Pre- and post-conceptional tobacco effects on the CD-1 mouse fetus

The objective of this study was to examine the effect of subchronic administration of an aqueous extract of smokeless tobacco (ST) on the development of the CD-1 mouse fetus. Mice were administered ST for approximately 5 weeks: for 2 weeks prior to breeding, during breeding, and during gestational days 0 to 17. Thus the initial peak nicotine levels occurred prior to breeding and not during the critical periods of gestation. Two ST dosages were administered by gastric intubation three times daily: ST/D-1, equivalent to a dose of 12 mg nicotine/kg of body weight, and ST/D-2, equivalent to 20 mg nicotine/kg body weight. Maternal plasma nicotine levels were determined 30 min after the second intubation during the pretreatment and gestational phases of treatment. At these ST dosages, the weight gain of ST-treated dams was not significantly affected in comparison to treated controls. The mean maternal plasma nicotine level for the low-dosage group was 363 ng/ml, and 481 ng/ml for the high-dosage group, with maternal lethality observed at 9.6% and 28.2%, respectively. No significant differences were seen between control and ST/D-1 maternal and/or fetal values, except for placental weights which were heaviest in the ST group (P less than 0.05). Several differences were noted between the ST/D-2 group and controls: fetal weights were reduced by 5.4% (P less than 0.05); decreased ossification was seen in femur measurements and in nine of ten characteristics measured (P less than 0.05); the frequency of resorptions (7.6%) was almost doubled (controls 4.2%); and the frequency of deaths and malformations was not affected. Under these experimental conditions, the low dose produced a negligible effect on the CD-1 mouse fetus and the dam. The high dose demonstrated growth retardation (P less than 0.05), increased embryotoxicity, and a significant decrease in ossification (P less than 0.05).     

Effect of smokeless tobacco on the development of the CD-1 mouse fetus

The objective of this study was to examine the effect of an aqueous extract of smokeless tobacco (ST) on the development of the CD-1 mouse fetus. Three ST dosages were administered three times daily by gastric intubation during gestational days 1-17: 1 X ST equivalent to a dose of 4 mg nicotine/kg body weight, 3 X ST equivalent to 12 mg nicotine, and 5 X ST equivalent to 20 mg nicotine/kg body weight. Maternal plasma nicotine levels were determined 30 minutes after the second daily intubation at five different times during the gestational period. At these ST dosages, the weight gain of ST-treated dams was not significantly affected in comparison to treated controls, though the difference was significant (P less than .05) in comparison to untreated controls. The mean maternal plasma nicotine level for the low dosage (1 X) group was 99.0 ng/ml, which reasonably approximates human consumption levels. The 3 X ST and 5 X ST dosages produced higher nicotine plasma values, 398 ng/ml and 623 ng/ml, respectively, were considerably more toxic to the dams, and resulted in 18% and 31% maternal deaths. Fetal weights were reduced by 7.4% (P less than .001) in the highest ST dosage group (5 X), whereas at the 1 X and 3 X dosages fetal weight differences were not significantly different from treated controls. Resorptions increased in a dose-related manner (P less than .05), ranging from 4.7% in the 1 X, to 6.4% in the 3 X and 8.9% in the 5 X dosage compared to 3.2% in treated controls. External malformations were few and minor in extent. Internal malformations increased in a linear, dose-related manner (P less than .05). Placental weights were unaffected by ST. The results of skeletal examinations were inconclusive. Precocious ossification was seen in 60% and 70% of the parameters measured in the 1 X and 3 X dosage groups, respectively, in comparison to controls. In the 5 X ST group ossification levels were less than in controls for 30% of the parameters measured. Under these experimental conditions the lowest ST dosage (1 X) produced a negligible effect on the CD-1 mouse fetus and the dam. The highest ST dose (5 X) demonstrated embryotoxicity, growth retardation, few malformations, and maternal toxicity. The intermediate dose (3 X) showed a range of effects between the highest and lowest doses to both the fetus and the dam.     

Teratogenic effects on the CD-1 mouse embryo exposed to concurrent doses of ethanol and aspirin

Human fetal alcohol syndrome characteristics have been seen in the mouse fetus by several investigators who dosed the dam with only one or two doses of alcohol. The purpose of this study was to determine if the fetal effects of acute doses of alcohol (ethanol) are altered by aspirin. CD-1 mice were given two IP doses of a 25% v/v solution of 95% ethanol/saline (2.5 hours apart) and intubated with 250 mg/kg aspirin. The treatment regimen, begun at 8 days, 4 hours gestation, consisted of either aspirin pretreatment 1 hour before or posttreatment 1 hour after the ethanol. Control animals were treated similarly and included vehicle only, ethanol/vehicle, and aspirin/vehicle groups. One group was untreated. On gestational day 18, the dams were killed and the uterine horns were examined for live, dead, and resorbed fetuses. The live were weighed and examined for external malformations and either skeletal or visceral abnormalities. With the litter as the unit of analysis, no significant difference was found in the number of dead and resorbed among groups. There was a significant difference (P less than .01) in average fetal weight in the aspirin-pretreated group. When the total number of fetuses affected was considered, the aspirin pretreatment group showed significantly (P less than .05) more external and visceral malformations. The skeletal examination revealed a significant (P less than .05) difference in anomalies plus delayed ossification in both groups treated with the aspirin/ethanol combination. No significant differences were seen in any category in the groups receiving aspirin alone or ethanol alone. These results indicate an additive effect of aspirin and ethanol on the developing CD-1 mouse fetus.     

Morphometric analysis of the craniofacial development of the CD-1 mouse fetus exposed to alcohol on gestational day eight

Fetal alcohol syndrome (FAS) describes a pattern of dysmorphogenesis observed in some offspring of women who consumed alcohol during pregnancy; partial expression of this pattern are fetal alcohol effects (FAE). The purpose of this investigation was to measure selected craniofacial parameters in the CD-1 mouse fetus following exposure to alcohol on gestational day (D) 8. CD-1 mice were mated for 1 hr; D0.0 designated by the presence of a vaginal plug. On D8, 0 hr, and D8, 4 hr, 33 dams were injected intraperitoneally (IP) with 25% (v/v) alcohol in physiological saline solution (0.015 ml/gm maternal body weight). Appropriate controls were maintained. The animals were sacrificed every 12 hr from D12.0 through D17.0. Implantation sites were examined and recorded as live, dead, or resorbed fetuses. All live fetuses were weighed, examined for gross defects, and fixed in Bouin's solution. Twenty-three bilateral parameters were recorded for linear dimensions defining face and cranium. The fetal weights were statistically lower in treated as compared to control fetuses only on D16.0 through D17.0. Statistical analysis of the morphometrics identified five distinct growth patterns in treated mice as compared to controls. The anomalies induced in the CD-1 mouse fetus following exposure to alcohol on D8.0 resembled FAE rather than FAS. Morphometric analysis of the craniofacial region may be an important clinical tool for the quantitative identification of alcohol-related effects in the offspring of women who consumed alcohol while pregnant.     

LHRH and LH in peripubertal female rats following prenatal and/or postnatal ethanol exposure

The effects of pre- and postnatal exposure to ethanol (ETOH) on LHRH and LH were investigated. Pregnant and/or lactating dams were fed ETOH during: 1) gestation, 2) lactation, or 3) gestation-lactation. Female offspring were decapitated at 30 or 40 days-of-age; trunk blood was collected for plasma LH RIA; and hypothalamic tissues were collected for LHRH RIA. Hypothalamic LHRH content of all ETOH-exposed groups was less than that of non-ETOH-fed controls at 30 and 40 days-of-age (p less than 0.05). Plasma LH concentrations of all ETOH-exposed groups were less than those of non-ETOH-fed controls at 30 and 40 days-of-age (p less than 0.05). Also, at 30 and 40 days-of-age, the plasma LH concentrations of the animals exposed to ETOH during lactation and gestation-lactation were less than those of the animals exposed to ETOH during gestation (p less than 0.05). These data suggest that ETOH exposure during gestation and/or lactation negatively affects hypothalamic LHRH content of female rat offspring. Decreased hypothalamic LHRH content with corresponding lowered plasma LH concentration suggests that ETOH influences development or maturation of hypothalamic LHRH neurons by possibly decreasing their number or synthesizing capability.     

Effect of dietary protein, zinc, and carbon monoxide on fetal zinc concentration in mice

Dietary protein and zinc deficiencies known to be detrimental to the developing fetus are common in pregnant women in developing countries. Everyone in modern society is at risk of exposure to carbon monoxide (CO). This study was conducted to observe the effect of dietary protein, zinc, and exposure to CO on the fetal zinc concentrations by factorial experimentation. Pregnant mice of CD-1 strain were maintained on 17% (control) or 9% (deficient) protein diets mixed with deficient, normal (control), or supplemental zinc throughout gestation. The dams in each dietary group were exposed to air (control) or 500 ppm CO in air in environmental chambers from gestation day 8 to gestational day 18. The dams were sacrificed on d 18 and fetal zinc levels were measured by atomic absorption spectrophotometry. Carbon monoxide levels used in this study had no significant effect on fetal zinc concentration in any treatment group. When both dietary protein and zinc levels were normal, the mean fetal zinc concentrations were higher than all other dietary protein/zinc combinations (15.2±6.0 and 14.2±4.1 μg Zn/g of tissue for 0 and 500 ppm CO levels). However, when dietary protein levels were deficient, supplemental zinc increased the fetal zinc concentrations significantly (12.7±3.8 and 13.1±0.3.6 μg Zn/g of tissue, in 0 and 500 ppm CO groups) as compared to zinc-deficient groups (8.7±3.0 and 10.0±3.3 μg Zn/g of tissue in 0 and 500 ppm CO groups). The results of this study may be relevant to populations that experience both marginal zinc and protein diets during gestation.     

The effects of continuous exposure to 20-kHz sawtooth magnetic fields on the litters of CD-1 mice.

Mated CD-1 mice were exposed to 20-kHz sawtooth magnetic fields similar to those associated with video display terminals (VDT). Four groups of animals were continuously exposed from day 1 to day 18 of pregnancy to field strengths of 0, 3.6, 17, or 200 microT. There were no less than 185 mated dams in each exposure group. On day 18, the dams were sacrificed and assessed for weight gain and pregnancy. The litters were evaluated for numbers of implantations, fetal deaths and resorptions, gross external, visceral and skeletal malformations, and fetal weights. There were no less than 140 pregnant females in each group, and there were no significant differences between any of the exposure groups and the sham group (0 microT) for any of the end points. The results of this study do not support the hypothesis that the 20-kHz VLF magnetic fields associated with video display terminals are teratogenic in mammals.     

Placental transfer of halogenated benzenes (pentachloro-, pentachloronitro-, and hexabromo-) in rats.

The present study was carried out to provide information on the placental transfer of three organohalogens of environmental concern. Pentachloro-, pentachloronitro-, and hexabromobenzene were administered per os to rats daily on days 6 through 15 of gestation at level of 40, 100, and 200 mg/kg body weight. On day 22, the dams were killed and fetuses removed by caesarean section. Maternal brain, heart, kidney, liver, spleen and adipose tissue as well as whole fetus, fetal liver and fetal brain were analyzed for organohalogen residue by GLC. Pentachlorobenzene accumulated in the fetus to a greater extent than hexabromobenzene. In maternal tissues pentachlorobenzene accumulated to the greatest extent in adipose tissue, followed by liver, spleen, brain, heart and kidney. With hexabromobenzene, the greatest accumulation was observed in adipose tissue, followed by spleen, liver, heart, kidney and brain. Pentachloronitrobenzene was not detected (0.05 p.p.m.) in any maternal or fetal tissue.     

Ontogenic Development of Corticotrophs in Fetal Buffalo (Bubalus Bubalis) Pituitary Gland

To evaluate the subpopulation of corticotrophs in developing buffalo (Bubalus bubalis) fetus, pituitary glands were recovered (n=6 per group) from late first, second and third gestational female buffalo dams. The corticotrophs were identified by using specific antibodies against proopiomelanocortin (POMC) and adrenocorticotrophic hormone (ACTH) through immunohistochemistry. There was a significant (P≤0.05) increase of immunoreactive (ir) ir-ACTH cells during late 2^nd trimester while, ir-POMC cells were more (P≤0.05) at late 3^rd trimester of gestation as compared to other age groups. The quantity of co-localized cells for POMC and ACTH was significantly (P≤0.05) greater at the end of 1^st gestation rather than 2^nd and 3^rd gestational fetal adenohypophyseal cells. This study is the first to demonstrate co-localization of POMC+ACTH and the affect of gestational age on the expression of these cells in buffalo fetus adenohypophysis.Key words: buffalo, corticotrophs, fetus, pituitary gland, immunohistochemistry     

Risk factors for dystocia in pigtailed macaques (Macaca nemestrina)

Dystocia (difficult labor) is an important component of the management of nonhuman primates and results in significant fetal and maternal morbidity and increased use of veterinary resources. Dystocias can arise from abnormalities of the maternal pelvis or fetus or uncoordinated uterine activity. Although risk factors for stillbirths have been established in nonhuman primates, risk factors for dystocias have not. The objective of this study was to determine maternal and fetal risk factors for dystocia in macaques. Retrospective data were collected from 83 pigtailed macaques (Macaca nemestrina) diagnosed with dystocia. The diagnosis of dystocia was made based on clinical or pathologic evidence. Maternal records of age, reproductive history, experimental history, clinical records, and fetal birth weight and any applicable fetal necropsy reports were reviewed. The gestational age of the fetus, the infant's birth weight, total previous births by the dam, and the proportions of both viable delivery (inverse effect) and surgical pregnancy interventions (direct effect) in the dam's history generated a model that maximized the experimental variance for predicting dystocia in the current pregnancy and explained 24% of the dystocia deliveries. The number of total previous births and proportion of previous cesarean sections accounted for the greatest effect. This model can identify individual dams within a colony that are at risk for dystocias and allow for changes in breeding colony management, more intense monitoring of dams at risk, or allocation of additional resources.     

Behavioral effects of prenatal folate deficiency in mice

BACKGROUND: Folate supplementation decreases the incidence of birth defects such as neural tube defects (NTDs). We and others have shown that gestational dietary folate deficiency that does not produce overt NTDs can alter fetal neural histology. Accordingly, murine offspring were examined for the possible functional consequences of prenatal folate deficiency. METHODS: CD-1 mice were fed a diet of chow containing 400, 600, or 1200 nmol of folic acid/kg of chow for eight weeks prior to breeding and until GD18, at which time all dams were placed on folate-replete chow. Behavioral tests of male and female offspring included righting reflex, negative geotaxis, forelimb hanging, motor coordination, open field activity, and elevated plus maze activity. RESULTS: Of greatest significance, the adult offspring that were prenatally folate-deficient exhibited more anxiety-related behavior in the elevated plus maze. Offspring of the 400 nmol of folic acid/kg of chow diet group exhibited significantly shorter durations in the open arms and longer durations in the closed arms. Further, these two behaviors were dose-related. There was also a trend for the prenatally folate-deficient adult mice to exhibit more thigmotaxis (wall-hugging) behavior in the open field, entering the central area less frequently than controls. There were few other differences in tested behaviors between folate-deficient and folate-replete mice. CONCLUSIONS: Prenatal folate deficiency that is repleted at birth can manifest later with increased anxiety 9-12 weeks after birth.     

Effect of maternal hypercholesterolemia on fetal sterol metabolism in the Golden Syrian hamster.

The fetus obtains a significant amount of cholesterol from de novo synthesis. Studies have suggested that maternal cholesterol may also contribute to the cholesterol accrued in the fetus. Thus, the present studies were completed to determine whether diet-induced maternal hypercholesterolemia would affect fetal sterol metabolism. To accomplish this, maternal plasma cholesterol concentrations were increased sequentially by feeding hamsters 0.0%, 0.12%, 0.5%, and 2.0% cholesterol. At 11 days into a gestational period of 15.5 days, cholesterol concentrations and sterol synthesis rates were measured in the three fetal tissues: the placenta, yolk sac, and fetus. In the placenta and yolk sac, the cholesterol concentration increased significantly when dams were fed as little as 0.12% cholesterol (P < 0.0167), and sterol synthesis rates decreased in dams fed at least 0.5% or 2% cholesterol, respectively (P < 0.0167). In the fetus, changes in fetal cholesterol concentration and sterol synthesis rates occurred only when dams were fed at least 0.5% cholesterol, which corresponded to a greater than 2-fold increase in maternal plasma cholesterol concentrations. When the cholesterol concentration in the fetal tissues in each animal was plotted as a function of maternal plasma cholesterol concentration, a linear relationship was found (P < 0.001).These studies demonstrate that sterol homeostasis in fetal tissues, including the fetus, is affected by maternal plasma cholesterol concentration in a gradient fashion and that sterol metabolism in the fetus is dependent on sterol homeostasis in the yolk sac and/or placenta.     

Neuronal maturation in an experimental model of brain tissue heterotopia in the lung

Neural maturation involves diverse interaction and signaling mechanisms that are essential to the development of the nervous system. However, little is known about the development of neurons in heterotopic brain tissue in the lung, a rare abnormality observed in malformed babies and fetuses. The aim of this study was to identify the neurons and to investigate their maturation in experimental brain tissue heterotopia during fetal and neonatal periods. The fetuses from 24 pregnant female Swiss mice were used to induce brain tissue heterotopia on the 15th gestational day. Briefly, the brain of one fetus of each dam was extracted, disaggregated, and injected into the right hemithorax of siblings. Six of these fetuses with pulmonary brain tissue implantation were collected on the 18th gestational day (group E18), and six others were collected on the 8th postnatal day (group P8). The brain of each fetus from dams not submitted to any experimental procedure was collected on the 18th gestational day (group CE18) and on the 8th postnatal day (group CP8) to serve as a control for neuronal quantitation and maturation. Immunohistochemical staining of NeuN was used to assess neuron quantity and maturation. The NeuN labeling index was greater in the postnatal period than in the fetal period for the experimental and control groups (P8 > E18 and CP8 > CE18), although there were fewer neurons in experimental than in control groups (P8 < CP8 and E18 < CE18) (P < 0.005). These results indicate that fetal neuroblasts/neurons not only survive a dramatic event such as mechanical disaggregation, in the same way as it happens in human cases, but also they retain their development in heterotopia, irrespective of local tissue influences.     

Effects of sodium valproate and oxygen on the craniofacial skeletal pattern in the CD-1 mouse embryo

Growth retardation is a consistent finding in animal studies on the effect of sodium valproate (NaVP) in the embryo. Apart from fetal weight, the state of ossification in the embryo may be regarded as an indication of growth. The present study was to determine what effect sodium valproate at human therapeutic drug plasma levels had on the craniofacial skeletal pattern in the CD-1 mouse embryo relative to oxygen conditions, drug treatment or the interaction of the two. Two NaVP-filled Alzet osmotic minipumps were implanted subcutaneously on day 5 of gestation for continuous delivery of a total daily dosage of 850 mg/kg for 7 days. During this same time period the dams were also exposed to either normoxic (21% oxygen), hyperoxic (50% oxygen), or hypoxic (12% oxygen) controlled environments. Dams were removed from the oxygen chambers on day 12 and killed on day 18 of gestation. The fetuses were then processed for skeletal evaluation of the craniofacial region. Ossification centers were present in all but six of the skeletal elements studied. The primary ossification delay was in the tympanic bony labyrinth. In addition, there was a decrease in maxillary and mandibular length and cranial base measurements. The greatest toxic effect on the fetus for all skeletal components studied was in the NaVP/hypoxia treated group. This finding suggests that fetal skeletal maturation may be affected by a combination of intrauterine as well as external factors.     

Prenatal programming of adult thyroid function by alcohol and thyroid hormones

Increasing evidence associates environmental challenges early in life with permanent alterations of physiological functions in adulthood. These changes in fetal environment can trigger physiological adaptations by the fetus, called fetal programming, which may be beneficial before birth but permanently influence the physiology of the organism. In this study, we investigated the potential connection between alcohol-induced decreased maternal thyroid function and the hypothalamic-pituitary-thyroid (HPT) function of adult rat offspring. Plasma 3,5,3'-triiodothyronine (T(3)), thyroxine (T(4)), and thyroid-stimulating hormone (TSH) levels were decreased in alcohol-consuming (E) dams on gestational day 21 compared with ad libitum- (C) and pair-fed (PF) controls. No significant differences were found in HPT function in young offspring (3 wk of age) between diet groups. However, adult fetal alcohol-exposed (FAE) offspring had significantly decreased levels of T(3) along with elevated TSH compared with control offspring. T(4) administration to the mother did not normalize the hypothyroid state of the adult FAE offspring. Interestingly, administration of T(4) to control pregnant dams decreased plasma T(3) of the adult female offspring only, whereas T(4) together with maternal alcohol consumption or pair-feeding led to decreased TSH and T(4) in the adult female offspring. Our results suggest that ethanol consumption and T(4) administration alter maternal HPT function, leading to prenatally programmed permanent alterations in the thyroid function of the adult offspring.     

Pharmacological studies on the potentiation of phenytoin teratogenicity by acetaminophen

An in vivo murine model was developed to measure maternal phenytoin biotransformation along with the covalent binding of phenytoin to fetal tissues in the same fetuses which were assessed for fetal anomalies. Acetaminophen was administered to pregnant CD-1 mice 1 hour prior to phenytoin, both given i.p. at varying doses and gestational times between days 11 and 13. Dams were killed between days 12 and 19. Metabolites reflecting the enzymatic bioactivation of phenytoin were quantified in maternal plasma and urine with high-performance liquid chromatography (HPLC). Acetaminophen pretreatment caused a threefold increase in phenytoin-induced fetal cleft palates without increasing resorptions. The covalent binding of radiolabeled phenytoin to fetal and placental tissues measured on day 13 was increased twofold and threefold, respectively, by acetaminophen pretreatment. Phenytoin covalent binding measured on day 16 was significantly increased in the livers of fetuses with cleft palates, but not in the livers of dams with fetuses having cleft palates. Binding to fetal brain on day 16 was over fourfold higher than that in maternal brain. Acetaminophen pretreatment differentiated dams into poor and extensive metabolisers of phenytoin, with only the latter group carrying fetuses with cleft palates. The incidence of fetal cleft palates correlated positively with maternal urinary levels of phenytoin (r = +.81, P less than .01) and its dihydrodiol metabolite (r = +.61, 0.05 less than P less than .1), and negatively with levels of para-hydroxylated phenytoin (r = -.85, P less than .01). These findings related both to the mechanism of phenytoin teratogenicity and its potentiation by acetaminophen.     

Doppler studies in the growth retarded fetus and prediction of neonatal necrotising enterocolitis,haemorrhage, and neonatal morbidity.

In 82 consecutive cases of intrauterine growth retardation managed by established criteria fetal Doppler studies identified 29 fetuses with absence of end diastolic frequencies in the fetal aorta. These same fetuses were significantly more growth retarded (p less than 0.001) and had an earlier gestational age at delivery (p less than 0.001) than those with end diastolic frequencies present. A subgroup of these cases was analysed in more detail to examine the prognostic value of this phenomenon for the neonate. Two groups of neonates of equivalent gestational age and with a birth weight below 2000 g were compared. There were 26 neonates with absent end diastolic frequencies (group 1) and 20 with end diastolic frequencies (group 2) in the fetal aorta. Those in group 1 were more likely to suffer perinatal death (p less than 0.05), necrotising enterocolitis (p less than 0.01), and haemorrhage (p less than 0.05). Only 4 (15%) of the babies in group 1 had an uncomplicated neonatal period compared with 15 (75%) in group 2 (p less than 0.001). The circulatory changes identified in these cases may provide a more sensitive measure of critical fetal compromise than current techniques and thus allow the clinician to deliver the fetus before irreversible tissue damage has occurred.     

Teratogenicity of carbamazepine in rats

The teratogenicity of carbamazepine (CBZ) was investigated in Sprague-Dawley CD rats at doses of 0, 200, 400, and 600 mg/kg administered by gavage in corn oil on days 7-18 of gestation in a dosage volume of 2 ml/kg. The CBZ-600 dose was maternally toxic in that dams in this group weighed 30.6% less than controls by E20. This group had significantly increased resorptions, reduced live fetal weight (51.6% less than controls), and increased skeletal and visceral abnormalities. The CBZ-400 dose also significantly reduced maternal weight gain during gestation to 26.6% less than controls by E20. No significant increase in resorptions occurred in this group; live fetuses weighted 42.9% less than controls and showed an increase in visceral, but not skeletal, abnormalities. The CBZ-200 dose did not significantly affect maternal weight gain or increase resorptions or fetal abnormalities but did reduce fetal body weight (20.3% less than controls). Maternal serum total CBZ concentrations 1 hr after the final dose were 22.9, 27.9, and 34.4 micrograms/ml for the 200, 400, and 600 mg/kg groups, respectively. These levels were little changed 6 h post-treatment. CBZ was 65-70% serum protein bound across dose groups. Human therapeutic levels of CBZ are 4-12 micrograms/ml and the drug is typically 80% serum protein bound. This suggests that abnormalities in rats occur at concentrations well above the human therapeutic range. However, a no-effect level was not found for fetal body weight. Further experiments will be required to determine how much lower doses will need to be in order to find a no-effect level for fetal body weight. Nevertheless, the present data suggest that CBZ is not potent at inducing malformations in rats.