methodologic and regulatory aspects in risk assessment of developmental toxicity and to debate alternative strategies in testing developmental effects in the future. Proposals for improvement of the categorization of developmental effects were discussed as well as the update of the DevTox database as valuable tool for harmonization. The development of adverse outcome pathways relevant to developmental neurotoxicity (DNT) was debated as a fundamental improvement to guide the screening and testing for DNT using alternatives to animal methods. A further focus was the implementation of an in vitro mechanism-based battery, which can support various regulatory applications associated with the assessment of chemicals and mixtures. More interdisciplinary and translation research should be initiated to accelerate the development of new technologies to test developmental toxicity. Technologies in the pipeline are (i) high throughput imaging techniques, (ii) models for DNT screening tests, (iii) use of computer tomography for assessment of thoracolumbar supernumerary ribs in animal models, and (iv) 3D biofabrication of bone development and regeneration tissue models. In addition, increased collaboration with the medical community was suggested to improve the relevance of test results to humans and identify more clinically relevant endpoints. Finally, the participants agreed that this conference facilitated better understanding innovative approaches that can be useful for the identification of developmental health risks due to exposure to chemical substances.

Report from the BfR expert hearing on practicability of hormonal measurements: recommendations for experimental design of toxicological studies with integrated hormonal end points

This publication summarizes discussions that were held during an international expert hearing organized by the German Federal Institute for Risk Assessment (BfR) in Berlin, Germany, in October 2017. The expert hearing was dedicated to providing practical guidance for the measurement of circulating hormones in regulatory toxicology studies. Adequate measurements of circulating hormones have become more important given the regulatory requirement to assess the potential for endocrine disrupting properties for all substances covered by the plant protection products and biocidal products regulations in the European Union (EU). The main focus was the hypothalamus-pituitary-thyroid axis (HPT) and the hypothalamus-pituitary-gonadal axis (HPG). Insulin, insulin-like growth factor 1 (IGF-1), parathyroid hormone (PTH) and vitamins A and D were also discussed. During the hearing, the experts agreed on specific recommendations for design, conduct and evaluation of acceptability of studies measuring thyroid hormones, thyroid stimulating hormone and reproductive hormones as well as provided some recommendations for insulin and IGF-1. Experts concluded that hormonal measurements as part of the test guidelines (TGs) of the Organisation for Economic Co-operation and Development (OECD) were necessary on the condition that quality criteria to guarantee reliability and reproducibility of measurements are adhered to. Inclusion of the female reproductive hormones in OECD TGs was not recommended unless the design of the study was modified to appropriately measure hormone concentrations. The current report aims at promoting standardization of the experimental designs of hormonal assays to allow their integration in OECD TGs and highlights research needs for better identification of endocrine disruptors using hormone measurements.

Differences between NMRI and DBA/2J mice in the development of somites and susceptibility to methylnitrosourea-induced skeleton anomalies

The development of DBA/2J mouse strain embryos is nearly 12 h - or 6 somite pairs - delayed as compared to the outbred NMRI mouse embryos of the same age on gestation days (GD) 8-12. To evaluate inter-strain differences in susceptibility to teratogens, dams were treated with methylnitrosourea (MNU, 5 mg/kg body weight i.p.) on defined gestation days (NMRI: GD 9, 91/2 or 10; DBA/2J: GD 10 or 101/2). Skeletal anomalies produced by MNU on both mouse strains varied with the GD of treatment. The pattern of anomalies produced by MNU on a given GD markedly differed between the two mouse strains, yet they were similar -with a few exceptions- when exposures at equivalent embryonic stages are compared. Findings from this study indicated that strain-dependent differences in the developmental stage of mouse embryos of the same gestational age occur, a possibility that has been often neglected when inter-strain differences in susceptibility to developmental toxicants are interpreted.

Scientific principles for the identification of endocrine-disrupting chemicals: a consensus statement

Endocrine disruption is a specific form of toxicity, where natural and/or anthropogenic chemicals, known as "endocrine disruptors" (EDs), trigger adverse health effects by disrupting the endogenous hormone system. There is need to harmonize guidance on the regulation of EDs, but this has been hampered by what appeared as a lack of consensus among scientists. This publication provides summary information about a consensus reached by a group of world-leading scientists that can serve as the basis for the development of ED criteria in relevant EU legislation. Twenty-three international scientists from different disciplines discussed principles and open questions on ED identification as outlined in a draft consensus paper at an expert meeting hosted by the German Federal Institute for Risk Assessment (BfR) in Berlin, Germany on 11-12 April 2016. Participants reached a consensus regarding scientific principles for the identification of EDs. The paper discusses the consensus reached on background, definition of an ED and related concepts, sources of uncertainty, scientific principles important for ED identification, and research needs. It highlights the difficulty in retrospectively reconstructing ED exposure, insufficient range of validated test systems for EDs, and some issues impacting on the evaluation of the risk from EDs, such as non-monotonic dose-response and thresholds, modes of action, and exposure assessment. This report provides the consensus statement on EDs agreed among all participating scientists. The meeting facilitated a productive debate and reduced a number of differences in views. It is expected that the consensus reached will serve as an important basis for the development of regulatory ED criteria.

Prenatal exposure to the phytoestrogen daidzein resulted in persistent changes in ovarian surface epithelial cell height, folliculogenesis, and estrus phase length in adult Sprague-Dawley rat offspring

Daidzein (DZ), an isoflavone with the potential to interfere with estrogen signaling, is found in soy products, which have gained popularity due to purported beneficial effects on the cardiovascular and skeletal systems and potential antineoplastic properties. However, the ingestion of phytoestrogens has been associated with impaired reproductive function in many species. The aim of this study was to determine the long-term effects on the ovaries of rat offspring exposed to DZ or ethinyl estradiol (EE) during prenatal development. Gravid rats were administered either vehicle or 5 or 60 mg DZ/kg body weight/d or 0.002 mg 17-α EE /kg body weight/d on gestational days 6-21. Ovarian-related endpoints were investigated during adulthood in female offspring. The mean cell height of the ovarian surface epithelium was significantly reduced in all treated groups. Alterations in folliculogenesis included increased follicular atresia, a reduction in secondary and tertiary follicle numbers, and cyst formation. An elevated prevalence of a slightly prolonged estrus phase was also observed. The morphological changes to the ovarian surface epithelium are consistent with an antiproliferative effect, while ovarian folliculogenesis was adversely affected. The effects of the high dose DZ were similar to those observed with 17-α EE.

Biological and tumor-promoting effects of dioxin-like and non-dioxin-like polychlorinated biphenyls in mouse liver after single or combined treatment

To assess the impact of a mixture containing dioxin-like and non-dioxin-like polychlorinated biphenyls (PCBs), male mice were initiated with N-nitroso-diethylamine and subsequently treated with PCB126, an Ah-Receptor agonist, and PCB153, acting via activation of the constitutive androstane receptor. The two congeners were given at two dose levels: the low dose was adjusted to induce ~150-fold increases in cytochrome P450 (Cyp)1a1 (PCB126) and Cyp2b10 mRNAs (PCB153), and the high dose was chosen as twice the low dose. To keep the liver PCB levels constant, mice were given initial loading doses followed by weekly maintenance doses calculated on the basis of the PCBs' half-lives. Mice were treated with the individual congeners (low and high dose) or with a mixture consisting of the low doses of the 2 PCBs. The following results were obtained: (1) the 2 PCBs produced dose-dependent increases in Cyp1a1 and Cyp2b10 mRNA, protein, and activity when given individually; (2) combined treatment caused more than additive effects on Cyp1a1 mRNA expression, protein level, and ethoxyresurofin activity; (3) changes in the levels of several proteins were detected by proteome analysis in livers of PCB-treated mice; (4) besides these biological responses, the individual PCBs caused no significant increase in the number of glucose-6-phospatase (G6Pase)-deficient neoplastic lesions in liver, whereas a moderate significant effect occurred in the combination group. These results suggest weak but significant response-additive effects of the 2 PCBs when given in combination. They also suggest that the Cyp biomarkers tend to overestimate the carcinogenic response produced by the PCBs in mouse liver.

Harmonization of description and classification of fetal observations: achievements and problems still unresolved: report of the 7th Workshop on the Terminology in Developmental Toxicology Berlin, 4-6 May 2011

This article summarizes the 7th Workshop on the Terminology in Developmental Toxicology held in Berlin, May 4-6, 2011. The series of Berlin Workshops has been mainly concerned with the harmonization of terminology and classification of fetal anomalies in developmental toxicity studies. The main topics of the 7th Workshop were knowledge on the fate of anomalies after birth, use of Version 2 terminology for maternal-fetal observations and non-routinely used species, reclassification of "grey zone" anomalies and categorization of fetal observations for human health risk assessment. The paucity of data on health consequences of the postnatal permanence of fetal anomalies is relevant and further studies are needed. The Version 2 terminology is an important step forward and the terms listed in this glossary are considered also to be appropriate for most observations in non-routinely used species. Continuation of the Berlin Workshops was recommended. Topics suggested for the next Workshop were grouping of fetal observations for reporting and statistical analysis.

Urinary, Circulating, and Tissue Biomonitoring Studies Indicate Widespread Exposure to Bisphenol A

Bisphenol A (BPA) is one of the highest-volume chemicals produced worldwide, and human exposure to BPA is thought to be ubiquitous. Thus, there are concerns that the amount of BPA to which humans are exposed may cause adverse health effects. We examined many possibilities for why biomonitoring and toxicokinetic studies could come to seemingly conflicting conclusions. More than 80 published human biomonitoring studies that measured BPA concentrations in human tissues, urine, blood, and other fluids, along with two toxicokinetic studies of human BPA metabolism were examined. Unconjugated BPA was routinely detected in blood (in the nanograms per milliliter range), and conjugated BPA was routinely detected in the vast majority of urine samples (also in the nanograms per milliliter range). In stark contrast, toxicokinetic studies proposed that humans are not internally exposed to BPA. Available data from biomonitoring studies clearly indicate that the general population is exposed to BPA and is at risk from internal exposure to unconjugated BPA. The two toxicokinetic studies that suggested human BPA exposure is negligible have significant deficiencies, are directly contradicted by hypothesis-driven studies, and are therefore not reliable for risk assessment purposes.

Sex-dependent aromatase activity in rat offspring after pre- and postnatal exposure to triphenyltin chloride

Triphenyltin (TPT) is an organotin compound (OTC) previously widely used as an antifouling agent in paints applied in the marine environment, a fungicide, and as an agricultural pesticide. In female aquatic invertebrates, certain OTCs induce the so-called imposex, an abnormal induction of male sex characteristics. OTC-induced environmental endocrine disruption also occurs in fish and mammals and a number of in vivo and in vitro studies have argued that OTCs may act through inhibition of the aromatase enzyme. In vivo studies supporting the aromatase inhibition hypothesis in mammals are lacking. Recently, the causal relationship between inhibition of aromatase and imposex was questioned, suggesting aromatase independent mechanisms of action for this phenomenon. We conducted a comprehensive investigation to identify the most sensitive window of exposure to TPTCl and to examine the effects of pre- and postnatal exposure on postnatal development in rats. The results on brain and gonadal aromatase activity obtained from offspring of dams exposed to 2 mg TPTCl/kg bw are reported here. Female and male offspring rats were exposed to 2 mg TPTCl/kg bw/d in utero from gestation day 6 through lactation until weaning on PND 21, or from gestation day 6 until termination at adulthood. Male offspring were sacrificed from PND 58 and female offspring at first estrus after PND 58. Pre- and postnatal TPT exposure clearly affected brain and gonadal aromatase activity in a sex-dependent fashion. While brain aromatase activity was significantly increased on PND 21 and at adulthood in female offspring, male offspring exhibited a significant decrease in brain aromatase activity only at adulthood. Ovarian aromatase activity was unaffected at both time points investigated. In contrast, testicular aromatase activity was significantly increased in males on PND 21 and significantly decreased at adulthood independent from the duration of treatment. The results of the present study confirm our previously reported observations regarding sex-dependent differences in sexual development after TPT exposure with the male rat being more susceptible to disturbances through this endocrine active compound than the female. We conclude that TPT administered during the particularly vulnerable period of development can affect aromatase activity in rats.

Urinary, circulating, and tissue biomonitoring studies indicate widespread exposure to bisphenol A

BACKGROUND

Bisphenol A (BPA) is one of the highest-volume chemicals produced worldwide, and human exposure to BPA is thought to be ubiquitous. Thus, there are concerns that the amount of BPA to which humans are exposed may cause adverse health effects. Importantly, results from a large number of biomonitoring studies are at odds with the results from two toxicokinetic studies.

OBJECTIVE

We examined several possibilities for why biomonitoring and toxicokinetic studies could come to seemingly conflicting conclusions.

DATA SOURCES

We examined > 80 published human biomonitoring studies that measured BPA concentrations in human tissues, urine, blood, and other fluids, along with two toxicokinetic studies of human BPA metabolism.

DATA EXTRACTION AND SYNTHESIS

The > 80 biomonitoring studies examined included measurements in thousands of individuals from several different countries, and these studies overwhelmingly detected BPA in individual adults, adolescents, and children. Unconjugated BPA was routinely detected in blood (in the nanograms per milliliter range), and conjugated BPA was routinely detected in the vast majority of urine samples (also in the nanograms per milliliter range). In stark contrast, toxicokinetic studies proposed that humans are not internally exposed to BPA. Some regulatory agencies have relied solely on these toxicokinetic models in their risk assessments.

CONCLUSIONS

Available data from biomonitoring studies clearly indicate that the general population is exposed to BPA and is at risk from internal exposure to unconjugated BPA. The two toxicokinetic studies that suggested human BPA exposure is negligible have significant deficiencies, are directly contradicted by hypothesis-driven studies, and are therefore not reliable for risk assessment purposes.

Biomonitoring studies should be used by regulatory agencies to assess human exposure levels and safety of bisphenol A

BACKGROUND

Within the past 3 years, four major evaluations of bisphenol A (BPA) safety have been undertaken. However, these assessments have arrived at quite different conclusions regarding the safety of BPA at current human exposure levels.

OBJECTIVES

We compared the reasons provided by the European Food Safety Authority (EFSA) BPA risk assessment panel for their conclusion that human exposures are negligible with the conclusions reached by the other panels, with all panels having the same body of literature at their disposal.

DISCUSSION

The EFSA panel dismissed > or = 80 biomonitoring studies that documented significant levels of BPA exposure in humans, including internal exposures to unconjugated BPA, on the basis that they did not match a model of BPA metabolism. Instead, the EFSA panel relied on two toxicokinetic studies-conducted in 15 adults administered BPA-to draw conclusions about exposure levels in the population, including exposures of neonates.

CONCLUSIONS

As with all exposure assessments, models should be developed to explain actual data that are collected. In the case of BPA, samples from a large number of human subjects clearly indicate that humans are internally exposed to unconjugated BPA. The dismissal of these biomonitoring studies simply because their results do not conform to a model violates scientific principles. Expert panels should evaluate all data-including human biomonitoring studies-to make informed risk assessments.

An appreciation of Diether Neubert and Hans-Joachim Merker's contributions to Reproductive and Developmental Toxicology on their 80th birthday

Diether Neubert, toxicologist, and Hans-Joachim Merker, histopathologist and embryologist, made significant contributions to the field of Developmental and Reproductive Toxicology. They worked under the same roof at the Institute of Toxicology and Embryopharmacology in Berlin, and actively collaborated with each other for over 25 years. Both scientists are now retired and turned 80 this year (2009). This celebratory article reports some remarkable events of their long and prolific scientific careers.

Influence of litter size on the postnatal growth of rat pups: is there a rationale for litter-size standardization in toxicity studies?

The standardization of rodent litter sizes (or culling) in reproductive toxicity studies has become a common practice because it is believed that litter size affects pup postnatal growth and development. A claim has also been made that culling on postnatal day 4 or earlier reduces litter-size-induced variability in the pup growth thereby making statistical detection of toxic effects more sensitive. Although these statements remain controversial, culling has been either recommended or considered optional in current proposals for new OECD guidelines for reproductive/developmental toxicity testing. This study was undertaken to provide data useful for a discussion on the need for culling in reproductive toxicity testing. Along this line, we investigated the effects of rat litter size on maternal body weight gain during pregnancy and lactation as well as on pup growth, somatic maturation and survival to weaning (PND 21). Two-hundred-forty-one untreated pregnant rats (Wistar, Bor:spf, TOR) delivered litters with 1-13 pups, being 10 the most frequent (24%) litter size. Pup mortality was 5.4%, 3.0% and 0.4% in the first, second and third postnatal weeks, respectively. Maternal and pup body weight gains, and the day of appearance of milestones of somatic maturation (fur development, incisor eruption and eye opening) were examined in a subset of litters/mothers (N=180) in which all pups survived to PND 21. An inverse relationship between litter size and pup body weight was found on day of birth (PND 1) and thereafter until PND 21. Delays in the attainment of maturational milestones as litter size increases were also found. These observations indicated that the rate of growth and development of rat pups during suckling period is dependent on the litter size. The consequences of litter-size standardization in toxicity studies are discussed in the light of these findings. Alternative procedures to attenuating litter-size-induced variability in pup growth or its impact on toxicity data evaluation are presented as well.

Dose-response relationships of rat fetal skeleton variations: Relevance for risk assessment

In developmental toxicity studies, skeleton abnormalities found in fetuses at term are classified as variations or malformations. The relevance of skeleton variations for human risk assessment, however, is a controversial issue. This paper is a contribution to the discussion on the interpretation of fetal skeleton variations in the context of risk assessment. Dose-response relationships of skeleton variations and malformations induced by three antineoplastic drugs (FUDR: 5-fluoro-2'-deoxyuridine, HU: hydroxyurea and 6-MPr: 6-mercaptopurine-riboside) were evaluated. FUDR (0, 3, 14, 25, 35, 45, 55 and 65mg/kg body wt sc) and HU (0, 250, 300, 350, 400, 450, 500 and 550mg/kg body wt ip) were administered to rats on gestation day 11 (GD 11) while 6-MPr (0, 3, 7, 10 and 14mg/kg body wt sc) was given on GD 11, or on GD 12. Caesarean sections were performed on GD 21 and all fetuses were cleared and stained with alizarin red S for skeleton examination. Drugs given on GD 11 increased the incidence of thoracic and lumbar vertebra (dumbbell-shaped and bipartite ossification center (o.c.) and sternum (misaligned sternebrae) variations in a dose-dependent manner. Occurrence of zygomatic bone fused with maxilla (a variation in our rats) was also increased by HU and 6-MPr (GD 11) but it was not altered by FUDR. Spontaneous occurrence of wavy ribs was reduced by all treatments. Malformations such as cleft palate, tympanic bone absent and tibia absent were also increased in a dose-dependent manner by the three compounds. No observed effect levels (NOEL) for variations, irrespective of the compound administered, were generally lower than NOELs for malformations. In the discussion, we supported the view that any dose-related increase in the incidence of variations should be taken into account for determination of NOELs in routine studies. Increased occurrences of skeleton variations in term fetuses are also to be considered in risk assessment, unless experimental evidence exists that a particular change has no detrimental effect on the animal survival or health after birth or that it does not occur in humans.

Why public health agencies cannot depend on good laboratory practices as a criterion for selecting data: the case of bisphenol A

BACKGROUND

In their safety evaluations of bisphenol A (BPA), the U.S. Food and Drug Administration (FDA) and a counterpart in Europe, the European Food Safety Authority (EFSA), have given special prominence to two industry-funded studies that adhered to standards defined by Good Laboratory Practices (GLP). These same agencies have given much less weight in risk assessments to a large number of independently replicated non-GLP studies conducted with government funding by the leading experts in various fields of science from around the world.

OBJECTIVES

We reviewed differences between industry-funded GLP studies of BPA conducted by commercial laboratories for regulatory purposes and non-GLP studies conducted in academic and government laboratories to identify hazards and molecular mechanisms mediating adverse effects. We examined the methods and results in the GLP studies that were pivotal in the draft decision of the U.S. FDA declaring BPA safe in relation to findings from studies that were competitive for U.S. National Institutes of Health (NIH) funding, peer-reviewed for publication in leading journals, subject to independent replication, but rejected by the U.S. FDA for regulatory purposes.

DISCUSSION

Although the U.S. FDA and EFSA have deemed two industry-funded GLP studies of BPA to be superior to hundreds of studies funded by the U.S. NIH and NIH counterparts in other countries, the GLP studies on which the agencies based their decisions have serious conceptual and methodologic flaws. In addition, the U.S. FDA and EFSA have mistakenly assumed that GLP yields valid and reliable scientific findings (i.e., "good science"). Their rationale for favoring GLP studies over hundreds of publically funded studies ignores the central factor in determining the reliability and validity of scientific findings, namely, independent replication, and use of the most appropriate and sensitive state-of-the-art assays, neither of which is an expectation of industry-funded GLP research.

CONCLUSIONS

Public health decisions should be based on studies using appropriate protocols with appropriate controls and the most sensitive assays, not GLP. Relevant NIH-funded research using state-of-the-art techniques should play a prominent role in safety evaluations of chemicals.

Epoxiconazole causes changes in testicular histology and sperm production in the Japanese quail (Coturnix coturnix japonica)

The fungicide epoxiconazole (Epox), a triazole, belongs to the group of azole compounds that are extensively used as fungicides in various fruit crops. The frequent use of agricultural lands for wintering by migrating birds can be the source of their increased dietary intake of agricultural pesticides. We investigated whether exposure to Epox causes effects on avian fertility and reproduction, using the Japanese quail (Coturnix coturnix japonica) as a model species for the assessment of reproductive effects of pesticides in wild birds. Epox was administered to adult Japanese quail for three weeks at dietary levels of 10, 50, and 500 ppm, and possible effects on reproduction were investigated. Epox administration resulted in a significantly decreased number of spermatids in the 50- and 500-ppm dose groups. Histopathology showed a reduced number of testicular canaliculi with visible germ cells and a reduction in spermatid number. However, testis weight was not affected up to the highest dose level. No impact was observed on hormone levels, fertility, and reproductive outcome, as laying rate and percentage of fertile eggs were not altered. Likewise, treatment had no influence on the egg or chick parameters evaluated. A time- and dose-related transfer of Epox into the eggs was determined in all treatment groups. We conclude that dietary treatment of Japanese quail with 50 and 500 ppm of the triazole fungicide Epox resulted in a clear impact on the testis. The evaluation of the additional endpoints spermatid count and testicular histology have proven useful and are recommended for future studies on avian reproduction.

In utero and lactational exposures to low doses of polybrominated diphenyl ether-47 alter the reproductive system and thyroid gland of female rat offspring

BACKGROUND

Polybrominated diphenyl ethers (PBDEs) are capable of disrupting thyroid hormone homeostasis. PBDE-47 (2,2',4,4'-tetrabromodiphenyl ether) is one of the most abundant congeners found in human breast adipose tissue and maternal milk samples.

OBJECTIVES

We evaluated the effects of developmental exposure to low doses of PBDE-47 on the female reproductive system.

METHODS

Pregnant Wistar rats were administered vehicle (peanut oil) or PBDE-47 [140 or 700 microg/kg body weight (bw)] on gestation day (GD) 6, or 5 mg 6-n-propyl-2-thiouracil (PTU)/L in the drinking water from GD7 through postnatal day (PND) 21.

RESULTS

In female offspring sacrificed on PND38, there was a significant decrease in ovarian weight after exposure to PTU or 140 microg/kg PBDE-47. Alterations in folliculogenesis were apparent: we observed a decrease in tertiary follicles and serum estradiol concentrations in the offspring exposed to either PTU or 700 microg/kg PBDE-47. PTU exposure also resulted in a decrease in primordial follicles. On PND100, persistent effects on the thyroid glands included histologic and morphometric changes after exposure to either PTU or PBDE-47. No relevant changes in reproductive indices were observed after mating the exposed F1 females with nontreated males.

CONCLUSIONS

Administration of PBDE-47 at doses relevant to human exposure led to changes in the rat female reproductive system and thyroid gland.

Effects of in utero and lactational exposure to triphenyltin chloride on pregnancy outcome and postnatal development in rat offspring

The organotin compound (OTC) triphenyltin (TPT) is used extensively as a herbicide, pesticide and fungicide in agriculture as well as, together with tributyltin (TBT), in marine antifouling paints. We studied the effects of in utero exposure to 2 or 6 mg triphenyltinchloride (TPTCl)/kgb.w. on pregnancy outcome and postnatal development in rat offspring. Gravid Wistar rats were treated per gavage from gestational day 6 until the end of lactation. In the 6 mg TPTCl dose group gestational mortality in dams as well as an increased incidence of anticipated and delayed parturition was observed. Furthermore, treatment resulted in a significant increase in perinatal mortality, a decrease in lactational body weight gain as well as in delayed physical maturation of offspring. Similarily, exposure to 2mg TPTCl/kgb.w. resulted in a significant increase in perinatal mortality and in delayed eye opening. Lactational body weight gain and other landmarks of physical maturation were unaffected in the low dose group. We conclude, that in utero exposure to TPTCl at the described dose levels severely affected pregnancy outcome and perinatal survival of offspring. These results were unexpected, as in two earlier studies with pubertal rats TPTCl at the same dose levels no signs of general toxicity were observed.

A dose–response study following in utero and lactational exposure to di-(2-ethylhexyl) phthalate (DEHP): Reproductive effects on adult female offspring rats

Di(2-ethylhexyl) phthalate (DEHP) is used in numerous consumer products, mainly imparting flexibility and durability to polyvinyl chloride (PVC) based plastics. It is a known reproductive and developmental toxicant in male rodents. However, data regarding effects of DEHP on female reproductive health are particularly sparse. We performed an extensive dose-response study following developmental exposure to DEHP and evaluated the effects on adult female reproductive function. Two wide ranges of doses, low and high, were tested. Female Wistar rats were treated daily with DEHP and peanut oil (vehicle control) by gavage from gestation day 6 to lactation day 21. The low doses were: 0.015, 0.045, 0.135, 0.405 and 1.215mgDEHP/kg/bw/day and the high doses were: 5, 15, 45, 135 and 405mg DEHP/kg/bw/day. At the doses tested, no effects on organ (liver, kidney, spleen, thymus, thyroid, ovary and uterus) or body weights were detected. Female offspring presented a normal pattern of estrous cyclicity with no hormonal alterations (serum estradiol and progesterone). A statistically significant increase in tertiary atretic follicles was observed at the highest dose (405mgDEHP/kg/day). Morphometric analysis indicated that uterus and vagina luminal epithelial cell height were unaffected by treatment. An increase in the number of ovarian atretic tertiary follicles was the only effect observed in adult female offspring exposed in utero and during lactation to DEHP.

A dose response study following in utero and lactational exposure to di-(2-ethylhexyl) phthalate (DEHP): Reproductive effects on adult male offspring rats

The reproductive effects of in utero and lactational exposure to di-(2-ethylhexyl) phthalate (DEHP) in adult male offspring rats were investigated. The selected endpoints included reproductive organ weights, testicular function, hormonal status, sexual behaviour and fertility. Two wide ranges of doses, low and high, were tested. Female Wistar rats were treated daily with DEHP and peanut oil (vehicle control) by gavage from gestation day 6 to lactation day 21. The low-doses were 0.015, 0.045, 0.135, 0.405 and 1.215 mg DEHP/kg body weight (bw)/day, and the high-doses were 5, 15, 45, 135 and 405 mg DEHP/kg bw/day. A reduction in daily sperm production of 19-25% in relation to control was observed in animals exposed to 15, 45, 135 and 405 mg/kg/day. Quantitation of specific cell types shows that the observed effects in daily sperm production are not related to changes in the number of Sertoli cells or their capability to support early stages spermatocytes. A low incidence of cryptorchidism was observed in DEHP exposed groups with a lowest observed adverse effect level of 5mg/kg/day. Serum testosterone concentration was similar to control at most doses but was significantly increased at 0.045, 0.405 and 405 mg DEHP/kg/day. In spite of this effect, the weight of seminal vesicle with coagulating glands was significantly reduced at 405 mg/kg/day. Testis, epididymis and prostate weights were similar among groups. Fertility and sexual behaviour were not affected by DEHP treatment at any dose. Overall, our results show that in utero and lactational DEHP exposure reduces daily sperm production and has the potential to induce reproductive tract abnormalities (of which cryptorchidism seems to be the most sensitive in our rat strain) in male offspring rats. The lowest observed adverse effect levels (LOAELs) for these effects were 15 and 5 mg/kg/day, respectively. Therefore, the no observed adverse effect level (NOAEL) for this study can be set at 1.215 mg/kg/day.

A dose-response study following in utero and lactational exposure to di-(2-ethylhexyl)-phthalate (DEHP): non-monotonic dose-response and low dose effects on rat brain aromatase activity

Di-(2-ethylhexyl)-phthalate (DEHP) is a commonly used plasticizer which can act as an endocrine disruptor. It has been suggested that in addition to its antiandrogenic effects, DEHP may interfere with estrogen metabolism through suppression of aromatase enzyme activity. This enzyme catalyzes the conversion of testosterone to estradiol and plays a critical role in brain sexual differentiation. We investigated the effects of two wide ranges of DEHP doses on brain aromatase activity of male and female rat offspring. Wistar rat dams were treated daily with DEHP and peanut oil (control) by gavage from gestation day 6 to lactation day 21 at doses of 0.015, 0.045, 0.135, 0.405 and 1.215mgDEHP/kgbodyweight(bw)/day (low doses) and at 5, 15, 45, 135 and 405mgDEHP/kgbw/day (high doses). Aromatase activity was determined in hypothalamic/preoptic area (HPOA) brain sections from male and female pups on postnatal days (PNDs) 1 and 22. In males on PND 1, aromatase activity was inhibited at low doses and increased at high doses resulting in a non-monotonic dose-response profile which resembled a J-shaped curve. Inhibition was statistically significant at 0.135 and 0.405mgDEHP/kg/day, while increased activity was observed at 15, 45 and 405mg/kg/day. In contrast to findings on PND 1, aromatase activity at weaning (PND 22) was more affected in females than in males. An increase in aromatase activity was observed at only one dose in males (0.405mg/kg/day) while an increase in activity was observed at all doses in the females except for 0.045 and 5mgDEHP/kg/day. Overall, these results indicate that males and females respond differently to DEHP not only in regard to the age at which effects are manifested, but also in the shape of the dose-response curve. To our knowledge, this is the first study to report biological effects of DEHP at doses that overlap with the estimated exposure of the general human population.

A dose-response study following in utero and lactational exposure to di-(2-ethylhexyl) phthalate (DEHP): effects on androgenic status, developmental landmarks and testicular histology in male offspring rats

An extensive dose-response study following in utero and lactational exposure to di-(2-ethylhexyl) phthalate (DEHP) was conducted. A wide range of low and high DEHP doses were tested. Reproductive effects were evaluated on male offspring rats. Female Wistar rats were treated daily with DEHP and peanut oil by gavage from gestation day 6 to lactation day 21 at doses of 0.015, 0.045, 0.135, 0.405 and 1.215 mg DEHP/kg body weight (bw)/day (low doses) and at 5, 15, 45, 135 and 405 mg DEHP/kg bw/day (high doses). Nipple retention and reduced anogenital distance, both sensitive markers of anti-androgenic effects during development, were only seen in males exposed to the highest dose (405 mg/kg/day). Delayed preputial separation was observed in animals exposed to 15 mg DEHP/kg/day and higher doses. Histopathological examination of the testis on postnatal days (PNDs) 1 and 22 revealed changes at 135 and 405 mg DEHP/kg/day. The most prominent finding on PND 1 was the presence of bi- and multinucleated gonocytes. On PND 22 signs of reduced germ cell differentiation in seminiferous tubules of exposed animals were observed. Testis weight on PND 22 was significantly increased at 5, 15, 45 and 135 mg/kg/day, an effect that qualitatively differs from exposure to higher doses. The current results show that DEHP acts as an anti-androgen at a high dose exposure (405 mg/kg/day). However, these results also indicate that other subtle developmental effects occur at lower DEHP doses.

Effects of peripubertal exposure to triphenyltin on female sexual development of the rat

Triphenyltin (TPT) belongs to the group of organotin compounds which have been shown to affect reproduction in mammals. It is used as a fungicide and antifouling agent and the main source of human exposure is via food. We studied the effects of 2 or 6 mg TPT/kg bw on female sexual development using a modification of the Rodent 20-Day Thyroid/Pubertal Female Assay. Moreover, the effect of TPT before the onset of puberty was investigated. Beginning at postnatal day (PND) 23 female Wistar rats were treated per gavage until either PND 33 or the first estrus after PND 53. A delay in the completion of vaginal opening (VO) was observed in the 6 mg TPT group, while the 2mg TPT group showed advanced VO. Significantly increased ovarian weights were observed in both treatment groups. Steroid hormone levels and ovarian aromatase activity were affected after exposure to 6 mg TPT/kg bw, while treatment with 2mg TPT/kg bw resulted in minor changes of these endpoints. We conclude that peripubertal exposure to 6 mg TPT/kg bw, and to a lesser extent to 2mg TPT/kg bw, affects female sexual development.

Effects of fentin hydroxide on reproduction of the Japanese quail (Coturnix coturnix japonica)

In a one-generation reproductive study, the fungicidal compound triphenyltin hydroxide (fentin) was administered to adult Japanese quail for 6 weeks at dietary levels of 3 and 30 ppm. Reproduction was significantly impaired in the high-dose group. The principal adverse finding was a marked increase in embryonic mortality, resulting in a lower hatch rate. Furthermore, a reduction in egg production was observed with ongoing duration of treatment. Most of the other reproduction-related parameters were not affected. The in ovo losses are assumed to result from a direct toxic effect of the test substance on chick embryos. At the low dietary level, reproduction was not altered. In contrast to the obvious reproductive toxicity, there was only limited evidence of adverse treatment-related findings in the adult birds. However, because such minor effects as an increase in mean liver weight, which was accompanied by macroscopic liver findings and a decrease in T4 serum concentration, were still seen at 3 ppm, a no-observed-effect level could not be established.

A Dose-Response Study Following In Utero and Lactational Exposure to Di(2-ethylhexyl)phthalate: Effects on Female Rat Reproductive Development

Phthalates, a class of chemicals used as plasticizers, are economically important due to several industrial applications. Di(2-ethylhexyl)phthalate (DEHP) is the most commonly used phthalate plasticizer, and it has been described as a potent antiandrogen in males. We performed an extensive dose-response study following developmental exposure to DEHP and evaluated the effects on female reproductive development. Two wide ranges of doses that included dose levels relevant for human exposure as well as high doses typically used in toxicological studies were tested. Female Wistar rats were treated daily with DEHP and peanut oil (vehicle control) by gavage from gestation day 6 to lactation day 22. The low doses were 0.015, 0.045, 0.135, 0.405, and 1.215 mg DEHP/kg body weight (bw)/day, and the high doses were 5, 15, 45, 135, and 405 mg DEHP/kg bw/day. At the dose levels tested, no signs of maternal toxicity were observed. A significant delay in the age at vaginal opening (approximately 2 days) at 15 mg DEHP/kg bw/day and above, as well as a trend for a delay in the age at first estrus at 135 and 405 mg DEHP/kg bw/day (approximately 2 days), was observed. Liver enlargement (characteristic of phthalate exposure in rats) was limited to the 135- and 405-mg DEHP/kg bw/day doses. Anogenital distance and nipple development were unaffected. Based on the results of delayed pubertal onset, the no observed adverse effect level for female reproductive development may be set at 5 mg DEHP/kg bw/day.

Effects of methyltestosterone on reproduction in the Japanese quail (Coturnix coturnix japonica)

Although the hormone-mediated effects of the synthetic androgenic hormone methyltestosterone (MT) are well characterized in mammals, little is known about endocrine and other toxic effects on reproduction in birds. In a one-generation study, MT was administered to adult Japanese quail (12 pairs per group) at dietary dose levels of 0, 10, 50, and 110 ppm for a period of 3 weeks. Reproductive performance was severely affected in the groups receiving 50 and 110 ppm MT. In females, the egg-laying rate was reduced not only related to the dose administered but also to the duration of treatment. The administration of 110 ppm, and to a lesser extent, of 50 ppm MT resulted in an immediate and dramatic decrease in the total number of eggs laid, which complicated reliable assessment of other reproduction-related parameters. In males, the findings suggested inhibition of spermatogenesis at dose levels of 50 ppm and above, resulting in a subsequent reduction in male fertility.

Ultrastructural changes observed in rat ovaries following in utero and lactational exposure to low doses of a polybrominated flame retardant

Polybrominated diphenyl ethers (PBDEs), used as flame retardants in textiles, plastics and electrical appliances, have been shown to interfere with thyroid homeostasis. We evaluated the effects of environmentally relevant concentrations (low doses) of 2,2',4, 4',5-pentabromodiphenyl ether (PBDE-99) on the female reproductive system. A single dose of either 60 microg or 300 microg PBDE-99/kg body weight (BW) was administered on gestation day 6 to gravid Wistar rats. A reference control was treated with 6-n-propyl-2-thiouracil (PTU) on gestation days 7-21. Ultrastructural changes compatible with altered mitochondrial morphology were observed in the ovaries of the F1 offspring. No statistically significant changes in ovarian follicle counts were observed. Mating of the F1 females with untreated males revealed resorption rates in the PBDE groups greater than the limits considered normal for our controls. External and skeletal anomalies were detected in offspring (F2) from two different dams (F1) with early developmental exposure to 300 microg PBDE-99/kg BW. Exposure to PBDE-99 resulted in female reproductive tract changes in the F1 generation which were apparent at adulthood.

Relationships between fetal body weight of Wistar rats at term and the extent of skeletal ossification

We investigated the relationship between fetal body weight at term (pregnancy day 21) and the extent of ossification of sternum, metacarpus, metatarsus, phalanges (proximal, medial and distal) of fore- and hindlimbs and cervical and coccygeal vertebrae in Wistar rats. The relationships between fetal body weight and sex, intrauterine position, uterine horn, horn size, and litter size were determined using historical control data (7594 fetuses; 769 litters) of untreated rats. Relationships between body weight and degree of ossification were examined in a subset of 1484 historical control fetuses (154 litters) which were subsequently cleared and stained with alizarin red S. Fetal weight was independent of horn size, uterine horn side (left or right) or intrauterine position. Males were heavier than females and fetal weight decreased with increasing litter size. Evaluation of the skeleton showed that ossification of sternum, metacarpus and metatarsus was extensively complete and independent of fetal weight on pregnancy day 21. In contrast, the extent of ossification of fore- and hindlimb phalanges and of cervical and sacrococcygeal vertebrae was dependent on fetal body weight. The strongest correlation between body weight and degree of ossification was found for hindlimb, medial and proximal phalanges. Our data therefore suggest that, in full-term rat fetuses (day 21), reduced ossification of sternum, metacarpus and metatarsus results from a localized impairment of bone calcification (i.e., a malformation or variation) rather than from general growth retardation and that ossification of hindlimb (medial and proximal) phalanges is a good indicator of treatment-induced fetal growth retardation.

Developmental exposure to low dose PBDE 99: effects on male fertility and neurobehavior in rat offspring

In utero exposure to a single low dose of 2,2 ,4,4 ,5-pentabromodiphenyl ether (PBDE-99) disrupts neurobehavioral development and causes permanent effects on the rat male reproductive system apparent in adulthood. PBDEs, a class of flame retardants, are widely used in every sector of modern life to prevent fire. They are persistent in the environment, and increasing levels of PBDEs have been found in biota and human breast milk. In the present study we assessed the effects of developmental exposure to one of the most persistent PBDE congeners (PBDE-99) on juvenile basal motor activity levels and adult male reproductive health. Wistar rat dams were treated by gavage on gestation day 6 with a single low dose of 60 or 300 microg PBDE-99/kg body weight (bw). In offspring, basal locomotor activity was evaluated on postnatal days 36 and 71, and reproductive performance was assessed in males at adulthood. The exposure to low-dose PBDE-99 during development caused hyperactivity in the offspring at both time points and permanently impaired spermatogenesis by the means of reduced sperm and spermatid counts. The doses used in this study (60 and 300 microg/kg bw) are relevant to human exposure levels, being approximately 6 and 29 times, respectively, higher than the highest level reported in human breast adipose tissue. This is the lowest dose of PBDE reported to date to have an in vivo toxic effect in rodents and supports the premise that low-dose studies should be encouraged for hazard identification of persistent environmental pollutants.

Effects of organotin compounds on pubertal male rats

Tributyltin (TBT) and triphenyltin (TPT) induce effects in male and female reproductive organs of rodents. They also cause tumors in these organs and it is theorized that they result from endocrine disruption. We studied the effects of 40 mg methyltestosterone (MTT), 0.5 or 15 mg TBT and 2, 6 or 12 mg TPT/kg bw on the male sexual development using a modification of the Rodent 20-Day Thyroid/Pubertal Male Assay. Male Wistar rats were treated per gavage for 30 days beginning at 23 days of age. A delay in the completion of preputial separation was observed after administration of MTT and 15 mg/kg TBT. Changes in weights of one or more reproductive organs were observed in all treatment groups. Testosterone concentration was decreased in the MTT, the 15 mg TBT as well as in the 6 and 12 mg TPT groups. A decrease in luteinizing hormone (LH) concentration was observed in the MTT and 15 mg TBT groups while an increase was seen after exposure to 6 mg TPT/kg bw. We conclude that peripubertal exposure to 15 mg TBT and 6 mg TPT/kg bw clearly affected male sexual development.

In utero exposure to low-dose 2,3?,4,4?,5-pentachlorobiphenyl (PCB 118) impairs male fertility and alters neurobehavior in rat offspring

Neurobehavior (motor activity and developmental reflexes) and male reproductive parameters were evaluated in rat offspring after in utero exposure to a low dose of PCB 118 comparable to human exposure levels. Sprague-Dawley dams were treated on gestation day 6 by gavage with a single dose of 375 microg PCB 118/kg body weight or peanut oil (control). The dose was calculated to be approximately 100-fold higher than that found in human breast milk. Postnatal reflexes, motor activity and male reproductive performance were evaluated in rat offspring after exposure to PCB 118. Evaluation of locomotor activity for five consecutive days during puberty (PND 70-74) revealed hyperactivity in offspring from PCB 118-exposed dams. In adult males (PND 170), clear effects on reproductive organs were observed in PCB-exposed animals which had smaller testes, epididymides and seminal vesicles (absolute and relative weights). Decreases in sperm and spermatid numbers and impairment of daily sperm production were also observed. Our results clearly demonstrate that low-dose exposure to PCB 118 alters neurobehavior and impairs adult male fertility in offspring. This is in contrast to the reported increases in sperm production and testis weight in rat after high dose PCB exposures. PCBs appear to possess variable dose-related effects and therefore low-dose studies are important to obtain a complete picture for human risk assessment.

Developmental effects of prenatal exposure to bisphenol a on the uterus of rat offspring

Exposure to estrogenic compounds during critical periods of fetal development could result in adverse effects on the development of reproductive organs that are not apparent until later in life. Bisphenol A (BPA), which is employed in the manufacture of a wide range of consumer products, is a prime candidate for endocrine disruption. We examined BPA to address the question of whether in utero exposure affects the uterus of the offspring and studied the expression and distribution of the estrogen receptors alpha (ERalpha) and beta (ERbeta), because estrogens influence the development, growth, and function of the uterus through both receptors. Gravid Sprague-Dawley dams were administered by gavage either 0.1 or 50 mg/kg per day BPA or 0.2 mg/kg per day 17alpha-ethinyl estradiol (EE2) as reference dose on gestation days 6 through 21. Female offspring were killed in estrus. Uterine morphologic changes as well as ERalpha and ERbeta distribution and expression were measured by immunohistochemistry and Western blot analysis. Striking morphologic changes were observed in the uterine epithelium of postpubertal offspring during estrus of the in utero BPA-treated animals (the thickness of the total epithelium was significantly reduced). ERalpha expression was increased in the 50-mg BPA and EE2-treated group. In contrast, we observed significantly decreased ERbeta expression in all BPA- and EE2-treated animals when compared with the control. In summary, these results clearly indicate that in utero exposure of rats to BPA promotes uterine disruption in offspring. We hypothesize that the uterine disruption could possibly be provoked by a dysregulation of ERalpha and ERbeta.

Effects of vinclozolin on spermatogenesis and reproductive success in the Japanese quail (Coturnix coturnix japonica)

In a one-generation reproduction study, the major agricultural fungicide vinclozolin was administered to adult Japanese quail for a period of 6 weeks at dietary levels of 125 and 500 ppm. Fertility and reproductive performance were not affected up to the highest concentration, although the examination of additional endpoints in the drakes (spermatid count, histology of the testis) provided some evidence of an inhibition of spermatogenesis at both dietary concentrations. Likewise, there were no indications of systemic toxicity in the adult birds. Plasma hormone concentrations (estradiol, testosterone, progesterone, T3, and T4) showed a large interindividual variance but treatment-related differences between the groups could not be established. There were no clear-cut indications of antiandrogenic effects in quail, although a limited transfer of the test substance into the eggs was proven.

Blood burden of di(2-ethylhexyl) phthalate and its primary metabolite mono(2-ethylhexyl) phthalate in pregnant and nonpregnant rats and marmosets

A comparison of the dose-dependent blood burden of di(2-ethylhexyl) phthalate (DEHP) and mono(2-ethylhexyl) phthalate (MEHP) in pregnant and nonpregnant rats and marmosets is presented. Sprague-Dawley rats and marmosets were treated orally with 30 or 500 mg DEHP/kg per day, nonpregnant animals on 7 (rats) and 29 (marmosets) consecutive days, pregnant animals on gestation days 14-19 (rats) and 96-124 (marmosets). In addition, rats received a single dose of 1000 mg DEHP/kg. Blood was collected up to 48 h after dosing. Concentrations of DEHP and MEHP in blood were determined by GC/MS. In rats, normalized areas under the concentration-time curves (AUCs) of DEHP were two orders of magnitude smaller than the normalized AUCs of the first metabolite MEHP. Metabolism of MEHP was saturable. Repeated DEHP treatment and pregnancy had only little influence on the normalized AUC of MEHP. In marmosets, most of MEHP concentration-time courses oscillated. Normalized AUCs of DEHP were at least one order of magnitude smaller than those of MEHP. In pregnant marmosets, normalized AUCs of MEHP were similar to those in nonpregnant animals with the exception that at 500 mg DEHP/kg per day, the normalized AUCs determined on gestation days 103, 117, and 124 were distinctly smaller. The maximum concentrations of MEHP in blood of marmosets were up to 7.5 times and the normalized AUCs up to 16 times lower than in rats receiving the same daily oral DEHP dose per kilogram of body weight. From this toxicokinetic comparison, DEHP can be expected to be several times less effective in the offspring of marmosets than in that of rats if the blood burden by MEHP in dams can be regarded as a dose surrogate for the MEHP burden in their fetuses.

Harmonization of rat fetal external and visceral terminology and classification Report of the Fourth Workshop on the Terminology in Developmental Toxicology, Berlin, 18–20 April 2002

This article is a report on the Fourth Berlin Workshop on Terminology in Developmental Toxicology, which was held in April 2002. The workshop is part of an international project in the field of harmonization of terminology in developmental toxicology supported by IPCS. The goal of the Harmonization Project is to ensure better chemical risk assessment. The aim of this Fourth Workshop was to discuss the results of a previously conducted survey on classification of external and visceral anomalies, which are listed in the international glossary, developed under the auspices of IFTS (1997 glossary). The discussions among experts from research institutions, regulatory agencies, and industries were mainly focussed on terms for which there was disagreement and/or uncertainties and the possible reasons. For the illustration of "gray-zone" anomalies, pictures were provided by the participants, which constituted the basis for detailed discussions. There was high agreement that most of the external anomalies (>66%) should be classified as malformations. The few external anomalies for which there was low agreement to classify as a malformation were discussed in detail. None of the external findings, which had in the survey a high agreement, were categorized as a variation.A high agreement regarding the classification of approximately one-third of visceral anomalies was achieved with 34 and 2% being described as malformation and variation, respectively. Most of the visceral findings had low agreement indices and there appeared to be several reasons for this. Thus, the response, 'Not known/not used in the laboratory' (N) was often given. A couple of reasons for difficulties in the classification of an anomaly were that it is only rarely seen upon fetal examination or tends to be species specific. Furthermore, the classification of some anomalies as malformation or variation will remain vague as the decision must be made on a case-by-case basis. Factors affecting the decision include: the availability of appropriate historical control data, description of the grading and severity, whether the anomaly occurs in isolation or whether there is a relationship with an abnormal process, and finally, if the change represents an irreversible one, affecting human and/or animal health. It was concluded that a severity grading, supported by pictures of the anomaly, would be especially helpful to classify certain changes as malformation or as variation. Several of the soft tissue changes were considered likely to be the consequence of functional disorders and thus not strictly developmental anomalies. The possibility to describe a finding as 'Not Malformation' (Unclassified) was agreed upon. As a general conclusion it was emphasized that the observation of a permanent structural change should be considered to be a warning of possible consequences to humans, even when there is no apparent adverse effect on health and survival in adult animals of the species under investigation. Therefore, research is needed to further investigate postnatal consequences. Future collaboration in the field of reproductive and developmental toxicology should aim to further develop and implement a harmonized approach to the interpretation of study data. Therefore, this terminology work will continue in close cooperation with the IPCS Harmonization Project. A Steering Group should be established to facilitate the implementation of harmonized terminology into daily scientific work and its regulatory application.

Effect of low dose mono-ortho 2,3',4,4',5 pentachlorobiphenyl on thyroid hormone status and EROD activity in rat offspring: consequences for risk assessment

Toxic equivalency factor (TEF) has been proposed to estimate the risk of polychlorinated biphenyl (PCB) congeners. However, ortho chlorine substitution in the two phenyl rings gives each PCB its own pattern of toxicity which is different from the mechanism of action of 2,3,7,8-tetrachlorodibenzo-p-dioxin. The present study evaluated the effect of prenatal and postnatal exposure to a low dose of the mono-ortho pentachlorobiphenyl PCB 118 on thyroid hormone concentrations and EROD activity in rats. Moreover, the tissue distribution of PCB 118 following one oral dose was evaluated. Sprague-Dawley rats were treated by gavage on GD 6 with 375 microg of PCB 118/kg b.w. Decreases in thyroxine and TSH levels were observed in dams at the end of lactation. Perinatal exposure to a low dose of PCB 118 permanently disrupted the hypothalamo-pituitary-thyroid (HPT) axis leading to a significant increase in thyroxine levels in offspring, as a 'thyroid resistance syndrome'. It is noteworthy that no changes in hepatic EROD activity were detected in dams at the end of lactation, even in the presence of high amounts of PCB in liver. Based on hepatic EROD activity (as a biomarker for aryl hydrocarbon receptor (AhR) induction), the mechanism of thyroid homeostasis disruption seems to be AhR-independent. Additionally, the 'thyroid resistance syndrome' observed in our study indicates the need for further detailed investigations on the HPT axis. We conclude that not only TEF, but also AhR-independent responses should be taken into account for risk assessment of mono-ortho PCB congeners.