Ordinal dose-response modeling approach for the phthalate syndrome

BACKGROUND

The phthalate syndrome (PS) is a collection of related male reproductive developmental effects, ranging in severity, that have been observed in rats after gestational exposure to developmentally-toxic phthalates. For statistical purposes, the PS is defined as a single endpoint and one dose-response analysis is conducted, rather than conducting multiple analyses on each individual endpoint.

OBJECTIVE

To improve dose-response modeling approaches for the PS and other syndromes of effects by accounting for differing severity levels among the endpoints.

METHODS

Ordinal dose-response modeling was performed on PS data from a published study of diisobutyl phthalate (DIBP) gestational exposure to male Sprague-Dawley rats. To incorporate PS endpoint severity, the endpoints were categorized into ordinal levels based on the expected impact of male developmental endpoint's on fertility. Then, a benchmark dose was estimated for each ordinal level. A bootstrap procedure was used to account for the nested nature of the data, and a sensitivity analysis was performed to assess the bootstrap results. A comparison of the estimates between the ordinal and the dichotomous model was performed.

RESULTS

The ordinal version of the log-logistic model applied to the data categorized by PS endpoint severity level provided benchmark dose estimates that were closer to each other in value and had lower variability than the traditional dichotomous application. The sensitivity analysis confirmed the validity of the bootstrap results.

CONCLUSION

The ordinal dose-response modeling method accounts for severity differences among dichotomous PS endpoints, can be expanded in the future to include more severity levels, and can be used in both single and cumulative phthalate risk assessments.

Recent biomonitoring reports on phosphate ester flame retardants: a short review

Organophosphate triesters (PEFRs) are used increasingly as flame retardants and plasticizers in a variety of applications, such as building materials, textiles, and electric and electronic equipment. They have been proposed as alternatives to brominated flame retardants. This updated review shows that biomonitoring has gained incrementally greater importance in evaluating human exposure to PEFRs, and it holds the advantage of taking into account the multiple potential sources and various intake pathways of PEFRs. Simultaneous and extensive internal exposure to a broad range of PEFRs have been reported worldwide. Their metabolites, mainly dialkyl or diaryl diesters, have been used as biomarkers of exposure and have been ubiquitously detected in the urine of adults and children in the general population. Concentrations and profiles of PEFR urinary metabolites are seen to be variable and are highly dependent on individual and environmental factors, including age, country regulation of flame retardants, and types and quantities of emissions in microenvironments, as well as analytical procedures. Additional large biomonitoring studies, using a broad range of urinary diesters and hydroxylated metabolites, would be useful to improve the validity of the biomarkers and to refine assessments of human exposure to PEFRs.

Developmental toxic potential of di-n-propyl phthalate administered orally to rats

The objective of this study was to evaluate the developmental toxic potential of di-n-propyl phthalate (DnPP) in rats. Pregnant Sprague-Dawley rats were given DnPP at doses of 0 (olive oil), 0.5, 1 and 1.5 g kg⁻¹ per day, by gavage, on gestation days 6-20. Benchmark doses were calculated for the effects of DnPP on fetal weight and anogenital distance of the male fetuses. Maternal body weight gain was significantly reduced at 1.5 g kg⁻¹ per day, over gestation days 6-9. DnPP-treated dams also showed a statistically significant increase in liver weight and a mild but statistically significant peroxisomal enzyme induction at 1 or 1.5 g kg⁻¹ per day. Male and female fetal body weights were significantly reduced at 1.5 g kg⁻¹ per day. There was a statistically significant decrease in the anogenital distance of the male fetuses at 1 and 1.5 g kg⁻¹ per day, and three males (of 75) showed malpositioned testis at the high dose. The mean percentage of fetuses per litter with cervical and thoracic rudimentary ribs was significantly increased at 1 and 1.5 g kg⁻¹ per day. Delayed ossification was seen at 1 g kg⁻¹ per day (phalanges) and 1.5 g kg⁻¹ per day (hyoid, sternebrae, and phalanges). No treatment-related effects on prenatal viability or on fetal external or visceral malformations or variations were observed at any dose. Thus, there was no evidence of teratogenicity up to the high dose of 1.5 g kg⁻¹ per day. The no-observed-adverse-effect level (NOAEL) for developmental toxicity was 0.5 g kg⁻¹ per day.

Differential developmental toxicities of di-n-hexyl phthalate and dicyclohexyl phthalate administered orally to rats

The objective of this study was to evaluate the developmental toxic potential of di-n-hexyl phthalate (DnHP) and dicyclohexyl phthalate (DCHP) in rats. Pregnant Sprague-Dawley rats were exposed to DnHP or DCHP at doses of 0 (olive oil), 250, 500 and 750 mg kg(-1) per day, by gavage, on gestational days (GD) 6-20. Maternal food consumption and body weight gain were significantly reduced at 750 mg kg(-1) per day of DnHP and at the two high doses of DCHP. Slight changes in liver weight associated with peroxisomal enzyme induction were seen in dams treated with DnHP or DCHP. DnHP caused dose-related developmental toxic effects, including marked embryo mortality at 750 mg kg(-1) per day, and presence of malformations (mainly cleft palate, eye defects and axial skeleton abnormalities) and significant decreases in fetal weight at 500 and 750 mg kg(-1) per day. Significant delay of ossification and increase in the incidence of skeletal variants (e.g. supernumerary lumbar ribs) also appeared at 250 mg kg(-1) per day. DCHP produced fetal growth retardation at 750 mg kg(-1) per day, as evidenced by significant reduction of fetal weight. DnHP and DCHP induced a significant and dose-related decrease in the anogenital distance of male fetuses at all doses, and there was a significant increase in the incidence of male fetuses with undescended testis at 500 and 750 mg kg(-1) per day of DnHP. In conclusion, DnHP showed clear embryolethality and teratogenicity, but not DCHP. There was evidence that both phthalates could alter the development of the male reproductive system after in utero exposure, DnHP being much more potent than DCHP.

Diisobutyl phthalate impairs the androgen-dependent reproductive development of the male rat

Diisobutyl phthalate (DIBP) is the branched isomer of DBP; DBP side chains have a four-carbon backbone (C4), whereas DIBP has its four-carbon alkyl side chains rearranged into a three-carbon backbone (C3) with a methyl branch. Di-n-butyl phthalate (DBP), and several other ortho-phthalate esters with side-chain lengths of C4-C6, are known to disrupt the androgen-dependent sexual differentiation in the male rat. This study was performed to determine whether in utero exposure to DIBP would induce permanent and dose-responsive alterations of male reproductive development. Pregnant Sprague-Dawley rats were administered olive oil (vehicle control), DIBP or DBP, by gavage on gestation Days 12-21, at doses of 125, 250, 500, 625mgDIBP/(kg day) and 500mgDBP/(kg day). DIBP caused no overt maternal toxicity, nor reduced litter size. Male offspring displayed reduced neonatal anogenital distance (Postnatal day 1, PND) at 250mgDIBP/(kg day) and higher doses, and dose-related retention of areolas/nipples (PND 12-14). Preputial separation (onset of puberty) was delayed in male offspring at 500 and 625mgDIBP/(kg day). Hypospadias, cleft prepuce, and undescended testis were observed in males (11-12 or 16-17 weeks old) exposed in utero to 500 and 625mgDIBP/(kg day). Histopathological lesions were also present in adult testes, mainly consisting in seminiferous tubule degeneration. Our results show that DIBP can cause severe and specific adverse effects on the male rat reproductive development, with a pattern similar to that of DBP. However, DIBP appeared slightly less potent than DBP in inducing malformations.

Developmental toxic effects of ethylbenzene or toluene alone and in combination with butyl acetate in rats after inhalation exposure

First, the developmental toxic potential of n-butyl acetate (BA) was examined in Sprague-Dawley rats following whole body inhalation exposure, 6 h day(-1), from day 6 to 20 of gestation, at concentrations of 0, 500, 1000, 2000 and 3000 ppm. Maternal toxicity was evidenced by significant decreases in body weight gain at 2000 and 3000 ppm, and by reduced food consumption at 1000 ppm and higher concentrations. The effects on prenatal development were limited to a significant decrease in fetal weight at 3000 ppm. Thus, inhaled BA was not a selective developmental toxicant. In the second part of this study, the developmental toxic effects of simultaneous exposures to ethylbenzene (EB) and BA, or to toluene (TOL) and BA were evaluated. Pregnant rats were administered EB (0, 250 or 1000 ppm) and BA (0, 500 or 1500 ppm), or TOL (0, 500 or 1500 ppm) and BA (0, 500, 1500 ppm), separately and in combinations, using a 2 x 2 factorial design. The maternal weight gain was reduced after exposure to 1000 ppm EB, to 1500 ppm BA, or to 1500 ppm TOL, either alone or in binary combinations. A significant reduction of fetal weight was associated with exposure to 1000 ppm EB alone, to either mixtures of EB with BA, or to 1500 ppm TOL alone or combined with BA at either concentration. No embryolethal or teratogenic effects were observed whatever the exposure. There was no evidence of interaction between EB and BA or between TOL and BA in causing maternal or developmental effects.

Developmental toxic effects ofN-ethyl-2-pyrrolidone administered orally to rats

The developmental toxicity of N-ethyl-2-pyrrolidone (NEP) was studied in Sprague-Dawley rats after oral administration. Pregnant rats were given NEP at doses of 0 (distilled water), 50, 250, 500 and 750 mg kg(-1) day(-1), by gavage (5 ml kg(-1)), on gestational days (GD) 6-20. Maternal toxicity, as evidenced by reduction in body weight gain and food consumption, was observed in all NEP groups at the beginning of treatment (GD 6-9). The incidence of resorptions was significantly increased at 500 mg kg(-1) day(-1), and reached 83% at 750 mg kg(-1) day(-1). There was a dose-related decrease in fetal weight, which was significantly lower than control at 250 mg kg(-1) day(-1) and higher doses. The incidence of malformed fetuses per litter and the number of litters with malformed fetuses were significantly increased at 500 and 750 mg kg(-1) day(-1). Malformations mainly consisted of edema, anal atresia with absent tail, cardiovascular defects and fused cervical arches. Ossification of skull bones and sternebrae was significantly reduced at 500 and 750 mg kg(-1) day(-1). The incidence of supernumerary ribs was significantly elevated at 250 mg kg(-1) day(-1) and higher doses. In conclusion, NEP administered by gavage is embryotoxic and teratogenic at maternal toxic doses.

Comparative developmental toxicities of the three major metabolites ofN-methyl-2-pyrrolidone after oral administration in rats

The developmental toxicity of the three main metabolites of N-methyl-2-pyrrolidone (NMP) was studied in Sprague-Dawley rats. Pregnant rats were given 5-hydroxy-N-methyl-2-pyrrolidone (5-HNMP; 0, 250, 500, 750 or 1000 mg kg(-1) day(-1)), N-methylsuccinimide (MSI; 0, 500, 750, 1000 or 1250 mg kg(-1) day(-1)), or 2-hydroxyN-methylsuccinimide (2-HMSI; 0, 250, 500, 1000 or 1500 mg kg(-1) day(-1)), by gavage, on gestational days (GD) 6-20. No evidence of maternal toxicity was observed in dams given 5-HNMP. Administration of 2-HMSI resulted in overt maternal toxicity at 500 mg kg(-1) day(-1) and higher doses, as indicated by a significant reduction in weight gain and food consumption at the beginning of treatment. There was no evidence of embryo/fetal toxicity in any of the groups treated with 5-HNMP or 2-HMSI. MSI produced marked developmental toxicity in the presence of maternal effects. Maternal body weight gain and food consumption were affected at 750 mg kg(-1) day(-1) MSI, and above. A significant increase in post-implantation loss occurred at 1250 mg kg(-1) day(-1) MSI, and the incidence of fetuses with external or with visceral malformations was significantly increased at 1000 and 1250 mg kg(-1) day(-1) MSI. Malformations mainly consisted of anasarca, cardiovascular defects and diaphragmatic hernia. Fetal weight was significantly reduced at 1000 and 1250 mg kg(-1) day(-1). The incidence of skeletal variations (predominantly cervical ribs, and delayed ossification of skull bones and sternebrae) was significantly elevated at 750 mg kg(-1) day(-1) and higher doses. However, MSI was much less potent than the parent compound. These results indicate that the embryotoxic and teratogenic effects of NMP are not attributable to these metabolites.

Developmental toxicity of combined ethylbenzene and methylethylketone administered by inhalation to rats

Pregnant Sprague-Dawley rats were exposed to ethylbenzene (EB; 0, 250, or 1000 ppm) and methylethylketone (MEK; 0, 1000, or 3000 ppm), alone and in combination, by inhalation, for 6h/day, during days 6-20 of gestation. Maternal toxicity, evidenced by decreased in body weight gain and food consumption, tended to be greater after simultaneous exposures to the high concentrations of 1000 ppm EB and 3000 ppm MEK, when compared to the treatments with individual compounds. No significant increase in embryo/fetal lethality or incidence of malformations and variations was observed in any of the treatment groups. Fetal body weight was significantly reduced after individual treatment with 1000 ppm EB or 3000 ppm MEK, and in the combined groups. There was no evidence of interaction between EB and MEK in causing developmental toxicity.

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.

Developmental toxicity of two trimethylbenzene isomers, mesitylene and pseudocumene, in rats following inhalation exposure

The developmental toxicity of two trimethylbenzene isomers, mesitylene (1,3,5-trimethylbenzene) and pseudocumene (1,2,4-trimethylbenzene) was studied in Sprague-Dawley rats following inhalation exposure. Pregnant rats were exposed whole body to vapours of mesitylene (0, 100, 300, 600, and 1200 ppm) or pseudocumene (0, 100, 300, 600, and 900 ppm), 6h/day, on gestational days (GD) 6 through 20. Significant decrease in maternal body weight gain and food consumption was observed at concentrations of 300 ppm mesitylene, 600 ppm pseudocumene, or greater. Fetal toxicity, expressed as significant reduction in fetal body weight, occurred at 600 and 1200 ppm mesitylene, and at 600 and 900 ppm pseudocumene. There was no evidence of embryolethal or teratogenic effects following inhalation exposure to either of these chemicals. In summary, the no-observed-adverse-effect-level (NOAEL) for maternal toxicity was 100 ppm for mesitylene and 300 ppm for pseudocumene, and the NOAEL for developmental toxicity was 300 ppm for mesitylene and pseudocumene.

Effects of aliphatic nitriles in micromass cultures of rat embryo limb bud cells

The relative effects of a series of eight saturated (acetonitrile, propionitrile and n-butyronitrile) and unsaturated (acrylonitrile, allylnitrile, methacrylonitrile, cis-2-pentenenitrile, and 2-chloroacrylonitrile) aliphatic nitriles were evaluated using an in vitro test for embryotoxicity, the rat limb bud micromass assay. The concentrations that produced 50% inhibition (IC50) of viability and differentiation of the cultured embryonic cells were of the same order of magnitude, whatever tested compound. The IC50 values spread over a wide concentration range from 7-11 microM to 150 mM. Acetonitrile and 2-chloroacrylonitrile were the least and most potent compounds, respectively. The tested chemicals were evaluated using different criteria proposed to identify teratogens in the micromass system, based on either active concentrations or specific inhibition of cell differentiation. A few incorrect classifications were obtained with both nonteratogens and teratogens, when comparing the activity in limb bud cell cultures with the data available on their in vivo teratogenic potential in rats. The concordance between the in vitro and in vivo responses of this set of nitriles was judged insufficient to consider the micromass assay valuable for predicting the in vivo teratogenic outcome of this class of compounds.

Developmental toxicity of N-methyl-2-pyrrolidone in rats following inhalation exposure

The developmental toxicity of inhaled N-methyl-2-pyrrolidone (NMP) was studied in Sprague-Dawley rats. Pregnant rats were exposed whole body to NMP vapours at concentrations of 0, 30, 60 and 120 ppm, 6 h/day, on gestational days (GD) 6 through 20. Maternal body weight gain was significantly decreased at 60 and 120 ppm on GD 6-13 and maternal food consumption was reduced at 120 ppm on GD 13-21. No significant difference in the gestational weight change corrected for the weight of the gravid uterus was observed, whatever NMP concentration. There were no adverse effects on embryo/fetal viability or evidence of teratogenicity at any concentration tested. Fetal toxicity indicated by reduced fetal weight was observed at 120 ppm. Thus, the no-observed-adverse-effect level (NOAEL) for maternal and developmental toxicity was 30 and 60 ppm, respectively.

Developmental toxicities of ethylbenzene, ortho-, meta-, para-xylene and technical xylene in rats following inhalation exposure

The developmental toxicities of ethylbenzene, o-, m-, p-xylene and technical xylene were studied in Sprague-Dawley rats after inhalation exposure. Animals were exposed to either of these agents at 100, 500, 1000 or 2000 ppm, for 6 h/day, during days 6-20 of gestation. All the agents tested caused maternal toxicity expressed as a reduction in maternal body weight gain at 1000 and 2000 ppm. Decreased corrected weight gain and food consumption were observed at 1000 and 2000 ppm ethylbenzene, o-, m- or p-xylene, and at 2000 ppm technical xylene. No evidence of teratogenic effects was found after exposure to any of these agents up to 2000 ppm. Fetal toxicity evidenced by significant decreases in fetal body weights occurred at concentrations of 500 ppm or greater of o-xylene or technical xylene, and 1000 ppm or greater of ethylbenzene, m- or p-xylene. A significant increase in the mean percentage of fetuses per litter with skeletal variations was also noted at 2000 ppm ethylbenzene, o- and p-xylene. In summary, all tested agents produced developmental toxicity at 1000 and 2000 ppm, concentrations that also produced significant maternal toxicity. With o-xylene and technical xylene, developmental toxicity also occurred at 500 ppm, in the absence of maternal toxic effects. However, the only indication of a treatment-related effect was a slight decrease in fetal weight.

Developmental toxicity of N-methyl-2-pyrrolidone administered orally to rats

The developmental toxicity of N-methyl-2-pyrrolidone (NMP) was studied in Sprague-Dawley rats after oral administration. Pregnant rats were given NMP at doses of 0 (distilled water), 125, 250, 500, and 750 mg/kg/day, by gavage, on gestational days (GD) 6 through 20. Significant decreases in maternal body weight gain and food consumption during treatment, and a reduction in absolute weight gain were observed at 500 and 750 mg/kg. The incidence of resorptions per litter was significantly higher than control at 500 mg/kg, and rose to 91% at 750 mg/kg. Examination of the foetuses revealed treatment-related malformations, including imperforate anus and absence of tail, anasarca, and malformations of the great vessels and of the cervical arches. The incidence of malformed foetuses per litter, and of litters with malformed foetuses was significantly increased at 500 and 750 mg/kg. At 250 mg/kg, one foetus showed malformations similar to those recorded at higher dosages. There was a dose-related decrease in foetal body weights (male, female, and total) that reached statistical significance at 250 mg/kg. A significant increase in incomplete ossification of skull bones and of sternebrae was also present at 500 and 750 mg/kg. In summary, the no-observed-adverse-effect level (NOAEL) for maternal and developmental toxicity was 250 and 125 mg/kg/day, respectively. Thus, oral administration of NMP produced developmental toxicity below maternally toxic levels.

Physical and Chemical Factors in the Home and Workplace before and during Pregnancy

OBJECTIVE

To present and discuss current knowledge about the relationship between physical and chemical factors in the home and workplace and adverse reproductive outcomes in the offspring.

DESIGN AND METHODS

Critical review of the scientific literature, focusing mostly on epidemiological research. Reviews and original papers involving human occupational and home exposures to physical and chemical agents and their relation to adverse reproductive outcomes were screened and commented upon.

RESULTS

Only a small proportion of the several thousands of occupational/home exposures have been adequately assessed for reproductive or developmental toxicity. This is reflected in the difficulties of identifying causal associations in humans and in the lack of data.

CONCLUSION

According to present knowledge, very few authors confirmed that reproductive hazards exist in environmental agents, but increased surveillance of occupational exposures in relation to workers' reproductive health is highly desirable in order to assess moderate risks.

Effects of mono-n-butyl phthalate on the development of rat embryos: in vivo and in vitro observations

The present study was conducted to further characterize the embryotoxic effects mono-n-butyl phthalate, a major metabolite of the plasticizer di-n-butyl phthalate, and evaluate its role in the developmental toxicity of di-n-butyl phthalate. The embryotoxic effects of mono-n-butyl phthalate were compared to those of the parent compound di-n-butyl phthalate after a single oral administration of 1.8, 3.6, 5.4, or 7.2 mmol/kg di-n-butyl phthalate or mono-n-butyl phthalate to Sprague-Dawley rats on gestational day 10 (Day 10). Embryos were evaluated for growth and development on Day 12. Both chemicals induced concentration-dependent developmental toxicity (i.e. decreased growth and malformations) which became apparent at 3.6 mmol/kg. Di-n-butyl phthalate and mono-n-butyl phthalate were approximately equally potent and produced qualitatively similar dysmorphogenic effects. Macroscopically, the most common malformations involved the prosencephalon, the optic system, and the mandibular and maxillary processes. In addition, the embryotoxic potential of mono-n-butyl phthalate was evaluated in vitro using the rat whole embryo culture system. Day 10 embryos were cultured for 48 hr in the presence of 0.5 to 5 mM mono-n-butyl phthalate and were then evaluated as the embryos grown in utero. Mono-n-butyl phthalate was a potent direct acting embryotoxicant, causing concentration-related growth retardation and dysmorphogenesis. The spectrum of morphological defects observed in mono-n-butyl phthalate-exposed embryos in vitro was comparable to those seen in vivo in the embryos at the same developmental stage after maternal administration of di-n-butyl phthalate or mono-n-butyl phthalate. These data provide additional evidence in support of the hypothesis that mono-n-butyl phthalate may be the active species for the developmental toxicity of ingested di-n-butyl phthalate in rats.

[Occupational exposure to organic solvents and pregnancy. Review of current epidemiologic knowledge]

The findings and methodological issues of recent epidemiological studies (1989-1999) on adverse developmental effects of maternal occupational exposure to organic solvents are reviewed. Several studies suggest the possibility of a moderate increase in the risk of spontaneous abortion and congenital malformations, especially facial clefts, associated with maternal exposure to solvents. A common methodological weakness of these studies is the inaccuracy of data on exposures. Positive findings encourage further epidemiological studies of high-quality design and use of protective measures to minimize exposure to these agents from the preconceptional period to the end of pregnancy.

Comparative developmental toxicities of aliphatic nitriles: in vivo and in vitro observations

The effects on embryonic development of a series of eight saturated (acetonitrile, propionitrile, and n-butyronitrile) and unsaturated (acrylonitrile, methacrylonitrile, allylnitrile, cis-2-pentenenitrile, and 2-chloroacrylonitrile) nitriles were compared in vitro using the whole embryo culture system. Day 10 rat embryos were cultured for 46 h in rat serum in the presence of either of these chemicals. All the tested chemicals produced concentration-dependent decreases in growth and differentiation and increases in the incidences of morphologically abnormal embryos. A wide range of embryotoxic potency was observed, with 2-chloroacrylonitrile and acetonitrile at the extremes (lowest effect levels of 50 microM and 40 mM, respectively). No common pattern could be drawn for all the eight nitriles tested in vitro, although there were some similarities between the malformations elicited by propionitrile and n-butyronitrile or between those elicited by the five unsaturated nitriles. Presence of a rat hepatic microsomal fraction and NADPH in the culture medium enhanced the embryotoxic effects of the five unsaturated nitriles tested but had no effects on saturated nitriles embryotoxicity. In addition to these in vitro experiments, pregnant rats were given a single oral dose of each compound on Day 10 of gestation and the embryos were evaluated on Day 12 of gestation, i.e., at a time of development corresponding to the developmental stage at the end of the whole embryo culture. All the nitriles investigated produced the characteristic defects developed by embryos exposed to sodium cyanide in utero or in culture. Our results provide further evidence that maternal production of cyanide may contribute to the developmental toxicity of saturated and unsaturated nitriles and suggest that distinct metabolites derived from microsomal metabolism of unsaturated nitriles may also play a role.

Assessment of the developmental toxicity and placental transfer of 1,2-diethylbenzene in rats

Sprague-Dawley rats were administered 1,2-diethylbenzene (1,2-DEB) by gavage on gestational days (GD) 6 through 20 at dose levels of 0 (corn oil), 5, 15, 25 or 35 mg/kg. The dams were euthanized on GD21 and the offspring were weighed and examined for external, visceral and skeletal alterations. Maternal toxicity, indicated by significant decreases in body weight gain and food consumption, was observed at doses of 15 mg/kg and above. Developmental toxicity, expressed as significantly reduced foetal body weights, was seen at doses of 15 mg/kg and higher. There was no evidence of embryolethal or teratogenic effects at any dose tested. The placental transfer of 1,2-DEB was examined after a single oral dose of 25 mg [14C]1,2-DEB/kg on GD18. Maternal and foetal tissues were collected at intervals from 1 to 48 hours. Placental and foetal tissues accounted for less than 0.35% of the administered dose. Levels of radiocarbon in foetuses were lower than those in maternal plasma and placenta at all time points. Analysis performed at 1, 2 and 4 hours indicated that ethyl acetate extractable (acidic) metabolites were predominant in the maternal plasma while n-hexane extractable (neutral) compounds represented the major part of radioactivity in the placenta and foetus. In conclusion, this study demonstrated that 1,2-DEB causes mild foetotoxicity at maternal toxic doses and that the exposure of the developing rat foetus to 1,2-DEB and/or metabolites after maternal administration of 1,2-DEB in late gestation is small.

Developmental toxicities of methacrylic acid, ethyl methacrylate, n-butyl methacrylate, and allyl methacrylate in rats following inhalation exposure

The developmental toxicities of 4 methacrylates were studied in Sprague-Dawley rats after inhalation exposure for 6 h/day, during days 6 to 20 of gestation. The exposure concentrations were, for methacrylic acid, 0, 50, 100, 200, or 300 ppm; for ethyl methacrylate, 0, 600, 1200, 1800, or 2400 ppm; for n-butyl methacrylate, 0, 100, 300, 600, or 1200 ppm; and for allyl methacrylate, 0, 12, 25, 50, or 100 ppm. No significant increases in embryo/fetal lethality or fetal malformations were observed after exposure to any of these methacrylates. Fetal toxicity evidenced by statistically significant decreases in fetal body weights was observed at exposure levels > or = 1200 ppm ethyl methacrylate, > or = 600 ppm n-butyl methacrylate, and at 100 ppm allyl methacrylate. Statistically significant increases in the incidence of fetuses with skeletal variations and of fetuses with any variations were noted at 1200 ppm n-butyl methacrylate. These developmental effects were observed in the presence of overt signs of maternal toxicity. While maternal toxicity was observed, methacrylic acid caused no evidence of developmental toxicity up to 300 ppm.

Relative developmental toxicities of acrylates in rats following inhalation exposure

The developmental toxicities of seven acrylates were studied in Sprague-Dawley rats after inhalation exposure for 6 h/day, during days 6 to 20 of gestation. The exposure concentrations were: for acrylic acid, 50, 100, 200, or 300 ppm; for methyl acrylate, 25, 50, or 100 ppm; for ethyl acrylate, 25, 50, 100, or 200 ppm; for butyl acrylate, 100, 200, or 300 ppm; for ethylhexyl acrylate, 50, 75, or 100 ppm; for hydroxyethyl acrylate, 1, 5, or 10 ppm; and for hydroxypropyl acrylate, 1, 5, or 10 ppm. No treatment-related increases in embryo/fetal mortality or fetal malformations were observed after exposure to any of these acrylates. Fetal toxicity, indicated by reduced fetal body weight, was observed after exposure to 300 ppm acrylic acid, 100 ppm methyl acrylate, 200 ppm ethyl acrylate, and 200 or 300 ppm butyl acrylate in the presence of overt signs of maternal toxicity. While there was evidence of maternal toxicity, no significant developmental toxic effects were observed after exposure to ethylhexyl acrylate, hydroxyethyl acrylate, or hydroxypropyl acrylate at any concentration. These results indicate that inhaled acrylic acid, methyl acrylate, ethyl acrylate, butyl acrylate, ethylhexyl acrylate, hydroxyethyl acrylate, and hydroxypropyl acrylate are not selectively toxic to the embryo or fetus.

Assessment of the developmental toxicity, metabolism, and placental transfer of Di-n-butyl phthalate administered to pregnant rats

The developmental toxicity and placental transfer of di-n-butyl phthalate (DBP) were evaluated in Sprague-Dawley rats given a single oral dose of DBP on Gestational Day 14. In the developmental toxicity study, dams were dosed with 0, 0.5, 1, 1.5, or 2 g DBP/kg and were necropsied on GD21. Increased incidence of resorptions and reduced fetal body weight were observed at 1.5 and 2 g/kg. Higher incidences of skeletal variations were found at doses > or = at 1 g/kg. No embryotoxic or teratogenic effects were observed at a dose of 0.5 g/kg. In the placental transfer study, dams were dosed with 0.5 or 1.5 g [14C]DBP/kg. Maternal and embryonic tissues were collected at intervals from 0.5 to 48 h. Embryonic tissues accounted for less than 0.12-0.15% of the administered dose. Levels of radiocarbon in placenta and embryo were one-third or less of those in maternal plasma. No accumulation of radioactivity was observed in the maternal or embryonic tissues. From HPLC analyses, it was shown that unchanged DBP and its metabolites mono-n-butyl phthalate (MBP) and MBP glucuronide were rapidly transferred to the embryonic tissues, where their levels were constantly lower than those in maternal plasma. MBP accounted for most of the radioactivity recovered in maternal plasma, placenta, and embryo. Unchanged DBP was found only in small amounts. These findings support the hypothesis that MBP, a potent teratogen, largely contributes to the embryotoxic effects of DBP.

Assessment of the developmental toxicity, metabolism, and placental transfer of N,N-dimethylformamide administered to pregnant rats

This study evaluates the developmental toxicity and placental and milk transfer of N,N-dimethylformamide (DMF) in rats. Sprague-Dawley rats were given 0, 50, 100, 200, and 300 mg DMF/kg/day, by gavage, on Gestational Days (GD) 6 through 20. Maternal toxicity was indicated by depressions in weight gain and food consumption at doses >/=100 mg/kg. Fetal toxicity was indicated by decreased fetal body weight at doses >/=100 mg/kg, and by increased incidences of two skeletal variations (absent or poorly ossified supraoccipital and sternebrae) at 200 and 300 mg/kg. Thus, the maternal and developmental no-observed-adverse-effect level was 50 mg/kg/day. The time course disposition of [14C]DMF was examined over a 48-hr period in GD12- and GD18-pregnant rats after a single oral dose of 100 mg [14C]DMF/kg. Peak concentrations of radiocarbon occurred within 1 hr after dosing. Embryonic (GD12) and fetal (GD18) tissues accounted for 0.15 and 6% of the administered dose, respectively. Levels of radiocarbon in embryonic and fetal tissues were equal or slightly less than in maternal plasma up to 8 and 24 hr, respectively, and higher thereafter. HPLC analysis performed at intervals from 1 to 8 hr on GD12 and 1-24 hr on GD18 indicated that unchanged DMF and metabolites were readily transferred to the embryonic and fetal tissues, where their levels were generally equal to those in maternal plasma. The parent compound accounted for most of the radioactivity until 4-8 hr and then decreased. N-Hydroxymethyl-N-methylformamide (HMMF) and N-methylformamide (NMF) were the predominent metabolites and increased with time. Much lower concentrations were found for formamide and N-acetyl-S-(N-methylcarbamoyl)cysteine. Transfer of radioactivity into milk was studied in dams given a single oral administration of 100 mg [14C]DMF on Lactation Day 14. DMF, HMMF, and NMF were found in the milk at concentrations equal to those in plasma.

Postnatal hepatic and renal consequences of in utero exposure to halothane or its oxidative metabolite trifluoroacetic acid in the rat

In utero exposure of rats to low levels of the anaesthetic halothane has been reported to produce ultrastructural changes in the liver and kidney at birth. The current study examined the postnatal functional capacities of the liver and the kidney following prenatal exposure to halothane. Halothane or its oxidative metabolite trifluoroacetic acid (TFAA) were given to Sprague-Dawley rats on gestational days 10-20. Halothane was administered by inhalation at concentration of 50 or 500 ppm 6 h-1 day-1, and TFAA was administered by gavage at doses of 75 or 150 mg kg-1 day-1. The exposed offsprings were examined on postnatal days 3, 12 or 49 for hepatic and renal biochemistry and/or function through measurements of several serum and urinary parameters. Neither halothane nor TFAA treatments had statistically significant effect on litter size, neonatal survival or postnatal growth. Both prenatal halothane and TFAA exposure produced changes in liver biochemistry of newborns, as indicated by significant increases in the serum activities of glutamate dehydrogenase and aspartate aminotransferase. In addition, TFAA caused a functional deficit of the proximal tubule in newborns, as evidenced by the significant increase in the urinary excretion of beta 2-microglobulin. However, these hepatic and renal alterations were restricted to the early postnatal period and were no longer observed by postnatal day 49. It is concluded that prenatal exposure to relatively low levels of halothane can cause slight and transient changes in the neonatal rat liver.

Developmental toxicity of inhaled ethylene oxide in rats following short-duration exposure

The developmental toxicity of ethylene oxide (EtO) was examined in Sprague-Dawley rats following inhalation exposure during Days 6 to 15 of gestation. Two different exposure regimens were used: (1) exposure for 0.5 hr once a day to 0, 400, 800, or 1200 ppm EtO; or (2) exposure for 0.5 hr three times a day to 0, 200, or 400 ppm EtO or 0, 800, or 1200 ppm EtO. Repeated brief exposures (3 x 0.5 hr/day) to EtO caused fetal toxicity indicated by reduced fetal weight at 800 and 1200 ppm, and overt maternal toxicity manifested as reduced body weight gain at 1200 ppm. Neither embryolethality nor teratogenicity occurred following any exposure regimen.

Hepatotoxicity of N, N-dimethylformamide in rats following intraperitoneal or inhalation routes of administration

Male Sprague-Dawley rats were administered a single intraperitoneal injection of N, N-dimethylformamide (DMF, 0.01-1.5 g kg-1) or were exposed for 4 h to DMF vapours (75-900 ppm). The serum activities of the enzymes sorbitol deshydrogenase and glutamate deshydrogenase were used as indicators of liver damage, and were determined at 24, 48 or 72 h post-treatment. Following either route of administration DMF caused concentration-dependent elevations in enzyme activities, the maxima of which occurred later after administration of higher concentrations of DMF than after lower concentrations.

Developmental toxicity of trichloroethylene, tetrachloroethylene and four of their metabolites in rat whole embryo culture

The embryotoxicity of trichloroethylene (TRI), tetrachloroethylene (PER), and of four of their oxidative metabolites i.e. trichloroacetic acid, dichloroacetic acid, chloral hydrate, and trichloroacetyl chloride, was studied in vitro, using the rat whole embryo culture system. Embryos from Sprague-Dawley rats were explanted on gestational day 10 (plug day = day 0) and cultured for 46 h in the presence of the test chemical. All of the tested chemicals produced concentration-dependent decreases in growth and differentiation and increases in the incidence of morphologically abnormal embryos. TRI and PER produced qualitatively similar patterns of abnormalities, while TRI and/or PER metabolites, each elicited clearly distinguishable dysmorphogenic profiles. The presence of hepatic microsomal fractions in the culture medium produced marked decreases in TRI- and PER-induced embryotoxic effects, including mortality, severity of malformations, and delayed growth and differentiation.

Assessment of the developmental toxicity and placental transfer of 1,2-dichloroethane in rats

This study evaluates the developmental toxicity and placental transfer of 1,2-dichloroethane (DCE) in rats. Sprague-Dawley rats were given 0-2.4 mmol DCE kg-1 day-1 by gavage, or were exposed for 6 hr per day to 0-300 ppm DCE by inhalation, from Day 6 to 20 of gestation. Maternal toxicity was observed after inhalation exposure to 300 ppm DCE and oral administration of 2.0 or 2.4 mmol DCE kg-1. There was no evidence of altered growth nor teratogenic effects after either inhalation or oral administration of DCE at any concentration tested. The time course disposition of 14C was examined over a 48-hr period in 12- and 18-day pregnant rats after a single oral dose of 1.6 mmol [14C]DCE kg-1. Peak concentrations of radiocarbon occurred between 2 and 4 hr postdose. Conceptus (Day 12) and fetal (Day 18) tissues accounted for 0.06 and 0.4% of the administered dose, respectively. Up to 4 hr, levels of radiocarbon in placenta and fetus were slightly less than in maternal plasma of 18-day pregnant rats and were two to five times higher at later periods. At 2 hr, unchanged DCE accounted for most of radioactivity (78-86%) recovered in maternal plasma, placenta, and fetus. Acidic metabolites and radioactivity bound to macromolecules increased up to 24 hr (0.01 mumol-eq DCE g-1) in either placental or fetal tissues. Thereafter, their levels declined more slowly than those in the maternal plasma. Results from this developmental toxicity study in rats confirm embryonic exposure to radiocarbon associated with [14C]DCE and/or its metabolites and has demonstrated the lack of observable teratogenic effects.

Specific amino acids modulate the embryotoxicity of nickel chloride and its transfer to the rat embryo in vitro

To investigate the effects of amino acids on the embryotoxicity and placental transfer of nickel chloride (NiCl2), Day 10 rat embryos were cultured in rat serum medium containing NiCl2 or 63NiCl2 (0.34 or 0.68 mM Ni), with or without L-histidine (2 mM), L-aspartic acid, glycine (2 or 8 mM), or L-cysteine (2 mM). After 26 hr, conceptuses were assessed for survival, growth and development, and malformations. The 63Ni contents of embryos and yolk sacs and the extent of 63Ni binding to the proteins of the culture medium were also determined. NiCl2 alone did not affect the embryonic development at 0.34 mM and caused growth retardation and brain and caudal abnormalities at 0.68 mM. Coincubation of L-histidine with 0.34 mM Ni increased Ni concentrations in embryonic tissues compared to 0.34 mM 63Ni alone, but did not elicit NiCl2 embryotoxicity. Coincubation of L-cysteine with 0.34 mM Ni elicited growth retardation and brain abnormalities caused by NiCl2 and increased yolk sac concentrations of 63Ni compared to 0.34 mM 63Ni alone. In contrast, coincubation of L-histidine, L-cysteine, or L-aspartic acid with 0.68 mM Ni reduced the growth retardation and the incidence and/or severity of brain defects caused by NiCl2 and decreased the concentrations of 63Ni in the yolk sacs, compared to 0.68 mM 63Ni alone. L-Histidine also reduced the percentage of NiCl2-elicited caudal defects. Coincubation with glycine did not NiCl2-elicited caudal defects. Coincubation with glycine did not affect the embryotoxic profile, nor the placental transfer of NiCl2. In the presence of L-histidine, L-cysteine, or L-aspartic acid, there was a shift of 63Ni binding from the high-molecular-weight proteins of the culture medium to the low-molecular-weight fraction. Thus, specific extracellular amino acids can modulate the embryotoxicity and placental transfer of NiCl2 in vitro. The pattern of this modulation is dependent on the concentration of NiCl2, as well as on the amino acid.

Modulation of acrylonitrile-induced embryotoxicity in vitro by glutathione depletion

The effects of glutathione (GSH) depletion on the embryotoxicity of acrylonitrile were assessed in vitro using the rat whole-embryo culture system. Day 10 rat embryos were cultured in rat serum medium for 6 h in the presence of 250 microM L-buthionine-S,R-sulfoximine (BSO), a specific inhibitor of GSH synthesis, to deplete GSH in both embryo and visceral yolk sac. Following pretreatment, conceptuses were cultured for an additional 21 h in the presence of 152, 228, or 304 microM acrylonitrile. At the end of the culture period, conceptuses were assessed for survival, growth and development, malformations, and the protein and glutathione content of embryos and yolk sacs were assayed. Acrylonitrile alone produced concentration-related and statistically significant decreases in yolk sac diameter, crown-rump length, head length and number of somite pairs, as well as in embryonic and yolk sac proteins. The chemical also caused dysmorphogenesis of the brain and of the caudal extremity, and a concentration-related and statistically significant increase in GSH content in the yolk sac. Pretreatment with BSO significantly enhanced the embryotoxic effects of acrylonitrile. The conceptuses displayed further decreases in functional yolk sac circulation, yolk sac diameter, crown-rump and head length, when compared to either acrylonitrile or BSO alone. The incidence of caudal malformations and the severity of brain malformations produced by acrylonitrile were also increased. Marked decreases in embryonic and yolk sac GSH contents were observed after exposure to BSO alone or in combination with acrylonitrile.(ABSTRACT TRUNCATED AT 250 WORDS)

Relative developmental toxicities of inhaled aliphatic mononitriles in rats

The developmental toxicities of eight aliphatic mononitriles were studied in Sprague-Dawley rats after inhalation exposure for 6 hr/day, during Days 6 to 20 of gestation. The range of exposure concentrations for acetonitrile was 900 to 1800 ppm; for propionitrile and n-butyronitrile, 50 to 200 ppm; for isobutyronitrile, 50 to 300 ppm; for acrylonitrile and methacrylonitrile, 12 to 100 ppm; for allylnitrile 12 to 50 ppm; and for 2-chloroacrylonitrile, 1 to 12 ppm. Embryolethality was observed after exposure to 1800 ppm acetonitrile, 200 ppm propionitrile, 300 ppm isobutyronitrile; fetotoxicity was observed after exposure to 200 ppm propionitrile, n-butyronitrile, or isobutyronitrile, or to 25 ppm acrylonitrile in the presence of overt signs of maternal toxicity. In the absence of significant maternal toxicity, allylnitrile caused embryolethality, fetotoxicity, and clear teratogenicity at 50 ppm, and n-butyronitrile and methacrylonitrile caused fetotoxicity at 200 ppm and 100 ppm, respectively. While maternal toxicity was observed for 2-chloroacrylonitrile, it did not cause significant embryonal or fetal toxicity up to 12 ppm.

Indirect and lactation-associated changes in renal alkaline phosphatase of newborn rats prenatally exposed to cadmium chloride

Pregnant Sprague-Dawley rats were intraperitoneally injected with physiological saline solution (vehicle) or cadmium chloride (CdCl2) at 2.5 mg kg-1 body wt. on days 8, 10, 12 and 14 of gestation. Offspring were examined for renal alkaline phosphatase activity (ALP) on postnatal days (PND) 3 and 12, and for kidney metallothionein (MTh) and for liver, kidney and entire gastrointestinal tract 109Cd content at birth and on PND 3 and 12. No effects were observed on neonatal survival or on body, liver and kidney weights of pups up to PND 12. Newborns born and fed by mothers exposed to CdCl2 during pregnancy exhibited a significant decrease in ALP activity on PND 3. Conversely, no significant changes were observed in newborns lactated by surrogate non-treated mothers. Renal MTh increased with age but was not influenced by maternal treatment. Traces of 109Cd were present in the liver at birth (5-7 ng). Thereafter, 109Cd was mainly found in the gastrointestinal tract of newborns lactated by their biological mothers (610-690 ng on PND 12), with a marginal uptake in the liver (10-12 ng on PND 12). 109Cd was not detectable in the kidneys at any age (less than 4 ng). These results show that prenatal exposure to Cd cannot be the sole aetiological agent in the induction of the subtle and transitory changes in renal biochemistry observed in offspring born and fed by female rats intraperitoneally injected with 2.5 mg CdCl2 kg-1 body wt. on days 8, 10, 12 and 14 of gestation. The results also contradict the role of a direct effect on the kidney.

Difference in the developmental toxicity of ethylenethiourea and three N,N'-substituted thiourea derivatives in rats

Sprague-Dawley rats were administered ethylenethiourea (ETU), 1,3-dimethyl-2-thiourea (DMT), 1,3-dibutyl-2-thiourea (DBT), or 1,3-diphenyl-2-thiourea (DPT) by gavage from Days 6 to 20 of gestation. Daily dosage levels (mg/kg/day) were ETU at 0, 15, 25 and 35; DMT at 0, 15, 25, 50, 100, and 200; DBT at 0, 15, 25, 50, 100, and 200; and DPT at 0, 25, 50, 100, and 200. There was evidence of maternal toxicity at all doses of DMT and at doses greater than or equal to 50 mg DBT/kg/day. DPT was embryolethal at 200 mg/kg/day. Fetotoxicity was observed at doses greater than or equal to 15 mg DMT/kg/day, greater than or equal to 15 mg DBT/kg/day, and greater than or equal to 100 mg DPT/kg/day. ETU was the only chemical tested that proved to be teratogenic.

Changes in urinary proximal tubule parameters in neonatal rats exposed to cadmium chloride during pregnancy

Pregnant Sprague-Dawley rats were injected intraperitoneally with physiological saline solution (vehicle) or cadmium chloride (CdCl2) at 2.0 or 2.5 mg kg-1 on days 8, 10, 12 and 14 of gestation. On postnatal day (PND) 3, 12 or 49, the offspring were examined for 8- or 24-h urinary excretion of beta 2-microglobulin (beta 2-m), metallothionein (MT) and urinary activity of three proximal tubular enzymes: gammaglutamyl transferase (GGT), alkaline phosphatase (ALP) and N-acetyl-beta-glucosaminidase (NAG). Treatment with CdCl2 did not affect growth or survival of offspring. Significant decreases in the urinary excretion of GGT, ALP and NAG were observed on PND 3, at both doses. Exposure to 4 x 2.5 mg kg-1 resulted in functional deficit of the proximal tubule on PND 3, as evidenced by the significant increase in beta 2-m. Except for a slight but significant increase of beta 2-m in 49-day-old males, all the other urinary parameters returned to control values on PND 12. There was no effect on MT. Results from this study show that prenatal exposure to CdCl2 can induce significant changes in the kidney biochemistry of rats in the early postnatal period.

Pregnancy-associated changes in renal toxicity of cadmium-metallothionein: possible role of intracellular metallothionein

Nulliparous female, 10-day and 20-day pregnant rats were injected intraperitoneally with saline or labelled cadmium-metallothionein (109Cd-MTh) at a single dose of 25 or 250 micrograms Cd as cadmium-metallothionein (Cd-MTh)/kg and sacrificed at 24 h. The renal toxicity was manifested by increased 24-h urinary excretion of beta 2-microglobulin (beta 2-m) and the increased number of damaged convoluted proximal tubules at 24 h. The renal excretion of 109Cd and 109Cd content in the maternal liver and kidney and in the foeto-placental unit were determined. The binding of 109Cd to kidney proteins and the level of intracellular metallothionein (MTh) in livers and kidneys were also determined. It was found that the nephrotoxicity of injected Cd-MTh did not differ in nulliparous and 10-day pregnant rats. This result was consistent with the absence of difference in the renal uptake of 109Cd, its binding to kidney proteins and in the content of endogenous MTh in the kidneys between nulliparous and 10-day pregnant rats. In contrast, 20-day pregnant rats exhibited much more nephrotoxicity than nulliparous rats. The most prominent finding in relation to the extreme sensitivity of 20-day pregnant rats was a lower basal level of intracellular MTh in the kidneys and the accumulation of 109Cd in the high molecular weight proteins in the soluble fraction. It is suggested that the decrease of intracellular MTh in the kidneys of 20-day pregnant rats is the reason for the low protection against the renal toxicity of injected Cd-MTh.

The effects of maternally inhaled formaldehyde on embryonal and foetal development in rats

Sprague-Dawley rats were exposed to 0, 5, 10, 20 or 40 ppm formaldehyde for 6 hr/day from day 6 to 20 of gestation. On day 21 of gestation the rats were killed for evaluation of maternal reproductive and foetal parameters. No effect on embryonic or foetal lethality, nor significant alterations in the external, visceral or skeletal appearance of the foetuses were noted in any of the exposed groups. Significant concentration-related reduction of foetal body weight occurred at 20 and 40 ppm, and at 40 ppm foetal body weights were 20% less than those of the controls. Maternal toxicity, indicated by significant reduction in body weight and absolute weight gain, was observed at 40 ppm. The results of this study show that formaldehyde is slightly foetotoxic at 20 ppm. Neither embryolethal nor teratogenic effects were observed following inhalation exposure at levels up to 40 ppm.

Effects of inhalation exposure to carbon disulfide and its combination with hydrogen sulfide on embryonal and fetal development in rats

Pregnant rats were exposed to 0, 100, 200, 400 or 800 ppm of carbon disulfide (CS2), 100 ppm of hydrogen sulfide (H2S) alone or in combination with 400 and 800 ppm CS2, 6 h/d during days 6-20 of gestation. Maternal reproduction and fetal parameters were evaluated on gestational day 21. Treatment with 100 or 200 ppm CS2 or with 100 ppm H2S caused no maternal toxicity or adverse effects on the developing embryo or fetus. Exposure to 400 or 800 ppm CS2 resulted in a low incidence of club foot and in a significant reduction of maternal weight gain. Significant increases in unossified sternebrae occurred at 800 ppm CS2 and reduction of fetal body weight at 400 and 800 ppm CS2. The latter effect was enhanced by combination with 100 ppm H2S. These results support the conclusion that, at levels of exposure associated with maternal toxicity, CS2 leads to an increase in incidence of club foot and to fetal toxicity which is enhanced by simultaneous exposure to H2S.

Inhalation teratology study on hexachloro-1,3-butadiene in rats

Pregnant rats were exposed to 0, 2, 5, 10 or 15 ppm hexachloro-1,3-butadiene (HCBD) 6 h/d during days 6-20 of gestation. Maternal reproduction and fetal parameters were evaluated on gestational day 21. A significant reduction in maternal weight gain and in fetal body weight occurred at 15 ppm. The incidences of external, visceral and skeletal alterations were not significantly increased in any of the HCBD-exposed groups. It is concluded that exposure of pregnant rats to HCBD by inhalation of concentrations high enough to cause maternal and slight fetal toxicity is neither embryotoxic nor teratogenic.

Effects of prenatal methylmercury exposure on urinary proximal tubular enzyme excretion in neonatal rats

The basal developmental pattern of excretion of 3 proximal tubular enzymes was determined in 8-h urinary specimens from neonatal rats. Gammaglutamyltransferase (GGT), alkaline phosphatase (ALP), and N-acetyl-beta-glucosaminidase (NAG) activities were measured at 3, 6, 9 and 12 days after birth. Subsequently, methylmercury chloride (CH3HgCl), known to induce foetotoxic changes in the proximal tubule was administered on days 8, 10 and 12 of gestation at 3 or 6 mg/kg and its effects on the enzyme activities were examined. Dose-related increases in the 3 enzyme activities occurred at dose levels that produced no maternal or postnatal toxicity, nor overt morphological malformation of the kidney. The peak of enzyme activities averaged about 200% and 130% of the control values for GGT, ALP, and NAG respectively, and occurred on days 3 and 6 in the treated groups. Urinary enzyme activities returned to the control levels from days 6 to 12. Our data point to the possibility of detecting CH3HgCl-induced prenatal effect on the kidney by measuring the 8-h urinary excretion of enzymes by rats in the early postnatal period.