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25. Scientific and Technological Support on in vivo assays for the Agency's Endocrine Disrupter Screening and Testing program. LE Gray, J Ostby, J Furr, R Cooper, T Stoker, S Laws, J Goldman, R Tyl. . Uterotropic Assay Protocol Required endpoints: Growth Uterine Wet and Dry Weights

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25.Scientific and Technological Support on in vivo assays for the Agency's Endocrine Disrupter Screening and Testing program.

LE Gray, J Ostby, J Furr, R Cooper, T Stoker, S Laws, J Goldman, R Tyl.

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Uterotropic Assay Protocol

Required endpoints:


Uterine Wet and Dry Weights

Ovarian Weights (Immature Females)

Vaginal cytology (Adult Ovariectomized Females)

Optional measures

Uterine histology

Liver, kidney, pituitary and adrenal weights

Receptive Behavior - Lordosis quotient

Detects exogenous estrogenic compounds.

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OECD Hershberger Assay Protocol

Required endpoints:

Glans Penis Weights

Ventral Prostate Weights

Seminal Vesicle/Coagulating Gland Weights with and without fluid

Levator Ani/Bulbocavernosus Muscle Weights

Cowper’s Glands Weights

Liver Weight

Adrenals Weight

Kidneys Weight

Optional measures:

Cardiac Blood for Serum Hormone Analysis

Liver, kidney and adrenal histology

Detects exogenous (anti)androgens which inhibit or stimulate growth of androgen-dependent tissues (Testosterone Propionate stimulates growth of androgen-dependent tissues after the regression of these tissues following castration).

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Immature (21 - 43 Days of Age) Intact Female Rat Protocol to

Evaluate Pubertal Development and Thyroid Function

Required endpoints: Growth

Age and weight at vaginal opening (VO)

Vaginal cytology

Serum thyroxine (T4) and thyroid-stimulating hormone (TSH)

Ovarian and uterine weights and histology

Liver, kidney, pituitary and adrenal weights

Detects exogenous antithyroid or estrogenic compounds which alter pubertal development or thyroid function.

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Immature (23 - 54 Days of Age) Intact Male Rat Protocol to Evaluate Pubertal Development and Thyroid Function

Required Endpoints


Age and body weight at preputial separation

Serum thyroxin (T4) and thyroid-stimulating hormone (TSH)

Thyroid histology

Seminal vesicle plus coagulating gland weight (with/without fluid)

Ventral prostate weight

Levator ani/bulbocavernosus muscle weight

Testis and epididymal weights and histology

Optional Measures

Serum testosterone, estradiol, LH, prolactin and tri-iodothyronine (T3)

Liver, kidney, adrenal and pituitary weights and histology

ex vivo testis and pituitary hormone production

Hypothalamic neurotransmitter levels

Detects exogenous antithyroid, estrogenic, androgenic or antiandrogenic compounds and EDCs which alter pubertal development via follicle stimulating hormone (FSH), luteinizing hormone (LH), prolactin, growth hormone (GH) or hypothalamic function.

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Transgenerational Protocol Evaluate Pubertal Development and Thyroid Function

Required endpoints:

Maternal Growth

F1 Pup Growth and Viability (Count and Weigh Litter by Sex Weekly Until Weaning)

Pups at Birth – Weigh Litters by Sex to Determine Litter Size, Average Bodyweight by Sex and Sex Ratio for Each Litter

Anogenital Distance and Bodyweight (All F1 Pups - PND 2)

Areolas and Position/Male and Weigh Litters by Sex (PND 13) Wean – Sacrifice Dams and Count Implantation Scars, House F1 Offspring in Unisexual Littermate Groups of 2 – 3 Pups/Cage

Puberty - Start Checking Females (PND 27) for Vaginal Opening and Record Age and Bodyweight at VO and Start Checking Males (PND 37)for Preputial Separation and Record Age and Bodyweight at PPS

Male Necropsy:

Serum for Hormone Analysis

Shave and Check for Nipples and External Malformations

Glans Penis Weight

Ventral Prostate Weight

Seminal Vesicles/Coagulating Glands (with/without fluid) Weight

Right and Left Testes Weights and Histology

Right and Left Epididymal Weights and Histology

Levator Ani/Bulbocavernosus Muscle Weight

Paired Cowper’s Glands Weight

Liver Weight

Adrenals Weight

Kidneys Weight

Note any Internal Malformations (Particularly Androgen-Dependent Tissues)

Optional Measures

Mating and/or Play Behavior

Sonication Resistant Testicular Sperm Head Counts

Cauda and Caput Epididymal Sperm Counts

Ventral Prostate, Seminal Vesicle/Coagulating Gland, Liver, Kidney, and Adrenal Histology

AR Immunohistochemistry (Androgen-Dependent Tissues such as Ventral Prostate)

Ex-vivo Testicular Testosterone Production (hCG stimulated and unstimulated)

Detects exogenous estrogenic and (anti)androgenic compounds which permanently alter reproductive development and can be used to establish low and no observed effects levels.

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Research Impact Evaluate Pubertal Development and Thyroid Function

EDC action can seriously alter reproductive development when administered during critical, sensitive life stages. In utero, perinatal and pubertal exposures to EDCs can produce severe effects on both male and female offspring, depending upon the mechanism of action. Some effects are not obvious until late in life or are latent and not expressed until after maturity or old age. The only protocols that can detect these types of effects are long-term transgenerational or multigenerational studies because they are the only protocols that 1) expose the animals during development and 2) evaluate the reproductive system in the offspring throughout life. Our studies typically dose the mother during gestation and lactation and observe the development of male and female rat offspring through maturity. The determination of the cellular and molecular mechanism of action of an EDC is critical to understanding its potential to affect other species, including humans. In order to elucidate mechanisms of action, we execute parallel in vitro or ex vivo studies with EDCs or their active metabolites. In addition, we are attempting to obtain data on fetal tissue levels of the active metabolites during the critical exposure period.

Over the last few years we have examined a variety of chemicals with different mechanisms of endocrine action. We have studied estrogens (methoxychlor, zearalenone, and chlordecone), inhibitors of steroidogenesis (ketoconazole, fenarimol (inhibits aromatase), germ cell toxicants (busulfan and benzidine-based diazo dyes), phthalate esters (inhibit fetal testosterone production) and fungicides that are AR antagonists. We are now beginning to study environmental chemicals with androgenic activity.

Over the last seven years, most of our work has been with environmental antiandrogens. In 1994 we published the first study that demonstrated that a pesticide altered male rat sexual differentiation by acting as an AR antagonist. This mechanism was confirmed using in vitro AR binding and transcriptional activation assays, and by examining AR-dependent ventral prostate gene expression (1997). In 1995 we were the first to report in Nature that the p,p’ DDE also was an AR antagonist. These studies have now been extended to several other original observations on pesticides like procymidone and linuron. Our work on linuron was the first to demonstrate that this herbicide induced reproductive tract malformations, and points to weaknesses in former and current Agency multigenerational test guidelines, as these malformations had been missed in several published developmental toxicology and multigenerational tests. In addition to AR antagonists, we, along with the laboratory of Dr P Foster at CIIT, have been studying the antiandrogenic effects of phthalate esters. We published the only report to date that demonstrates that diethyl hexyl phthalate (DEHP) inhibits masculinization of the male rat reproductive system by inhibiting fetal testosterone production. Currently, we are attempting to increase our ability to examine the cellular and molecular events associated with the effects of these chemicals on the fetal reproductive tract and testis. We also have collected tissues from some of these studies for chemical residue or mRNA analyses. For example, we have submitted fetal amniotic fluid and maternal urine samples from two phthalate ester studies to the Center for Disease Control (CDC) for determination of MEHP and MBP levels. We can then compare the dose to the fetus associated with adverse developmental effects in the rat and we can compare MEHP and MBP levels to those seen in humans.

In a risk assessment, the Agency considers many different exposure scenarios besides intrauterine development. For example, EDC administration during puberty can alter this developmental process. Estrogens accelerate pseudoprecocious puberty in the female, while antiandrogens delay puberty in the male rat. In this regard, our pubertal studies on vinclozolin (1999) were the first demonstration that an antiandrogenic pesticide could delay the onset of pubertal landmarks in the male rat. These data were used by EPA to restrict uses of this chemical that were likely to result in childhood exposures to vinclozolin at “levels of concern”. We also found that linuron, di-n-butyl phthalate, diethyl hexyl phthalate and p,p’ DDE delay the onset of puberty in the male rat.

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Products Evaluate Pubertal Development and Thyroid Function

Goldman, J.M., Laws, S.C., Balchak, S.K., Cooper, R.L., and Kavlock, R.J. Endocrine-disrupting chemicals: prepubertal exposures and effects on sexual maturation and thyroid activity in the female rat. A focus on the EDSTAC recommendations. Crit Rev Toxicol. 30:135-196, 2000.

Gray LE Jr, Ostby J, Sigmon R, Ferrell J, Rehnberg G, Linder R, Cooper R, Goldman J, Laskey J. The development of a protocol to assess reproductive effects of toxicants in the rat. Reprod Toxicol. 1988;2(3-4):281-7. Review.

Gray LE Jr, Ostby JS, Ferrell JM, Sigmon ER, Goldman JM. Methoxychlor induces estrogen-like alterations of behavior and the reproductive tract in the female rat and hamster: effects on sex behavior, running wheel activity, and uterine morphology. Toxicol Appl Pharmacol. 1988 Dec;96(3):525-40.

Gray LE Jr, Ostby J, Ferrell J, Rehnberg G, Linder R, Cooper R, Goldman J, Slott V, Laskey J. A dose-response analysis of methoxychlor-induced alterations of reproductive development and function in the rat. Fundam Appl Toxicol. 1989 Jan;12(1):92-108.

Gray LE Jr, Kelce WR, Wiese T, Tyl R, Gaido K, Cook J, Klinefelter G, Desaulniers D, Wilson E, Zacharewski T, et al. (33 authors). Endocrine Screening Methods Workshop Report: Detection of Estrogenic and Androgenic Hormonal and Antihormonal Activity for Chemicals that act via Receptor or Steroidogenic Enzyme Mechanisms. Reproductive Toxicology 11(4):719-750, 1997.

Gray LE Jr, Wolf C, Lambright C, Mann P, Price M, Cooper RL, Ostby. Administration of potentially antiandrogenic pesticides (procymidone, linuron, iprodione, chlozolinate, p,p'-DDE, and ketoconazole) and toxic substances (dibutyl- and diethylhexyl phthalate, PCB 169, and ethane dimethane sulphonate) during sexual differentiation produces diverse profiles of reproductive malformations in the male rat. J Toxicol Ind Health 15 (1-2):94-118, 1999.

Gray LE Jr, Ostby J, Cooper RL, Kelce WR. The estrogenic and antiandrogenic pesticide methoxychlor alters the reproductive tract and behavior without affecting pituitary size or LH and prolactin secretion in male rats.Toxicol Ind Health 15(1-2):37-47, 1999.

Gray LE Jr , Ostby J, Furr J, Wolf CJ, Lambright C, Parks L, Veeramachaneni DNR, Wilson V, Price M, Hotchkiss A, Orlando E, Guillette L. Effects of environmental antiandrogens on reproductive development in experimental animals. Human Reprod Update. 7(3):248-64. 2001.

Gray LE Jr, Lambright C, Parks L, Tyl R, Orlando E, Guillette L, Wolf C, Seely J, Chang TS, WilsonV, Hotchkiss A, Ostby J. (In press) Emerging issues related to endocrine disrupting chemicals and environmental androgens and antiandrogens. In: Handbook of Environmental Chemistry: Endocrine distuptors. (M Metzler Ed). 2001.

Monosson E, Kelce WR, Lambright C, Ostby J, Gray LE Jr. Peripubertal exposure to the antiandrogenic fungicide, vinclozolin, delays puberty, inhibits the development of androgen-dependent tissues, and alters androgen receptor function in the male rat. Toxicol Ind Health 15(1-2):65-79, 1999.

Stoker, TE, Parks, LG, Gray, LE, and Cooper, RL. Endocrine-disrupting chemicals: prepubertal exposures and effects on sexual maturation and thyroid function in the male rat. A focus on the EDSTAC recommendations. Endocrine Disrupter Screening and Testing Advisory Committee. Crit Rev Toxicol. 30:197-252, 2000.

Hertzberg VS, Lemasters GK, Hansen K, Zenick HM. Statistical issues in risk assessment of reproductive outcomes with chemical mixtures. Environ Health Perspect. 1991 Jan;90:171-5. Review.

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  • Future Directions Evaluate Pubertal Development and Thyroid Function


  • Hershberger Assay.

  • As the Lead Laboratory Ananalyze final Phase 1 OECD interlaboratory studies and draft report.

  • Design Phase 2 and present proposal to OECD VMG for approval.

  • Initiate Phase 2, analyze data and complete report and publish results after OECD approval.

  • Publish background document on this Assay.