Reproductive toxicity and tissue concentrations of low doses of 2,3,7,8-tetrachlorodibenzo-p-dioxin in male offspring rats exposed throughout pregnancy and lactation

Transepithelial transport and cellular accumulation of steroid hormones and polychlorobiphenyl in porcine kidney cells expressed with human P-glycoprotein

Endocrine disrupters such as sex hormone-like chemicals and the non-physiological ligands for aryl hydrocarbon receptor (AhR) exert many adverse biological effects. The ligands for AhR disturb gene expression downstream of the gene induced by estrogen receptor at a very low concentration. Thus, transepithelial transport and cellular accumulation of cortisol (COR) and estrogen as congeners of sex hormone-like chemicals, and 3,3',4,4'-tetrachlorobiphenyl (TeCB) as one of the ligands for AhR were examined in a monolayer of porcine kidney cells transfected with human P-glycoprotein (LLC-COL). The net basal-to-apical transport of COR increased in LLC-COL compared to that in the wild type cells (LLC-PKI) the same as in vinblastine, whereas the net transport of estradiol (EST) was not detected in either cell group. Though the diffusion transports of EST for both directions, basal-to-apical and apical-to-basal, were higher than that of COR, cellular accumulation of EST was higher than that of COR. Transepithelial transport of TeCB was very low and the net basal-to-apical transport was not detected, while it was highly accumulated in the epithelial cells. The accumulation was slightly higher in LLC-COL than in LLC-PKI at high dose.

Impaired cued delayed alternation behavior in adult rat offspring following exposure to 2,3,7,8-tetrachlorodibenzo-p-dioxin on gestation day 15

This investigation used random ratio (RR) and cued delayed alternation procedures to examine the operant behavior of adult male and female rats following prenatal 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD). Offspring were exposed to a single maternal dose of 0.0, 0.06, 0.18 or 0.54 microg/kg po of TCDD on gestation day (GD) 15. For RR, adult subjects were trained to respond on one lever in a two-lever chamber for food reinforcement. The response requirement was increased across sessions. Male offspring responded at higher rates than females regardless of RR value and prenatal exposure history. For delayed alternation, animals were required to alternate responses on both apparatus levers and to inhibit responding during randomly interpolated delay intervals. The performance of male and female offspring exposed to 0.18-microg/kg TCDD was significantly less accurate and this group committed more errors by responding during the delay intervals than the other exposure groups. A similar trend was observed in the 0.54- microg/kg group. Overall, response accuracy during the delayed alternation procedure was inversely related to delay length and tended to improve with experience. Interpretations of these outcomes include the possibility that TCDD interfered with the development of attentional processes, impaired response inhibition or promoted response perseveration despite the presence of cues, indicating changes in reinforcement contingencies.

Determination of tissue-blood partition coefficients for a physiological model for humans, and estimation of dioxin concentration in tissues

The tissue-blood partition coefficients for a physiologically based pharmacokinetic (PBPK) model were determined, and the concentrations of 17 congeners of polychlorinated dibenzo-p-dioxins and polychlorinated dibenzofurans (PCDD/Fs) in tissues in Japanese people were estimated using the model. According to the PBPK model established by Lawrence and Gobas [Chemosphere 35 (1997) 427-452], we assumed a steady-state fugacity model for Japanese people in general, and set the route of PCDD/Fs exposure only from food intake. The required partition coefficients for liver, kidney, adipose, muscle, skin, bile, gut and viscera (richly perfused tissue) were calculated using available autopsy data from eight Japanese men and women who were not accidentally exposed to PCDD/Fs. For validation of the partition coefficients, estimated PCDD/F concentrations in liver, kidney, fat, blood and muscle using the model were compared to other two sets of measured concentration data in Japanese tissues. Good agreement was obtained between estimated data and measured data, and most of the measured data were within the simulated concentration range in liver, kidney, blood and muscle. From these results, our model and calculated partition coefficients seem applicable for the estimation of congener-specific concentrations in human tissues.

Reproductive consequences of EDCs in birds: what do laboratory effects mean in field species?

The varied reproductive strategies of birds present a challenge in developing reliable indices for the assessment of effects of endocrine disrupting chemicals (EDCs). Precocial species, such as quail, appear to be most sensitive to EDC effects during embryonic development. Although the Japanese quail (Coturnix japonica) is a nonnative lab species, its reproductive strategy is similar to that of many free-ranging species. Because a great deal is known about the reproductive biology of this species and Japanese quail have a short generation time, this species is an ideal candidate for testing EDC effects. In this review, we present data collected in a two-generation design with embryonic exposure to estradiol benzoate (EB). This study was conducted to provide fundamental information for establishing reliable reproductive endpoints associated with estrogenic EDC exposure. Data were collected for a variety of endpoints, which were chosen as measures of reproductive capability and success. These reproductive fitness measures included fertility, hatching success, and offspring viability. Endocrine measures consisted of plasma hormone levels and gonad weight/condition. Neuroendocrine systems, such as the monoamine neurotransmitter systems, regulate hypothalamic gonadotropin releasing hormone (GnRH) and reproductive behavior. Therefore, these variables should potentially be very sensitive indicators. Behavioral measures included reproductive behavior. Results showed that embryonic estradiol exposure affected endocrine and behavioral responses in males and impacted productivity in females. Therefore, quails provide an excellent model to determine fundamental actions of EDCs. The laboratory trials then serve as a basis for the extrapolation of findings of controlled laboratory studies to effects that may be observable in free-ranging species.

Prenatal testosterone and luteinizing hormone levels in male rats exposed during pregnancy to 2,3,7,8-tetrachlorodibenzo-p-dioxin and diethylstilbestrol

Changes in the perinatal testosterone surge have been related to demasculinization of the central nervous system and androgen-dependent growth of the reproductive organs in male mammals. Earlier reports suggest that 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) interferes with androgen production, but the perinatal effects have remained elusive. In the present study we explored in utero-effects of TCDD (0.05, 0.1, 0.5, and 1.0 microg/kg), introduced on day 13.5 of pregnancy, on prenatal (day 19.5 post-conception [p.c.]) testosterone (T) surge and pituitary luteinizing hormone (LH) production in TCDD-resistant Han/Wistar (H/W) and TCDD-sensitive Long-Evans (L-E) rats. To elucidate estrogenic effects on T and LH production, Sprague-Dawley (S-D) fetuses with previously known DES-sensitivity were exposed in utero to diethylstilbestrol (DES, 100-300 microg/kg) on days 13.5, 15.5, and 17.5 p.c. For comparison, H/W fetuses that responded to TCDD treatments were exposed to DES at concentration of 100 microg/kg. It was found that TCDD has a stimulatory effect on testicular T synthesis in the H/W fetuses and that their circulating T concentrations increased significantly. The effect was not seen in the inbred L-E fetuses, which throughout the study showed considerably low testicular T levels. Pituitary LH concentrations also increased in the H/W fetuses exposed to TCDD. Effects of TCDD (1.0 microg/kg) in the H/W fetuses could be confirmed in vitro by human chorionic gonadotropin (hCG) stimulation assay showing the highest response rate in the TCDD exposed testes. Stimulation of cyclic AMP (adenosine-3', 5'-cyclic monophosphate[cAMP]) production was not considerably altered by in utero TCDD exposure. A significant depression in testicular and plasma T content was seen in the DES-exposed S-D and H/W fetuses, but pituitary LH levels did not alter considerably. In the presence of hCG, DES-exposed testes showed lower in vitro T and cAMP production rates compared to the untreated testes. TCDD (1.0 microg/kg) increased and DES decreased the male body weight gain, but the changes were not sex-dependent. It is concluded that TCDD may increase the amplitude of the prenatal testosterone surge in male rats by stimulating pituitary LH production and enhancing the sensitivity of the fetal testis to LH. DES, on the contrary, apparently impairs testicular steroidogenesis and pituitary function.

Effects of binary mixtures of six xenobiotics on hormone concentrations and morphometric endpoints of northern bobwhite quail (Colinus virginianus)

This study investigated the effects of six endocrine disrupters in five different doses (0.1, 0.3, 1, 3, 10 mg/kg or microg/kg) in ethanol administered by oral gavage to bobwhite quail eggs. Six eggs each were in each dose group of coumestrol, ethynyl estradiol, indole-3-carbinol, o,p'-DDE, p,p'-DDE, or TCDD. Eggs were also dosed in two sets. One set was ethynyl estradiol (0, 0.03, 0.1, 0.3, 1.0, 3.0, 10.0 microg/kg) and TCDD (0, 0.003, 0.01, 0.03, 0.1, 0.3 microg/kg). This set was dosed below the air cell with corn oil as vehicle. Also, northern bobwhite quail eggs were injected in ovo with nine binary mixtures of six xenobiotics prior to incubation (coumestrol (0.3 mg/kg), ethynyl estradiol (3.0 microg/kg), indole-3-carbinol (3.0 mg/kg), o,p'-DDE (1.0 mg/kg), p,p'-DDE (1.0 mg/kg), TCDD (0.1 microg/kg)). The mixtures injected were p,p'-DDE+indole-3-carbinol, coumestrol+indole-3-carbinol, TCDD+indole-3-carbinol, p,p'-DDE+o,p'-DDE, p,p'-DDE+ethynyl estradiol, coumestrol+ethynyl estradiol, coumestrol+TCDD, o,p'-DDE+ethynyl estradiol, TCDD+ethynyl estradiol. Eggs were dosed once prior to initiating incubation. Quail were allowed to hatch and were sacrificed at 21 days of age. Blood, measurements, and tissues were collected. Survival was significantly affected by increasing concentrations of TCDD in ethanol as revealed by trend analysis. Survival was also affected significantly by o,p'-DDE in ethanol but not by trend. Survival results of mixtures indicate significant differences among mixture, mixture components, and controls for coumestrol+TCDD, ethynyl estradiol+TCDD, and indole-3-carbinol+TCDD. Some trends from doses of single compounds that are supported by results in the literature were observed for hatchling weight of ethynyl estradiol dosed females, weight gain of indole-3-carbinol dosed males, weight gain and liver somatic index of o,p'-DDE dosed males, spleen somatic index of TCDD dosed males, and weight gain, gonad somatic index and egg gland somatic index of TCDD dosed females. In conclusion, the dose response treatments appeared to have effects beyond effects on survival of in ovo dosed quail. For mixtures, plasma estradiol concentrations were significantly different among coumestrol+ethynyl estradiol, ethynyl estradiol, coumestrol, and vehicle treatments. Liver somatic index among the same treatments was also significantly different. Kidney somatic index among ethynyl estradiol+p,p'-DDE, ethynyl estradiol, p,p'-DDE, and vehicle treatments was significantly different. Plasma estradiol and plasma testosterone ratios were very different among o,p'-DDE+p,p'-DDE, o,p'-DDE, p,p'-DDE, and vehicle treatments. Coumestrol and ethynyl estradiol appear antagonistic for plasma estradiol concentrations and liver somatic index when both chemicals are present together. Ethynyl estradiol and p,p'-DDE appear to act additively on kidney somatic index when combined together. Mixtures of compounds, used in this study indicate effects very different from either or both mixture components, indicating the lack of predictability of chemicals when combined in mixtures.

The mammalian testis accumulates lower levels of organochlorine chemicals compared with other tissues

Tissues were obtained from three separate experiments in order to quantify the tissue distribution of organochlorine chemicals that are thought to be potential reproductive toxicants in males: 1) Sprague Dawley rats received 1 microCi of 14C-Aldrin or 14C-Dieldrin (20.6 microCi/micromole) i.p. once a week for three weeks. One week and four weeks after the last injection, tissues were harvested and stored at -80 degrees C. Tissue 14C levels were quantified by scintillation spectrometry. 2) Cis- or trans-nonachlor (0, 0.25, 2.5, 25 mg/kg body weight) were administered daily in corn oil to male rats by gavage for 28 days. Tissues were harvested and frozen at -80 degrees C on the 29th day. Organochlorine residues were extracted and quantified by gas chromatography with electron capture detection. 3) Technical grade toxaphene (0, 0.1, 0.4 or 0.8 mg/kg body weight) was ingested daily by female cynomolgus monkeys of reproductive age for 18 months prior to being mated with control males. Dosing continued during pregnancy and lactation. Their infants received toxaphene via breast milk, and upon weaning, they ingested the same dose as their mothers for 48 to 49 weeks until, at 77 to 80 weeks of age, tissues were harvested and stored at -80 degrees C. Organochlorine residues were extracted and quantified as previously stated. In all three experiments, organochlorine residues in the testis were lower than in most of the other reproductive tract and nonreproductive tract tissues we examined. For example, testicular aldrin and dieldrin levels were <5% the epididymal content; testicular cis- and trans-nonachlor were <25% the epididymal content and, testicular toxaphene levels were <15% of the epididymal content. The reasons for the low degree of accumulation by the testis in comparison with other tissues are unknown. However, the lower testicular content may afford germ cells some protection from the potentially toxic effects of these chemicals.

Estrogenic and antiestrogenic effect of in vitro treatment of follicular cells with 2,3,7,8-tetrachlorodibenzo-p-dioxin

OBJECTIVE

Two types of follicular cells from preovulatory ovary were cultured in vitro separately and in co-culture to test difference in 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) action on particular cell types.

METHODS

The accumulation of TCDD in follicular wall was analysed using coupled capillary gas chromatography mass spectrometry. Whole preovulatory follicles were isolated from ovary and incubated with prolonged exposure to 0.1 nM TCDD or single exposure to 10 nM TCDD for four days. In the second part of experiments direct effects of TCDD on steroidogenesis were investigated in porcine theca cells (Tc) and granulosa cells (Gc) cultured alone and in co-culture (GT). The media were collected after four days for steroid analysis.

RESULTS

59.3% and 81.2% of TCDD added to the culture medium was accumulated after 0.1 and 10 nM, respectively. TCDD in a dose-dependent manner increased estradiol secretion with concomitant progesterone secretion by theca interna cells. On the other hand decrease of both progesterone and estradiol secretion by granulosa cells cultured alone and in co-culture with theca cells was noted.

CONCLUSION

Different cell-specific estrogenic or antiestrogenic effect of TCDD were found in ovarian follicles.

Semen quality after prenatal exposure to polychlorinated biphenyls and dibenzofurans

Large-scale poisoning occurred in central Taiwan in 1979 from ingestion of cooking oil contaminated by polychlorinated biphenyls (PCBs) and polychlorinated dibenzofurans. To determine whether in-utero exposure to these chemicals alters reproductive function, all prenatally exposed boys and appropriate controls were contacted for medical examination in 1998. Sperm of exposed children have increased abnormal morphology, reduced motility, and reduced capacity to penetrate hamster oocytes. Whether this will cause reduced fecundity, and how these effects can be extrapolated to the general population exposed to background levels of PCBs and dioxin-like chemicals, warrants further investigation.

Paternal concentrations of dioxin and sex ratio of offspring

BACKGROUND

2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD or dioxin), is commonly considered the most toxic man-made substance. We have previously shown that high serum concentrations of TCDD in parents from Seveso, Italy, were linked to their having a relative increase in the number of female births after the parents exposure to a release of dioxin in 1976. We have continued the study to determine whether the parents' sex and/or age at exposure affected the sex ratio of their children.

METHODS

We measured the TCDD concentrations in serum samples from potentially exposed parents collected in 1976 and 1977, and investigated the sex ratio of their offspring.

FINDINGS

Serum samples were collected from 239 men and 296 women. 346 girls and 328 boys were born to potentially exposed parents between 1977 and 1996, showing an increased probability of female births (lower sex ratio) with increasing TCDD concentrations in the serum samples from the fathers (p=0.008). This effect starts at concentrations less than 20 ng per kg bodyweight. Fathers exposed when they were younger than 19 years of age sired significantly more girls than boys (sex ratio 0.38 [95% CI 0.30-0.47]).

INTERPRETATION

Exposure of men to TCDD is linked to a lowered male/female sex ratio in their offspring, which may persist for years after exposure. The median concentration of dioxin in fathers in this study is similar to doses that induce epididymal impairments in rats and is about 20 times the estimated average concentration of TCDD currently found in human beings in industrialised countries. These observations could have important public-health implications.

Reproductive effects of endosulfan on male offspring of rats exposed during pregnancy and lactation

1. The reproductive effects of endosulfan on the male offspring of rats were examined. Dams were treated orally with 0, 1.5 or 3.0 mg endosulfan/kg from day 15 of pregnancy to postnatal day (PND) 21 of lactation. The male offspring rats were investigated at PND 65 or 140, corresponding to the pubertal and adulthood stage of development. 2. The dose of 3.0 mg endosulfan/kg induced a decrease in maternal body weight during pregnancy, but litter size and mean birth weight were not affected. Similarly, the age at testis descent and preputial separation was not affected on the male offspring. 3. The daily sperm production (x10(6)) was permanently decreased in the highest dose group when investigated at puberty and at adulthood. At the lowest dose, however, the daily sperm production was significantly reduced only at puberty. 4. Histologically, the percentage of seminiferous tubules showing complete spermatogenesis was significantly decreased at puberty. This finding may explain the decrease in daily sperm production observed in the endosulfan-exposed male rats. 5. The results of this study show that low doses of endosulfan have no apparent effect on developmental landmarks or on the weight of reproductive and accessory sex organ. Daily sperm production was the most susceptible endpoint in the male offspring exposed to endosulfan during pregnancy and lactation. To further understand the reproductive effects of endosulfan on male rat offspring, additional reproductive and toxicokinetic studies should be carried out to determine the extent of endosulfan exposure in male rat offspring in utero and during lactation.

An optimized approach for the assessment of sexual behavior in male rats

The improvement and optimization of methods used to detect reproductive disorders in experimental animals are among the main challenges facing researchers in this field. The conventional method for testing male sexual behavior uses ovariectomized females rendered sexually receptive by injection of estradiol benzoate and progesterone prior to testing. The receptive females are then mated with exposed male rats during the dark phase of the cycle under dim red light followed by direct visual and momentary observation of the mating activity. The ovariectomized females may respond differently to hormonal injection (individual differences), leading to variations in the intensity of lordosis. Additionally, the data obtained by the direct visual and momentary evaluation of copulatory activity are very subjective and may produce inaccurate results. In the optimized method, the sexual cycles of female rats are determined, and only those in estrus are selected and mated with sexually experienced male rats. The mating activity is videotaped, enabling the correct observation and evaluation of the different components of mating behavior. This method fosters animal welfare by avoiding surgical intervention and enables the videotape to be kept as permanent documentation.