Time-specific effects of mono-n-butyl phthalate on the transabdominal descent of the testis in rat fetuses

The Production of Testosterone and Gene Expression in Neonatal Testes of Rats Exposed to Diisoheptyl Phthalate During Pregnancy is Inhibited

Background: Diisoheptyl phthalate (DIHP) is a phthalate plasticizer, which is a branched phthalate. Here, we reported the effects of gestational exposure to DIHP on testis development in male rats.

Methods: Pregnant Sprague-Dawley rats were orally fed with vehicle (corn oil, control) or DIHP (10, 100, 500, and 1,000 mg/kg) from gestational day (GD) 12–21. At GD21, serum testosterone levels, the number and distribution of fetal Leydig cells, and testicular mRNA and protein levels, the incidence of multinucleated gonocytes, and focal testicular hypoplasia in the neonatal testis were measured.

Results: DIHP increased the fetal Leydig cell cluster size and decreased the fetal Leydig cell size with LOAEL of 10 mg/kg. DIHP did not affect the fetal Leydig cell number. DIHP significantly lowered serum testosterone levels, down-regulated the expression of steroidogenesis-related genes (Lhcgr, Star, Cyp11a1, Hsd3b1, Cyp17a1, and Hsd17b3) and testis descent-related gene (Insl3) as well as protein levels of cholesterol side-chain cleavage enzyme (CYP11A1) and insulin-like 3 (INSL3). DIHP dose-dependently increased the percentage of multinucleated gonocytes with the low observed adverse-effect level (LOAEL) of 100 mg/kg. DIHP induced focal testicular hypoplasia.

Conclusion: Gestational exposure to DIHP causes testis dysgenesis in rats.

A suggested bisphenol A metabolite (MBP) interfered with reproductive organ development in the chicken embryo while a human-relevant mixture of phthalate monoesters had no such effects

Bisphenol A (BPA) and phthalate diesters are ubiquitous environmental contaminants. While these compounds have been reported as reproductive toxicants, their effects may partially be attributed to metabolites. The aim of this study was to examine reproductive organ development in chicken embryos exposed to the BPA metabolite, 4-methyl-2,4-bis(4-hydroxyphenyl)pent-1-ene (MBP; 100 µg/g egg) or a human-relevant mixture of 4 phthalate monoesters (85 µg/g egg). The mixture was designed within the EU project EDC-MixRisk based upon a negative association with anogenital distance in boys at 21 months of age in a Swedish pregnancy cohort. Chicken embryos were exposed in ovo from an initial stage of gonad differentiation (embryonic day 4) and dissected two days prior to anticipated hatching (embryonic day 19). No discernible effects were noted on reproductive organs in embryos exposed to the mixture. MBP-treated males exhibited retention of Müllerian ducts and feminization of the left testicle, while MBP-administered females displayed a diminished the left ovary. In the left testicle of MBP-treated males, mRNA expression of female-associated genes was upregulated while the testicular marker gene SOX9 was downregulated, corroborating a feminizing effect by MBP. Our results demonstrate that MBP, but not the phthalate monoester mixture, disrupts both male and female reproductive organ development in an avian embryo model.

Di-(2-ethylhexyl) phthalate (DEHP)-induced testicular toxicity through Nrf2-mediated Notch1 signaling pathway in Sprague-Dawley rats

Di-(2-ethylhexyl) phthalate (DEHP) is an environmental endocrine disruptor widely used in China that is harmful to the male reproductive system. Many studies have shown that DEHP causes testicular toxicity through oxidative stress, but the specific mechanism is unknown. Because the Notch pathway is a key mechanism for regulating cell growth and proliferation, we investigated whether Notch is involved in DEHP-induced testicular toxicity and whether vitamins E and C could rescue testicular impairment in Sprague-Dawley (SD) rats. Compared with the control group, we found that DEHP exposure induced testicular toxicity through oxidative stress injury, and it decreased the testosterone level (P < .01) and upregulated nuclear factor-erythroid 2 related factor (Nrf2) expression (P < .01). Therefore, because oxidative stress might be the initiating factor of DEHP-induced testicular toxicity, treatment with the antioxidant vitamins E and C activated the Notch1 signaling pathway in the testis and in Leydig cells. Treatment with vitamins E and C normalized the oxidative stress state after DEHP exposure and restored testicular development to be similar to the control group. In summary, antioxidant vitamins E and C may be used to treat DEHP-induced testicular toxicity.

Validation of an automated counting procedure for phthalate-induced testicular multinucleated germ cells

In utero exposure to certain phthalate esters results in testicular toxicity, characterized at the tissue level by induction of multinucleated germ cells (MNGs) in rat, mouse, and human fetal testis. Phthalate exposures also result in a decrease in testicular testosterone in rats. The anti-androgenic effects of phthalates have been more thoroughly quantified than testicular pathology due to the significant time requirement associated with manual counting of MNGs on histological sections. An automated counting method was developed in ImageJ to quantify MNGs in digital images of hematoxylin-stained rat fetal testis tissue sections. Timed pregnant Sprague Dawley rats were exposed by daily oral gavage from gestation day 17 to 21 with one of eight phthalate test compounds or corn oil vehicle. Both the manual counting method and the automated image analysis method identified di-n-butyl phthalate, butyl benzyl phthalate, dipentyl phthalate, and di-(2-ethylhexyl) phthalate as positive for induction of MNGs. Dimethyl phthalate, diethyl phthalate, the brominated phthalate di-(2-ethylhexyl) tetrabromophthalate, and dioctyl terephthalate were negative. The correlation between automated and manual scoring metrics was high (r = 0.923). Results of MNG analysis were consistent with these compounds' anti-androgenic activities, which were confirmed in an ex vivo testosterone production assay. In conclusion, we have developed a reliable image analysis method that can be used to facilitate dose-response studies for the reproducible induction of MNGs by in utero phthalate exposure.

Effects of in Utero Exposure to Dicyclohexyl Phthalate on Rat Fetal Leydig Cells

Dicyclohexyl phthalate (DCHP) is one of the phthalate plasticizers. The objective of the present study was to investigate the effects of DCHP on fetal Leydig cell distribution and function as well as testis development. Female pregnant Sprague Dawley dams orally received vehicle (corn oil, control) or DCHP (10, 100, and 500 mg/kg/day) from gestational day (GD) 12 to GD 21. At GD 21.5, testicular testosterone production, fetal Leydig cell number and distribution, testicular gene and protein expression levels were examined. DCHP administration produced a dose-dependent increase of the incidence of multinucleated gonocytes at ≥100 mg/kg. DCHP dose-dependently increased abnormal fetal Leydig cell aggregation and decreased fetal Leydig cell size, cytoplasmic size, and nuclear size at ≥10 mg/kg. DCHP reduced the expression levels of steroidogenesis-related genes (including Star, Hsd3b1, and Hsd17b3) and testis-descent related gene Insl3 as well as protein levels of 3β-hydroxysteroid dehydrogenase 1 (HSD3B1) and insulin-like 3 (INSL3) at ≥10 mg/kg. DCHP significantly inhibited testicular testosterone levels at ≥100 mg/kg. The results indicate that in utero exposure to DCHP affects the expression levels of fetal Leydig cell steroidogenic genes and results in the occurrence of multinucleated gonocytes and Leydig cell aggregation.

Plasticizer endocrine disruption: Highlighting developmental and reproductive effects in mammals and non-mammalian aquatic species

Due to their versatility, robustness, and low production costs, plastics are used in a wide variety of applications. Plasticizers are mixed with polymers to increase flexibility of plastics. However, plasticizers are not covalently bound to plastics, and thus leach from products into the environment. Several studies have reported that two common plasticizers, bisphenol A (BPA) and phthalates, induce adverse health effects in vertebrates; however few studies have addressed their toxicity to non-mammalian species. The aim of this review is to compare the effects of plasticizers in animals, with a focus on aquatic species. In summary, we identified three main chains of events that occur in animals exposed to BPA and phthalates. Firstly, plasticizers affect development by altering both the thyroid hormone and growth hormone axes. Secondly, these chemicals interfere with reproduction by decreasing cholesterol transport through the mitochondrial membrane, leading to reduced steroidogenesis. Lastly, exposure to plasticizers leads to the activation of peroxisome proliferator-activated receptors, the increase of fatty acid oxidation, and the reduction in the ability to cope with the augmented oxidative stress leading to reproductive organ malformations, reproductive defects, and decreased fertility.

Short-time exposure to mono-n-butyl phthalate (MBP)-induced oxidative stress associated with DNA damage and the atrophy of the testis in pubertal rats

Phthalates are widely used as plasticizer in various consumer domestic products and are known to disturb the male reproductive function in rodents. This study investigated the involvement of oxidative stress and the atrophy of the testes in pubertal rats exposed to mono-n-butyl phthalate (MBP). Four-week-old pubertal male rats were separated into three groups. In group I, 21 rats were fed rat chow containing 2 % MBP for 3 days. In group II, 21 rats were fed rat chow containing 2 % MBP for 3 days and antioxidant vitamins C (250 mg/kg/day) and E (50 mg/kg/day) were injected daily. In group III, 21 rats were fed standard rat chow and used as controls. After 3 days, each testis was weighed and the germ cell development was evaluated using the Johnsen score. The urinary 8-hydroxy-2'-deoxyguanosine (8-OHdG) levels were measured as a biological marker of oxidative DNA damage. The mean testis weight was significantly lower for group I than groups II or III (p < 0.05). The mean Johnsen score was significantly lower for group I than for groups II or III (p < 0.05). Urinary 8-OHdG concentrations were higher in group I than in groups II or III. Short-time exposure to MBP may therefore induce oxidative DNA damage in rat testes, while antioxidant vitamins administered during exposure may protect against this stress.

What is new in cryptorchidism and hypospadias--a critical review on the testicular dysgenesis hypothesis

It has been hypothesized that poor semen quality, testis cancer, undescended testis, and hypospadias are symptoms of one underlying entity--the testicular dysgenesis syndrome--leading to increasing male fertility impairment. Though testicular cancer has increased in many Western countries during the past 40 years, hypospadias rates have not changed with certainty over the same period. Also, recent studies demonstrate that sperm output may have declined in certain areas of Europe but is probably not declining across the globe as indicated by American studies. However, at the same time, there is increasing recognition of male infertility related to obesity and smoking. There is no certain evidence that the rates of undescended testes have been increasing with time during the last 50 years. In more than 95% of the cases, hypospadias is not associated with cryptorchidism, suggesting major differences in pathogenesis. Placental abnormality may occasionally cause both cryptorchidism and hypospadias, as it is also the case in many other congenital malformations. The findings of early orchidopexy lowering the risk of both infertility and testicular cancer suggest that the abnormal location exposes the cryptorchid testis to infertility and malignant transformation, rather than there being a primary abnormality. Statistically, 5% of testicular cancers only are caused by cryptorchidism. These data point to the complexity of pathogenic and epidemiologic features of each component and the difficulties in ascribing them to a single unifying process, such as testicular dysgenesis syndrome, particularly when so little is known of the actual mechanisms of disease.

Reproductive toxicity and pharmacokinetics of di-n-butyl phthalate (DBP) following dietary exposure of pregnant rats

Most rodent developmental toxicity studies of dibutylphthalate (DBP) have relied on bolus gavage dosing. This study characterized the developmental toxicity of dietary DBP. Pregnant CD rats were given nominal doses of 0, 100, or 500 mg DBP/kg/day in diet (actual intake 0, 112, and 582 mg/kg/day) from gestational day (GD) 12 through the morning of GD 19. Rats were killed 4 or 24 hr thereafter. DBP dietary exposure resulted in significant dose-dependent reductions in testicular mRNA concentration of scavenger receptor class B, member 1; steroidogenic acute regulatory protein; cytochrome P450, family 11, subfamily a, polypeptide 1; and cytochrome P450 family 17, subfamily a, polypeptide 1. These effects were most pronounced 4 hr after the end of exposure. Testicular testosterone was reduced 24 hr post-exposure in both DBP dose groups and 4 hr after termination of the 500-mg DBP/kg/day exposure. Maternal exposure to 500 mg DBP/kg/day induced a significant reduction in male offspring's anogenital distance indicating in utero disruption of androgen function. Leydig cell aggregates, increased cord diameters, and multinucleated gonocytes were present in DBP-treated rats. Monobutyl phthalate, the developmentally toxic metabolite of DBP, and its glucuronide conjugate were found in maternal and fetal plasma, amniotic fluid, and maternal urine. Our results, when compared to previously conducted gavage studies, indicate that approximately equal doses of oral DBP exposure of pregnant rats, from diet or gavage, result in similar responses in male offspring.

Effect of fetal or neonatal exposure to monobutyl phthalate (MBP) on testicular development and function in the marmoset

BACKGROUND

Fetal exposure of male rats to some phthalates induces reproductive abnormalities, raising concerns for similar effects in humans. In order to address this in a more appropriate animal model, the aim of the present studies was to investigate the effect of fetal/neonatal exposure to monobutyl phthalate (MBP) in a non-human primate, the marmoset. In particular, to determine if exposure resulted in effects at birth, or in adulthood, similar to those in male rats, and whether there was evidence for induction of carcinoma-in-situ (CIS) or testicular germ cell tumours (TGCT).

METHODS

Pregnant female marmosets were dosed from ∼7–15 weeks gestation with 500 mg/kg/day MBP and male offspring studied at birth (1–5 days; n = 6) or in adulthood (n = 5). In another study, newborn males (n = 5 co-twins) were dosed with 500 mg/kg/day MBP for 14 days, commencing at ∼4 days of age.

RESULTS

Fetal exposure of marmosets to MBP did not affect gross testicular morphology, reproductive tract development or testosterone levels at birth, nor were germ cell number and proliferation, Sertoli cell number or germ:Sertoli cell ratio affected. In two of six MBP-exposed animals, unusual clusters of undifferentiated germ cells were found, but their significance is unclear. Neonatal MBP treatment did not affect germ cell numbers or differentiation. Fetal exposure to MBP did not affect testis size/morphology, germ cell numbers or fertility in adulthood. There was no evidence for CIS or TGCT.

CONCLUSIONS

Fetal exposure of marmosets to MBP does not measurably affect testis development/function or cause testicular dysgenesis, and no effects emerge by adulthood. Some effects on germ cell development were found, but these were inconsistent and of uncertain significance.

Development and descent of the testis in relation to cryptorchidism

The testis descends in two phases. Animal studies suggest, that the transabdominal descent of the testis depends on the insulin-like hormone 3 (INSL3). Androgens are important in the inguinoscrotal testicular descent in animals and humans. In general, the cause of cryptorchidism is unknown and the aetiology is possibly multifactorial. Histological changes in cryptorchid testes demonstrate disturbed development.

CONCLUSION

Since testicular descent is regulated by testis-derived hormones, cryptorchidism may reflect a functional defect of the testis.

Environmental effects on hormonal regulation of testicular descent

Regulation of testicular descent is hormonally regulated, but the reasons for maldescent remain unknown in most cases. The main regulatory hormones are Leydig cell-derived testosterone and insulin-like factor 3 (INSL3). Luteinizing hormone (LH) stimulates the secretion of these hormones, but the secretory responses to LH are different: INSL3 secretion increases slowly and may reflect the LH dependent differentiated status of Leydig cells, whereas testosterone response to LH is immediate. Testosterone contributes to the involution of the suspensory ligament and to the inguinoscrotal phase of the descent, while INSL3 acts mainly in transabdominal descent by stimulating the growth of the gubernaculum. INSL3 acts through a G-protein coupled receptor LGR8. In the absence of either INSL3 or LGR8 mice remain cryptorchid. In humans only few INSL3 mutations have been described, whereas LGR8 mutations may cause some cases of undescended testis. Similarly, androgen insensitivity or androgen deficiency can cause cryptorchidism. Estrogens have been shown to down regulate INSL3 and thereby cause maldescent. Thus, a reduced androgen-estrogen ratio may disturb testicular descent. Environmental effects changing the ratio can thereby influence cryptorchidism rate. Estrogens and anti-androgens cause cryptorchidism in experimental animals. In our cohort study we found higher LH/testosterone ratios in 3-month-old cryptorchid boys than in normal control boys, suggesting that cryptorchid testes are not cabable of normal hormone secretion without increased gonadotropin drive. This may be either the cause or consequence of cryptorchidism. Some phthalates act as anti-androgens and cause cryptorchidism in rodents. In our human material we found an association of a high phthalate exposure with a high LH/testosterone ratio. We hypothesize that an exposure to a mixture of chemicals with anti-androgenic or estrogenic properties (either their own activity or their effect on androgen-estrogen ratio) may be involved in cryptorchidism.

Endocrine disrupting chemicals: a new and emerging public health problem?

Coordination of targeted toxicological studies is needed

Developmental toxic effects of diisobutyl phthalate, the methyl-branched analogue of di-n-butyl phthalate, administered by gavage to rats

The developmental toxicity of diisobutyl phthalate (DIBP) was studied in Sprague-Dawley rats after oral administration. Pregnant rats were given DIBP at doses of 0 (olive oil), 250, 500, 750, and 1000 mg/kg/day, by gavage (5 ml/kg), on gestational days (GD) 6 through 20. Maternal toxicity, as evidenced by reduction in body weight gain, was observed at the beginning of treatment (GD 6-9), at 500 mg/kg and higher doses. The incidence of resorptions was significantly increased at 750 mg/kg, and reached 60% at 1000 mg/kg. There was a dose-related decrease in fetal weight, which was significantly lower than control from 500 mg/kg. A significant increase in the incidence of fetuses with visceral and skeletal malformations was seen at 750 and 1000 mg/kg. In particular, fused sternebrae occurred at a significantly higher frequency. Two skeletal variations were increased at 750 and 1000 mg/kg: retarded ossification of vertebrae, and predominantly, supernumerary ribs. The incidence of male fetuses with undescended testes was also significantly elevated at the two highest doses. In conclusion, DIBP administered by gavage is embryotoxic and teratogenic, and affects the developing male reproductive tract, at maternal toxic doses.

In utero exposure to mono-n-butyl phthalate impairs insulin-like factor 3 gene expression and the transabdominal phase of testicular descent in fetal rats

PURPOSE

Phthalate esters have been shown to cause undescended testes (UT) in rats. It has been proposed that Leydig insulin-like factor 3 (INSL3) may play an important role in testicular descent. The aim of this study was to investigate the effect of mono-n-butyl phthalate (MBP) on both the INSL3 gene expression and the transabdominal testicular descent in rats.

METHODS

On the 19th gestational day, the male fetuses that had been exposed to MBP on the 15th to 18th gestational days were dissected and the degree of testicular ascent was examined. Next, quantitative reverse transcriptase polymerase chain reaction was performed to analyze the testicular INSL3 gene expression. At 60 days of age, the testicular position was recorded in the rest of MBP-treated male offspring.

RESULTS

On the 19th gestational day, INSL3 messenger RNA expression was significantly decreased in the MBP-treated testes, and the associated degree of testicular ascent was significantly higher than in the controls. At 60 days of age, 12 (54.5%) of 22 rats had either unilateral or bilateral UT.

CONCLUSIONS

Prenatal MBP may inhibit the INSL3 gene expression associated with the transabdominal testicular ascent in fetal rats, thereby causing UT in postnatal offspring.

Pharmacokinetics of monobutylphthalate, the active metabolite of di-n-butylphthalate, in pregnant rats

Di-n-butylphthalate (DBP) is a phthalic acid ester used as a plasticizer and solvent. DBP is a developmental toxicant in rats and mice, with adverse effects arising from the monoester metabolite monobutyl phthalate (MBP). The objective of this study was to evaluate the pharmacokinetics of MBP and monobutyl phthalate glucuronide (MBP-G) in pregnant rats following intravenous (i.v.) dosing with MBP. Pregnant dams were i.v. dosed with aqueous MBP (10, 30, or 50mg MBP/kg body weight) on gestation day (GD) 19. The pharmacokinetics of MBP and MBP-G were rapid: MBP was metabolized to MBP-G within 5 min, and MBP and MBP-G disappeared from maternal and fetal plasma within 24h of dosing. Results were consistent with two previous studies that utilized oral doses of DBP, suggesting that chemical (DBP versus MBP), vehicle (oil versus aqueous), dose level, and route (oral versus i.v.) have minimal effects on the maternal pharmacokinetics of MBP and MBP-G. This study provides direct pharmacokinetic analysis for MBP and MBP-G in pregnant rats during fetal male reproductive development, and indicates that future pharmacokinetic or toxicology studies can reliably utilize oral dosing with DBP.

Long-term effects of intrauterine exposure to mono-n-butyl phthalate on the reproductive function of postnatal rats

PURPOSE

Although it is well known that phthalate esters induce testicular dysfunction in both adult and immature rats, there have been few reports on the long-term effect of phthalate esters on the testicular function of male rats exposed to phthalate esters in utero. This study was designed to assess the long-term effects of the mono-n-butyl phthalate (MBP) ester on the testicular function of neonatal and adult rat offspring from pregnant dams exposed to phthalate esters during gestation.

METHODS

Pregnant rats were administered MBP [0.5 g/(kg body weight/.d); 4 days] by gavage from the 15th to the 18th gestational day. Rats administered solvent only were used as control subjects. After the rats' puberty, using male pups whose testes descended normally, the authors examined their fertility while also measuring their testicular weights, mean seminiferous tubular diameter, and the developmental grade of the germ cells (Johnsen score) in their testes. Next, in neonatal rats, the authors measured the testicular concentration of the Mullerian inhibiting substance (MIS) protein using enzyme-linked immunoassay and the expression level of the MIS messenger RNA using the quantitative polymerase chain reaction method as a marker of the Sertoli cells' function. Next the concentration of testosterone protein using a radioimmunoassay as a marker of the Leydig cells' function was measured.

RESULTS

The pregnancy rate of the female rats coupled with MBP-treated male rats decreased significantly in comparison with that of the female rats coupled with control male rats (P < .01). Both the testicular weight and the Johnsen score in the MBP-treated group were decreased significantly more than those of the control group (P < .05). Neither the concentration of the MIS protein nor the expression level of the MIS messenger RNA in the MBP-treated neonatal testes differed from those of the control testes, whereas the concentration of testosterone protein in the neonate testes decreased significantly in the MBP-treated group in comparison with that of the control group (P < .01).

CONCLUSIONS

A prenatal short-time exposure to MBP induces a long-term effect on postnatal rats and impairs reproductive function in male offspring probably by inhibiting the Leydig cells' rather than Sertoli cells' function in the fetal period.

Pharmacokinetics of dibutylphthalate in pregnant rats

Dibutylphthalate (DBP) can cause adverse effects on the developing male reproductive tract when administered late in gestation to pregnant rats. The objectives of this study were to evaluate the metabolism of DBP in female rats, and the pharmacokinetics of DBP in pregnant rats on gestational day (g.d.) 20. The identities of DBP metabolites in urine and in maternal and fetal plasma were confirmed by LC-MS/MS, as monobutylphthalate (MBP) and its glucuronide, monohydroxybutylphthalate and its glucuronide, and butanoic acid phthalate and its glucuronide. An LC-MS/MS method was developed for the quantitation of MBP and its glucuronide. MBP and MBP glucuronide were quantitated in maternal and fetal plasma, and in amniotic fluid from pregnant rats administered a single dose of DBP (50, 100, or 250 mg/kg by gavage in corn oil) on g.d. 20. The pharmacokinetics of MBP and MBP glucuronide were determined. MBP was the major metabolite in maternal and fetal plasma. With increasing dose, there was a nonlinear increase in area under the curve (AUC) for MBP, with a ten-fold increase in maternal plasma, and an eight-fold increase in fetal plasma between 50 mg/kg and 250 mg/kg. In amniotic fluid, the major metabolite initially was MBP, but by 24 h after dosing, the major metabolite was MBP glucuronide. Isomers of the MBP glucuronide were detected in amniotic fluid, suggesting acyl group migration, known to occur with acyl glucuronides. This study indicated that MBP, thought to be the active metabolite of DBP, can cross the placenta in late gestation, and that the metabolism of MBP is saturable.

NTP center for the evaluation of risks to human reproduction reports on phthalates: addressing the data gaps

Between 1998 and 2000 an Expert Panel convened by the National Toxicology Program's Center for the Evaluation of Risks to Human Reproduction (NTP-CERHR) reviewed information related to the developmental and reproductive toxicity of seven phthalate esters; DBP, BBP, DnHP, DEHP, DnOP, DINP, and DIDP. Information on exposures was also considered. The objectives were to determine whether any of these phthalates posed potential human reproductive risks, and if so, to define the circumstances. The Expert Panel also identified some areas of uncertainty. These assessments, ultimately published in 2002, concluded that reproductive risks were minimal to negligible in most cases although some specific uses were considered potentially more problematic. Since the evaluations were completed, numerous studies dealing with both hazard characterization and underlying mechanism have been carried out. Additionally, exposures of the general population have been much better characterized through the use of urinary measurements developed by the Centers for Disease Control (CDC). This additional information makes several important points. First, calculations based on the urinary metabolite measurements indicate that exposures within the general population are at levels similar to or lower than the estimates used by the NTP-CERHR. The demonstration that exposures were not underestimated by the CERHR has removed a substantial portion of the uncertainty. Second, new hazard characterization studies on several phthalates have established NOAELs similar to or higher than those used by the Expert Panel. Thus, these data demonstrate that, to the extent that the rodent data are useful for human health risk assessment, the no effect levels and dose-response relationships are now more precisely defined. In some cases, the no effect levels may be substantially higher than those estimated by the Expert Panel. Third, studies of underlying mechanism and/or hazard characterization studies in other species suggest that primates may be less sensitive than rodents to the reproductive effects of certain phthalates. Finally, the two specific situations that the CERHR identified as potentially problematic, the exposure of young children to DINP through the use of toys or to DEHP from medical devices, have been assessed by the responsible regulatory authorities. The Consumer Product Safety Commission concluded that exposure to DINP from toys was well below effect levels in animals, and, therefore, there was no risk. The Food and Drug Administration estimates of exposures from medical devices indicated that for some limited, intensive medical procedures, DEHP exposures could be similar to or greater than the NOAELs selected by the NTP-CERHR. However, the FDA also acknowledged that more recent information indicates that the NOAELs identified in rodent studies may be substantially higher than values previously proposed by the NTP-CERHR. In summary, much of the uncertainty identified by the CERHR has now been addressed, and the overall conclusions that levels of concern are minimal to negligible in most situations are much better established. The overall objective of this report is to summarize this new research and comment on its relevance to the NTP-CERHR assessments.

Reproductive toxicity evaluation of dietary butyl benzyl phthalate (BBP) in rats

Butyl benzyl phthalate (BBP) was administered in the diet at 0, 750, 3750, and 11,250 ppm ad libitum to 30 rats per sex per dose for two offspring generations, one litter/breeding pair/generation, through weaning of F2 litters. Adult F0 systemic toxicity and adult F1 systemic and reproductive toxicity were present at 11,250 ppm (750 mg/kg per day). At 11,250 ppm, there were reduced F1 and F2 male anogenital distance (AGD) and body weights/litter during lactation, delayed acquisition of puberty in F1 males and females, retention of nipples and areolae in F1 and F2 males, and male reproductive system malformations. At 3750 ppm (250 mg/kg per day), only reduced F1 and F2 offspring male AGD was present. There were no effects on parents or offspring at 750 ppm (50 mg/kg per day). The F1 parental systemic and reproductive toxicity no observable adverse effect level (NOAEL) was 3750 ppm. The offspring toxicity NOAEL was 3750 ppm. The offspring toxicity no observable effect level (NOEL) was 750 ppm, based on the presence of reduced AGD in F1 and F2 males at birth at 3750 ppm, but no effects on reproductive development, structures, or functions.

Impact of exposure to endocrine disrupters in utero and in childhood on adult reproduction

Recent reports have demonstrated a decline in human male reproductive health: high and probably increasing prevalence of cryptorchidism and hypospadias, low and probably decreasing semen quality, a rising incidence of testicular cancer and a growing demand for assisted reproduction. These changes seem to be interrelated and may be symptoms of a common underlying entity, the testicular dysgenesis syndrome, with foundations in fetal life due to adverse environmental influences. Wildlife experience and animal studies have provided evidence that fetal or perinatal exposure to endocrine disrupters results in disturbed sexual differentiation and urogenital malformations followed by decreased reproductive health in adult life. This chapter reviews existing evidence for a connection between (i) exposure to endocrine disrupters in fetal life and childhood and (ii) adult reproductive health in humans. This topic is not only relevant to basic scientists but also to clinical endocrinologists, who should also be encouraged to participate in research concerning this problem.

Testicular dysgenesis syndrome: an increasingly common developmental disorder with environmental aspects

Numerous reports have recently focused on various aspects of adverse trends in male reproductive health, such as the rising incidence of testicular cancer; low and probably declining semen quality; high and possibly increasing frequencies of undescended testis and hypospadias; and an apparently growing demand for assisted reproduction. Due to specialization in medicine and different ages at presentation of symptoms, reproductive problems used to be analysed separately by various professional groups, e.g. paediatric endocrinologists, urologists, andrologists and oncologists. This article summarizes existing evidence supporting a new concept that poor semen quality, testis cancer, undescended testis and hypospadias are symptoms of one underlying entity, the testicular dysgenesis syndrome (TDS), which may be increasingly common due to adverse environmental influences. Experimental and epidemiological studies suggest that TDS is a result of disruption of embryonal programming and gonadal development during fetal life. Therefore, we recommend that future epidemiological studies on trends in male reproductive health should not focus on one symptom only, but be more comprehensive and take all aspects of TDS into account. Otherwise, important biological information may be lost.