Blood flow during pregnancy in the rat: II. Dynamics of and litter variability in uterine flow

Therapeutic Effect of Alpha Lipoic Acid in a Rat Preclinical Model of Preeclampsia: Focus on Maternal Signs, Fetal Growth and Placental Function

Chronic hypertension is a major risk factor for preeclampsia (PE), associated with significant maternal and neonatal morbidity. We previously demonstrated that pregnant stroke-prone spontaneously hypertensive rats (SHRSP) display a spontaneous PE-like phenotype with distinct placental, fetal, and maternal features. Here, we hypothesized that supplementation with alpha lipoic acid (ALA), a potent antioxidant, during early pregnancy could ameliorate the PE phenotype in this model. To test this hypothesis, timed pregnancies were established using 10 to 12-week-old SHRSP females (n = 19-16/group), which were assigned to two treatment groups: ALA (injected intraperitoneally with 25 mg/kg body weight ALA on gestation day (GD1, GD8, and GD12) or control, receiving saline following the same protocol. Our analysis of maternal signs showed that ALA prevented the pregnancy-dependent maternal blood pressure rise (GD14 blood pressure control 169.3 ± 19.4 mmHg vs. 146.1 ± 13.4 mmHg, p = 0.0001) and ameliorated renal function, as noted by the increased creatinine clearance and improved glomerular histology in treated dams. Treatment also improved the fetal growth restriction (FGR) phenotype, leading to increased fetal weights (ALA 2.19 ± 0.5 g vs. control 1.98 ± 0.3 g, p = 0.0074) and decreased cephalization indexes, indicating a more symmetric fetal growth pattern. This was associated with improved placental efficiency, decreased oxidative stress marker expression on GD14, and serum soluble fms-like tyrosine kinase 1 (sFlt1) levels on GD20. In conclusion, ALA supplementation mitigated maternal signs and improved placental function and fetal growth in SHRSP pregnancies, emerging as a promising therapy in pregnancies at high risk for PE.

Early spiral arteriole remodeling in the uterine-placental interface: A rat model

The mammalian placenta's interface with the parent is a richly vascularized tissue whose development relies upon communication between many different cell types within the uterine microenvironment. The uterine blood vessels of the interface are reshaped during pregnancy into wide-bore, flaccid vessels that convey parental blood to the exchange region of the placenta. Invasive trophoblast as well as parental uterine macrophages and Natural Killer cells are involved in the stepwise remodeling of these vessels and their respective contributions to this crucial process are still being delineated. However, the earliest steps in arteriole remodeling are understudied as they are difficult to study in humans, and other species lack the deep trophoblast invasion that is so prominent a feature of placentation in humans. Here, we further characterize the rat, with deep hemochorial placentation akin to humans, as a model system in which to tease apart the earliest, relatively understudied events in spiral arteriole remodeling. We show that the rat uterine-placental interface increases in size and vascularity rapidly, before trophoblast invasion. The remodeling stages in the arterioles of the rat uterine-placental interface follow a sequence of anatomical changes similar to those in humans, and there are changes to the arterioles' muscular tunica media prior to the marked influx of immune cells. The rat is a tractable model in which to better understand the cell/cell interactions occurring in vivo in an intact tissue microenvironment over time.

Appropriate glycemic management protects the germline but not the uterine environment in hyperglycemia

Emerging evidence indicates that parental diseases can impact the health of subsequent generations through epigenetic inheritance. Recently, it was shown that maternal diabetes alters the metaphase II oocyte transcriptome, causing metabolic dysfunction in offspring. However, type 1 diabetes (T1D) mouse models frequently utilized in previous studies may be subject to several confounding factors due to severe hyperglycemia. This limits clinical translatability given improvements in glycemic control for T1D subjects. Here, we optimize a T1D mouse model to investigate the effects of appropriately managed maternal glycemic levels on oocytes and intrauterine development. We show that diabetic mice with appropriate glycemic control exhibit better long-term health, including maintenance of the oocyte transcriptome and chromatin accessibility. We further show that human oocytes undergoing in vitro maturation challenged with mildly increased levels of glucose, reflecting appropriate glycemic management, also retain their transcriptome. However, fetal growth and placental function are affected in mice despite appropriate glycemic control, suggesting the uterine environment rather than the germline as a pathological factor in developmental programming in appropriately managed diabetes.

Why is human uterine artery blood flow during pregnancy so high?

In healthy near-term women, blood flow to the uteroplacental circulation is estimated as 841 mL/min, which is greater than in other mammalian species. We argue that as uterine venous Po2 sets the upper limit for O2 diffusion to the fetus, high uterine artery blood flow serves to narrow the maternal arterial-to-uterine venous Po2 gradient and thereby raise uterine vein Po2. In support, we show that the reported levels for uterine artery blood flow agree with what is required to maintain normal fetal growth. Although residence at high altitudes (>2,500 m) depresses fetal growth, not all populations are equally affected; Tibetans and Andeans have higher levels of uterine artery blood flow than newcomers and exhibit normal fetal growth. Estimates of uterine venous Po2 from the umbilical blood-gas data available from healthy Andean pregnancies indicate that their high levels of uterine artery blood flow are consistent with their reported, normal birth weights. Unknown, however, are the effects on placental gas exchange of the lower levels of uterine artery blood flow seen in high-altitude newcomers or hypoxia-associated pregnancy complications. We speculate that, by widening the maternal artery to uterine vein Po2 gradient, lower levels of uterine artery blood flow prompt metabolic changes that slow fetal growth to match O2 supply.

Placental Glycoredox Dysregulation Associated with Disease Progression in an Animal Model of Superimposed Preeclampsia

Pregnancies carried by women with chronic hypertension are at increased risk of superimposed preeclampsia, but the placental pathways involved in disease progression remain poorly understood. In this study, we used the stroke-prone spontaneously hypertensive rat (SHRSP) model to investigate the placental mechanisms promoting superimposed preeclampsia, with focus on cellular stress and its influence on galectin-glycan circuits. Our analysis revealed that SHRSP placentas are characterized by a sustained activation of the cellular stress response, displaying significantly increased levels of markers of lipid peroxidation (i.e., thiobarbituric acid reactive substances (TBARS)) and protein nitration and defective antioxidant enzyme expression as early as gestation day 14 (which marks disease onset). Further, lectin profiling showed that such redox imbalance was associated with marked alterations of the placental glycocode, including a prominent decrease of core 1 O-glycan expression in trophoblasts and increased decidual levels of sialylation in SHRSP placentas. We also observed significant changes in the expression of galectins 1, 3 and 9 with pregnancy progression, highlighting the important role of the galectin signature as dynamic interpreters of placental microenvironmental challenges. Collectively, our findings uncover a new role for the glycoredox balance in the pathogenesis of superimposed preeclampsia representing a promising target for interventions in hypertensive disorders of pregnancy.

Integrating in vitro data and physiologically based kinetic (PBK) modelling to assess the in vivo potential developmental toxicity of a series of phenols

Toxicity outcomes derived in vitro do not always reflect in vivo toxicity values, which was previously observed for a series of phenols tested in the embryonic stem cell test (EST). Translation of in vitro data to the in vivo situation is therefore an important, but still limiting step for the use of in vitro toxicity outcomes in the safety assessment of chemicals. The aim of the present study was to translate in vitro embryotoxicity data for a series of phenols to in vivo developmental toxic potency values for the rat by physiologically based kinetic (PBK) modelling-based reverse dosimetry. To this purpose, PBK models were developed for each of the phenols. The models were parameterised with in vitro-derived values defining metabolism and transport of the compounds across the intestinal and placental barrier and with in silico predictions and data from the literature. Using PBK-based reverse dosimetry, in vitro concentration–response curves from the EST were translated into in vivo dose–response curves from which points of departure (PoDs) were derived. The predicted PoDs differed less than 3.6-fold from PoDs derived from in vivo toxicity data for the phenols available in the literature. Moreover, the in vitro PBK-based reverse dosimetry approach could overcome the large disparity that was observed previously between the in vitro and the in vivo relative potency of the series of phenols. In conclusion, this study shows another proof-of-principle that the in vitro PBK approach is a promising strategy for non-animal-based safety assessment of chemicals.

Disposition of intravenously or orally administered silver nanoparticles in pregnant rats and the effect on the biochemical profile in urine

Few investigations have been conducted on the disposition and fate of silver nanoparticles (AgNP) in pregnancy. The distribution of a single dose of polyvinylpyrrolidone (PVP)-stabilized AgNP was investigated in pregnant rats. Two sizes of AgNP, 20 and 110 nm, and silver acetate (AgAc) were used to investigate the role of AgNP diameter and particle dissolution in tissue distribution, internal dose and persistence. Dams were administered AgNP or AgAc intravenously (i.v.) (1 mg kg^-1 ) or by gavage (p.o.) (10 mg kg^-1 ), or vehicle alone, on gestation day 18 and euthanized at 24 or 48 h post-exposure. The silver concentration in tissues was measured using inductively-coupled plasma mass spectrometry. The distribution of silver in dams was influenced by route of administration and AgNP size. The highest concentration of silver (μg Ag g^-1 tissue) at 48 h was found in the spleen for i.v. administered AgNP, and in the lungs for AgAc. At 48 h after p.o. administration of AgNP, the highest concentration was measured in the cecum and large intestine, and for AgAc in the placenta. Silver was detected in placenta and fetuses for all groups. Markers of cardiovascular injury, oxidative stress marker, cytokines and chemokines were not significantly elevated in exposed dams compared to vehicle-dosed control. NMR metabolomics analysis of urine indicated that AgNP and AgAc exposure impact the carbohydrate, and amino acid metabolism. This study demonstrates that silver crosses the placenta and is transferred to the fetus regardless of the form of silver. Copyright © 2016 John Wiley & Sons, Ltd.

A Reproductive and Developmental Toxicity Study in CD Rats of LY275585, [Lys(B28),Pro(B29)]-Human Insulin

LY275585, [Lys(B28),Pro(B29)]-human insulin, was administered daily by subcutaneous injection at doses of 0, 1, 5, or 20 U/kg. Male rats were treated with LY275585 beginning 2 weeks prior to cohabitation and throughout the mating period. Females assigned to the teratology component of the study were treated for 2 weeks prior to cohabitation with the males and through gestation day (GD) 19. These dams were killed on GD 20 and uterine and fetal examinations were performed. Female rats assigned to the delivery component were treated for 2 weeks prior to cohabitation through postpartum day (PD) 20. Dams were allowed to deliver and maintain their progeny through a 21-day lactation period. After weaning, 1 pup/sex/litter was assigned to the F1 generation, and these animals received no treatment. Survival, growth, behavior, and reproductive performance were evaluated, and reproductive organs were collected for histological evaluation. Treatment of F0 male and female rats with LY275585 resulted in isolated incidences of severe hypoglycemia at 5 and 20 U/kg/day and some modest changes in food consumption and body weight measures at all treatment levels. These changes were anticipated and attributed to the pharmacology of this compound. Mating and fertility of the F0 animals were unaffected by treatment. While slight decreases in fetal body weights and increased fetal runts/litter were observed in the 20-U/kg/day group, PD 1 progeny weights were not affected in the delivery component, and there was no indication of teratogenicity in this study. There were no remarkable treatment-related effects on offspring growth patterns, survival, or reproductive performance, but the F1 animals from the 20-U/kg/day treatment-derived group were more reactive than controls in the startle habituation test. Thus, F0 parental toxicity, related to the hypoglycemic action of LY275585, was found at all doses. A dose of 5 U/kg/day was considered a no-adverse-effect level for developmental toxicity. There were no remarkable effects of LY275585 treatment on F0 or F1 generation reproductive performance at 20 U/kg/day, the highest dose tested in this study.

Use of Pharmacokinetic Data Under the FDA's Redbook II Guidelines for Direct Food Additives

Experience with food additive petitions submited after publication of the Food and Drug Administration's Redbook I (U. S. FDA, 1982) guide lines indicated a number of areas in which improvements were needed, and advances in toxicol-ogy testing during the last decade required additional rev is ions. In March 1993, the FDA's Center for Food Safety and Applied Nutrition (CFSAN) distributed copies of a draft of Redbook II for public comment. Since that time, revisions have been made based on comments received on the initial draft. This article describes the rationale for Redbook II guidance on the design of pharm acoki-netic studies and discusses some common problems the FDA has encountered in reviewing pharmacokine tic data submitted as part of food additive petitions. Points emphasized are that (1) pharmaco kinetic information is needed for the interpretation of toxicity studies and is most use ful when conducted before major toxicity studies, (2) the use of whole-body autoradiography is encouraged as a means to select tissues of interest, and as a substitute for dissection and tis-sue sampling, (3) kinetic and mechanistic studies conducted with blood compo-nents, tissue slices, hepatocytes, and othercell types in vitro ofien provide more useful information on the fate of chemicals in specific tissues than information extracted from whole-animal studies. The intention of th e new guide lines for pharmaco kinetic studies is to increase the information content of data gathered and to encourage the use of pharmaco kinetic models and results in the selection of doses for subchronic, chronic, and developmental toxicity studies.

Distribution and biomarker of carbon-14 labeled fullerene C60 ([(14) C(U)]C60 ) in pregnant and lactating rats and their offspring after maternal intravenous exposure

A comprehensive distribution study was conducted in pregnant and lactating rats exposed to a suspension of uniformly carbon-14 labeled C60 ([(14) C(U)]C60 ). Rats were administered [(14) C(U)]C60 (~0.2 mg [(14) C(U)]C60 kg(-1) body weight) or 5% polyvinylpyrrolidone (PVP)-saline vehicle via a single tail vein injection. Pregnant rats were injected on gestation day (GD) 11 (terminated with fetuses after either 24 h or 8 days), GD15 (terminated after 24 h or 4 days), or GD18 (terminated after 24 h). Lactating rats were injected on postnatal day 8 and terminated after 24 h, 3 or 11 days. The distribution of radioactivity in pregnant dams was influenced by both the state of pregnancy and time of termination after exposure. The percentage of recovered radioactivity in pregnant and lactating rats was highest in the liver and lungs. Radioactivity was quantitated in over 20 tissues. Radioactivity was found in the placenta and in fetuses of pregnant dams, and in the milk of lactating rats and in pups. Elimination of radioactivity was < 2% in urine and feces at each time point. Radioactivity remained in blood circulation up to 11 days after [(14) C(U)]C60 exposure. Biomarkers of inflammation, cardiovascular injury and oxidative stress were measured to study the biological impacts of [(14) C(U)]C60 exposure. Oxidative stress was elevated in female pups of exposed dams. Metabolomics analysis of urine showed that [(14) C(U)]C60 exposure to pregnant rats impacted the pathways of vitamin B, regulation of lipid and sugar metabolism and aminoacyl-tRNA biosynthesis. This study demonstrated that [(14) C(U)]C60 crosses the placenta at all stages of pregnancy examined, and is transferred to pups via milk.

Developmental toxicity in rats of a hemoglobin-based oxygen carrier results from impeded function of the inverted visceral yolk sac

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Infusion HBOC into pregnant rats causes developmental toxicity.

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Sensitive from GD 7 to 11 when inverted yolk sac placenta (invYSP) supplies nutrition.

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Controls for protein content, oncotic properties and Hb show effects are due to Hb.

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Whole embryo culture verified HBOC interference with invYSP function.

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Humans lack invYSP and are unlikely to be affected by HBOC.

HBOC-201 is a bovine-derived, cross-linked, and stabilized hemoglobin (250 kDa) in physiological saline. Daily intravenous infusions of HBOC (1.95, 3.90, or 5.85 g/kg/day) during gestational days (GDs) 6–18 in Sprague-Dawley rats caused fetal mortality, reduced birth weight, and malformations. Subsequent single-day infusions (5.85 g/kg/day) showed that developmental toxicity was limited to GDs 7–9 when histiotrophic nutrition via the inverted visceral yolk sac (invVYS) is essential. Histiotrophic nutrition is receptor-mediated endocytosis of bulk maternal proteins and subsequent lysosomal degradation providing amino acids and other nutrients for embryonic growth. Controls for protein content, oncotic properties, and hemoglobin content indicated that toxicity was due to hemoglobin. Rat whole embryo cultures verified HBOC interference with invVYS transport capacity and resultant deficient embryonic nutrition. These mechanisms of action are not expected to impact human development based on differences in VYS morphology and function, although a complete understanding of early human embryonic nutrition is lacking.

Hyperglycemia induces embryopathy, even in the absence of systemic maternal diabetes: an in vivo test of the fuel mediated teratogenesis hypothesis

Embryonic exposure to excess circulating fuels is proposed to underlie diabetic embryopathy. To isolate the effects of hyperglycemia from the many systemic anomalies of diabetes, we infused 4 mg/min glucose into the left uterine artery of non-diabetic pregnant rats on gestation days (GD) 7-9. Right-sided embryos and dams exhibited no glucose elevation. Embryos were assessed on GD13, comparing the left versus right uterine horns. Hyperglycemic exposure increased rates of embryopathy, resorptions, and worsened embryopathy severity. By contrast, saline infusion did not affect any of these parameters. To assess for possible embryopathy susceptibility bias between uterine horns, separate dams were given retinoic acid (25mg/kg, a mildly embryopathic dose) systemically on GD7.5. The resultant embryopathy rates were equivalent between uterine horns. We conclude that hyperglycemia, even in the absence of systemic maternal diabetes, is sufficient to produce in vivo embryopathy during organogenesis.

Timing of ischemic insult alters fetal growth trajectory, maternal angiogenic balance, and markers of renal oxidative stress in the pregnant rat

Increased uterine artery resistance and angiogenic imbalance characterized by increased soluble fms-like tyrosine kinase-1 (sFlt-1) and decreased free vascular endothelial growth factor (VEGF) are often associated with placental insufficiency and preeclampsia but not synonymous with hypertension. We hypothesized chronic reductions in utero-placental perfusion (RUPP) for 5 days (d) during either mid- (d12-d17) or late (d14-d19) gestation would have disparate effects on plasma sFlt-1 and VEGF levels and blood pressure. Five days of chronic RUPP was achieved by placement of silver clips on the abdominal aorta and ovarian arteries on either gestational d12 or d14. Arterial pressure was increased (P < 0.05) in RUPP vs. normal pregnant (NP) in both d17 (10%) and d19 (25%) groups, respectively. Circulating free VEGF was decreased (P < 0.05) and sFlt-1:VEGF ratio increased (P < 0.05) after 5 days of RUPP ending on d19 but not d17 compared with NP controls. Angiogenic imbalance, measured by an endothelial tube formation assay, was present in the d19 RUPP but not the d17 RUPP compared with age-matched NP rats. Five days of RUPP from days 14 to 19 decreased fetal and placental weights 10% (P < 0.01) compared with d19 NP controls. After 5 days of RUPP, from days 12 to 17 of pregnancy, fetal weights were 21% lighter (P < 0.01) compared with d17 NP controls, but placental weight was unchanged. These findings suggest that the timing during which placental insufficiency occurs may play an important role in determining the extent of alterations in angiogenic balance, fetal growth restriction, and the severity of placental ischemia-induced hypertension.

Evaluation of placental and lactational pharmacokinetics of PFOA and PFOS in the pregnant, lactating, fetal and neonatal rat using a physiologically based pharmacokinetic model

Perfluoroalkyl carboxylates and sulfonates (PFAAs) have many consumer and industrial applications. Developmental toxicity studies in animals have raised concern about potential developmental effects of PFOA and PFOS in humans. We have developed PBPK models for PFAAs in the rat to help define a relationship between external dose, internal tissue concentrations, and observed adverse effects, and to understand how physiological changes that occur during gestation and lactation affect tissue distribution of PFAAs in the mother, fetus, and neonate. The models developed here expand upon a PBPK model for PFAAs in the adult female rat, and are consistent with available PK data. These models, along with the adult rat PFAA models, published in the companion paper, will help address concerns about possible health effects due to PFAA exposure in the fetus and neonate and will be useful in comparing PK across life stages.

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.

Evaluation of physiologically based models of pregnancy and lactation for their application in children's health risk assessments

In today's scientific and regulatory climates, an increased emphasis is placed on the potential health impacts for children exposed either in utero or by nursing to drugs of abuse, pharmaceuticals, and industrial or consumer chemicals. As a result, there is a renewed interest in the development and application of biologically based computational models that can be used to predict the dosimetry (or ultimately response) in a developing embryo, fetus, or newborn. However, fundamental differences between animal and human development can create many unique challenges. For example, unlike models designed for adults,biologically based models of pre-and postnatal development must deal with rapidly changing growth dynamics (maternal embryonic, fetal, and neonatal), changes in the state of differentiation of developing tissues, uniquely expressed or uniquely functioning signal transduction or enzymatic pathways, and unusual routes of exposure (e.g., maternal-mediated placental transfer and lactation). In cases where these challenges are overcome or addressed, biological modeling will likely prove useful in assessments geared toward children's health, given the contributions that this approach has already made in cancer and non-cancer human health risk assessments. Therefore, the purpose of this review is to critically evaluate the current state of the art in physiologically based pharmacokinetic (PBPK) and pharmacodynamic (PD) modeling of the developing embryo, fetus, or neonate and to recommend potential steps that could be taken to improve their use in children's health risk assessments. The intent was not to recommend improvements to individual models per se, but to identify areas of research that could move the entire field forward. This analysis includes a brief summary of current risk assessment practices for developmental toxicity, with an overview of developmental biology as it relates to species-specific dosimetry. This summary should provide a general context for understanding the tension that exists in modeling between describing biological proceses in exquisite detail vs. the simplifications that are necessary due to lack of data (or through a sensitivity analysis, determined to be of little impact) to develop individual PBPK or PD models. For each of the previously published models covered in this review, a description of the underlying assumptions and model structures as well as the data and methods used in model development and validation are highlighted. Although several of the models attempted to describe target tissues in the developing embryo, fetus, or neonate of laboratory animals, extrapolations to humans were largely limited to maternal blood or milk concentrations. Future areas of research therefore are recommended to extend the already significant progress that has been made in this field and perhaps address many of the technical policy, and ethical issues surrounding various approaches for decreasing the uncertainty in extrapolating from animal models to human pregnancies or neonatal exposures.

Cocaine decreases uteroplacental blood flow in the rat

Although cocaine administration reduces blood flow to the fetus in the pregnant ewe, the effects of cocaine on uterine and placental blood flow in the pregnant rat have not been adequately documented. The current study tested the hypothesis that cocaine decreased uterine and placental blood flow in awake and freely moving pregnant rats 17 min following gastric intubation. Blood flow was determined using [14C]iodoantipyrine in pregnant Sprague-Dawley rats 1 day prior to parturition. On the day of the experiment, rats were intubated with either 60 mg/kg cocaine or the vehicle and 17 min later infused i.v. with 75 microCi [14C]iodoantipyrine. Ten arterial blood samples were taken over 1 min through a femoral arterial catheter placed on the previous day. At 1 min the animal was decapitated and the entire uterus rapidly removed and frozen. After processing for autoradiography, the amounts of radioactivity in the tissues were determined by computerized image analysis. The results show that cocaine reduced blood flow in the uterus by 27% and decreased blood flow in the placenta by 30%. While cocaine reduced the total amount of iodoantipyrine reaching the fetus, the distribution of tracer within the fetus did not appear to be altered by cocaine. Maternal blood pressure and heart rate decreased by 5% and 13% respectively (paired t-test), while maternal and fetal blood gases were not altered. These data indicate that acute cocaine administration reduces uteroplacental blood flow in the rat. The duration of this effect and whether these decreases are sufficient to produce neurobehavioral changes in the offspring remain to be determined.

An assessment of the developmental toxicity of inorganic arsenic

A critical analysis of the literature base regarding the reproductive and developmental toxicity of arsenic compounds, with emphasis on inorganic arsenicals, was conducted. The analysis was stimulated by the great number of papers that have purported to have shown an association between exposure of pregnant laboratory animals to arsenic compounds and the occurrence of offspring with cranial neural tube defects, particularly exencephaly. For the most part, the literature reports of arsenic developmental toxicity in experimental animals are inadequate for human risk assessment purposes. Despite the shortcomings of the experimental database, several conclusions are readily apparent when the animal studies are viewed collectively. First, cranial neural tube defects are induced in rodents only when arsenic exposure has occurred early in gestation (on Days 7 [hamster, mouse], 8 [mouse], or 9 [rat]). Second, arsenic exposures that cause cranial neural tube defects are single doses that are so high as to be lethal (or nearly so) to the pregnant animal. Third, the effective routes of exposure are by injection directly into the venous system or the peritoneal cavity; even massive oral exposures do not cause increases in the incidence of total gross malformations. Fourth, repetition of similar study designs employing exaggerated parenteral doses is the source of the large number of papers reporting neural tube defects associated with prenatal arsenic exposure. Fifth, in five repeated dose studies carried out following EPA Guidelines for assessing developmental toxicity, arsenic was not teratogenic in rats (AsIII, 101 micromol/kg/d, oral gavage; 101 micromol/m3, inhalation), mice (AsV, 338 micromol/kg/d, oral gavage; est. 402 micromol/kg/d, diet), or rabbits (AsV, 21 micromol/kg/d, oral gavage). Data regarding arsenic exposure and adverse outcomes of pregnancy in humans are limited to several ecologic epidemiology studies of drinking water, airborne dusts, and smelter environs. These studies failed to (1) obtain accurate measurements of maternal exposure during the critical period of organogenesis and (2) control for recognized confounders. The lone study that examined maternal arsenic exposure during pregnancy and the presence of neural tube defects in progeny failed to confirm a relationship between the two. It is concluded that under environmentally relevant exposure scenarios (e.g., 100 ppm in soil), inorganic arsenic is unlikely to pose a risk to pregnant women and their offspring.

The selective estrogen receptor modulator, raloxifene: segment II studies in rats and rabbits

Raloxifene is a nonsteroidal, selective estrogen receptor modulator developed by Eli Lilly and Company primarily as a therapeutic agent for postmenopausal osteoporosis. Two Segment II studies were conducted that examined maternal reproductive parameters and fetal outcome following gestational exposure to raloxifene. Pregnant CD rats (25/group) and New Zealand white rabbits (20/group) were dosed once daily by oral gavage with 0, 0.1, 1, or 10 mg/kg on Gestation Days (GD) 6 through 17 and 7 through 19, respectively. Maternal body weight and food consumption were monitored throughout pregnancy. Caesarean sections were performed on GD 20 and GD 28 for rats and rabbits, respectively, to evaluate fetal viability, weight, and morphology. In rats, maternal body weight, body weight gain, and food consumption were reduced in all raloxifene treatment groups. Fetal viability was depressed in the 10-mg/kg group and was often associated with signs of hemorrhaging from the vagina. Fetal growth retardation was indicated in the 1- and/or 10-mg/kg groups by increased incidences of fetal runts and the developmental deviations, wavy ribs and kidney cavitation. There was no evidence of treatment-related malformations in rat fetuses. In rabbits, depressions in body weight gain and food consumption occurred in the 10-mg/kg group, and a single abortion occurred in the 1-mg/kg group. Fetal viability and weights were not affected in any of the raloxifene treatment groups. The overall proportions of fetuses with malformations, deviations, or variations were not affected by treatment with raloxifene; however, one fetus each from the 0.1-, 1-, and 10-mg/kg groups had incomplete closure of the interventricular septum. Therefore, maternal and fetal no-effect levels were not obtained in this study of raloxifene.

The selective estrogen receptor modulator, raloxifene: reproductive assessments following premating exposure in female rats

Raloxifene HCl is a nonsteroidal, selective estrogen receptor modulator developed as a therapeutic agent for postmenopausal osteoporosis. Two studies were conducted that examined the effects of premating exposure to raloxifene HCl. In the first study, adult female CD rats (20/group) were given diets containing 0, 0.01, or 0.1% raloxifene (providing an average of 0, 6, or 63 mg/kg/d, respectively) for 2 weeks, after which the treated diets were replaced with control diet. Following a 2-week period without treatment, each female that had displayed at least three conversions in vaginal cytology from cornified cells to leukocytes was cohabited for 1 to 2 d with an untreated male as she entered proestrus. Females were killed at midgestation and examined for evidence of pregnancy. In the second study, adult female CD rats (40/group) were given oral gavage doses of raloxifene (0, 0.1, 1, or 10 mg/kg/d) for 4 weeks. Immediately or following a 2-week period without treatment, 20 females/group were cohabited with untreated males (1:1) for up to 3 weeks. The females were allowed to deliver and rear their offspring until Postpartum Day 21. Progeny survival, growth, and development were evaluated. Maternal body weight, body weight gain, and food consumption were depressed in all raloxifene treatment groups. Doses > or =1 mg/kg caused disruptions in estrous cycles. In Study 1, 90% of the females treated with raloxifene resumed normal cycling, and fertility was not significantly affected. Although there were no statistically significant differences in time-to-mating, fertility, or liveborn indices in Study 2, females in the 10-mg/kg immediate-cohabitation group had slightly increased gestation lengths and smaller litter sizes. Progeny from these litters were larger on Postpartum Day 1 and had advanced incisor eruption and eye opening. In addition, slight delays were seen in physical landmark appearance in the 0.1- and 1-mg/kg immediate-cohabitation groups and in the 1- and 10-mg/kg delayed-cohabitation groups. Progeny viability, growth, and negative geotactic performance were not adversely affected. In these studies of maternal premating exposure to raloxifene, findings were consistent with established pharmacologic activity of the test chemical. Reproductive effects (disrupted estrous cycles and decreased litter size) occurred at doses > or =1 mg/kg and were generally reversible. Effects on offspring were seen at doses > or =0.1 mg/kg, were of minor importance, and were resolved during the lactation period.

Critical period of carbon tetrachloride-induced pregnancy loss in Fischer-344 rats, with insights into the detection of resorption sites by ammonium sulfide staining

Several low-molecular weight halocarbons have been shown to cause full-litter resorption (FLR), i.e., pregnancy loss, in Fischer-344 rats treated during organogenesis. To determine periods of gestation sensitive to acute exposure, a single dose of 150 mg carbon tetrachloride (CCl4)/kg was administered on gestation day (GD) 6, 7, 8, 10, or 12. Fetuses were delivered by cesarean section on GD 20. Non-gravid uteri were examined for resorption sites, placed in 10% ammonium sulfide, and re-examined for stained resorption sites approximately 1 and 4.5 hr later. FLR was seen in 4% (1/27) of control dams and 36% (4/11), 54% (7/13), 72% (18/25), 54% (7/13), and 0% (0/12) of dams treated on GD 6, 7, 8, 10, and 12, respectively. Ammonium sulfide staining clearly yielded a more accurate account of the incidence of FLR. The technique was most effective when the staining period was extended to 4.5 hr, as two cases of FLR were revealed that had been undetected after 1 hr of staining. For dams with FLR, staining was required to detect resorption sites in all dams treated on GD 6 or 7, most dams treated on GD 8, and one dam treated on GD 10. Fewer implantation sites were detected in the dams treated on GD 6, and the size of the stained resorption sites increased as the day of treatment was delayed. These findings demonstrate a relationship between the time of toxicant exposure and the size and detectability of resorption sites near term, suggesting that the size of the resorption site may reliably reflect the time of embryonic death. Treatment on GD 8 caused the highest incidence of FLR and will be used in subsequent mechanistic research.

Effects of the serotonin antagonist amesergide on reproduction in female rats

Amesergide, a serotonin (5-HT2) antagonist intended to treat depression, was administered orally to female CD rats (20/group) at doses of 0, 3, 10, or 30 mg/kg to evaluate effects on mating, fertility, litter size, live birth index (100 x total liveborn progeny/litter size), progeny survival, and weight gain of each litter. The treatment period extended from two weeks prior to mating through postpartum day 21 to cover possible effects of estrous cycle, mating, gestation, and postpartum events. Twenty additional female rats were given 30 mg/kg through gestation day 18, after which they received the acacia vehicle (recovery group). All females were allowed to deliver naturally and rear their progeny. On postpartum day 8, progeny in the control, 30 mg/kg and 30 mg/kg recovery groups were removed from dams for 4 h. Progeny were weighed as litters, returned to the dams for a 1-h nursing period, and then weighed again to provide an indication of milk intake. Mating and fertility, using the present study design, were not affected by treatment with amesergide. No effects were observed on litter size, live birth index, or progeny survival. In contrast, treatment with amesergide throughout gestation and lactation produced a significant dose-related depression in progeny body weight gains. However, when treatment was discontinued after day 18 of gestation (30 mg/kg recovery group), progeny body weight gains did not differ from those of the control group.(ABSTRACT TRUNCATED AT 250 WORDS)

Developmental toxicity of gemcitabine, an antimetabolite oncolytic, administered during gestation to CD-1 mice

Gemcitabine was given intravenously to female mice on gestation days (GD) 6-15 at doses of 0, 0.05, 0.25, or 1.5 mg/kg/day (0, 0.15, 0.75, or 4.5 mg/m2/day, respectively). Animals assigned to the teratology segment (25/group) were killed on GD 18 for examination of maternal hematologic parameters and organ weights, as well as fetal viability, weights, and morphology. The postnatal segment females (20/group) were allowed to deliver, and offspring physical, behavioral, and reproductive parameters were monitored. After offspring weaning, these dams were killed for hematologic and organ weight evaluations. At necropsy, 3 days after the final dose, the teratology segment dams showed dose-related increases in spleen and thymus weights. These changes were accompanied by a dose-related decrease in leukocytes and modest increases in mean corpuscular volume (MCV) and hemoglobin (MCH) at the two higher doses. On postpartum day (PPD) 21, the dams in the postnatal segment showed no treatment-related effects on these organ weights or hematologic parameters, indicating recovery of these maternal parameters within 3.5 weeks following termination of treatment. The decreases in maternal body weight and food consumption observed during gestation, and in liver and uterine weights at term in the 1.5 mg/kg/day group, were considered to be secondary to a high rate of prenatal mortality, evidenced by increased resorptions in the teratology segment and decreased live litter size in both segments of the study. Additional indications of developmental toxicity in this dose group were an increased incidence of malformations, primarily cleft palate, decreased fetal weights in the teratology segment, and decreased neonatal survival in the postnatal segment.(ABSTRACT TRUNCATED AT 250 WORDS)

Atrial natriuretic peptide binding in rat placenta, yolk sac, decidua, and maternal placental vessels

Using in vitro autoradiography, binding sites of 125I-ANP (atrial natriuretic peptide) were localized in the rat placenta, visceral yolk sac, and decidua at 16, 18, and 20 days of gestation. There was diffuse binding over the labyrinthine region of the placenta and an intense binding over the decidual gland and visceral yolk sac. In the yolk sac, ANP localized over the cores of the villi where it may be involved with the regulation of transport across the membranes or the flow of blood through the vitelline vessels. Of particular interest was binding over the maternal blood vessels supplying the decidual region and placenta. Receptors were located on the endothelial cells and smooth muscle cells of the arteries and veins, indicating that ANP may be involved with regional regulation of blood flow to the placenta.

A physiologically based kinetic model of rat and mouse gestation: disposition of a weak acid

A physiologically based toxicokinetic model of gestation in the rat and mouse has been developed. The model is superimposed on the normal growth curve for nonpregnant females. It describes the entire gestation period including the period of organogenesis. The model consists of uterus, mammary tissue, maternal fat, kidney, liver, other well-perfused maternal tissues, and other poorly perfused maternal tissues, embryo/fetal tissues, and yolk sac and chorioallantoic placentas. It takes into account the growth of maternal tissues such as uterus, mammary glands, fat, and liver during pregnancy, as well as growth of the conceptus. The gestation model is based on published values of organ volumes and blood flows for the rat throughout pregnancy. It is scaled to the mouse using conventional scaling procedures. Its descriptive utility has been examined with the test chemical 5,5'-dimethyloxazolidine-2,4-dione (DMO), a weak acid that is not bound measurably in plasma or tissues and is eliminated by excretion in the urine. Concentrations of DMO were monitored in maternal rat and embryo plasma and in homogenates of maternal rat muscle and whole embryo after ip administration at 9:00 AM on Day 13 of gestation. On the basis that distribution of DMO is determined solely by its pK and the pH's of body fluids, pH and excretion rate values were estimated by visual optimization of model predictions to the concentration profile. Successful prediction of concentrations of DMO in the same tissues of pregnant mice after its ip administration at 9:00 AM on Day 10 or 11 of gestation required only adjustment for pH's of mouse body fluids.

Susceptible period of nitrous oxide teratogenicity in Sprague-Dawley rats

The susceptible period of nitrous oxide (N2O) teratogenicity was studied in 170 Sprague-Dawley rats. Seven groups of 20 timed-pregnant rats were exposed to 60% N2O for 24 hours on each of days 6-12 of gestation; a control group of 30 timed-pregnant rats was exposed to air on day 9. On day 20 of gestation, dams were killed and reproductive indices were determined; their fetuses were subsequently examined for external, skeletal, and visceral abnormalities. There were no differences among the groups in the number of implantations and live fetuses, mean fetal weight, and sex ratio. The incidence of fetal wastage was higher than control in N2O-treated groups exposed on days 8 and 11 of gestation. Skeletal malformations of the ribs and vertebrae were increased following exposure on day 9 of gestation. However, the specific minor anomaly, cervical rib, was increased only following exposure on day 8 of gestation. The incidences of right-sided aortic arch and left-sided umbilical artery, abnormalities indicative of altered laterality, were increased following exposure on day 8 of gestation. Nitrous oxide administration during organogenesis causes several reproductive defects by mechanisms which remain to be determined.

Cadmium exposure on day 12 of gestation in the Wistar rat: distribution, uteroplacental blood flow, and fetal viability

The effects of cadmium exposure (40 mumole CdCl2/kg, s.c.) on day 12 of gestation were evaluated in the Wistar rat. At 16-18 hours following such cadmium exposure, blood flow (as determined by radiolabeled microspheres) to the chorioallantoic placenta (CAP) was significantly reduced by 35%; at 24-26 hours, blood flow to the CAP had returned to control levels and was still unaffected at 38-43 hours. Uterine blood flow was not significantly altered at any of these timepoints. Between 16-18 and 24-26 hours after cadmium exposure, the concentration of cadmium in the placenta decreased significantly, while total cadmium content did not change. By 38-43 hours after cadmium exposure, total cadmium content of the placenta had increased significantly, although cadmium concentration was unchanged. There were no adverse effects on fetal viability or growth, as determined on day 20 of gestation. In sharp contrast, near-term (day 18) exposure to 40 or 50 mumole CdCl2/kg (s.c.) resulted in 53% and 82% mean incidences of fetolethality, respectively, within 24 hours. Administration of 50 mumole CdCl2/kg (sc) on day 12 also had no effect on fetal growth but resulted in increased fetolethality (12%). Thus midgestational cadmium exposure and its accompanying alterations in placental blood flow do not compromise fetal viability or growth. The differential response to cadmium at mid- and late gestation, in terms of fetolethality, is not due to maternal cadmium dose.

The role of metabolism in the testing of developmental toxicants

The delivery of potential developmental toxicants to the conceptus is dependent on several metabolic and pharmacokinetic factors. Within the maternal-embryo/fetal unit, maternal, placental, and embryo/fetal factors must be considered. These factors include blood flow, permeability, biotransformation, and elimination. Pharmacokinetic models based on data gathered from appropriate in vivo and in vitro studies may be used to describe the effect of these factors on toxicant delivery to the conceptus. Several known human developmental toxicants are discussed in terms of the metabolic and pharmacokinetic factors controlling their delivery to the conceptus. Metabolic events, including activation and/or detoxification, have been reported for the majority of the toxicants examined. Thus it would appear that the role of metabolism should be considered during the testing of potential developmental toxicants.

Reduction of uterine blood flow by phenylephrine, an alpha-adrenergic agonist, in the day 11 pregnant rat: relationship to potentiation of acetazolamide teratogenesis

We have demonstrated previously that phenylephrine, a selective postsynaptic alpha-1-adrenergic agonist, significantly potentiates the incidence of acetazolamide-induced right forelimb ectrodactyly in a dose-response manner. As reported herein, phenylephrine also decreases maternal uterine blood flow in a dose-response manner as measured by radioactive microsphere methodology. At the potentiative dose of 12.5 mg/kg phenylephrine decreases uterine blood flow by 86.8% when compared to control. In turn, pretreatment with prazosin, a selective postsynaptic alpha-1-adrenergic antagonist, prevents this large decrease in uterine blood flow and abolishes the potentiation of acetazolamide teratogenesis by phenylephrine. Although the effects of acetazolamide or acetazolamide + phenylephrine on uterine blood flow were not measured the data suggest a correlation between decreased uterine blood flow and potentiation of acetazolamide teratogenesis.

Some aspects of amino acid metabolism in the rat fetus

1. In spite of an eventual catabolic phase during the last third of pregnancy, nitrogen retention seems to increase in pregnant rats. Furthermore, the high uterine blood flow and the high placental transfer of amino acids maintains an adequate nutrient supply to the fetuses. 2. The terminal rat fetus has a high circulating plasma amino acid level, as well as an increased free amino acid tissue pool when compared to its mother's. 3. In the rat fetus the development of enzymatic capabilities shows a sudden emergence (also denomined clustering) in late fetal life. In a general trend, the activities of enzymes related with amino acid metabolism are not well developed during rat fetal life. 4. The rate of amino nitrogen excretion in rat fetus is low, mainly due to the low development of urea cycle enzyme activities. 5. The rates of protein synthesis in many tissues are high in the rat fetus and they show a progressive decrease until delivery. On the other hand, the rates of protein breakdown are also higher during fetal life than in the adult.

A method to obtain maternal-fetal plasma samples using a microsampling technique in the rat: transplacental passage of cefoxitin

A microsampling technique that allows taking blood samples from the umbilical vein of the pregnant rat is described. Such techniques are needed in order to allow pharmacokinetic and embryo exposure to be correlated with teratogenic endpoints. Cefoxitin was administered intravenously (300 mg/kg) into tracheotomized, pentobarbital anesthetized dams on day 21 in gestation. Blood samples were collected via the carotid artery from the dam and the umbilical vein of the fetus at designated times. Up to three samples of 20 to 30 microliters each, were taken from individual fetuses at 20-min intervals. With few exceptions, fetal cefoxitin concentrations were homogeneous at each sampling period. Fetal concentrations were low compared to maternal concentrations as seen by the small fetal/maternal area under the curve ratio (0.053 +/- 0.006).

Analysis of pethidine disposition in the pregnant rat by means of a physiological flow model

The disposition of pethidine (meperidine) in the pregnant rat is described by means of a physiological flow model. The model includes arterial and venous blood, brain, fat, fetal, hepatic, intestinal, muscular, pulmonar, and renal tissues. The concentration-time profiles of pethidine calculated by the model are consistent with experimental data, except for the brain and renal tissues, where the model predicts initially higher concentrations. Simulations are carried out to further explore the contribution from different organs on the kinetics in blood and tissues. The tissue-to-blood partition coefficients vary over a range from 5 to 316, where fat has the lowest and liver the highest after a correction is made due to hepatic extraction. Rapid uptake occurs into highly perfused organs such as brain, kidneys, liver, and lungs, followed by fetus, intestines, muscle, and fat. Data indicate no marked membrane resistance to pethidine of the investigated organs, except for fetal tissues, but rather a perfusion-limited uptake. Simulations suggest that muscles and adipose tissue play an important role in the rat, becoming the major reservoir of drug during the intermediate and terminal elimination phase, respectively. Volume of distribution and the biological half-life agree with reported findings. Pethidine is subject to a high systemic blood clearance, which exceeds the total hepatic blood flow in the rat. No degradation of pethidine is found in blood, and therefore a pulmonary expression for pethidine clearance is added as a potential source of pethidine elimination. The elimination of pethidine after a single i.v. bolus does is found to be dependent on simulated changes in cardiac output and hepatic blood flow. A simulation is performed with the scaled model to mimic the human concentration-time profiles in maternal blood and brain tissues and fetal tissue during repetitive doses of pethidine.

Blood flow during pregnancy in the rat: I. Flow patterns to maternal organs

Normal blood flow patterns to several maternal organs were characterized in individual CD rats, nonpregnant (NP) or on day 6, 7, 8, 10, 11, 12, 13, 16, 18, or 20 of gestation using the radioactive microsphere technique. Weights and flow values were determined for several uterine tissue samples as well as maternal organs. No significant changes were found in blood flow to the stomach, spleen, and urinary bladder of these animals. There also were no remarkable changes as pregnancy progressed in blood flow to the lungs, suggesting that no marked arterial-venous shunting occurs in maternal placental tissues over gestation. Slight but consistent decreases in absolute (ml/min) and relative (ml/min/g tissue) blood flow to the brain were noted, and percent cardiac output (CO) was significantly decreased on all days of gestation except day 7. Complex changes were observed in blood flow to the kidneys, liver, adrenals, and heart. Absolute flow to the kidneys and liver reached maximum values on day 11, although percent CO delivered to both organs was consistently reduced throughout gestation. Absolute flow to the heart and adrenals peaked on day 13 and days 11-12, respectively. Absolute flow to the ovaries increased nearly 5-fold from the NP state (0.36 +/- 0.11) to day 20 of pregnancy (1.61 +/- 0.33). Interlitter differences in ovarian blood flow during midgestation were found to be a result of differences in litter size and distribution of embryo/fetuses between the two uterine horns. The fact that the majority of changes observed in maternal organ flow coincide with placental development, rapid augmentation of total uterine flow, and/or maternal hormonal changes suggests that these patterns may be important indicators of the dynamic physiology of pregnancy.