The effect of a prenatal androgen disruptor, vinclozolin, on gubernacular migration and testicular descent in rats

Toxicant exposure during pregnancy increases protective proteins in the dam and a sexually dimorphic response in the fetus

Endocrine disrupting compounds (EDCs) are ubiquitous environmental pollutants that alter endocrine system function, induce birth defects, and a myriad of other negative health outcomes. Although the mechanism of toxicity of many EDCs have been studied in detail, little work has focused on understanding the mechanisms through which pregnant dams and fetuses protect themselves from EDCs, or if those protective mechanisms are sexually dimorphic in fetuses. In this study, we examined proteomic alterations in the livers of mouse dams and their male and female fetuses induced by vinclozolin, a model antiandrogenic EDC. Dam livers upregulated nine phase I and phase II detoxification pathways and pathway analysis revealed that more pathways are significantly enriched in dam livers than in fetal livers. Phase I and II detoxification proteins are also involved in steroid and steroid hormone biosynthesis and vinclozolin likely alters steroid levels in both the dam and the fetus. The response of the fetal liver proteome to vinclozolin exposure is sexually dimorphic. Female fetal livers upregulated proteins in xenobiotic metabolism pathways, whereas male fetal livers upregulated proteins in oxidative phosphorylation pathways. These results suggest that female fetuses increase protective mechanisms, whereas male fetuses increase ATP production and several disease pathways that are indicative of oxidative damage. Females fetuses upregulate proteins and protective pathways that were similar to the dams whereas males did not. If this sexually dimorphic pattern is typical, then males might generally be more sensitive to EDCs.

Endocrine disrupting chemicals and reproductive disorders in women, men, and animal models

This chapter covers the known effects of endocrine disrupting chemicals (EDCs) on reproductive disorders. The EDCs represented are highly studied, including plasticizers (bisphenols and phthalates), chemicals in personal care products (parabens), persistent environmental contaminants (polychlorinated biphenyls), and chemicals in pesticides or herbicides. Both female and male reproductive disorders are reviewed in the chapter. Female disorders include infertility/subfertility, irregular reproductive cycles, early menopause, premature ovarian insufficiency, polycystic ovarian syndrome, endometriosis, and uterine fibroids. Male disorders include infertility/subfertility, cryptorchidism, and hypospadias. Findings from both human and animal studies are represented.

Review of the Effects of Perinatal Exposure to Endocrine-Disrupting Chemicals in Animals and Humans

Maternal exposure to endocrine-disrupting chemicals (EDCs) is associated with long-term hormone-dependent effects that are sometimes not revealed until maturity, middle age, or adulthood. The aim of this study was to conduct descriptive reviews on animal experimental and human epidemiological evidence of the adverse health effects of in utero and lactational exposure to selected EDCs on the first generation and subsequent generation of the exposed offspring. PubMed, Web of Science, and Toxline databases were searched for relevant human and experimental animal studies on 29 October 29 2018. Search results were screened for relevance, and studies that met the inclusion criteria were evaluated and qualitative data extracted for analysis. The search yielded 73 relevant human and 113 animal studies. Results from studies show that in utero and lactational exposure to EDCs is associated with impairment of reproductive, immunologic, metabolic, neurobehavioral, and growth physiology of the exposed offspring up to the fourth generation without additional exposure. Little convergence is seen between animal experiments and human studies in terms of the reported adverse health effects which might be associated with methodologic challenges across the studies. Based on the available animal and human evidence, in utero and lactational exposure to EDCs is detrimental to the offspring. However, more human studies are necessary to clarify the toxicological and pathophysiological mechanisms underlying these effects.

Risk factors for cryptorchidism

Undescended testis - known as cryptorchidism - is one of the most common congenital abnormalities observed in boys, and is one of the few known risk factors for testicular cancer. The key factors that contribute to the occurrence of cryptorchidism remain elusive. Testicular descent is thought to occur during two hormonally-controlled phases in fetal development - between 8-15 weeks (the first phase of decent) and 25-35 weeks gestation (the second phase of descent); the failure of a testis to descend permanently is probably caused by disruptions to one or both of these phases, but the causes and mechanisms of such disruptions are still unclear. A broad range of putative risk factors have been evaluated in relation to the development of cryptorchidism but their plausibility is still in question. Consistent evidence of an association with cryptorchidism exists for only a few factors, and in those cases in which evidence seems unequivocal the factor is likely to be a surrogate for the true causal exposure. The relative importance of each risk factor could vary considerably between mother-son pairs depending on an array of genetic, maternal, placental and fetal factors - all of which could vary between regions. Thus, the role of causative factors in aetiology of cryptorchidism requires further research.

The regulation of testicular descent and the effects of cryptorchidism

The first half of this review examines the boundary between endocrinology and embryonic development, with the aim of highlighting the way hormones and signaling systems regulate the complex morphological changes to enable the intra-abdominal fetal testes to reach the scrotum. The genitoinguinal ligament, or gubernaculum, first enlarges to hold the testis near the groin, and then it develops limb-bud-like properties and migrates across the pubic region to reach the scrotum. Recent advances show key roles for insulin-like hormone 3 in the first step, with androgen and the genitofemoral nerve involved in the second step. The mammary line may also be involved in initiating the migration. The key events in early postnatal germ cell development are then reviewed because there is mounting evidence for this to be crucial in preventing infertility and malignancy later in life. We review the recent advances in what is known about the etiology of cryptorchidism and summarize the syndromes where a specific molecular cause has been found. Finally, we cover the recent literature on timing of surgery, the issues around acquired cryptorchidism, and the limited role of hormone therapy. We conclude with some observations about the differences between animal models and baby boys with cryptorchidism.

Cryptorchidism and endocrine disrupting chemicals

Prospective clinical studies have suggested that the rate of congenital cryptorchidism has increased since the 1950s. It has been hypothesized that this may be related to environmental factors. Testicular descent occurs in two phases controlled by Leydig cell-derived hormones insulin-like peptide 3 (INSL3) and testosterone. Disorders in fetal androgen production/action or suppression of Insl3 are mechanisms causing cryptorchidism in rodents. In humans, prenatal exposure to potent estrogen diethylstilbestrol (DES) has been associated with increased risk of cryptorchidism. In addition, epidemiological studies have suggested that exposure to pesticides may also be associated with cryptorchidism. Some case-control studies analyzing environmental chemical levels in maternal breast milk samples have reported associations between cryptorchidism and chemical levels. Furthermore, it has been suggested that exposure levels of some chemicals may be associated with infant reproductive hormone levels.

Prenatal epoxiconazole exposure effects on rat postnatal development

Although some studies have pointed out to embryo/fetal toxicity, knowledge about the potential toxicity of the fungicide epoxiconazole is still limited. Once the results of these previous studies have raised some concern, this study studied the effects of epoxiconazole maternal exposure on the physical endpoints in the development of rat pups. To accomplish that, the effects of epoxiconazole (50.0, 100.0, and 150.0  mg/kg) were examined when rats were exposed at two different developmental stages: during the first 6 days of pregnancy or in the organogenesis period (6-15 days). After parturition, pups were tested for growth and maturational milestones. Maternal exposure to the fungicide, independently of phase, resulted in significantly early mean time to vaginal opening and delayed time to testes descent in pups. Weight gain rate in pups and their mothers was not affected for the tested exposure period. The findings of this study emphasize that epoxiconazole maternal exposure may lead to alterations in developmental patterns in nursing pups, consistent with the known influence of epoxiconazole on steroid hormone synthesis.

Embryology of the testicular descent

Numerous researchers studied the morphology of the testicular descent, including the possible function of the gubernaculum. However, a clear illustration of this process is still missing. The aim of this paper was to illustrate the embryology of the testicular descent in the rat by scanning electron microscopy. In a first phase of the intra-abdominal testicular descent, the testis moves actively from the lower pole of the kidney towards the bladder neck. In a second inguinal phase the testis enters groin and moves in the developing processus vaginalis peritonei caused by the disappearance of the bulb of the gubernaculums testis.

The testicular descent in the rat: a scanning electron microscopic study

PURPOSE

Numerous researchers studied the morphology of testicular descent including the possible function of gubernaculum. However, a clear illustration of this process is still missing. The aim of this study was to illustrate testicular descent using scanning electron microscopy (SEM) in a rat model.

METHODS

The abdomen of rat fetuses between gestational day (E) 15 and E 22 and newborns at postnatal day (D) 0 and D 1.5 was opened by microsurgery. Standard preparation for SEM was carried out. The position of the testis and gubernaculum testis was documented.

RESULTS

The gubernaculum was obvious in male rat embryos at E 17.5. In a first phase (E 16-E 21) the testis moved from cranio-lateral and dorsal to caudo-medial and ventral, while clear signs of an active role of the gubernaculum were missing. In a second phase (E 22-D 1.5) the processus vaginalis peritonei (PVP) developed, while the conus of the gubernaculum disappeared, after which, the testis moved out of the abdominal cavity and entered the PVP.

CONCLUSION

In our study, we could not specify the role of gubernaculum for testicular descent. However, our data showed that the testis lay intraperitoneal throughout the descensus testis.

Biotransformation of vinclozolin in rat precision-cut liver slices: comparison with in vivo metabolic pattern

Vinclozolin is a dicarboxymide fungicide that presents antiandrogenic properties through its two hydrolysis products M1 and M2, which bind to the androgen receptor. Because of the lack of data on the biotransformation of vinclozolin, its metabolism was investigated in vitro in precision-cut rat liver slices and in vivo in male rat using [ (14)C]-vinclozolin. Incubations were performed using different concentrations of substrate, and the kinetics of formation of the major metabolites were studied. Three male Wistar rats were fed by gavage with [ (14)C]-VZ. Urine was collected for 24 h and analyzed by radio-HPLC for metabolic profiling. Metabolite identification was carried out on a LCQ ion trap mass spectrometer. In rat liver slices and in vivo, the major primary metabolite has been identified as 3',5'-dichloro-2,3,4-trihydroxy-2-methylbutyranilide (M5) and was mainly present as glucuronoconjugates. M5 is produced by dihydroxylation of the vinyl group of M2. Other metabolites have been identified as 3-(3,5-dichlorophenyl)-5-methyl-5-(1,2-dihydroxyethyl)-1,3-oxazolidine-2,4-dione (M4), a dihydroxylated metabolite of vinclozolin, which undergoes further conjugation to glucuronic acid, and 2-[[(3,5-dichlorophenyl)-carbamoyl]oxy]-2-methyl-3,4-dihydroxy-butanoic acid (M6), a dihydroxylated metabolite of M1.

Impaired reproductive development in sons of women occupationally exposed to pesticides during pregnancy

OBJECTIVES

The aim of this prospective study was to investigate whether occupational pesticide exposure during pregnancy causes adverse effects on the reproductive development in the male infants.

DESIGN AND MEASUREMENTS

Pregnant women employed in greenhouses in Denmark were consecutively recruited, and 113 mother-son pairs were included. The mothers were categorized as occupationally exposed (91 sons) or unexposed (22 sons) to pesticides during pregnancy. Testicular position and volume, penile length, and position of urethral opening were determined at 3 months of age using standardized techniques. Concentrations of reproductive hormones in serum from the boys were analyzed.

RESULTS

The prevalence of cryptorchidism at 3 months of age was 6.2% [95% confidence interval (CI), 3.0-12.4]. This prevalence was considerably higher than among Danish boys born in the Copenhagen area (1.9%; 95% CI, 1.2-3.0) examined by the same procedure. Boys of pesticide-exposed mothers showed decreased penile length, testicular volume, serum concentrations of testosterone, and inhibin B. Serum concentrations of sex hormone-binding globulin, follicle-stimulating hormone, and the luteinizing hormone:testosterone ratio were increased compared with boys of nonexposed mothers. For individual parameters, only the decreased penile length was statistically significant (p = 0.04). However, all observed effects were in the anticipated direction, and a joint multivariate test showed that this finding had a p-value of 0.012.

CONCLUSIONS

Our findings suggest an adverse effect of maternal occupational pesticide exposure on reproductive development in the sons despite current greenhouse safeguards and special measures to protect pregnant women.

Structural analysis of gubernaculum testis in cryptorchid patients submitted to treatment with human chorionic gonadotrophin

OBJECTIVES

To make a histological and stereological analysis of gubernaculum testis elastic system fibers, collagen and striated muscle cells in patients with cryptorchidism treated with human chorionic gonadotrophin (hCG).

MATERIALS AND METHODS

Gubernacula tissue samples were obtained from 12 patients with cryptorchidism. Patients' ages ranged from 1 to 3 years (mean 1.8). Of the 12 patients, 6 were treated with hCG. The samples were stained with Masson's trichrome to highlight muscle fibers and collagen, and Weigert's resorcin-fuchsin to highlight the elastic system fibers. The volumetric density of these components was determined by stereological methods.

RESULTS

The volumetric density of collagen was increased in patients treated with hCG, ranging from 85.62% to 94.48%, while in patients not submitted to hCG treatment the volume density ranged from 52.12% to 89.46% (p=0.0052). The volumetric density of the elastic system fibers was higher in patients treated with hCG, ranging from 9.62% to 19.62%, while patients not submitted to hCG treatment the volume density of elastic system fibers was between 10.38% and 12.38% (p=0.0030). The volume density of striated muscle fibers in patients treated with hCG ranged from 4.76% to 39.16%, while and in patients not treated hCG it ranged from 3.24% to 11.14% (p=0.0052).

CONCLUSION

Gubernacular components alter significantly when submitted to treatment with hCG. Patients who underwent hCG treatment and had no complete testicular migration had an increase in the concentration of elastic and striated muscle fibers and a decrease in the volumetric density of collagen.

Xenoandrogenic activity in serum differs across European and Inuit populations

BACKGROUND

Animal and in vitro studies have indicated that human male reproductive disorders can arise as a result of disrupted androgen receptor (AR) signalling by persistent organic pollutants (POPs). Our aim in the present study was to compare serum xenoandrogenic activity between study groups with different POP exposures and to evaluate correlations to the POP proxy markers 2,2',4,4',5,5'-hexachlorobiphenyl (CB-153) and 1,1-dichloro-2,2-bis(p-chlorophenyl)-ethylene (p,p'-DDE).

METHODS

We determined xenoandrogenic activity in the serum fraction containing the lipophilic POPs but free of endogenous hormones. Adult male serum (n = 261) from Greenland, Sweden, Warsaw (Poland), and Kharkiv (Ukraine) was analyzed. Xenoandrogenic activity was determined as the effect of serum extract alone (XAR) and in the presence of the synthetic AR agonist R1881 (XARcomp) on AR transactivated luciferase activity.

RESULTS

The study groups differed significantly with respect to XARcomp activity, which was increased in the Inuits and decreased in the European study groups; we observed no difference for XAR activity. We found the highest level of the AR antagonist p,p'-DDE in Kharkiv, and accordingly, this study group showed the highest percent of serum samples with decreased XARcomp activities. Furthermore, the percentage of serum samples with decreased XARcomp activities followed the p,p'-DDE serum level for the European study groups. No correlations between serum XAR or XARcomp activities and the two POP markers were revealed.

CONCLUSIONS

The differences in XARcomp serum activity between the study groups suggest differences in chemical exposure profiles, genetics, and/or lifestyle factors.

Endocrine disruptors and hypospadias: role of genistein and the fungicide vinclozolin

OBJECTIVES

The phytoestrogen (plant estrogen) genistein, present in soy products, is of interest because in utero exposure to genistein can cause hypospadias in our mouse model and maternal consumption of soy is prevalent in human populations. Another compound of interest is the fungicide vinclozolin, which also causes hypospadias in the mouse and rat and can occur concurrently with genistein in the diet as a residue on exposed foods. A study in the United Kingdom found no relationship between a maternal organic vegetarian diet and hypospadias frequency, but women who consumed nonorganic vegetarian diets had a greater percentage of sons with hypospadias. Because nonorganic diets can include residues of pesticides such as vinclozolin, we sought to assess the interaction of realistic daily exposures to genistein and vinclozolin and their effects on the incidence of hypospadias.

METHODS

Pregnant mice were fed a soy-free diet and orally gavaged from gestational days 13 to 17 with 0.17 mg/kg/day of genistein, 10 mg/kg/day of vinclozolin, or genistein and vinclozolin together at the same doses, all in 100 microL of corn oil. The controls received the corn oil vehicle. The male fetuses were examined at gestational day 19 for hypospadias, both macroscopically and histologically.

RESULTS

We identified no hypospadias in the corn oil group. The incidence of hypospadias was 25% with genistein alone, 42% with vinclozolin alone, and 41% with genistein and vinclozolin together.

CONCLUSIONS

These findings support the idea that exposure to these compounds during gestation could contribute to the development of hypospadias.

Cryptorchidism in common eutherian mammals

Cryptorchidism is failure of one or both testes to descend into the scrotum. Primary fault lies in the testis. We provide a unifying cross-species interpretation of testis descent and urge the use of precise terminology. After differentiation, a testis is relocated to the scrotum in three sequential phases: abdominal translocation, holding a testis near the internal inguinal ring as the abdominal cavity expands away, along with slight downward migration; transinguinal migration, moving a cauda epididymidis and testis through the abdominal wall; and inguinoscrotal migration, moving a s.c. cauda epididymidis and testis to the bottom of the scrotum. The gubernaculum enlarges under stimulation of insulin-like peptide 3, to anchor the testis in place during gradual abdominal translocation. Concurrently, testosterone masculinizes the genitofemoral nerve. Cylindrical downward growth of the peritoneal lining into the gubernaculum forms the vaginal process, cremaster muscle(s) develop within the gubernaculum, and the cranial suspensory ligament regresses (testosterone not obligatory for latter). Transinguinal migration of a testis is rapid, apparently mediated by intra-abdominal pressure. Testosterone is not obligatory for correct inguinoscrotal migration of testes. However, normally testosterone stimulates growth of the vaginal process, secretion of calcitonin gene-related peptide by the genitofemoral nerve to provide directional guidance to the gubernaculum, and then regression of the gubernaculum and constriction of the inguinal canal. Cryptorchidism is more common in companion animals, pigs, or humans (2–12%) than in cattle or sheep (≤1%). Laboratory animals rarely are cryptorchid. In respect to non-scrotal locations, abdominal testes predominate in cats, dogs, and horses. Inguinal testes predominate in rabbits, are common in horses, and occasionally are found in cats and dogs. S.c. testes are found in cattle, cats and dogs, but are most common in humans.

Embryonic exposure to the fungicide vinclozolin causes virilization of females and alteration of progesterone receptor expression in vivo: an experimental study in mice

BACKGROUND

Vinclozolin is a fungicide that has been reported to have anti-androgenic effects in rats. We have found that in utero exposure to natural or synthetic progesterones can induce hypospadias in mice, and that the synthetic progesterone medroxyprogesterone acetate (MPA) feminizes male and virilizes female genital tubercles. In the current work, we selected a relatively low dose of vinclozolin to examine its in utero effects on the development of the genital tubercle, both at the morphological and molecular levels.

METHODS

We gave pregnant dams vinclozolin by oral gavage from gestational days 13 through 17. We assessed the fetal genital tubercles from exposed fetuses at E19 to determine location of the urethral opening. After determination of gonadal sex, either genital tubercles were harvested for mRNA quantitation, or urethras were injected with a plastic resin for casting. We analyzed quantified mRNA levels between treated and untreated animals for mRNA levels of estrogen receptors alpha and beta, progesterone receptor, and androgen receptor using nonparametric tests or ANOVA. To determine effects on urethral length (males have long urethras compared to females), we measured the lengths of the casts and performed ANOVA analysis on these data.

RESULTS

Our morphological results indicated that vinclozolin has morphological effects similar to those of MPA, feminizing males (hypospadias) and masculinizing females (longer urethras). Because these results reflected our MPA results, we investigated the effects of in utero vinclozolin exposure on the mRNA expression levels of androgen, estrogen alpha and beta, and progesterone receptors. At the molecular level, vinclozolin down-regulated estrogen receptor alpha mRNA in females and up-regulated progesterone receptor mRNA. Vinclozolin-exposed males exhibited up-regulated estrogen receptor alpha and progesterone receptor mRNA, effects we have also seen with exposure to the synthetic estrogen, ethinyl estradiol.

CONCLUSION

The results suggest that vinclozolin virilizes females and directly or indirectly affects progesterone receptor expression. It also affects estrogen receptor expression in a sex-based manner. We found no in vivo effect of vinclozolin on androgen receptor expression. We propose that vinclozolin, which has been designated an anti-androgen, may also exert its effects by involving additional steroid-signaling pathways.

Seminiferous cord formation and germ-cell programming: epigenetic transgenerational actions of endocrine disruptors

The molecular and cellular control of embryonic testis development was investigated through an analysis of the embryonic testis transcriptome to identify potential regulatory factors for male sex determination and testis morphogenesis. One critical factor identified is neurotropin 3 (NT3). At the onset of male sex determination, Sertoli cells initiate differentiation and express NT3 to act as a chemotactic factor for mesonephros cells to migrate and associate with Sertoli-germ cell aggregates to promote cord formation. Promoter analysis suggests that NT3 may be an initial downstream gene to SRY and helps promote testis morphogenesis. Endocrine disruptors were used to potentially interfere with embryonic testis development and further investigate this biological process. The estrogenic pesticide methoxychlor and antiandrogenic fungicide vinclozolin were used. Previous studies have shown that methoxychlor and vinclozolin both interfere with embryonic testis cord formation and cause increased spermatogenic cell apoptosis in the adult testis. Interestingly, transient in vivo exposure to endocrine disruptors at the time of male sex determination caused a transgenerational phenotype (F1-F4) of spermatogenic cell apoptosis and subfertility. This apparent epigenetic mechanism involves altered DNA methylation and permanent re-programming of the male germ-line. A series of genes with altered DNA methylation and imprinting are being identified. Observations reviewed demonstrate that a transient embryonic in utero exposure to an endocrine disruptor influences the embryonic testis transcriptome and through epigenetic effects (e.g., DNA methylation) results in abnormal germ-cell differentiation that subsequently influences adult spermatogenic capacity and male fertility, and that this phenotype is transgenerational through the germ-line. The novel observations of transgenerational epigenetic endocrine disruptor actions on male reproduction critically impact the potential hazards of these compounds as environmental toxins. The literature reviewed provides insight into the molecular and cellular control of embryonic testis development, male sex determination, and the programming of the male germ-line.

Endocrine disrupters: a human risk?

Endocrine disrupters (EDs) alter normal hormonal regulation and may be naturally occurring or environmental contaminants. Classically, EDs act genomically, with agonistic or antagonistic effects on steroid receptors and may alter reproductive function and/or cause feminisation by binding to oestrogen or androgen receptors; their binding to the thyroid receptor may dysregulate the neuroendocrine system. Recently, it has been shown that EDs can also act by non-genomic mechanisms, altering steroid synthesis (inhibition of cytochrome P450 isoforms) or steroid metabolism. The alkylphenol and phthalate plasticisers inhibit the inactivation of oestrogens by sulphation (via SULT 1A1 and 1E1 isoforms) and so cause a rise in levels of the free active endogenous oestrogens. A range of ED effects have been shown in mammals, fish, birds, reptiles, amphibia and aquatic invertebrates but it is not yet clear whether these processes also occur in human beings. It is evident that EDs, as well as altering reproduction, can cause changes in neurosteroid levels and so have the potential to affect immune function, behaviour and memory. This may be of long-term concern since traces of EDs such as plasticisers, brominated fire retardants, sunscreen agents and cosmetic ingredients are widely distributed in the environment and in human biofluids.

EFFECTS OF FLUTAMIDE ON SEX MATURATION AND BEHAVIOR OF OFFSPRING BORN TO FEMALE RATS TREATED DURING LATE PREGNANCY

Flutamide, when administered subcutaneously to female rats at doses of 3, 10, or 30 mg/kg/day during late pregnancy (gestational days 16-21), significantly and dose-dependently decreased anogenital distance (AGD) of the male offspring in each dose group compared to controls. Significant delays in preputial separation were found in males at a dose of 30 mg/kg, but body weight gain was not inhibited. Cryptorchidism and absence of the prostate gland and seminal vesicles were found in males at doses > or = 10 mg/kg, and testicular hypoplasia at a dose of 30 mg/kg. Hypospadias was noted in all dose groups and vaginal pouches at doses of > or =10 mg/kg. The effects on the accessory reproductive organs were severe, although the effects on the testes themselves were mild. However, those effects appeared to become more pronounced with growth, as evaluated on Days 30 and 42 and Weeks 16 to 18. Most of these affected animals displayed cryptorchidism. Male offspring exposed to flutamide in utero showed impairments of sexual behavior as adults in a dose-related manner. Number and frequency of mounts with intromissions was markedly decreased in all treated groups as compared to controls. At 10 mg/kg, no mounting with ejaculation was observed, and at a dose of 30 mg/kg, no mounting with intromission or ejaculation was observed. These changes in sexual behavior were closely associated with abnormalities of the external genitalia. Animals with hypospadias did not display mounts with ejaculation. However, F1 males that copulated at a dose of 3 mg/kg had a normal reproductive function. Histological examination of the reproductive organs revealed degeneration of the seminiferous tubules, hypospermatogenesis, and hypoplasia and inflammation of the seminal vesicles and prostate. Serum levels of FSH, LH, and testosterone in these animals were comparable between control and all dose groups. Therefore, the male reproductive dysfunction seen in the present study could not be attributed to abnormal sex hormone levels during maturation, but to possible demasculinization of the brain and progressively delayed dysmorphology of the male genitalia caused by fetal exposure to flutamide.