Embryonic catch-up growth after exposure to the ketone body D,L,-beta-hydroxybutyrate in vitro

Ketone Bodies in Diabetes Mellitus: Friend or Foe?

In glucose-deprived conditions, ketone bodies are produced by the liver mitochondria, through the catabolism of fatty acids, and are used peripherally, as an alternative energy source. Ketones are produced in the body under normal conditions, including during pregnancy and the neonatal period, when following a ketogenic diet (KD), fasting, or exercising. Additionally, ketone synthesis is also augmented under pathological conditions, including cases of diabetic ketoacidosis (DKA), alcoholism, and several metabolic disorders. Nonetheless, diet is the main regulator of total body ketone concentrations. The KDs are mimicking the fasting state, altering the default metabolism towards the use of ketones as the primary fuel source. Recently, KD has gained recognition as a medical nutrition therapy for a plethora of metabolic conditions, including obesity and diabetes mellitus (DM). The present review aims to discuss the role of ketones, KDs, ketonemia, and ketonuria in DM, presenting all the available new evidence in a comprehensive manner.

Prenatal catch-up growth: A study in avian embryos

Whether the growth of embryos after a period of stunt becomes accelerated (Catch-Up Growth, CUGr), as it occurs postnatally, has rarely been examined experimentally in any class of animals. Here, hypoxia or cold of different degrees and durations caused growth retardation in chicken embryos during the first or second week of incubation. On average, on the day of removal of the growth-inhibition, the weight of the experimental groups was 73% (wet) and 61% (dry) of control embryos, while near end-incubation (embryonic day E18) their weight averaged significantly more, respectively, 80% and 84% of controls (P < 0.001). When compared as function of developmental time, the post-intervention growth of experimental embryos was faster than that of controls. The faster growth was fully accounted for by their smaller weight at end-intervention, because embryonic growth is higher the smaller the weight. Hence, their growth was appropriate for their weight, rather than for their age. In fact, out of eight different models of growth based on age and weight (wet or dry) in various combination, the model based on embryonic wet weight at end-intervention, and weight alone, was the best predictor of the embryo's post-intervention growth. The oxygen consumption of the experimental embryos during CUGr was appropriate for their weight. In conclusion, in this experimental model of CUGr, the embryo's weight at the end of a stunt could fully predict and explain the rate of growth during the post-intervention recovery period.

The status of diabetic embryopathy

Diabetic embryopathy is a theoretical enigma and a clinical challenge. Both type 1 and type 2 diabetic pregnancy carry a significant risk for fetal maldevelopment, and the precise reasons for the diabetes-induced teratogenicity are not clearly identified. The experimental work in this field has revealed a partial, however complex, answer to the teratological question, and we will review some of the latest suggestions.

Influence of maternal metabolism and parental genetics on fetal maldevelopment in diabetic rat pregnancy

The purpose of this study was to investigate the influence of parental transgenerational genetics and maternal metabolic state on fetal maldevelopment in diabetic rat pregnancy. Rats from an inbred malformation-resistant (W) strain, and an inbred malformation-prone (L) strain, were cross-mated to produce two different F(1) hybrids, WL and LW. Normal (N) and manifestly diabetic (MD) WL and LW females were mated with normal males of the same F(1) generation to obtain WLWL and LWLW F(2) hybrids. Maternal diabetes increased malformation and resorption rates in both F(2) generations. MD-WLWL offspring had higher resorption rate but similar malformation rate compared with the MD-LWLW offspring. Malformed MD-WLWL offspring presented with 100% agnathia/micrognathia, whereas malformed MD-LWL offspring had 60% agnathia/micrognathia and 40% cleft lip and palate. The MD-WL dams showed increased β-hydroxybutyrate levels and alterations in concentrations of several amino acids (taurine, asparagine, citrulline, cystine, glutamic acid, leucine, tyrosine, and tryptophan) compared with MD-LW dams. Fetal glyceraldehyde-3-phosphate dehydrogenase (Gapdh) activity and gene expression were more altered in MD-WLWL than MD-LWLW. Fetal gene expression of reactive oxygen species (ROS) scavenger enzymes was diminished in MD-WLWL compared with MD-LWLW. Glial cell line-derived neurotrophic factor and Ret proto-oncogene gene expression was decreased in both MD-WLWL and MD-LWLW fetuses, whereas increased bone morphogenetic protein 4 and decreased Sonic hedgehog homolog expression was found only in MD-LWLW fetuses. Despite identical autosomal genotypes, the WL and LW dams gave birth to offspring with markedly different malformation patterns. Together with fetal differences in enzymatic activity and expression of Gapdh, ROS scavengers, and developmental genes, these results may suggest a teratological mechanism in diabetic pregnancy influenced by maternal metabolism and parental strain epigenetics.

Congenital anomalies in diabetic pregnancy

Congenital malformations are more common in infants of diabetic women than in children of non-diabetic women. The etiology, pathogenesis and prevention of the diabetes-induced malformations have spurred considerable clinical and basic research efforts. The ultimate aim of these studies has been to obtain an understanding of the teratogenic process, which may enable precise preventive therapeutic measures in diabetic pregnancies. The results of the clinical and basic studies support the view of an early gestational induction of the malformations in diabetic pregnancy by a teratogenic process of multifactorial etiology. There may be possible targets for new therapeutic efforts revealed by the research work. Thus, future additions to the therapeutic efforts may include supplementation with antioxidants and/or folic acid, although more research is needed to delineate the dosages and compounds to be used. As the research into genetic predisposition for the teratogenic induction of malformations by maternal diabetes starts to reveal new genes and gene products involved in the etiology of the malformations, a set of new targets for intervention may arise.

Pregnancy outcome in ethanol-treated mice with folic acid supplementation in saccharose

INTRODUCTION

Maternal folic acid deficiency is the most important metabolic factor in the etiology of neural tube defects (NTD) and is reduced by ethanol, which is extensively consumed by young women.

OBJECTIVE

The objective of the study was to determine whether folic acid supplementation in dietary saccharose is efficient in the prevention NTD induced by ethanol in fetuses of Swiss mice.

MATERIALS AND METHODS

Pregnant mice were divided into four groups of six animals each: control (C), ethanol (E), deficient-supplemented (DS), and deficient-supplemented + ethanol (DSE). Groups C and E received commercial mouse chow (containing 3 mg/kg folic acid) throughout the experiment, while groups DS and DSE received a folic acid-free diet with the addition of saccharose supplemented with folic acid (2 mg/kg folic acid) in water. Group E and DSE animals received ethanol (4 g/kg) administered intraperitoneally from the seventh to the ninth gestational day (gd) and were euthanized on the 18th gd, while groups C and DS received saline.

RESULTS

Congenital anomalies were observed in groups E and DSE. The fetal weight and length of the animals in group E were lower than in groups C and DS and, in group DSE, were lower than in groups C and DS. The placental diameter of group E was smaller than that of group C, and the placental weight of group C animals was lower than that of groups E, DSE, and DS.

CONCLUSION

The study demonstrated that dietary supplementation with folate in saccharose is an accessible means of consumption that could be further diffused but in an increased dose than recommended to reduce the teratogenic effects of ethanol.

An experimental study on the effects of ethanol and folic acid deficiency, alone or in combination, on pregnant Swiss mice

INTRODUCTION

Ethanol is teratogenic, interferes with folic acid and is extensively used by young women. Our objective was to determine the effects of ethanol and/or folate deficiency on mouse fetuses.

METHOD

In Experiment 1, pregnant mice receiving a commercial diet were divided into three groups: control (C), low ethanol dose (LE, 0.4 g/kg), and high ethanol dose (HE, 4.0 g/kg). In Experiment 2, pregnant mice receiving a folate-free diet (FFD) were divided into three groups: folate deficiency (FD), folate deficiency plus a low ethanol dose (FDLE), and folate deficiency plus a high ethanol dose (FDHE). Groups C and FD received saline and the remaining groups received ethanol administered i.p. from the 7th to the 9th gestational day (GD) and were sacrificed on the 18th GD.

RESULTS

In Experiment 1, Group HE presented congenital anomalies, late fetal death (LFD), lower fetal length and weight and placental weight and diameter than Groups C and LE. In Experiment 2, there was a smaller number of live fetuses, a larger number of reabsorptions and LFD, a smaller length and lower fetal weight, placental weight and diameter in Groups FDLE and FDHE than in Group FD.

CONCLUSION

In animals receiving a commercial diet, a high ethanol dose is deleterious to the pregnancy, inducing congenital anomalies, intrauterine growth restriction, reduction of the placenta and increased LFD, events that did not occur with the low dose. However, with a folate free diet, a low ethanol dose is as deleterious as a high dose.

Analysis of polyploid cells in mouse embryonic cells cultured under diabetic conditions

To clarify the cytogenetic effects of glucose and ketone bodies on the pathogenesis of diabetes-associated congenital anomalies, we cultured cells from gestation-day-8 ICR mouse embryos under the diabetic condition. Cells were cultured in the medium with glucose (300 mg/dL) plus DL-2-hydroxybutyric acid (32 mM) (G + B group), glucose alone (G group), or neither of them (C group) for 5 days. At the end of the culture, cells were analyzed for the chromosomes. After 3-4 days culture, when the living cells grew into a mono-layered sheet, cells floating in the medium were observed and showed morphological features of apoptosis. Ratio of the floating cells was significantly higher in the G + B group than in the G or C group (P < 0.05), suggesting the deleterious effect of glucose and ketone body. Polyploidy was observed in the cultured cells more frequently in the G + B group (64.1%) than in the G group (49.0%), which was higher than the C group (20.5%) (G + B vs G: P < 0.05, G vs C: P < 0.001). The higher ratio of the polyploidy, but not of the aneuploidy, in the G + B and G groups suggested the specific effect of glucose and ketone body for inducing polyploidy. These results suggest that diabetic condition causes polyploidy in cultured embryonic cells.

Investigation of the effects of folate deficiency on embryonic development through the establishment of a folate deficient mouse model

BACKGROUND

Folic acid (FA) has been shown to reduce the incidence of neural tube, craniofacial, and cardiovascular defects and low birth weight. The mechanism(s) by which the vitamin is effective, however, has not been determined. Therefore, a folic acid deficient mouse model was developed.

METHODS

To create a folic acid deficiency, ICR female mice were placed on a diet containing no FA and including 1% succinyl sulfathiazole (SS) for 4 weeks before mating. Control mice were fed diets with either: 1) FA and 1% SS [+SS only diet]; 2) FA [normal diet]; or 3) a breeding diet. Dams and fetuses were examined during various days of gestation.

RESULTS

Blood analysis showed that by gestational day 18, plasma folate concentrations in the -FA+SS fed dams decreased to 1.13 ng/ml, a concentration approximately 3% of that in breeding diet fed dams (33.24 ng/ml) and 8% of that in +SS only/normal fed dams (13.59 ng/ml). RBC folate levels showed a similar decrease, whereas homocysteine concentrations increased. Reproductive outcome in the -FA+SS fed dams was poor with increased fetal deaths, decreased fetal weight, and delays in palate and heart development.

CONCLUSIONS

Female mice fed a folic acid deficient diet and 1% succinyl sulfathiazole exhibited many of the characteristics common to human folic acid deficiency, including decreased plasma and RBC folate, increased plasma homocysteine, and poor reproductive outcomes. Thus, an excellent model has been created to investigate the mechanism(s) underlying the origin of birth defects related to folic acid deficiency.

Pathogenesis of diabetes-induced congenital malformations

The increased rate of fetal malformation in diabetic pregnancy represents both a clinical problem and a research challenge. In recent years, experimental and clinical studies have given insight into the teratological mechanisms and generated suggestions for improved future treatment regimens. The teratological role of disturbances in the metabolism of inositol, prostaglandins, and reactive oxygen species has been particularly highlighted, and the beneficial effect of dietary addition of inositol, arachidonic acid and antioxidants has been elucidated in experimental work. Changes in gene expression and induction of apoptosis in embryos exposed to a diabetic environment have been investigated and assigned roles in the teratogenic processes. The diabetic environment appears to simultaneously induce alterations in several interrelated teratological pathways. The complex pathogenesis of diabetic embryopathy has started to unravel, and future research efforts will utilize both clinical intervention studies and experimental work that aim to characterize the human applicability and the cell biological components of the discovered teratological mechanisms.

Detection, synthesis, structure, and function of oligo(3-hydroxyalkanoates): contributions by synthetic organic chemists

Two types of the biological macromolecules poly(R-3-hydroxyalkanoates) have been identified: the high-molecular-weight microbial storage material (sPHA) and a short-chain variety, consisting of butyrate and valerate residues, complexed with other biomacromolecules such as calcium polyphosphate or proteins (cPHB/PHV). While sPHA has attracted, and still enjoys, a lot of attention from numerous scientists around the world, research on cPHB and the structurally and functionally related polymalate (PMA) is still in its infancy. In this article, we present a review on the chemical synthesis, structure, function and interactions of monodisperse cPHAs, the oligo(3-hydroxyalkanoates), with emphasis on the butyrates (OHB); we report hitherto unpublished results on the enzymatic degradation of cPHB and PMA, on a new analytical method for HB/HV detection in biological samples, and on OHB-mediated Ca2+ transport through phospholipid bilayers of artificial vesicles; finally, we discuss possible mechanisms of ion transport through cell membranes, as caused by cPHB. The speculative--and provocative--question is asked whether the structurally simple PHAs may have evolved as storage materials and amphiphilic macromolecules before poly-peptides, -saccharides, and -nucleic acids, in the history of life, or under prebiotic conditions.

Murine fibroblast growth factor receptor 1alpha isoforms mediate node regression and are essential for posterior mesoderm development

Alternative splicing in the fibroblast growth factor receptor 1 (Fgfr1) locus generates a variety of splicing isoforms, including FGFR1alpha isoforms, which contain three immunoglobulin-like loops in the extracellular domain of the receptor. It has been previously shown that embryos carrying targeted disruptions of all major isoforms die during gastrulation, displaying severe growth retardation and defective mesodermal structures. Here we selectively disrupted the FGFR1alpha isoforms and found that they play an essential role in posterior mesoderm formation during gastrulation. We show that the mutant embryos lack caudal somites, develop spina bifida, and die at 9.5-12.5 days of embryonic development because they are unable to establish embryonic circulation. The primary defect is a failure of axial mesoderm cell migration toward the posterior portions of the embryos during gastrulation, as revealed by regional marker analysis and DiI labeling. In contrast, the anterior migration of the notochord is unaffected and the embryonic structures rostral to the forelimb are relatively normal. These data demonstrate that FGF/FGFR1alpha signals are posteriorizing factors that control node regression and posterior embryonic development.

Serine-enhanced restoration of 2-methoxyethanol-induced dysmorphogenesis in the rat embryo and near-term fetus

Effects of serine on restorative growth were characterized by comparing embryo/fetal responses after maternal exposure to 2-methoxyethanol (ME) and ME + serine by gavage on gestation day (gd) 13, a day of heightened limb sensitivity. Paws (gd 20) and limb buds (gd 15) were examined after ME alone at 50, 100, and 250 mg/kg, and after ME (either 100 or 250 mg ME/kg) + serine (1734 mg serine/kg) administered within minutes (0 hr) to 24 hr after ME. Paw development was not altered after ME at 100 mg/kg, but was highly sensitive to 250 mg ME/kg with all fetuses and litters exhibiting defects (ectrodactyly, syndactyly, and short digit) in the preaxial region. In contrast, the limb bud displayed dose-related incidences of abnormalities after maternal treatment with the low and high levels of ME. The condensing (precartilaginous, pentadactyl pattern) and noncondensing (undifferentiated mesenchymal cells) regions exhibited changes in their size, number, and location. Serine administration after 250 mg ME/kg was effective in reducing the occurrence of paw dysmorphogenesis with its protection potency inversely related to its delay of administration (i.e., 0% paw defect incidence after 0-hr delay, 25% after 4-hr delay, 41-45% after 8- and 12-hr delays, and 76% after 24-hr delay). The occurrences of limb bud pattern disturbances produced by ME were also markedly decreased by serine cotreatment. Higher incidences of embryonic defects versus those of fetal defects demonstrate that restorative growth followed ME exposure. Serine attenuation of ME teratogenicity appears to emanate from enhanced restorative growth so that tissue damage, which otherwise would be expressed as a defect at parturition, is repaired and replaced to resume development of the limb toward its normal structure.

Effects of 2-methoxyethanol on mouse neurulation

The potent developmental toxicant, 2-methoxyethanol (2-ME), elicits exencephaly in near-term mouse fetuses following a single maternal treatment early on gestation day (gd) 8. Deleterious morphological consequences to the neurulating embryo shortly after exposure have not been reported. The present study was designed to fill this gap and to investigate the impact of 2-ME treatment on cell death patterns in the embryonic neural folds. Dams were injected subcutaneously with saline, 250 or 325 mg 2-ME/kg 2 hr prior to the beginning of gd 8. The effect of 2-ME on gross and microscopic neural development was examined in conceptuses on gd 9, 6 hr (9:6), 10:6, and 18:0. Compared to saline, 2-ME treatment increased the percentage of embryos with open neural tubes (ONTs) at all gestation days. Although few statistically significant differences (P < 0.05) existed among the ONT rates on the 3 observation days, an interesting biological response occurred. Both high and low 2-ME doses appeared to elicit the greatest incidence of neural tube patency on gd 9:6 (affecting approximately 27% of embryos). During the subsequent 24 hr, recovery occurred and many neural folds apparently closed. Consequently, the ONT incidences on gd 10:6 (approximately 11%) were quite similar to the gd 18 exencephaly rates elicited by both chemical treatments (approximately 15%). A dose response was not seen due to a substantial increase in resorption rates following the 325 mg/kg dose. Compared to the other treatment groups, the low 2-ME dose significantly inhibited embryonic growth as indicated by reduced crown-rump and head lengths and increased incidence of developmentally delayed brain maturation. To evaluate chemically induced changes in cell death, neurulating embryos were collected on gd 8:6 and either immersed in the vital dye, Nile blue sulfate (NBS), or processed for histopathology. In 2-ME-exposed embryos, excessive NBS uptake occurred in neural fold neuroepithelium at sites of nonclosure. Using histopathology, the extent of cell death in the cephalic neural folds was dependent on the 2-ME dose, and the neuroepithelium was more severely affected than the mesenchyme. These observations suggest 1) a trend toward repair and catch-up growth later in gestation which may ameliorate the overt early effects of 2-ME, and 2) an association between enhanced cell death and regions of the neural tube particularly vulnerable to nonclosure.

Exencephaly and hydrocephaly in mice with targeted modification of the apolipoprotein B (Apob) gene

Apolipoprotein B (apoB) is a key structural component of several lipoproteins. These lipoproteins transport cholesterol, lipids, and vitamin E in the circulation. Humans that produce truncated forms of apoB have low plasma concentrations of apoB, beta-lipoproteins, cholesterol, and often vitamin E. This condition has been modeled in mice by targeted modification of the apoB gene. Homozygous transgenic mice display all of the hallmarks of the human disorder. Unexpectedly, approximately 30% of the perinatal homozygotes are exencephalic and of those that have closed neural tubes, approximately 30% are hydrocephalic. The latter condition has also been noted in a relatively small proportion of the heterozygous mice. Vital staining of gestational day 9 (GD9) homozygous offspring has illustrated a striking pattern of excessive cell death involving the alar plate of the hindbrain. Histological and scanning electron microscopic analyses have confirmed this finding. We speculate that varying degrees of affect, as noted among GD 9 and 10 embryos, lead to the spectrum of malformations, including hydrocephaly, present in term fetuses. Analysis of vitamin E deficiency as a possible causative factor has illustrated that homozygous fetuses, indeed, show this deficiency. Amelioration of the defects through alpha-tocopherol supplementation of the maternal diet has been explored. Further analyses of this transgenic mutant promise to provide significant information relative to the role of deficiency of vitamin E and other apoB dependent compounds in dysmorphogenesis.

Methanol-induced neural tube defects in mice: pathogenesis during neurulation

A spectrum of cephalic neural tube defects was observed in near-term (gestation day [GD] 17) mouse fetuses following maternal inhalation of methanol at a high concentration (15,000 ppm) for 6 hr/day during neurulation (GD 7-9). Dysraphism, chiefly exencephaly, occurred in 15% of fetuses, usually in association with reduction or absence of multiple bones in the craniofacial skeleton and ocular anomalies (prematurely open eyelids, cataracts, retinal folds). Measurements of cerebrocortical width in grossly normal, methanol-exposed fetuses revealed significant semiquantitative differences in the thicknesses of the frontal cortex and its constituent layers (neuroepithelium, intermediate cortex/subventricular plate, and cortical layer 1) as well as apparent increases in subventricular plate cellularity relative to controls. Subsequently, the early morphogenesis of these neural changes was investigated in neurulating mouse embryos to define tissue-specific patterns of methanol-induced damage that lead to cephalic axial dysraphism. Following daily 6-hr maternal inhalations of 15,000 ppm methanol during GD 7-8, the cephalic neural fold margins were swollen, blunted, and poorly elevated on GD 8.5 and 9 relative to controls. Histopathology of exposed GD 8.5 embryos revealed microcephaly in association with reductions in the cell density and mitotic index of at least 47% in the cranial mesoderm. The mitotic index in the embryonic neuroepithelium was also reduced by 55%, and groups of neural crest cells were displaced to the neural folds dorsal to the foregut (relative to the more ventral location in the facial regions of control embryos). When examined on GD 9.5 and 10.5, maternal methanol exposure (15,000 ppm for 6 hr/day) during GD 7-9 resulted in stunting, delayed rotation, and microcephaly in over 90% of the affected embryos. Persistent patency of the anterior neuropore and prosencephalic hypoplasia were seen in > 40% and up to 90% of embryos, respectively. Shallow optic vesicles, stunted branchial arches, scoliosis, and hydropericardium were also observed. Many 10.5-day-old embryos were edematous. Occult dysraphism, recognized grossly by abnormally narrow cephalic conformation and histopathologically by the absence of mesoderm in the mesencephalon, was present in at least 21% of methanol-exposed embryos on GD 9.5 and 10.5. Nile blue vital dye staining of methanol-exposed embryos revealed no difference in dye accumulation between control and treated embryos on GD 8.5, 9.0, or 9.5. There were no apparent dysmorphogenic effects in control embryos at any stage of development.(ABSTRACT TRUNCATED AT 400 WORDS)

Postulated mechanisms underlying the development of neural tube defects. Insights from in vitro and in vivo studies

In recent years, use of animal models has resulted in acquisition of a significant amount of new information regarding normal and abnormal neural tube development. Studies of mutant and of teratogen-exposed mice are complementary, with each providing insights that promise to advance our understanding of the other. Analysis of teratogen-exposed embryos is best suited for identifying susceptible developmental stages and vulnerable populations. Advances in molecular genetics, with the ability to identify gene products, their cell/tissue location, and, potentially, to understand their function, will make naturally occurring as well as man-made mutants invaluable for understanding the heterogeneous mechanisms that underly NTDs.

Effects of altered maternal metabolism during gastrulation and neurulation stages of embryogenesis

In summary, many congenital malformations are produced during gastrulation and neurulation stages of embryogenesis at a time when no definitive chorioallantoic placenta has been established. In rodents, altered maternal metabolism may have a direct impact on the embryo or an indirect impact via disruption of the nutritive function of the visceral yolk sac. If similar mechanisms operate in human embryos, these factors probably alter functions of the trophoblastic shell. In any case, it is crucial to remember that the metabolic status of the embryo is rapidly changing and during early stages of organogenesis may respond to alterations in nutrients quite differently during the first four weeks of gestation than at later stages of organogenesis and the fetal period.

Recovery by mouse embryos following teratogenic exposure to ketosis

Previous studies have shown that the ketone body D,L,-beta-hydroxybutyrate was teratogenic to mouse embryos exposed in culture during the period of neurulation. Inhibition of closure of the cranial and caudal neuropores was the most frequently occurring defect and these abnormalities were thought to be the forerunner of anencephaly and spina bifida, respectively. However, additional studies demonstrated that embryos could recover morphologically from these effects if the ketone body was removed from the culture medium and if the recovery period was of sufficient duration. In an attempt to define further the phenomenon responsible for this recovery and to determine the extent of the recovery process, the present study examining the cross-sectional area, cell number, and mitotic index of cranial neuroepithelial cells was conducted in mouse embryos cultured from the early somite stage under one of the following conditions: 1) control medium for 60 h; 2) medium containing 32 mmol/l D,L,-beta-hydroxybutyrate for 24 h followed by culture in control medium for an additional 36 h (recovery group); 3) medium containing 32 mmol/l D,L,-beta-hydroxybutyrate for 60 h (continuously exposed group). The results indicate that although neural tube closure occurred in the recovery group, complete recovery was limited to the ventral regions of the forebrain and that the remainder of the prosencephalon as well as the rhombencephalon failed to undergo complete catch-up growth. Thus, cell numbers in these areas were approximately 70% of control values. Therefore, while the gross anatomical disturbances produced by the ketone body may be compensated for, histological alterations in the affected tissues remain. Ultimately, these data suggest that neurological deficits may be an outcome of ketone body exposure during the early stages of embryogenesis.

Use of embryo culture to study normal development and developmental mechanisms

Mammalian embryo culture techniques have been used to study many aspects of embryonic development. The advantages and limitations of such studies as models for in vivo development are discussed by reference to the following specific examples: development of the paraxial mesoderm, regulation of growth, protein uptake and metabolism, and carbohydrate metabolism. Embryo culture techniques are useful for the study of morphogenesis and growth because the embryo is made accessible for manipulation and observation. Development in vivo and in vitro over equivalent periods can be compared. The limitations of the system have important implications for the interpretation of studies of embryonic metabolism. In vitro metabolic activity can be assessed by assays of the culture media and embryonic tissue at intervals throughout the culture. However, the sensitivity of the metabolic pathways to explantation remains unknown because of the technical difficulties involved in studying embryonic metabolism in vivo.

Biochemical basis for D,L,-beta-hydroxybutyrate-induced teratogenesis

Previous investigations have demonstrated that a potential mechanism for D,L,-beta-hydroxybutyrate (BOHB)-induced teratogenesis in neurulating mouse embryos (5-6 somite stage) after 24 hours of exposure in vitro is mediated by an inhibition of the pentose phosphate pathway (PPP) (Hunter, et al. '87). Employing conceptuses of an earlier stage (2-3 somite stage), the biochemistry of BOHB-induced abnormalities was examined further by exposing embryos to 32 mM BOHB for 24 hour and comparing results with controls with respect to the rate of metabolism via the PPP, de novo pyrimidine biosynthesis (PB), and BOHB utilization. Moreover, the capability of these BOHB-exposed embryos to recover from such an insult was also assessed by transferring them to fresh control medium and allowing them to grow for an additional 36 hours. Both controls and BOHB-exposed embryos showed a progressive increase in rate of BOHB utilization between days 9 and 11.5 of gestation in vitro. Exposure to ketone body produced a 100% rate of neural tube defects and a 25.2% decrease in total embryonic protein content. In contrast to results obtained at the 5-6 somite stage, no inhibition of the PPP in whole conceptuses, embryos, or visceral yolk sacs was observed in the group exposed to BOHB at the 2-3 somite stage. Furthermore, a 7.5 mM D-ribose supplement, an intermediate in the PPP, was unable to rescue the younger embryos from BOHB-induced abnormalities and growth retardation. On the other hand, BOHB produced a 34.3% decrease in pyrimidine biosynthesis in the 2-3 somite embryos, but not in the visceral yolk sac. In addition, embryos recovered biochemically after being transferred to control medium, demonstrating a 25.5% overshoot in pyrimidine biosynthesis. Therefore, the mechanism of BOHB-induced teratogenesis appears to differ depending on the stage of embryonic development at the time of initial exposure.

Embryonic resistance to chemical and physical factors: manifestation, mechanism, role in reproduction and in adaptation to ecology

Chemical and physical factors may adversely affect embryonic development. As an example of chemical factors, the effects of diabetic metabolic factors on embryonic development in mammals was reviewed. The existence of a stage-dependent reaction of embryos was found. At preimplantation stages diabetic metabolic factors are embryotoxic and lethal, and the blastocysts reacted by an "all-or-none" response. Early somite embryos showed a higher resistance to the effects of diabetic metabolic factors resulting in various types of malformations. Both groups of embryos showed a very high sensitivity to the effects of combined diabetic metabolic factors. Congenital defects in term foetuses were lower than those observed during middle phases of pregnancy because some of the severely malformed embryos resorb during gestation. The effects of temperature on embryonic development were presented as an example of physical influences. In man, hyperthermia in pregnancy seems to correlate with defects in the development of the nervous and skeletal systems. In domestic animals, changes in environmental temperature correlated with depressions of reproduction rate. In laboratory animals, hyperthermia caused the development of congenital malformations. Stage-dependent as well as genetic differences in embryonic susceptibility to hyperthermia were found. Critical periods in sensitivity of embryos to hyperthermic influences were also observed. It has been shown that, in spite of similar external manifestations of the reaction of embryos to effects of diabetes and hyperthermia, the mechanism of these reactions was different. High resistance of early reptile and bird embryos to influences of temperature was considered as an example of morphofunctional adaptations in early embryogenesis of vertebrates to their development in terrestrial conditions.