Pretreatment with periodate-oxidized adenosine enhances developmental toxicity of inorganic arsenic in mice

BACKGROUND: Inorganic arsenic, given by injection to pregnant laboratory animals, can induce malformations. Arsenic methylation can be inhibited by periodate‐oxidized adenosine (PAD). Severe human health effects from high chronic arsenic exposure have mainly been reported in populations with significant levels of malnutrition, which may enhance toxicity by diminishing arsenic methylating capacity. This study sought to determine the effect of inhibition of arsenic methylation on the developmental toxicity of arsenic in a mammalian model. METHODS: PAD (100 µM/kg, i.p.), was given to pregnant CD‐1 strain mice 30min before 7.5mg/kg sodium arsenite [As(III)], i.p., or 17.9mg/kg sodium arsenate [As(V)], i.p., on gestation day 8 (GD 8; copulation plug=GD 0). Control dams received As(III), As(V), or PAD alone or were untreated. Test dams were killed on GD 17, and their litters were examined for mortality and gross and skeletal defects. RESULTS: Pretreatment with PAD before either arsenical resulted in increased maternal toxicity and lower fetal weights. Pretreatment also caused higher prenatal mortality, with 8 of 21 and 5 of 17 litters totally resorbed in the PAD plus As(III) and PAD plus As(V) treatment groups, respectively. Significant increases in the incidences of exencephaly, ablepharia, and anomalies of the vertebral centra, sternebrae, and ribs were also associated with PAD pretreatment. Short tail (3 fetuses in 3 litters) was seen only following PAD plus As(III) treatment. CONCLUSIONS: These results demonstrate that the developmental toxicity of inorganic arsenic can be enhanced by PAD, due possibly to inhibited methylation of arsenic. Birth Defects Res B 68:335–343, 2003. © 2003 Wiley‐Liss, Inc.     

Stage-specific skeletal and visceral defects of the I(Kr)-blocker almokalant: further evidence for teratogenicity via a hypoxia-related mechanism.

BACKGROUND: As a class effect, potent I(Kr)-blockers have been shown to induce stage-specific external malformations. The aim of this study was to investigate whether I(Kr)-blockers also induce stage-specific visceral and skeletal defects and to further elucidate a proposed arrhythmia-hypoxia hypothesis. METHODS: Single oral doses of the selective I(Kr)-blocker almokalant (ALM) 25-150 micromol/kg, 7-14 dams/group, were given to Sprague-Dawley rats on gestation days (GD) 10-14, and the fetuses were examined for malformations on GD 21. One group was pretreated with the spin-trapping agent, alpha-phenyl-N-t-butylnitrone (PBN), given intraperitoneally 1 hr before ALM on GD 11. RESULTS: Cardiac ventricular septum defects and vascular malformations were observed after dosing on GD 10-11 and, to a lesser degree, on GD 12-13. Urogenital defects, absence/malposition of the postcaval lung lobe, and attenuated diaphragm were observed mainly on GD 10-11. Skeletal examination showed a high incidence of vertebral abnormalities on thoracic level on GD 10, on lower thoracic to caudal level on GD 11, and sternebral defects were observed all days. On GD 13 brachy-, oligo-, and syndactyly of the forepaw were induced, and of the hindpaw on GD 14. PBN reduced the incidence of both visceral and skeletal defects. CONCLUSIONS: The stage specificity of observed visceral and skeletal defects correlates well with what has been reported in the literature after temporary interruption of oxygen supply during the same stages of development. The protective effect by PBN present further evidence that the teratogenicity of potent I(Kr)-blockers is related to induction of hypoxia- reoxygenation injury due to embryonic cardiac arrhythmia.     

Effect of altering suckling intervals of early-weaned pigs on rebreeding performance of sows

Sows on two commerical farms were assigned to have their pigs weaned after a 3-week lactation (control, n=160) or after a 3-week lactation that included a 48-hr period of interrupted nursing before weaning (altered-suckling, n=122). Sows in the altered-suckling groups were paired, and each member of a pair was separated from both litters during the alternate 12-hr periods. Thus during the final 48 hr before weaning, each sow in the altered-suckling group had two 12-hr periods when no litters were present and two 12-hr periods when two litters were present. On farm 1, interval from weaning to estrus was 12.8 +/- 0.8 days for control sows compared to 8.4 +/- 1.0 days for sows in the altered-suckling group (P<.01). On farm 2, interval from weaning to estrus did not differ between sows in the control group and those in the altered-suckling group (6.2 vs 6.1 days, P>.05). Thus altered-suckling was effective in reducing the interval from weaning to estrus only when the normal rebreeding interval was prolonged (farm 1). Conception rates at first breeding and subsequent litter sizes did not differ between treatments. Altered-suckling may improve reproductive performance of sows in situations where prolonged postweaning anestrus is a problem.     

Detection of micronuclei after exposure to mitomycin C, cyclophosphamide and diethylnitrosamine by the in vivo micronucleus test in mouse splenocytes.

A micronucleus detection test using mouse splenocytes has been adapted from a method previously carried out using human lymphocytes. An ex vivo protocol was chosen: male C57B16 mice were treated with various compounds. Splenocytes were then isolated and placed in culture for 48 h and stimulated with concanavalin A and conditioned medium. The cytokinesis-block method reported by Fenech and Morley was used to detect and score micronuclei in the proliferating lymphocytes (3 micrograms/ml of cytochalasin B for 16 h). Three mutagenic clastogens, mitomycin C (MMC), a direct alkylating agent (0.4, 0.8 and 1.6 mg/kg), cyclophosphamide (CP), an indirect alkylating agent (25, 50 and 100 mg/kg) and diethylnitrosamine (DEN), an indirect alkylating agent with labile metabolites (25, 50 and 100 mg/kg), were tested at four sampling times (2, 4, 8 and 15 days). All three compounds were detected from 48 h after treatment. This method was indeed able to detect clastogenic compounds normally detected by the mouse bone marrow micronucleus test (MMC, CP) as well as a compound with labile metabolites which is not usually detected by this test (DEN). Maximum micronucleus induction was observed after 4 days for MMC, 2 days for CP and 15 days for DEN. This method thus appears to offer a potentially useful toxicological test for assessing in vivo clastogenicity.     

Placental improvement and reduced distal limb defects by maternal interferon-gamma injection in methylnitrosourea-exposed mice

BACKGROUND: Methylnitrosourea (MNU), an alkylating agent derived from creatinine metabolism, is cytotoxic, genotoxic, and mutagenic. Mid-gestational exposure to MNU leads to distal limb defects in mice. Previous studies have shown that nonspecific maternal immune stimulation protects against MNU-induced teratogenesis. A role for immune-mediated placental improvement in this effect remains uncertain. METHODS: The immune system of timed-pregnant C57BL/6N and CD-1 mice was stimulated by GD 7 intraperitoneal (IP) injection with the cytokine interferon-gamma (IFN-gamma). A teratogenic dose of MNU was then administered by IP injection on the morning of GD 9 to disrupt distal limb formation. Fetal limb length, body length, digital deformities, and placental integrity were evaluated on GD 14. RESULTS: The incidence of syndactyly, polydactyly, and interdigital webbing in MNU-exposed mice was decreased by maternal IFN-gamma treatment. In C57BL/6N mice, these defects were reduced by 47, 100, and 63%, respectively, as compared to previous reports on CD-1 mice, by 39, 71, and 20%, respectively. Administration of IFN-gamma significantly diminished MNU-induced endothelial and trophoblast placental damage in both strains of mice. CONCLUSIONS: These findings support a possible link between maternal immunity, placental integrity, and fetal distal limb development. Further, these results suggest that IFN-gamma might act through placental improvement to indirectly protect against MNU-induced fetal limb malformations.     

Artesunate-induced depletion of embryonic erythroblasts precedes embryolethality and teratogenicity in vivo

BACKGROUND: Artesunate (ART), an artemisinin antimalarial, is embryolethal and teratogenic in rats, with the most sensitive days being 10 and 11 postcoitum (pc), respectively (Clark et al.: Birth Defects Res B 71:380-394, 2004; White et al.: Birth Defects Res A 70:265, 2004). METHODS: In this study, pregnant rats were administered a single oral dose of 17 mg/kg ART on Days 10-11 pc and conceptuses were evaluated through Day 14 pc. RESULTS: Paling of visceral yolk sacs was observed within 3-6 hr after treatment. Within 24 hr, marked paling and embryonic erythroblast depletion were observed macroscopically, which preceded malformations and embryo death, and persisted through Day 14 pc. Histologically, embryonic erythroblasts were reduced and cells showed signs of necrosis within 24 hr, were maximally depleted by 48 hr, and had partially rebounded within 3-4 days after treatment (Days 13 and 14 pc). Iron accumulation was evident in treated erythroblasts as early as 6 hr after treatment, suggesting impairment of heme synthesis. Heart abnormalities (swollen or collapsed chambers) were observed within 24 hr in approximately 25-60% of embryos and within 48 hr in 100% of embryos, correlating with histologic signs of cardiac myopathy (thinned and underdeveloped heart walls and enlarged chambers). Delays in limb and tail development occurred by Day 13 pc. Embryos were viable through Day 13 pc, but approximately 77% of embryos had died by Day 14 pc, presumably due to hypoxia and/or cardiac abnormalities. CONCLUSIONS: In summary, embryonic erythroblasts are the primary target of ART toxicity in the rat embryo after in vivo treatment, preceding embryolethality and malformations.     

Target tissue specificity of retinoic acid-induced stress proteins and malformations in mice

Retinoic acid (RA) is teratogenic in rodents and also induces the synthesis of stress proteins in fetal mouse limb buds. To determine if the RA induction of stress proteins is target tissue specific, pregnant CD-1 mice were gavaged with 100 mg/kg RA on day 11 of gestation, and nuclei isolated from tissues susceptible to RA-induced malformations (target tissues) as well as nuclei isolated from nontarget tissues were examined for stress protein synthesis and malformations. Forelimb and hindlimb (target tissues), as well as heart and tail (nontarget tissues), were removed from embryos 2.5 hours after RA treatment (1.5 hr after [3H]leucine labeling). Cell nuclei were isolated, stained with a DNA specific fluorochrome, propidium iodide, and sorted from the G0 + G1 and G2 + M phases of the cell cycle. Forelimb and hindlimb target tissues showed the synthesis in these embryonic nuclear proteins of an 84,000 relative molecular mass (Mr) protein and a 90,000 Mr protein following RA treatment. Two 20,000-25,000 Mr stress proteins were also labeled both in forelimb and hindlimb. Forelimb and hindlimb from untreated dams showed no stress protein labeling. Neither heart nor tail, nontarget tissues, showed any stress protein labeling following RA treatment. Classical teratological evaluation of embryos treated on GD 11 and sacrificed on GD 17 showed that 100% of the fetuses had forelimb and/or hindlimb malformations, while no malformations were observed in either the heart or tail. Based on the correlation of teratological anomalies with the identification of stress proteins in target tissue only, we postulate that stress proteins may be involved in the teratogenic process. Further work is necessary to establish whether a causal relationship exists.     

Effects of protein deficient diets on the developmental toxicity of inorganic arsenic in mice

BACKGROUND: Inorganic arsenic, when given by injection to pregnant laboratory animals (mice, rats, hamsters), has been shown to induce malformations. Arsenic methylation may be a detoxification step, and diets deficient in protein are a poor source of methyl donors and may possibly result in impaired arsenic methylation. Human health effects from chronic arsenic exposure have been reported mainly in populations with low socioeconomic status. Individuals in such populations are likely to suffer from malnutrition, which can compromise embryonic/fetal development and diminish arsenic methylating capacity. We sought to determine if dietary protein deficiency affects the developmental toxicity of inorganic arsenic. METHODS: Mated females were randomly assigned to one of 12 treatment groups. Experimental groups received either AsIII or AsV i.p. on Gestation Day 8 (GD 8, plug=GD 0) and were maintained on a 5%, 10%, or 20% protein custom mixed diet from GD 1 until sacrifice. Controls received the custom diets alone, were given AsIII or AsV i.p. on GD 8 with Teklad LM-485 rodent diet, or were fed the LM-485 diet alone. Test females were sacrificed on GD 17, and their litters were examined for mortality and developmental defects. RESULTS: Arsenic plus dietary protein deficiency decreased maternal weight gain and increased the incidences of exencephaly, ablepharia, and skeletal defects, such as malformed vertebral centra, fused ribs, and abnormal sternebrae (bipartite, rudimentary, or unossified). CONCLUSIONS: These results demonstrate that dietary protein deficiency enhances the developmental toxicity of inorganic arsenic, possibly by impairment of arsenic methylation.     

Vitamin A-Mediated Homeotic Transformation of Tail to Limbs, Limb Suppression and Abnormal Tail Regeneration in the Indian Jumping Frog Polypedates maculatus

In this study the effects of vitamin A on tadpoles of Polypedates maculatus with an amputated tail were investigated. After amputation of half the tail at the hindlimb-bud stage, tadpoles were exposed to vitamin A (palmitate) 10 IU/ml solution for 24 hr (Group I), 48 hr (II), 72 hr (III), 96 hr (IV), 120 hr (V) or 144 hr (VI). Vitamin A was deleterious to survival of the tadpoles since 10, 30 and 30% tadpoles died from Group IV, V and VI, respectively before the emergence of forelimbs. Regeneration of the tail was abnormal in 91.7% of the tadpoles. Vitamin A induced homeotic transformation of the amputated tail to hindlimbs in 11.6% of the animals. Normal limb development was suppressed partially or completely in 48.3% tadpoles. These results indicate that in addition to traumatic effects, vitamin A can lead to homeotic transformation of the tail into hindlimbs and can also interfere with normal development of limbs.     

Effect of a light pulse during the dark on photoperiodic regulation of the rate of thyroxine-induced, spontaneous, and prolactin-inhibited metamorphosis in Rana pipiens tadpoles

Since Rana pipiens tadpoles injected with thyroxine (T4) early in the dark develop more slowly than those injected in the light, we studied the effect of giving a light pulse of 1 hr early in the dark. Tadpoles injected under a 7.5-W red light bulb in a darkened room with 0.2 microgram T4 daily at 2200 hr went through metamorphosis faster on a 12L:3D:1L:8D cycle with a light pulse after injection than on a 12L:12D cycle without a light pulse, and even faster on a 12L:1.5D:1L:9.5D cycle with a light pulse before the injection. Thus a 1-hr light pulse counteracted the metamorphic delay resulting from administration of T4 in the dark, and set in motion the conditions that resulted in a more rapid response to an injection of T4. However, a 1-hr light pulse in the early dark had no effect on growth and development of older or younger untreated tadpoles or those constantly immersed in 30 micrograms/liter T4. Larvae on 21L:3D with T4 injection in the dark and on 12L:3D:1L:8D with T4 injection at 0700 hr just before the start of the main light phase progressed faster than 12L:3D:1L:8D with injection at 2200 hr in the dark before only a 1-hr light pulse. Thus the length of the light phase immediately after T4 injection was significant. There was no difference on 12L:12D and 12L:3D:1L:8D cycles in the effectiveness of daily injections of 10 micrograms prolactin (PRL) in the early dark at 2200 hr in promoting tail growth or antagonizing tail resorption induced by T4 immersion. Under these conditions, PRL utilization did not appear to be inhibited by the light pulse.     

Regulation of estrogen-stimulated lordosis behavior and hypothalamic progestin receptor induction by antiestrogens in female rats

Two estrogen antagonists, CI-628 (CI) and tamoxifen (TX), were used to examine the relationship between estrogen priming of lordosis behavior and progestin receptor induction in the hypothalamus-preoptic area (HPOA) of ovariectomized female rats. Lordosis behavior was assessed by measuring lordosis quotients (LQ) in response to injection of 2 micrograms of estradiol benzoate (EB) followed 48 hr later by 500 micrograms of progesterone (P). Behavior testing began 4 hr after P injection. The effects of antiestrogens were assessed by injecting CI and TX (1-2 mg) from 0 to 48 hr prior to EB. Levels of cytosol progestin receptor in the HPOA were determined by quantifying the specific binding of 0.5 nM [3H]R5020 to cytosols from animals receiving the same EB and antiestrogen treatments used in behavioral testing. TX given concurrently with or CI given 2 hr before EB abolished both lordosis behavior and induction of HPOA progestin receptors. In contrast, CI given 12 hr prior to EB abolished lordosis but permitted a 95% elevation in the concentration of progestin binding sites in the HPOA. TX or CI given 48 hr before EB resulted in moderate levels of lordosis (mean LQs from 56 to 69) and induction of HPOA progestin receptors from 85 to 130% above noninjected controls. However, CI given 24 hr prior to EB produced less than a 40% increase in brain R5020 binding even though lordosis behavior was equivalent to that seen in the 48-hr animals (mean LQ = 53). These data indicate that the effects of antiestrogens on female sexual behavior and on the synthesis of brain progestin receptors depend on which antiestrogen is used and the time interval between administration of estrogen and antiestrogen. They also demonstrate that under some conditions estrogen induction of cytosol progestin receptors in the HPOA can be dissociated from estrogen priming of lordosis behavior in rats.     

Effect of Poly I:C on Experimental Respiratory Infection in Hamsters

The interferon inducer double-stranded polyinosinic acid and polycytidylic acid (poly I:C) was studied in hamsters experimentally infected with parainfluenza 3 virus. Upper intranasal, deep intranasal, or intraperitoneal treatment of hamsters with poly I:C (100 mug/100- to 120-g animal) 24 hr before an upper respiratory infection significantly reduced the virus yields taken 28 hr after infection. Deep intranasal and intraperitoneal treatment with poly I:C greatly decreased the virus titers in the lungs, as measured 48 hr after a deep lung infection with parainfluenza 3 virus; however, the upper respiratory poly I:C treatment was ineffective.     

Development of IVM-IVF produced 8-cell bovine embryos in simple,serum-free media after conditioning or Co-culture with buffalo rat liver cells

Development of 8-cell bovine embryos derived from in vitro matured/in vitro fertilized (IVM/IVF) oocytes was evaluated in two simple, serum-free media (CZB and SOM) with buffalo rat liver cells co-culture (BRLC) or after conditioning compared to a commonly used, serum-supplemented complex medium TCM-199. In a 3 x 4 factorial design, 578 eight-cell embryos were randomly assigned to 12 treatment groups. The factors were: first, type of culture medium (M199/FBS, CZBg and SOM), and second, the use of BRLC (as co-culture or to condition media for 24 hr and 48 hr) and unconditioned media. Development to morula was not affected by the type of medium, but co-culture and 48 hr conditioning within media type resulted in better development when compared to the 24-hr conditioned or unconditioned groups. Blastocyst development in SOM (38.9%) was different (P < 0.05) than in CZBg (46.6%) and M199/FBS (48.7%) and was lowest in the unconditioned group (27.8%) followed by 24 hr conditioned (33.3%), 48 hr (56.3%), and co-culture (59.6%). No blastocyst expansion was observed with unconditioned media and 24 hr conditioned SOM. Significant differences (P < 0.05) were found among all treatment groups except the co-culture and 48-hr conditioned groups. Hatching occurred only with co-culture and 48-hr conditioned groups of M199/FBS and CZBg media. These data show that CZB with glucose conditioned by BRLC monolayers for 48 hr can support the development of IVM/IVF produced bovine embryos to blastocyst compared to culture in TCM-199 with serum. © 1994 Wiley-Liss, Inc.     

Refinement of a morphological scoring system for postimplantation rabbit conceptuses

BACKGROUND: The rabbit is used extensively in developmental toxicity testing, yet basic information on rabbit embryo development is lacking. The goals of this study were to refine a rabbit embryo morphology scoring system, and use it to evaluate rabbit whole embryo cultures (WEC). METHODS: A total of 265 conceptuses were harvested between GD 8.0 and 12.0 (coitus = GD 0) at 6-hr intervals and examined in detail. Discreet developmental landmarks were then established for 18 morphological features and assigned scores ranging from 0 up to 6. The scoring system was then validated on a subset of randomly selected in vivo conceptuses, and was used to evaluate conceptuses grown for 12, 24, 36, or 48 hr in WEC beginning from GD 9.0 or 10.0. A few embryos also were examined using microscopic computed tomography (microCT)-based virtual histologytrade mark to assess the utility of this technology. RESULTS: Morphology scores of in vivo developed conceptuses increased linearly (r2 = 0.98) with advancing gestational age, from means of 0.0 on GD 8.0 to 67.9 on GD 12.0. Application of the scoring system, supplemented with evidence from Virtual histologytrade mark, indicated that the WEC system supported normal morphological development of rabbit conceptuses. However, when explanted at GD 9, the rate of development was about 20% slower than in vivo, whereas the rate of development in WEC from GD 10 was indistinguishable from in vivo. CONCLUSIONS: This work enhances the evaluation tools available to study mechanisms of normal and abnormal development in this widely used animal testing species.     

Mirex-induced adaptive liver growth: a corticosterone-mediated response

The adaptive liver growth response was investigated in intact and adrenalectomized rats. When adult male rats were given a single oral dose of mirex (100 mg/kg body weight) there was a 72% increase in relative liver weight (RLW) in 72 hr. Based on [3H]-thymidine [( 3H]TdR) incorporation into hepatic DNA, there was also a wave of DNA synthesis which peaked at 48 hr and decreased to essentially control values by 96 hr post mirex dose. In mirex-dosed adrenalectomised (Adx) animals, the RLW was increased by only 38% and there was sustained DNA synthesis. When mirex-dosed Adx rats were given corticosterone supplements, the RLW response was similar to the RLW response in intact mirex-dosed rats. However, the 48-hr DNA synthesis peak seen in intact mirex-dosed rats was eliminated. From these data it is suggested that mirex-induced adaptive liver growth has two components: a hypertrophic component which is mediated by corticosterone, and a hyperplastic component which is independent of corticosterone.     

Malformed foetuses and karyotype abnormalities in the offspring of cyclophosphamide and allyl alcohol-treated male rats

Litters sired by male rats chronically treated with cyclophosphamide (CP) or allyl alcohol (AA), were evaluated for the incidence of foetal malformations and karyotype abnormalities. The male rats were also examined for the induction of deleterious effects on various parameters including those involved in reproductive performance. A highly significant and consistent increase in the numbers of malformed foetuses was seen in the litters from CP-treated male rats. Chromosome preparations revealed that a large proportion of the malformed foetuses carried karyotypic abnormalities. These effects were paralleled by a large increase in the number of post-implantation losses without significant differences in several sperm and semen characteristics including sperm abnormalities. No adverse reproductive effects were observed with allyl alcohol treatment.     

Protection against gram-negative bacteremia in neutropenic mice with recombinant granulocyte-macrophage colony-stimulating factor

Granulocyte-macrophage colony-stimulating factor (GM-CSF) stimulates production of neutrophils in bone marrow and may decrease the incidence of infection during neutropenia. We evaluated the protective role of recombinant GM-CSF against Pseudomonas aeruginosa challenge in neutropenic mice. CD-1 mice treated with cyclophosphamide on days 1 and 2 of the experiment were given GM-CSF (1, 2, or 4 micrograms/day) starting at day 4 of the experiment according to the following protocol: 1) 1 microgram of GM-CSF 2 hr and 24 hr after challenge; 2) 1 microgram 24 hr before challenge, 2 hr and 24 hr after challenge; 3) 2 micrograms injected 24 hr before and 2 hr after challenge; 4) 2 micrograms given 24 hr before and 2 micrograms given 2 hr and 24 hr after challenge; 5) 4 micrograms administered 2 hr and 24 hr after challenge; and 6) saline and bovine albumin controls. The number of blood neutrophils by days 4 and 5 was similar for GM-CSF-treated and untreated animals. Survival was significantly greater in animals given 2 micrograms of GM-CSF at 24 hr before and at 2 hr and 24 hr after challenge with Pseudomonas. Neutrophils and splenic macrophages obtained from GM-CSF-treated mice (2 micrograms/animal) produced significantly greater amounts of O2- (204 +/- 36 nmoles/10(5) cells) than controls (21 +/- 10 nmoles/10(5) cells). Additionally, neutrophils and macrophages from GM-CSF-treated mice killed significantly more bacteria (P. aeruginosa) in vitro and had a greater number of C3b and Fc receptors (78 +/- 12% and 89 +/- 8%) than did cells obtained from control animals.(ABSTRACT TRUNCATED AT 250 WORDS)     

Mirex-Induced Adaptive Liver Growth: A Corticosterone-Mediated Response

The adaptive liver growth response was investigated in intact and adrenalectomized rats. When adult male rats were given a single oral dose of mirex (100 mg/kg body weight) there was a 72% increase in relative liver weight (RLW) in 72 hr. Based on [³H]-thymidine ([³H]TdR) incorporation into hepatic DNA, there was also a wave of DNA synthesis which peaked at 48 hr and decreased to essentially control values by 96 hr post mirex dose. In mirex-dosed adrenalectomised (Adx) animals, the RLW was increased by only 38% and there was sustained DNA synthesis. When mirex-dosed Adx rats were given corticosterone supplements, the RLW response was similar to the RLW response in intact mirex-dosed rats. However, the 48-hr DNA synthesis peak seen in intact mirex-dosed rats was eliminated. From these data it is suggested that mirex-induced adaptive liver growth has two components: a hypertrophic component which is mediated by corticosterone, and a hyperplastic component which is independent of corticosterone.     

Methanol exposure during gastrulation causes holoprosencephaly, facial dysgenesis, and cervical vertebral malformations in C57BL/6J mice

BACKGROUND: Exposure of pregnant outbred CD-1 mice to methanol during the period of gastrulation results in exencephaly, cleft palate, and cervical vertebra malformations [Rogers and Mole, Teratology 55: 364, 1997], while inbred C57BL/6J mice are sensitive to the teratogenicity of ethanol. C57BL/6J fetuses exhibit the holoprosencephaly spectrum of malformations after maternal exposure to ethanol during gastrulation, but the sensitivity of C57BL/6J mice to methanol-induced teratogenesis has not been previously described. METHODS: Pregnant C57BL/6J mice were administered two i.p. injections totaling 3.4 or 4.9 g/kg methanol or distilled water four hrs apart on gestation day 'GD' 7. On GD 17, litters were examined for numbers of live, dead and resorbed conceptuses, fetuses were weighed as a litter and examined externally, and all fetuses were double stained for skeletal analysis. RESULTS: No maternal intoxication was apparent, but the high dosage level caused a transient deficit in maternal weight gain. The number of live fetuses per litter was reduced at both dosages of methanol, and fetal weight was lower in the high dosage group. Craniofacial defects were observed in 55.8% of fetuses in the low dosage group and 91.0% of fetuses in the high dosage group, including micro/anophthalmia, holoprosencephaly, facial clefts and gross facial angenesis. Skeletal malformations, particularly of the cervical vertebrae, were observed at both dosages of methanol, and were similar to those previously reported in the CD-1 mouse following methanol exposure. CONCLUSIONS: The types of craniofacial malformations induced in the C57BL/6J mouse by methanol indicate that methanol and ethanol have common targets and may have common modes of action.