Axial skeletal malformations induced by acetazolamide in rabbits.

In order to evaluate the teratogenic potential of acetazolamide in rabbits, three groups of 18 artificially inseminated females were treated orally with 50, 100, or 150 mg/kg/day of acetazolamide on days 6-18 of gestation. These doses induced maternal acidosis and electrolyte changes, consistent with those reported in rats and considered to be a result of carbonic anhydrase inhibition, as well as reductions in maternal body weight gain. At cesarean sections, average fetal body weights in the acetazolamide groups were dose-dependently decreased compared with controls. There were no effects of acetazolamide on embryonic survival or external morphology of live fetuses. In the fetal skeletal examination, thoracic and lumbar vertebral malformations occurred in 0.7%, 3.9%, and 6.1% of fetuses in the 50, 100, and 150 mg/kg/day groups, respectively, compared with none in the control group. In addition, missing vertebra was seen in a small number of fetuses in the 100 and 150 mg/kg/day groups. These axial skeletal malformations were, in some cases, associated with costal malformations. These results indicate that acetazolamide at maternotoxic doses can produce axial skeletal malformations in the rabbit.     

Developmental toxicity of orally administered 2',3'-dideoxycytidine in mice

2',3'-Dideoxycytidine (DDC), a potent inhibitor of human immunodeficiency virus (HIV), is presently undergoing clinical trials as a promising anti-AIDS drug. Since there are very limited published animal toxicity data available, and nucleoside analogues are being considered for treatment of HIV-infected pregnant women, a study was conducted in mice to investigate the potential adverse developmental effects of this drug. DDC, suspended in 0.5% methyl cellulose, was administered via gavage twice per day during gestation days (gd) 6 through 15 to C57Bl/6N mice in a total dose of 0, 200, 400, 1,000, or 2,000 mg/kg/day. Maternal weight gain during the gestation and treatment period, as well as gravid uterine weight, decreased significantly in the 2,000 mg group, but weight gain, corrected for gravid uterine weight, was not affected by DDC. The percent resorptions per litter increased significantly in the highest dose group, and there were fewer live litters because of complete litter resorption in six dams. Among litters with live fetuses, the mean litter size was significantly reduced in the 2,000 mg group. Average fetal body weight per litter decreased significantly in the 1,000 and 2,000 mg groups. The number of fetuses with any malformation, the number of litters with one or more malformed fetuses and the percent of malformed fetuses per litter increased significantly in the 1,000 and 2,000 mg groups. There was an increase in malformations at 400 mg/kg/day; however, it was not statistically significant. In conclusion, DDC produced developmental toxicity (malformations, reduced fetal body weight, and resorptions) in the absence of overt maternal toxicity except for body weight changes due to resorptions and reduced fetal weights.     

Developmental toxicity evaluation of Bendectin in CD rats

Bendectin, composed of doxylamine succinate and pyridoxine HCl (1:1), is an antinauseant previously prescribed for nausea and vomiting during pregnancy. The present study examined the maternal and developmental effects of Bendectin (0, 200, 500, or 800 mg/kg/day, po) administered to timed-pregnant CD rats (36-41/group) during organogenesis (gestational days [gd] 6-15). At death (gd 20), all live fetuses were examined for external, visceral, and skeletal abnormalities. At 500 and 800 mg/kg/day, maternal toxicity included reduced food consumption during treatment and for the gestation period, increased water consumption in the posttreatment period, reduced weight gain during treatment, and sedation; water consumption was reduced during treatment and for the gestation period, and maternal mortality (17.1%) was observed only at the high dose. Developmental toxicity included reduced prenatal viability (800 mg/kg/day) and reduced fetal body weight/litter (500 and 800 mg/kg/day). In addition, reduced ossification of metacarpals (800 mg/kg/day), phalanges of the forelimbs (500 and 800 mg/kg/day), and of caudal vertebral centra (all doses) was observed. No increase in percent malformed live fetuses/litter was observed. The proportion of litters with one or more malformed fetuses was higher than vehicle controls only at 800 mg/kg/day, with short 13th rib (to which the test species is predisposed) as the predominant observation. By contrast, a positive control agent (nitrofen, 50 mg/kg/day, po, 14 dams) produced 85% malformed fetuses/litter with the predominant malformation being diaphragmatic hernia. In conclusion, the incidence of litters with one or more malformed fetuses was increased only at a dose of Bendectin which produced maternal mortality (17.1%) and other indices of maternal and developmental toxicity (see Discussion).     

Evaluation of heart malformations in B6C3F1 mouse fetuses induced by in utero exposure to methyl chloride

C57BL/6 female mice impregnated by C3H males mice to produce B6C3F1 fetuses were exposed daily for six hr to atmospheres containing 0, 250, 500, or 750 ppm methyl chloride, from gestation day 6 to gestation day 18. There were 74 to 77 females with copulation plugs per exposure concentration. Females exposed to 750 ppm ethyl chloride exhibited ataxia commencing on the seventh day of exposure (gestation day 12). They also showed hypersensitivity to touch or sound, tremors and convulsions. Six females in the 750 ppm group died and one was euthanized in extremis prior to scheduled sacrifice. On gestation day 18, all other females were euthanized for evaluation. Only dams exposed to 750 ppm exhibited significant decrease in body weight by gestation day 18, weight gain during the gestation period, and absolute weight gain (weight gain minus gravid uterine weight) versus controls. There were no treatment related-effects on these parameters in the other exposure groups. None of the groups exhibited exposure-related differences in pregnancy rate, gravid uterine weight, or maternal liver weight. There were no differences in the numbers of implantations, resorption, dead fetuses, nonlive (dead plus resorbed) fetuses, live fetuses, sex-ratio, or mean fetal body weight per litter. There was a significant exposure-related increase in the number and percentage of affected (nonlive plus malformed) fetuses per litter with the incidence of affected fetuses in the 750 ppm group significantly higher than controls. There was a statistically significant increase in the incidence of heart defects in the 500 and 750 ppm group relative to controls. Of the 37 fetuses in the study with heart defects, 23 were females, 14 were males. The heart defects observed included: absent or abnormal tricuspid valve, reduced number of papillary muscles and/or chordae tendineae on the right side, small right ventricle, globular heart, and white spots in the left ventricular wall. Multiple malformations were observed in one fetus from the 500 ppm group and in three fetuses in the 750 ppm group. It is concluded that methyl chloride inhalation exposure to pregnant C57BL/6 mice from gestation day 6 through gestation day 17 resulted in maternal toxicity only at the 750 ppm exposure concentration and was teratogenic to B6C3F1 conceptuses at exposure concentrations of 750 and 500 ppm, leading to fetal heart malformations. No evidence of embryo or fetotoxicity other than teratogenicity was seen at any of the exposure concentrations employed. No maternal, embryo or fetotoxicity or teratogenicity was associated with exposure of mice, during critical periods of embryo and fetal development, to 250 ppm of methyl chloride.     

Retinoic-acid-induced limb malformations resulting from apical ectodermal ridge cell death

Pregnant C57Bl/6J mice were treated with single oral doses of 400 mg/kg 13-cis retinoic acid (RA, isotretinoin, Accutane) in sesame oil at 9 days, 12 hours postfertilization. Among the live 16-day fetuses from ten treated mothers, 46% (26/56) had limb malformations including small fifth digits, preaxial and/or postaxial oligodactyly, and preaxial or postaxial polydactyly. Fetuses with preaxial digit deficiencies also had absent or malformed radii. Scanning electron microscopic and light microscopic analyses of the sequence of developmental alterations leading to these malformations demonstrated abnormalities in the apical ectodermal ridge (AER). Excessive cell death in the AER of 27-30 somite embryos (12 hours after treatment) appears to play a major role in the pathogenesis of the limb malformations observed. Previous investigations of retinoid-induced limb malformations have concentrated on later exposure times. Evidence from this study in addition to that from previous teratologic and clinical investigations has led to the hypothesis that 13-cis RA results in excessive cell death in regions of programmed cell death and subsequent malformations of affected regions.     

Interactive effects of cadmium and all-trans-retinoic acid on the induction of forelimb ectrodactyly in C57BL/6 mice

BACKGROUND: Most toxicological studies have tested single chemical agents at relatively high doses, and fewer studies have addressed the toxic effects of chemical interactions. It is important to understand the toxicity of chemical mixtures in order to assess the more realistic risks of environmental and occupational exposures. A number of chemicals are known to induce a predominantly postaxial forelimb ectrodactyly in C57BL/6 mice, including acetazolamide, ethanol, cadmium, valproic acid, carbon dioxide, dimethadione, phenytoin, and 13-cis-retinoic acid and all-trans-retinoic acid (RA). In the present study, the interactive effects of coadministration of cadmium and RA on developing limbs were investigated. METHODS: Pregnant C57BL/6 mice were treated with different intraperitoneal (IP) doses of cadmium chloride (CdCl2) and/or RA on gestational day (GD) 9.5, and fetuses were collected on GD 18 and double stained for examination of skeletal defects. RESULTS: When RA was given simultaneously with cadmium, a significant increase in the incidence and severity of forelimb ectrodactyly (predominantly postaxial) was observed compared to the results with corresponding doses of cadmium or RA alone. When mice were exposed to subthreshold doses of both cadmium (0.5 mg/kg) and RA (1 mg/kg), the combined treatment exceeded the threshold, resulting in forelimb ectrodactyly in 19% of the fetuses. Moreover, coadministration of cadmium and RA at doses exceeding the respective thresholds showed a synergistic effect, that is, 92% of fetuses were found with the forelimb defect as opposed to 10% if the response were additive. CONCLUSIONS: The findings demonstrate that concurrent exposure to these teratogens can have a synergistic effect and that subteratogenic doses may combine to exceed a threshold.     

Prevention of caffeine-induced limb malformations by maternal adrenalectomy

Caffeine at high doses is a known rodent teratogen and induces limb malformations along with cleft palate in various strains of rats and mice. Fujii and Nishimura ('74) postulated that caffeine was teratogenic by virtue of catecholamine release from maternal or embryonic tissue. We tested this hypothesis by surgically removing the maternal adrenal gland on day 6 of pregnancy and then administering 175 mg/kg of caffeine intraperitoneally at 1600 h day 11 and 900 h day 12. The teratogenic effects of caffeine in adrenalectomized versus nonadrenalectomized AKR mice were assessed in day 18 fetuses. Thirty percent of the surviving offspring were malformed in caffeine-treated, nonadrenalectomized dams compared to 7% of the offspring from adrenalectomized dams. Therefore we believe caffeine teratogenesis is initiated by release of catecholamines from the maternal adrenal gland.     

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.     

A gene(s) for all-trans-retinoic acid-induced forelimb defects mapped and confirmed to murine chromosome 11

All-trans-retinoic acid (RA) induces various anatomical limb dysmorphologies in mice dependent on the time of exposure. During early limb development, RA induces forelimb ectrodactyly (digital absence) with varying susceptibilities for different inbred mouse strains; C57BL/6N are highly susceptible while SWV are resistant. To isolate the genetic basis of this defect, a full-genome scan was performed in 406 backcross fetuses of F(1) males to C57BL/6N females. Fetuses were exposed via a maternal injection of 75 mg of RA per kilogram of body weight on gestational day 9.25. The genome-wide analysis revealed significant linkage to a chromosome 11 locus near D11Mit39 with a maximum LOD score of 9.0 and to a chromosome 4 locus near D4Mit170. An epistatic interaction was detected between loci on chromosome 11 (D11Mit39) and chromosome 18 (D18Mit64). Linkage to the chromosome 11 locus (D11Mit39) was confirmed in RA-treated backcross fetuses of F(1) females to C57BL/6N males. Loci associated with bone density/mass in both human and mouse were previously detected in the same region, suggesting a mechanistic linkage with bone homeostasis. The human syntenic region of this locus has been previously linked to Meckel syndrome; the phenotype includes postaxial polydactyly, an ectopic digital defect hypothesized to be induced by a common molecular pathway with ectrodactyly.     

Evaluation of the protective activity of deferiprone, an aluminum chelator, on aluminum-induced developmental toxicity in mice

BACKGROUND: Since deferiprone can be an effective chelating agent for the treatment of aluminum (Al) overload, in the present study we investigated whether this chelator could protect against Al-induced maternal and developmental toxicity in mice. METHODS: A single oral dose of Al nitrate nonahydrate (1,327 mg/kg) was given on gestation day 12, the most sensitive time for Al-induced maternal and developmental toxic effects in mice. At 2, 24, 48, and 72 hr thereafter, deferiprone was given by gavage at 0 and 24 mg/kg. Cesarean sections were performed on day 18 of gestation and fetuses were examined for malformations and variations. RESULTS: Aluminum-induced maternal toxicity was evidenced by significant reductions in body weight gain, corrected body weight change, and food consumption. Developmental toxicity was evidenced by a significant decrease in fetal weight per litter and an increase in the total number of fetuses and litters showing bone retardation. No beneficial effects of deferiprone on these adverse effects could be observed. By contrast, a more pronounced decrease in maternal weight gain and corrected body weight change, as well as a higher number of litters with fetuses showing skeletal variations was noted in the group exposed to Al nitrate and treated with deferiprone at 24 mg/kg. CONCLUSIONS: According to the current results, deferiprone would not be effective to prevent Al-induced maternal and embryo/fetal toxicity in mice.     

Developmental toxicity of pentostatin (2'-deoxycoformycin) in rats and rabbits

The developmental toxicity of the potent adenosine deaminase (ADA) inhibitor, pentostatin (2'-deoxycoformycin), was investigated in pregnant rats and rabbits administered daily iv doses during organogenesis. Rats received 0, 0.01, 0.10, or 0.75 mg/kg on gestation days 6-15 and rabbits received 0, 0.005, 0.01, or 0.02 mg/kg on gestation days 6-18 and maternal and fetal parameters were evaluated on gestation day 21 (rats) or 30 (rabbits). Live fetuses were examined for external, visceral, and skeletal malformations and variations. In rats, maternal body weight gain and food consumption were significantly suppressed at doses of 0.10 and 0.75 mg/kg during the treatment period but returned to control levels during posttreatment. Increased postimplantation loss and decreased numbers of live fetuses, litter size, and fetal body weight were observed at 0.75 mg/kg. A statistically significant increase in the incidence of vertebral malformations occurred at 0.75 mg/kg. The incidence of certain skeletal variations (extra presacral vertebrae, extra ribs, hypoplastic vertebrae) was also increased at 0.75 mg/kg. Ossification of cervical centra was reduced at 0.75 mg/kg compared with controls. In rabbits, marked maternal toxicity (death, body weight loss, and decreased food consumption) and reproductive toxicity (abortion and premature delivery) occurred in all pentostatin-treated groups. However, there were no significant effects on number of live fetuses, pre- or postimplantation loss, litter size, or fetal body weights in the animals with live litters. There was also no apparent increase in the incidence of malformations or variations in the live fetuses of pentostatin-treated rabbits. Thus, these studies demonstrate developmental toxicity of pentostatin in rats and rabbits, and teratogenicity in rats, at maternally toxic doses.     

Histological changes induced in developing limb buds of C57BL mouse embryos submitted in utero to the combined influence of acetazolamide and cadmium sulphate

Microscopic defects in limb buds of C57BL mouse embryos after the combined teratogenic action of acetazolamide plus cadmium sulphate administered on day 9 of gestation were studied in serial sections. Postaxial deficiencies observed in 12-15-day embryos and affecting preferentially the right forelimbs were classified in nine morphological types according to increasing amounts of missing parts. Type X defect consists of a nearly complete amelia in which all four limbs are represented only by the girdle and proximal end of the stylopod. Type XI abnormality appears as an intermediate reduction affecting the area of digit IV. In addition to modifications of the forelimb bud shape detected from the 10-day stage onwards, observations made 24 and 48 hr after treatment confirmed that the postaxial defects result from an absolute lack of postaxial mesoderm occurring without cell necrosis as a consequence of a postaxial shortening of the apical ectodermal ridge (aer). In 10-day embryos, the latter appears shortened and hypertrophied; it is later fragmented into alternate thick and thin portions in 11-day affected limb buds. These ectodermal changes might account for the genesis of all types of defects observed. Untreated 9-day embryos with 12-25 pairs of somites display a number of asymmetries between their right and left forelimb territories: Until the 19-somite stage, the vascular supply to that area is provided exclusively by the umbilical vein, which is larger on the right side; the initial amount of somatopleural limb mesoderm is greater in the right rudiment and the genesis of its aer is slightly protracted as compared to the left one. These asymmetries might contribute to the right side predominance of the forelimb defects induced by acetazolamide and cadmium.     

Potentiating effect of caffeine on the teratogenicity of acetazolamide in C57BL/6J mice

Pregnant C57BL/6J mice were treated with 0 or 50 mg of caffeine (CAFF) per kg, and 0, 200 mg/kg (L) or 1,000 mg/kg (H) of acetazolamide (ACZM) during day 9 of gestation (9DPC). Individual fetuses were examined for gross morphological abnormalities and skeletal variations. The increase in fetal malformations seen, especially right forelimb electrodactyly, was augmented at both dose levels of acetazolamide by concomitant exposure to caffeine. Both frequency and severity of ectrodactyly were potentiated by caffeine. Skeletal examination revealed a reduction of the number of ossified cervical and caudal vertebral centra among litters exposed to ACZM at either dose. In either case (ACZM-H, ACZM-L) that effect was augmented by co-administration of CAFF. The first cervical vertebra (C1) appeared to provide the most sensitive index of teratogenic exposure. This study provides evidence that a subteratogenic dose of caffeine can potentiate the teratogenic effect of acetazolamide in C57BL/6J mice when dams are treated on day 9 of gestation. In addition, skeletal examination provided evidence that simultaneous treatment with both agents delayed fetal development. Many litters exposed to ACZM or both agents displayed a reduction in skeletal ossification even in the absence of gross morphological abnormalities, suggesting that ossification can be used as an indicator of prenatal exposure to potentially harmful substances in the C57BL/6 mouse strain.     

Limb reduction defects in humans associated with prenatal isotretinoin exposure.

Retinoic acid has long been used to induce limb reductions defects in experimental animal studies. No limb malformations, however, have been reported among malformed retinoic acid-exposed human fetuses from case reports or epidemiologic studies. We report a child and a fetus with limb reduction malformations following maternal use of isotretinoin (13-cis-retinoic acid) during the first trimester of pregnancy. The child had a unilaterally absent clavicle and nearly absent scapula, with a short humerus and short, synostotic forearm bones. He also had ventriculomegaly and developmental delay, minor dysmorphic facial features, and a short sternum with a sterno-umbilical raphe. The fetus had a unilaterally absent thumb with normal proximal bony structures. Other findings included hydrocephalus, craniofacial anomalies, thymic agenesis, supracristal ventricular septal defect, single umbilical artery, anal and vaginal atresia, and urethral agenesis with dysplastic, multicystic kidneys. Although the limb malformations were quite dissimilar, a number of anomalies that are frequently found among isotretinoin-exposed fetuses/infants were present in both cases. This increases the probability that retinoic acid caused these limb defects, but a causal association cannot be conclusively drawn on the basis of these two retrospective case reports.     

Cadmium induced limb defects in mice: strain associated differences in sensitivity.

Cadmium (CdSO4) was given ip on day 9 at 12 or 24 mumol/kg to pregnant CD-1 (non-inbred) mice. Fetuses showed malformations of the limbs, face, trunk, and tail. There was a statistically significant relationship between the dose of cadmium and the malformation rate. Cadmium (12 mumol/kg ip on day 9) was then given to mice of six inbred strains three of which (A/J, BALB/cJ, and C57BL6J) carry a gene cdm for resistance to cadmium-induced testicular damage, and three strains (AKR/J, CBA/J, and DBA/2J) which do not. Paradoxically, the three strains resistant to cadmium induced testicular damage were significantly more sensitive to its teratogenic effects than were the other three strains. In all inbred strains most malformations involved the limbs. All forelimb defects found in inbred or non-inbred cadmium treated mice were postaxial and indistinguishable from those produced by acetazolamide in mice. The remarkable similarity of the cadmium- and acetazolamide-induced forelimb malformations may be a reflection of the limited number of ways that a rodent forelimb can react to a teratogenic insult. The hindlimb defects were all preaxial.     

Acetazolamide teratogenesis: association of maternal respiratory acidosis and ectrodactyly in C57BL/6J mice

Exposure of C57BL/6J mice to CO2 during a critical period of gestation results in predominantly right-sided, postaxial, forelimb ectrodactyly in the offspring. The incidence and severity of CO2-induced limb malformations has been shown to be dependent on the concentration of inspired CO2, the developmental age of the embryo at exposure and the duration of CO2 exposure. Offspring of acetazolamide-treated C57BL/6J mice also display this highly specific form of ectrodactyly (Green et al., '73). Since the drug has been shown to elevate tissue CO2 tension (Mithoefer and Davis, '58), the teratogenic effect of acetazolamide may be related to induction of a hypercapnic embryonic environment.     

Genetic differences in the frequency of acetazolamide-induced ectrodactyly in the mouse exhibit directional dominance of relative embryonic resistance

Eleven of the common inbred strains of the mouse were surveyed for their teratogenic response to acetazolamide that was administered three times per os at 1,000 mg/kg (9 A.M. and 4 P.M. on day 9 and 9 A.M. on day 10). The products of conception were examined for gross malformations on day 15. One strain, SJL/J, exhibited maternal toxicity to the dosage regime and was excluded from the survey. Five strains exhibited significantly increased resorption rates after treatment. All strains responded with the expected malformation of postaxial forelimb ectrodactyly with a right-sided predominance. Nine of the strains could be assigned to one of four mutually exclusive classes of frequency of ectrodactyly and the tenth strain (BALB/cByJ) showed overlap between the two intermediate classes. The data suggest major genes determine the difference in sensitivity to ectrodactyly rather than a polygenic mode of inheritance. Induced cleft lip was found in four strains and one of these strains, SWR/J, exhibited a significantly higher frequency. The strain differences in sensitivity to induced resorption, forelimb ectrodactyly, and cleft lip were genetically independent. A reciprocal cross study was conducted with five of the strains from the four classes of frequency of ectrodactyly response in order to determine gene action. A significant maternal effect on the ectrodactyly response was found only with one of the strain pairs in the ten sets of reciprocal crosses with the five strains. When there was a significant difference between two strains, the F1 embryos exhibited dominance of relative resistance to ectrodactyly. The directional dominance of relative resistance to acetazolamide-induced ectrodactyly suggests that regulatory genes control the embryonic differences in frequency of ectrodactyly response to acetazolamide. By analogy with other metric traits of development that exhibit directional dominance, the genetic variation in ectrodactyly response that has been observed so far in the mouse embryo may not be involved with the primary target of acetazolamide teratogenesis.     

Teratogenicity and developmental toxicity of valproic acid in rats

The teratogenicity and developmental toxicity of valproic acid (VPA) was investigated in Sprague-Dawley CD rats at doses of 0, 150, 200, 300, 400, and 600 mg/kg administered by gavage on days 7-18 of gestation. The VPA-600 dose was maternally toxic, causing death in two of four dams. This dose produced 100% embryonic resorption. The VPA-400 dose was maternally toxic in as much as maternal weight gain was reduced, but no deaths occurred. At this dose five of fifteen litters were completely resorbed, and 52% of all embryos were resorbed. Among survivors, 49% were malformed (68% having skeletal defects and 41% visceral defects). Fetal weight was reduced by 43% in this group. Most of the defects were ectrodactyly, hydronephrosis, cardiovascular defects, hypoplastic bladder, rib and vertebral defects, and other defects of the limbs and tail. The VPA-300 dose (nine litters) produced fewer defects, larger fetuses, and no increase in resorptions. The defects at this dose were primarily cariovascular, rib, and vertebral. The VPA-200 dose (12 litters) produced no reduction in fetal weight, no increase in resorptions, and few defects. The defects noted were hydronephrosis, cardiovascular abnormalities, and rib defects, primarily wavy ribs. Additional litters were prepared using doses of 150 and 200 mg/kg and were allowed to deliver and grow until 70 days. These doses produced no reduction in maternal weight gain, no reduction in litter size, birth weight, or sex ratio of the offspring. These doses produced no reduction in offspring weight to day 70, no increase in mortality, and only rare cases (two offspring of each dose) of tail defects.(ABSTRACT TRUNCATED AT 250 WORDS)     

Inhibition of isotretinoin teratogenicity by acetylsalicylic acid pretreatment in mice.

Although isotretinoin (ITR) has been suggested to cause malformations via cytopathic effects on embryonic cells, the molecular mechanisms of ITR cytotoxicity in teratogenesis are not clear. Since ITR undergoes metabolism by prostaglandin synthase to a potentially cytotoxic peroxyl free radical, the possible role of prostaglandin synthase metabolism as a modulator of ITR teratogenicity was evaluated. Craniofacial and limb abnormalities were noted in fetuses on day 18.5 of gestation following administration of ITR to pregnant CD-1 mice in a three dose regimen of 100 mg/kg at 4 hr intervals on day 10.5 of gestation (plug day = day 0.5 of gestation). Mice were also treated with acetylsalicylic acid (ASA), an irreversible inhibitor of the cyclooxygenase component of prostaglandin synthase, at doses of 20 and 60 mg/kg body weight 2 hr prior to each ITR dose. ASA pretreatment of mice receiving ITR treatment showed a dose-dependent decrease in the overall incidence of malformations, number of defects per fetus, and the incidence of specific craniofacial and limb defects. Equivalent doses of ASA given to control mice did not cause malformations or alter the incidence of resorptions. These results demonstrate that ASA is able to ameliorate the teratogenic effects of ITR observed in fetal mice near term and indicate that prostaglandin metabolism could play a mechanistic role in ITR teratogenicity.