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Phthalate diesters are chemicals to which humans are ubiquitously exposed. Exposure to certain phthalates during sexual differentiation causes reproductive tract malformations in male rats. In the fetal rat, exposure to the phthalates benzylbutyl phthalate (BBP), di(n)butyl phthalate (DBP), and diethylhexyl phthalate (DEHP) decreases testicular testosterone production and insulin-like 3 hormone mRNA levels. We characterized the dose-response effects of six individual phthalates (BBP, DBP, DEHP, diethyl phthalate [DEP], diisobutyl phthalate [DiBP], and dipentyl phthalate [DPP]) on gestation day (GD) 18 testicular testosterone production following exposure of Sprague-Dawley rats on GD 8–18. BBP, DBP, DEHP, and DiBP were equipotent (ED50 of 440 ± 16 mg/kg/day), DPP was about threefold more potent (ED50 = 130 mg/kg/day) and DEP had no effect on fetal testosterone production. We hypothesized that coadministration of these five antiandrogenic phthalates would reduce testosterone production in a dose-additive fashion because they act via a common mode of toxicity. In a second study, dams were dosed at 100, 80, 60, 40, 20, 10, 5, or 0% of the mixture. The top dose contained 1300 mg of total phthalates/kg/day including BBP, DBP, DEHP, DiBP (300 mg/kg/day per chemical), and DPP (100 mg DPP/kg/day). This mixture ratio was selected such that each phthalate would contribute equally to the reduction in testosterone. As hypothesized, testosterone production was reduced in a dose-additive manner. Several of the individual phthalates and the mixture also induced fetal mortality, due to pregnancy loss. These data demonstrate that individual phthalates with a similar mechanism of action can elicit cumulative, dose additive effects on fetal testosterone production and pregnancy when administered as a mixture. [ABSTRACT FROM AUTHOR]

In 1991, a group of expert scientists at a Wingspread work session on endocrine-disrupting chemicals (EDCs) concluded that “Many compounds introduced into the environment by human activity are capable of disrupting the endocrine system of animals, including fish, wildlife, and humans. Endocrine disruption can be profound because of the crucial role hormones play in controlling development.” Since that time, there have been numerous documented examples of adverse effects of EDCs in invertebrates, fish, wildlife, domestic animals, and humans. Hormonal systems can be disrupted by numerous different anthropogenic chemicals including antiandrogens, androgens, estrogens, AhR agonists, inhibitors of steroid hormone synthesis, antithyroid substances, and retinoid agonists. In addition, pathways and targets for endocrine disruption extend beyond the traditional estrogen/androgen/thyroid receptor–mediated reproductive and developmental systems. For example, scientists have expressed concern about the potential role of EDCs in increasing trends in early puberty in girls, obesity and type II diabetes in the United States and other populations. New concerns include complex endocrine alterations induced by mixtures of chemicals, an issue broadened due to the growing awareness that EDCs present in the environment include a variety of potent human and veterinary pharmaceutical products, personal care products, nutraceuticals and phytosterols. In this review we (1) address what have we learned about the effects of EDCs on fish, wildlife, and human health, (2) discuss representative animal studies on (anti)androgens, estrogens and 2,3,7,8-tetrachlorodibenzo-p-dioxin–like chemicals, and (3) evaluate regulatory proposals being considered for screening and testing these chemicals. [ABSTRACT FROM AUTHOR]

Many chemicals released into the environment are capable of disrupting normal sex steroid balance, including the oral contraceptive ethinyl estradiol (EE) and the plastic monomer bisphenol A (BPA). EE and BPA are reported to impair reproductive organ development in laboratory animals; however, effects of lower doses of these chemicals have been debated. The goal of the current study was to determine whether relatively low oral doses of EE or BPA would alter male reproductive morphology and associated hormone levels of Long Evans hooded rat. Dams were gavaged with corn oil vehicle, EE (0.05–50 μg/kg/day) or BPA (2, 20, and 200 μg/kg/day) during pregnancy through lactation from gestational day 7 to postnatal day (PND) 18. Anogenital distance was measured at PND2 and nipple retention was measured at PND14 in male pups. Male offspring were euthanized beginning at PND150, and sera and organs were collected for analyses. Adult body weight was significantly decreased in males exposed to 50 μg EE/kg/day. Developmental EE exposure reduced androgen-dependent tissue weights in a dose-dependent fashion; for example, seminal vesicle and paired testes weights were reduced with ≥ 5 μg EE/kg/day. Epididymal sperm counts were also significantly decreased with 50 μg EE/kg/day. In contrast, treatment with 2, 20, or 200 μg BPA/kg/day or EE at 0.05–1.5 μg/kg/day did not significantly affect any male endpoint in the current study. These results demonstrate that developmental exposure to oral micromolar doses of EE can permanently disrupt the reproductive tract of the male rat. [ABSTRACT FROM AUTHOR]

Exposure to plasticizers di(n-butyl) phthalate (DBP) and diethylhexyl phthalate (DEHP) during sexual differentiation causes male reproductive tract malformations in rats and rabbits. In the fetal male rat, these two phthalate esters decrease testosterone (T) production and insulin-like peptide 3 (insl3) gene expression, a hormone critical for gubernacular ligament development. We hypothesized that coadministered DBP and DEHP would act in a cumulative dose-additive fashion to induce reproductive malformations, inhibit fetal steroid hormone production, and suppress the expression of insl3 and genes responsible for steroid production. Pregnant Sprague Dawley rats were gavaged on gestation days (GD) 14–18 with vehicle control, 500 mg/kg DBP, 500 mg/kg DEHP, or a combination of DBP and DEHP (500 mg/kg each chemical; DBP + DEHP); the dose of each individual phthalate was one-half of the effective dose predicted to cause a 50% incidence of epididymal agenesis. In experiment one, adult male offspring were necropsied, and reproductive malformations and androgen-dependent organ weights were recorded. In experiment two, GD18 testes were incubated for T production and processed for gene expression by quantitative real-time PCR . The DBP + DEHP dose increased the incidence of many reproductive malformations by ≥ 50%, including epididymal agenesis, and reduced androgen-dependent organ weights in cumulative, dose-additive manner. Fetal T and expression of insl3 and cyp11a were cumulatively decreased by the DBP + DEHP dose. These data indicate that individual phthalates with a similar mechanism of action, but with different active metabolites (monobutyl phthalate versus monoethylhexyl phthalate), can elicit dose-additive effects when administered as a mixture. [ABSTRACT FROM AUTHOR]

The fungicide prochloraz (PCZ) induces malformations in androgen-dependent tissues in male rats when administered during sex differentiation. The sensitivity of fetal testicular steroidogenesis to PCZ was investigated to test the hypothesis that the reported morphological effects from maternal exposure were associated with reduced testosterone synthesis. Pregnant Sprague-Dawley rats were dosed by gavage with 0, 7.8, 15.6, 31.3, 62.5, and 125 mg PCZ/kg/day (n = 8) from gestational day (GD) 14 to 18. On GD 18, the effects of PCZ on fetal steroidogenesis were assessed by measuring hormone production from ex vivo fetal testes after a 3-h incubation. Lastly, PCZ levels in amniotic fluid and maternal serum were measured using liquid chromatography/mass spectroscopy and correlated to the inhibition of steroidogenesis. Fetal progesterone and 17α-hydroxyprogesterone production levels were increased significantly at every PCZ dose, whereas testosterone levels were significantly decreased only at the two high doses. These results suggest that PCZ inhibits the conversion of progesterone to testosterone through the inhibition of CYP17. To test this hypothesis, PCZ effects on CYP17 gene expression and in vitro CYP17 hydroxylase activity were evaluated. PCZ had no effect on testicular CYP17 mRNA levels as measured by quantitative real-time polymersase chain reaction. However, microsomal CYP17 hydroxylase activity was significantly inhibited by the fungicide (Ki = 865nM). Amniotic fluid PCZ concentrations ranged from 78 to 1512 ppb (207–4014nM) and testosterone production was reduced when PCZ reached ∼500 ppb, which compares favorably with the determined CYP17 hydroxylase Ki (326 ppb). These results demonstrate that PCZ lowers testicular testosterone synthesis by inhibiting CYP17 activity which likely contributes to the induced malformations in androgen-dependent tissues of male offspring. [ABSTRACT FROM AUTHOR]

Prochloraz (PCZ) is an imidazole fungicide that inhibits gonadal steroidogenesis and antagonizes the androgen receptor (AR). We hypothesized that pubertal exposure to PCZ would reduce testosterone production and delay male rat reproductive development. Sprague Dawley rats were dosed by gavage with 0, 31.3, 62.5, or 125 mg/kg/day of PCZ from postnatal day (PND) 23 to 42 or 51. There was a significant delay in preputial separation (PPS) at 125 mg/kg/day PCZ and several of the androgen-dependent organ weights were decreased significantly, but the significant organ weight effects were not consistent between the 2 necropsies (PND 42 vs. 51). At both ages, serum testosterone levels and ex vivo testosterone release from the testis were significantly decreased whereas serum progesterone and 17a-hydroxyprogesterone levels were significantly increased at dose levels below those that affected PPS or reproductive organ weights. The hormone results suggested that PCZ was inhibiting CYP17 activity. In a second pubertal study (0, 3.9, 7.8, 15.6, 31.3, or 62.5 mg/kg/day PCZ), serum testosterone levels and ex vivo testosterone production were significantly reduced at 15.6 mg/kg/day PCZ. In order to examine the AR antagonism effects of PCZ, independent of its effects on testosterone synthesis, castrated immature male rats were dosed with androgen and 0, 15.6, 31.3, 62.5, or 125 mg/kg/day PCZ for 10–11 days (Hershberger assay). In this assay, androgen-sensitive organ weights were only significantly decreased at 125 mg/kg/day PCZ. These data from the pubertal assays demonstrate that PCZ decreases testosterone levels and delays rat pubertal development, as hypothesized. However, the fact that hormone levels were affected at dosage eightfold below that which delayed the onset of puberty suggests that rather large reductions in serum testosterone may be required to delay puberty and consistently reduce androgen-dependent tissue weights. [ABSTRACT FROM AUTHOR]