4-Week repeated dose oral toxicity study of N-ethyl-2-pyrrolidone in Sprague Dawley rats.

The solvent N-ethyl-2-pyrrolidone (NEP) was evaluated in a 4-week repeated dose study in rats. NEP diluted in distilled water was orally administered by gavage to male and female Sprague-Dawley rats at doses of 0 (vehicle control), 5, 50, and 250 mg/kg/day for 28 consecutive days. Transient decreases in the body weight and in the body weight gain of the males was observed during the first days of treatment at the 50 and 250 mg/kg/day doses. There was a marked increase in urine volume at the beginning of treatment in males and female rats at doses of 50 and 250 mg/kg/day. No biologically significant differences were observed in hematological and clinical chemistry values in males and females at necropsy. Histological examination revealed an increase in hyaline droplets in the renal tubules of the kidneys and hepatocellular centrilobular hypertrophy in the liver of males at 250 mg/kg/day. Cytochrome P450 concentration in liver microsomes was slightly increased at 250 mg/kg/day in males. The results of this study demonstrate that NEP has mild to no effects at doses up to 250 mg/kg/day when administered orally to rats for 28 days with males being more susceptible than females.

Evaluation of the developmental toxicity of diallyl phthalate administered orally to rats.

The objective of this study was to evaluate the developmental toxic potential of diallyl phthalate (DAP) in rats. Pregnant Sprague-Dawley rats were given DAP at doses of 0 (olive oil), 100, 150, 200, and 250mg/kg/day, by gavage (5ml/kg), on Gestational Days (GD) 6 through 20. Gross examination at necropsy revealed liver lesions in dams given 150mg/kg/day or higher doses. In addition, maternal weight gain and food consumption were significantly reduced at 200 and 250mg/kg/day. There was no significant increase in the incidence of resorptions, or malformations, at any dose. Fetal body weight was significantly reduced at 200 and 250mg/kg/day. There was a significant increase in the incidence of fetuses with skeletal variations at 250mg/kg/day. Retarded ossification of certain bones (i.e. forelimb and hindlimb phalanges, metatarsals, and caudal vertebrae) was also observed. There was no sign of developmental toxicity at 100 and 150mg/kg/day. Thus, DAP caused fetal toxicity at doses which also produced maternal effects, but no embryolethality or teratogenicity.

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 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 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.

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.

Nickel chloride teratogenesis in cultured rat embryos.

Day 10 rat embryos were cultured in rat serum in the presence of 20-80 mug Ni as nickel chloride (NiCl(2))/ml of culture medium, or in serum taken from rats, on day 10 of pregnancy, 1 hr after ip injection of 4 mg Ni/kg body weight (as NiCl(2)). Embryos were exposed to these mediums either for 26 or for 4 hr, and were then transferred to fresh serum for the remainder of the 26-hr culture period. Normal development was observed in embryos cultured in serum from treated females (which was found to contain about 17 mug Ni and 3.4 mg glucose/ml) or in 20 mug Ni/ml (as NiCl(2)) added directly to the culture medium. Some embryos were killed by exposure to 80 or 40 (or more) mug Ni/ml for 4 or 26 hr, respectively. Regardless of the duration of exposure, malformations appeared at 30 mug Ni/ml primarily in the cephalic region. Reduced caudal neural tube and branchial arches, and dilated optic vesicles were observed in embryos exposed to 40 mug Ni/ml for 26 hr. High incidences of poor yolk-sac circulation and incomplete turning, and significant decreases in yolk-sac diameter and number of somite pairs were observed in embryos exposed to 60 or 70 mug Ni/ml for 4 hr, or to 30 to 40 mug Ni/ml for 26 hr. Our results indicate that the early maternal blood consequences of a single ip injection of NiCl(2) in mid-gestation are harmless to the development of day 10 cultured embryos and that nickel is embryotoxic in vitro at concentrations that are probably not reached in vivo under these maternal treatment conditions.

Embryotoxicity of acrylonitrile in whole-embryo culture.

Day 10 rat embryos were cultured in rat serum for 26 hr in the presence of acrylonitrile at concentrations ranging from 76 to 760 mum. Survival was not affected at any concentration tested. Normal development was observed at 76 mum. Acrylonitrile induced concentration-related decreases in growth parameters (yolk-sac diameter, crown-rump length, head length, number of somite pairs), which were statistically significant at concentrations of 304 mum or above. An acrylonitrile concentration of 152 mum induced a significant increase in the incidence of malformations, which rose by 100% at 304 mum. Malformations mainly consisted of a reduction of the brain and a shortened caudal extremity. The presence of 0.1-2.2 mm-reduced glutathione in the culture medium moderated the embryotoxic effects of 304 mum-acrylonitrile in a concentration-related manner. Growth retardation and severity of malformations induced by 304 mum-acrylonitrile were significantly increased by the addition of a hepatic microsomal preparation (S-9, microsomes) and cofactors for cytochrome P-450-dependent biotransformation (NADPH, glucose-6-phosphate) to the culture medium. Our results show that embryotoxicity of acrylonitrile does not require extra-embryonic biotransformation. However, the enhancement by exogenous cytochrome P-450-dependent monooxygenase systems supports a role for oxidative biotransformation in acrylonitrile embryotoxicity.

Interaction between mercuric chloride and zinc in rat whole-embryo culture.

Ten-day-old rat embryos were cultured in rat serum for 24 or 28 hr in the presence of mercuric chloride and zinc chloride alone or together, at concentrations ranging from 15 to 35 mum and 7 to 220 mum, respectively. At the end of the culture period, embryos were observed microscopically for growth parameters and malformations, and examined biochemically for protein and DNA contents. The effects of HgCl(2) on growth and development were related to concentration. Yolk-sac diameter, and head length, number of somites, protein and DNA contents were significantly reduced at 20 and 25 mum-HgCl(2), respectively. Viability decreased at 30 mum-HgCl(2), and malformations appeared at 20 mum-HgCl(2). These mainly consisted of lateral dilatation of prosencephale, swollen mandibular arches, protrusion of the allantois and the extremity of the caudal neural tube from the yolk-sac, turning failure, poor or absent yolk-sac circulation and open cranial neural folds. Embryos exposed to ZnCl(2) developed normally at all doses tested. Addition of ZnCl(2) to the culture medium at concentrations of up to 220 mum, simultaneously or 4 hr before the addition of 25 mum-HgCl(2), failed to ameliorate HgCl(2)-induced teratogenicity. It is concluded that zinc has no influence on the effects induced by HgCl(2) in the whole-embryo culture system.

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.

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.

Comparative developmental toxicities of the three major metabolites of N-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 toxic effects of N-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 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.

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.

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.

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.

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.

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.

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.