Fetal fuels. I. Utilization of ketones by isolated tissues at various stages of maturation and maternal nutrition during late gestation

Cardiac mitochondrial metabolism during pregnancy and the postpartum period

The goal of the present study was to characterize changes in mitochondrial respiration in the maternal heart during pregnancy and after birth. Timed pregnancy studies were performed in 12-wk-old female FVB/NJ mice, and cardiac mitochondria were isolated from the following groups of mice: nonpregnant (NP), midpregnancy (MP), late pregnancy (LP), and 1-wk postbirth (PB). Similar to our previous studies, we observed increased heart size during all stages of pregnancy (e.g., MP and LP) and postbirth (e.g., PB) compared with NP mice. Differential cardiac gene and protein expression analyses revealed changes in several mitochondrial transcripts at LP and PB, including several mitochondrial complex subunits and members of the Slc family, important for mitochondrial substrate transport. Respirometry revealed that pyruvate- and glutamate-supported state 3 respiration was significantly higher in PB vs. LP mitochondria, with respiratory control ratio (RCR) values higher in PB mitochondria. In addition, we found that PB mitochondria respired more avidly when given 3-hydroxybutyrate (3-OHB) than mitochondria from NP, MP, and LP hearts, with no differences in RCR. These increases in respiration in PB hearts occurred independent of changes in mitochondrial yield but were associated with higher abundance of 3-hydroxybutyrate dehydrogenase 1. Collectively, these findings suggest that, after birth, maternal cardiac mitochondria have an increased capacity to use 3-OHB, pyruvate, and glutamate as energy sources; however, increases in mitochondrial efficiency in the postpartum heart appear limited to carbohydrate and amino acid metabolism.NEW & NOTEWORTHY Few studies have detailed the physiological adaptations that occur in the maternal heart. We and others have shown that pregnancy-induced cardiac growth is associated with significant changes in cardiac metabolism. Here, we examined mitochondrial respiration and substrate preference in isolated mitochondria from the maternal heart. We show that following birth, cardiac mitochondria are "primed" to respire on carbohydrate, amino acid, and ketone bodies. However, heightened respiratory efficiency is observed only with carbohydrate and amino acid sources. These results suggest that significant changes in mitochondrial respiration occur in the maternal heart in the postpartum period.

Long-term reproductive effects of benzo(a)pyrene at environmentally relevant dose on juvenile female rats

Since studies on the reproductive consequences after the exposure to environmentally relevant doses of Benzo(a)pyrene (BaP) during critical stages of development are scarce, this study evaluated female reproductive parameters of adult rats exposed to a low dose of BaP during the juvenile phase. Female rats (Post-natal 21) were treated with BaP (0 or 0.1 µg/kg/day; gavage) for 21 consecutive days. During the treatment, no clinical signs of toxicity were observed. Nevertheless, the ages of vaginal opening and first estrus were anticipated by the BaP-exposure. At the sexual maturity, the juvenile exposure compromised the sexual behavior, as well as the placental efficiency, follicle stimulating hormone levels, placenta histological analysis, and ovarian follicle count. A decrease in erythrocyte, platelet, and lymphocyte counts also was observed in the exposed-females. Moreover, the dose of BaP used in this study was not able to produce estrogenic activity in vivo. These data showed that juvenile BaP-exposure, at environmentally relevant dose, compromised the female reproductive system, possibly by an endocrine deregulation; however, this requires further investigation.

Lactate Metabolism, Signaling, and Function in Brain Development, Synaptic Plasticity, Angiogenesis, and Neurodegenerative Diseases

Neural tissue requires a great metabolic demand despite negligible intrinsic energy stores. As a result, the central nervous system (CNS) depends upon a continuous influx of metabolic substrates from the blood. Disruption of this process can lead to impairment of neurological functions, loss of consciousness, and coma within minutes. Intricate neurovascular networks permit both spatially and temporally appropriate metabolic substrate delivery. Lactate is the end product of anaerobic or aerobic glycolysis, converted from pyruvate by lactate dehydrogenase-5 (LDH-5). Although abundant in the brain, it was traditionally considered a byproduct or waste of glycolysis. However, recent evidence indicates lactate may be an important energy source as well as a metabolic signaling molecule for the brain and astrocytes-the most abundant glial cell-playing a crucial role in energy delivery, storage, production, and utilization. The astrocyte-neuron lactate-shuttle hypothesis states that lactate, once released into the extracellular space by astrocytes, can be up-taken and metabolized by neurons. This review focuses on this hypothesis, highlighting lactate's emerging role in the brain, with particular emphasis on its role during development, synaptic plasticity, angiogenesis, and disease.

Edited magnetic resonance spectroscopy in the neonatal brain

J-difference-edited spectroscopy is a valuable approach for the detection of low-concentration metabolites with magnetic resonance spectroscopy (MRS). Currently, few edited MRS studies are performed in neonates due to suboptimal signal-to-noise ratio, relatively long acquisition times, and vulnerability to motion artifacts. Nonetheless, the technique presents an exciting opportunity in pediatric imaging research to study rapid maturational changes of neurotransmitter systems and other metabolic systems in early postnatal life. Studying these metabolic processes is vital to understanding the widespread and rapid structural and functional changes that occur in the first years of life. The overarching goal of this review is to provide an introduction to edited MRS for neonates, including the current state-of-the-art in editing methods and editable metabolites, as well as to review the current literature applying edited MRS to the neonatal brain. Existing challenges and future opportunities, including the lack of age-specific reference data, are also discussed.

Hepatic hexokinase domain containing 1 (HKDC1) improves whole body glucose tolerance and insulin sensitivity in pregnant mice

Hexokinase domain containing 1, a recently discovered putative fifth hexokinase, is hypothesized to play key roles in glucose metabolism. Specifically, during pregnancy in a recent genome wide association study (GWAS), a strong correlation between HKDC1 and 2-h plasma glucose in pregnant women from different ethnic backgrounds was shown. Our earlier work also reported diminished glucose tolerance during pregnancy in our whole body HKDC1 heterozygous mice. Therefore, we hypothesized that HKDC1 plays important roles in gestational metabolism, and designed this study to assess the role of hepatic HKDC1 in whole body glucose utilization and insulin action during pregnancy. We overexpressed human HKDC1 in mouse liver by injecting a human HKDC1 adenoviral construct; whereas, for the liver-specific HKDC1 knockout model, we used AAV-Cre constructs in our HKDC1fl/fl mice. Both groups of mice were subjected to metabolic testing before and during pregnancy on gestation day 17-18. Our results indicate that hepatic HKDC1 overexpression during pregnancy leads to improved whole-body glucose tolerance and enhanced hepatic and peripheral insulin sensitivity while hepatic HKDC1 knockout results in diminished glucose tolerance. Further, we observed reduced gluconeogenesis with hepatic HKDC1 overexpression while HKDC1 knockout led to increased gluconeogenesis. These changes were associated with significantly enhanced ketone body production in HKDC1 overexpressing mice, indicating that these mice shift their metabolic needs from glucose reliance to greater fat oxidation and ketone utilization during fasting. Taken together, our results indicate that hepatic HKDC1 contributes to whole body glucose disposal, insulin sensitivity, and aspects of nutrient balance during pregnancy.

Evaluation of placental glycogen storage in mild diabetic rats

PURPOSE: To evaluate the placental glycogen storage and fetal development in the pregnancy of neonatally streptozocin-induced diabetic rats and to establish relation with glycemia and insulin levels. METHODS: At the birth day, 147 female rats were randomly distributed in two experimental groups: 1) Non-diabetic Group (Control, n=45) - received the vehicle; 2) Diabetic Group (STZ, n=102) - received 100 mg streptozocin/kg in neonatal period. At day 0 of pregnancy, adult female rats were included in the control group when presented glycemia below 120 mg/dL and, in the group STZ with glycemia between 120 and 300 mg/dL. At day 21 of pregnancy, blood samples were collected for glycemia and insulin determination, and placentas withdrawn for placental glycogen determination. The newborns (NB) were classified in small (SGA), appropriate (AGA) and large (LGA) for gestational age. RESULTS: Rats STZ presented higher glycemia at days 0 and 14 of pregnancy. At end of pregnancy, rats STZ showed higher proportion of NB SGA and LGA; reduced rate of NB AGA and unaltered glycemia, insulin and placental glycogen determinations. CONCLUSION: Mild diabetes altered the maternal glycemia in the early pregnancy, impairing future fetal development, but it caused no alteration on insulin and placental glycogen determination, confirming that this glycemic intensity was insufficient to change glycogen metabolism.

Cerebral metabolic adaptation and ketone metabolism after brain injury

The developing central nervous system has the capacity to metabolize ketone bodies. It was once accepted that on weaning, the 'post-weaned/adult' brain was limited solely to glucose metabolism. However, increasing evidence from conditions of inadequate glucose availability or increased energy demands has shown that the adult brain is not static in its fuel options. The objective of this review is to summarize the body of literature specifically regarding cerebral ketone metabolism at different ages, under conditions of starvation and after various pathologic conditions. The evidence presented supports the following findings: (1) there is an inverse relationship between age and the brain's capacity for ketone metabolism that continues well after weaning; (2) neuroprotective potentials of ketone administration have been shown for neurodegenerative conditions, epilepsy, hypoxia/ischemia, and traumatic brain injury; and (3) there is an age-related therapeutic potential for ketone as an alternative substrate. The concept of cerebral metabolic adaptation under various physiologic and pathologic conditions is not new, but it has taken the contribution of numerous studies over many years to break the previously accepted dogma of cerebral metabolism. Our emerging understanding of cerebral metabolism is far more complex than could have been imagined. It is clear that in addition to glucose, other substrates must be considered along with fuel interactions, metabolic challenges, and cerebral maturation.

Lactate utilization by brain cells and its role in CNS development

We studied the role played by lactate as an important substrate for the brain during the perinatal period. Under these circumstances, lactate is the main substrate for brain development and is used as a source of energy and carbon skeletons. In fact, lactate is used actively by brain cells in culture. Neurons, astrocytes, and oligodendrocytes use lactate as a preferential substrate for both energy purposes and as precursor of lipids. Astrocytes use lactate and other metabolic substrates for the synthesis of oleic acid, a new neurotrophic factor. Oligodendrocytes mainly use lactate as precursor of lipids, presumably those used to synthesize myelin. Neurons use lactate as a source of energy and as precursor of lipids. During the perinatal period, neurons may use blood lactate directly to meet the need for the energy and carbon skeletons required for proliferation and differentiation. During adult life, however, the lactate used by neurons may come from astrocytes, in which lactate is the final product of glycogen breakdown. It may be concluded that lactate plays an important role in brain development.

Hematology and clinical chemistry values in pregnant Wistar Hannover rats compared with nonmated controls

BACKGROUND

The Wistar Hannover rat has been considered as an alternative animal model to the Sprague-Dawley rat in the safety evaluation of candidate pharmaceuticals for potential reproductive and developmental toxicity. Hematology and clinical chemistry results may provide useful evidence of maternal toxicity in the absence of fetal effects.

OBJECTIVE

The purpose of this study was to evaluate differences in routine laboratory values between nonmated and pregnant (near-term)Wistar Hannover rats during a control developmental study.

METHODS

One hundred fifty pregnant female Wistar Hannover rats (Tac:Glx:WlfBR) were dosed orally once per day with distilled water from gestation days (GDs) 6 through 17. An additional 150 nonmated (nonpregnant) females used as age-matched controls were dosed from study days (SDs) 7 through 18. Blood samples were collected on GD 18 or 19 (SD 19 or 20) for routine hematology and plasma clinical chemistry tests. Reference intervals were established for pregnant and nonmated animals.

RESULTS

On GD 18/19, pregnant rats had a lower RBC count, hemoglobin concentration, and HCT, and higher MCH, MCHC, reticulocyte percentage, and platelet, WBC, absolute reticulocyte, segmented neutrophil, lymphocyte, and monocyte counts compared with nonmated rats. Pregnant rats had lower albumin, glucose, urea, and chloride concentrations, lower creatine kinase and alkaline phosphatase activities, higher total bilirubin, cholesterol, triglyceride, calcium, phosphorus, and globulin concentrations, and higher ALT activity than nonmated rats. Serum triglyceride concentration was approximately fourfold higher in pregnant rats compared with nonmated controls.

CONCLUSION

Differences in hematology and chemistry values in pregnant Wistar Hannover rats are similar to those in Sprague-Dawley rats and support use of the Wistar Hannover rat as an animal model in the assessment of maternal toxicity. Differences in laboratory values of pregnant rats should be considered when interpreting data following exposure to candidate pharmaceuticals.

Lipoprotein metabolism during normal pregnancy

OBJECTIVE

We sought to investigate the changes in circulating serum lipids and lipoproteins, including lipoprotein (a), and low-density lipoprotein size in women during normal pregnancy.

STUDY DESIGN

Twenty-two women (mean age, 31 +/- 5 years; 13 primiparous subjects) were studied during uncomplicated pregnancy with normal outcome. Twenty-four nulliparous women of similar age (31 +/- 4 years) were studied as control subjects.

RESULTS

Serum triglycerides and total and low-density lipoprotein cholesterol increased significantly during pregnancy in all women. Women with changes in low-density lipoprotein during the second and third trimesters showed a more marked increase in serum triglycerides, and this effect was slightly more evident in the multiparous subjects. No other differences were evident between primiparous and multiparous women apart from high-density lipoprotein cholesterol levels, which were slightly decreased in the latter subjects.

CONCLUSIONS

Our results show that during normal pregnancy, the increase in plasma triglycerides may lead to the appearance of the atherogenic dense low-density lipoproteins in a subgroup of women. We suggest that the observed changes in low-density lipoprotein patterns during pregnancy might be used to identify those women who later in life will have these atherogenic small and dense low-density lipoproteins.

Insulin-like growth factors and binding proteins in the fetal rat: alterations during maternal starvation and effects in fetal brain cell culture

Maternal malnutrition adversely affects fetal body and brain growth during late gestation. We utilized a fetal brain cell culture model to examine whether alternations in circulating factors may contribute to reduce brain growth during maternal starvation; we then used specific immunoassay and western blotting techniques, and purified peptides to investigate the potential role that altered levels of insulin-like growth factors (IGFs) and IGF binding proteins (IGFBPs) may play in impaired growth during maternal nutritional restriction. Fetal, body, liver, and brain weight were reduced after 72 hr maternal starvation, and plasma from starved fetuses were less potent than fed fetal plasma in stimulating brain cell growth. Circulating levels of IGF-I were reduced in starved compared to fed fetuses, while levels of IGF-II were similar in both groups. In contrast, [125I]-IGF-I binding assay demonstrated an increase in the availability of plasma IGFBPs following starvation. Western ligand blotting and densitometry indicated that levels of 32 Kd IGFBPs were 2-fold higher in starved compared to fed fetal plasma. Immunoblotting and immunoprecipitation with antiserum against rat IGFBP-1 confirmed that heightened levels of immunoreactive IGFBP-1 accounted for the increase in 32 Kd IGFBPs in starved plasma. Levels of 34 Kd BPs, representing IGFBP-2, were unaffected by starvation. Reconstitution experiments in cell culture showed that IGF-I promoted fetal brain cell growth, and that when they were supplemented with IGF-I, the growth promoting activity of starved fetal plasma was restored to fed levels. These changes were measured using MTT to assess mitochondrial reductase activity.(ABSTRACT TRUNCATED AT 250 WORDS)

Retardation of fetal brain cell growth during maternal starvation: circulating factors versus altered cellular response

Maternal starvation inhibits fetal brain development during late gestation in the rat. To determine whether intrinsic or extrinsic factors might be the principal contributor to altered growth, brain cells from 20 day fetuses were cultured in a 96 well plate with MEM and 10% adult rat serum. Tissue growth was monitored by spectrophotometric measurement of the mitochondrial reduction of a chromagen 3-(4,5 dimethylthiazol-2-yl)-2,5 diphenyl tetrazolium bromide (MTT). After 1, 4 or 6 days incubation, MTT activity in non confluent cultures was shown to be directly related to tissue mass. When fetal brain cell cultures were incubated with 1% and 10% concentrations of adult rat serum, an 11-fold increase in MTT activity paralleled a 15-fold increase in tritiated thymidine incorporation. The impact of maternal starvation on fetal brain cell growth was examined by measuring MTT activity in fetal brain cells from fed and starved mothers. When cultures were incubated for 6 days with graded concentrations of fed adult serum (1.25-10%), the MTT response was slightly but consistently lower in cells from starved when compared with cells from fed mothers. By contrast, a marked difference in MTT activity which was paralleled by a lower DNA content became apparent when fetal rat brain cells were incubated with starved adult serum. Fetal serum and adult male serum were found to support growth equally well, while incubation of fetal brain cells with maternal sera resulted in lower MTT values than with the corresponding fetal sera. When cells were incubated with fetal sera pooled from starved mothers, MTT activity was decreased by 42 to 45%.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of beta-hydroxybutyrate infusion on hind limb metabolism in fetal sheep

OBJECTIVES

This study investigated the effects of high ketone levels on fetal carcass metabolism. Specifically, we aimed to determine whether beta-hydroxybutyrate was taken up by fetal muscle and whether lactate production by the fetal hind limb contributed to the raised circulating lactate levels seen in high ketone states.

STUDY DESIGN

Hind limb metabolism was studied in 10 chronically catheterized fetal sheep. Substrate/oxygen quotients were measured before and after 2 hour infusions of beta-hydroxybutyrate and compared with the Wilcoxon signed-rank test.

RESULTS

beta-Hydroxybutyrate was taken up by hind limb tissues in large amounts (butyrate/oxygen quotient = 1.02 +/- 0.40). Lactate was produced by the hind limb (lactate/oxygen quotient = -0.96 +/- 0.52) in amounts almost equivalent to glucose uptake (glucose/oxygen quotient = 1.32 +/- 0.29). Hind limb oxygen consumption increased 35% and fetal arterial oxygen content fell 16%.

CONCLUSION

beta-Hydroxybutyrate may be consumed by the fetal carcass in amounts sufficient to entirely substitute for glucose. Glucose may then be released as lactate for metabolism elsewhere. Ketones may be important fetal substrates during maternal starvation.

Fetal glucose utilization in response to maternal starvation and acute hyperketonemia

The effects of maternal hypoglycemia and/or hyperketonemia on glucose utilization by individual fetal rat tissues have been studied in vivo. To decrease blood glucose and to raise fetal blood ketone body concentrations, 19-day pregnant rats were submitted to 48 or 96 h of starvation. To differentiate between the effects of decreased blood glucose and increased ketone body concentrations, fed pregnant rats were infused for 2 h with DL-beta-hydroxybutyrate. After 96 h of maternal starvation, fetal 2-deoxy-D-glucose (2DG) uptake decreased from 13.6 +/- 0.5 to 8.6 +/- 1.15 micrograms.min-1.g-1. This was mainly due to a decrease in 2DG uptake by fetal hindlimb muscles and heart. By contrast, 2DG uptake in fetal liver and brain was not affected by maternal starvation. Acute hyperketonemia in fed pregnant rats induced a 23% decrease in 2DG uptake by the whole fetus mainly as the result of a lowered 2DG uptake in fetal hindlimb muscles. These data suggest that fetal 2DG uptake does not simply depend on lowered blood glucose level during maternal starvation but that other hormonal, cardiovascular, or metabolic adaptations are implicated. In the rat, most of the fetal tissues including brain are protected against maternal hypoglycemia.

Diabetes and pregnancy

Prior to the introduction of insulin, a vast majority of pregnancies complicated by diabetes ended in perinatal death, with an associated risk of maternal death. Currently, virtually all diabetic women can undergo pregnancy with the expectation of good maternal and fetal outcome. However, many challenges still remain in preventing congenital anomalies and macrosomia.

Metabolic response to starvation at late gestation in chronically ethanol-treated and pair-fed undernourished rats

To study the role of undernourishment in the negative effects of ethanol during pregnancy and to determine whether maternal ethanol intake modifies metabolic response to starvation at late gestation, female rats receiving ethanol in their drinking water before and during pregnancy (ethanol group) were compared with animals that received the same amount of solid diet as the ethanol group rats (pair-fed group) and with normal rats fed ad libitum (control group). All animals were killed on the 21st day of gestation, either in the fed state or after 24-hours fasting. The body weight of ethanol rats was lower than that of controls but higher than that of pair-fed rats. When compared with controls, ethanol and pair-fed rats had reduced fetal body weights, whereas fetal body length was reduced only in the former. In the fed state, blood glucose concentration was lower in the ethanol and pair-fed rats and fetuses than in controls. Twenty-four-hour starvation caused a reduction in this parameter only in control and ethanol mothers. In the fed state, maternal liver glycogen concentration was lower in ethanol and higher in pair-fed mothers than in controls. Blood beta-hydroxybutyrate levels were higher in ethanol-treated mothers than in the others, and 24-hour starvation increased this parameter in ethanol and control rats to a greater extent than in the pair-fed ones. Liver triacylglyceride concentration was higher in ethanol-treated mothers than in the other two groups, and starvation caused this concentration to increase in ethanol and control groups but not in the pair-fed group.(ABSTRACT TRUNCATED AT 250 WORDS)

Role of lipoprotein lipase activity on lipoprotein metabolism and the fate of circulating triglycerides in pregnancy

The mechanism that induces maternal hypertriglyceridemia in late normal pregnancy, and its physiologic significance are reviewed as a model of the effects of sex steroids on lipoprotein metabolism. In the pregnant rat, maternal carcass fat content progressively increases up to day 19 of gestation, then declines at day 21. The decline may be explained by the augmented lipolytic activity in adipose tissue that is seen in late pregnancy in the rat. This change causes maternal circulating free fatty acids and glycerol levels to rise. Although the liver is the main receptor organ for these metabolites, liver triglyceride content is reduced. Circulating triglycerides and very-low-density lipoprotein (VLDL)-triglyceride levels are highly augmented in the pregnant rat, indicating that liver-synthesized triglycerides are rapidly released into the circulation. Similar increments in circulating VLDL-triglycerides are seen in pregnant women during the third trimester of gestation. This increase is coincident with a decrease in plasma postheparin lipoprotein lipase activity, indicating a reduced removal of circulating triglycerides by maternal tissues or a redistribution in their use among the different tissues. During late gestation in the rat, tissue lipoprotein lipase activity varies in different directions; it decreases in adipose tissue, the liver, and to a smaller extent the heart, but increases in placental and mammary gland tissue. These changes play an important role in the fate of circulating triglycerides, which are diverted from uptake by adipose tissue to uptake by the mammary gland for milk synthesis, and probably by the placenta for hydrolysis and transfer of released nonesterified fatty acids to the fetus. After 24 hours of starvation, lipoprotein lipase activity in the liver greatly increases in the rat in late pregnancy; this change is not seen in virgin animals. This alteration is similar to that seen in liver triglyceride content and plasma ketone body concentration in the fasted pregnant rat. In the fasting condition during late gestation, heightened lipoprotein lipase activity is the proposed mechanism through which the liver becomes an acceptor of circulating triglycerides, allowing their use as ketogenic substrates, so that both maternal and fetal tissues may indirectly benefit from maternal hypertriglyceridemia. Changes in the magnitude and direction of lipoprotein lipase activity in different tissues during gestation actively contribute both to the development of hypertriglyceridemia and to the metabolic fate of circulating triglycerides.(ABSTRACT TRUNCATED AT 400 WORDS)

Nutrition and fetal brain maturation. I. Responses in vitro and in vivo

The glycolytic enzyme enolase increases during the perinatal period of brain development and was utilized as a marker for examining the effect of culture environment on differentiation of cells from 20-day fetal rat brain. Enolase activity in cell cultures increased from 0.91 +/- 0.03 (Day 0) to 2.11 +/- 0.10 mumol/min/mg protein (Day 6). Comparable levels were not reached in vivo until neonatal pups were 15 days old. The in vitro increase was inhibited by both cycloheximide and actinomycin D. Enolase activity in the cells responded to alterations in both incubation media and homologous serum. After 6 days in culture, cells incubated in rat serum (10%) added to MEM or RPMI produced twice as much enolase activity as cells incubated similarly in Ham's medium, i.e., 1.96 +/- 0.09 and 1.85 +/- 0.21 vs 1.02 +/- 0.09, P less than 0.001. Results of a comparable magnitude were obtained when fetal calf serum replaced adult rat serum, but enolase production was somewhat lower when newborn calf serum replaced adult rat or fetal calf serum. When cells were incubated for 6 days with graded concentrations of adult rat serum (2.5-15%), enolase activity increased progressively. The pattern of enolase response suggests that the fetal rat brain cell model described herein will provide a sensitive probe with which to gain insight into nutrition and fetal brain development.

Metabolism of D- and DL-beta-hydroxybutyrate by mouse embryos in vitro

Rates of 14CO2 production by mouse conceptuses in vitro from D- and DL-[3-14C]-beta-hydroxybutyrate (beta OHB) were determined during the period of organogenesis (days 9 through 12 of gestation) in the presence of 4 to 32 mmol/L DL-beta OHB. During this time period the rates 14CO2 production from D-beta OHB metabolism are concentration-dependent, increase on each day of gestation, and the site of metabolism appears to shift from the visceral yolk sac placenta to the embryo proper. In contrast to fetal and neonatal tissues, the rates of 14CO2 production from DL-beta OHB oxidation is significantly greater than from D-beta OHB suggesting that the utilization of the L-isomer may be equal to or greater than that of the D-form.

Effect of fetal growth on maternal protein metabolism in postabsorptive rat

Rates of protein synthesis were measured in whole fetuses and maternal tissues at 17 and 20 days of gestation in postabsorptive rats using continuous infusion of L-[1-14C]leucine. Fetal protein degradation rates were derived from the fractional rates of synthesis and growth. Whole-body (plasma) leucine kinetics in the mother showed a significant reduction of the fraction of plasma leucine oxidized in the mothers bearing older fetuses, a slight increase in the plasma flux, with total leucine oxidation and incorporation into protein remaining similar at the two gestational ages. Estimates of fractional protein synthesis in maternal tissues revealed an increase in placental and hepatic rates at 20 days of gestation, whereas the fractional synthetic rate in muscle remained unchanged. A model for estimation of the redistribution of leucine between plasma and tissues is described in detail. This model revealed a more efficient utilization of leucine in fetal protein synthesis in comparison with other maternal tissues, a greater dependency of the fetus on plasma supply of leucine, and a significant increase (2-fold) in the release of leucine from maternal muscle as the fetal requirements increased proportionately with its size. The latter conclusion, supported by nitrogen analysis and the ratio of bound-to-free leucine in maternal tissues, confirms the importance of maternal stores in maintaining the homeostasis of essential amino acids during late pregnancy.

The maximal activity of phosphate-dependent glutaminase and glutamine metabolism in late-pregnant and peak-lactating rats

The maximal activity of phosphate-dependent glutaminase was increased in the small intestine, decreased in the liver and unchanged in the kidney of late-pregnant rats. This was accompanied by increases in the size of both the small intestine and the liver. The maximal activity of phosphate-dependent glutaminase was increased in both the small intestine and liver but unchanged in the kidney of peak-lactating rats. Enterocytes isolated from late-pregnant or peak-lactating rats exhibited an enhanced rate of utilization of glutamine and production of glutamate, alanine and ammonia. Arteriovenous-difference measurements across the gut showed an increase in the net glutamine removed from the circulation in late-pregnant and peak-lactating rats, which was accompanied by enhanced rates of release of glutamate, alanine and ammonia. Arteriovenous-difference measurements for glutamine showed that both renal uptake and skeletal-muscle release of glutamine were not markedly changed during late pregnancy or peak lactation; but pregnant rats showed a hepatic release of the amino acid. It is concluded that, during late pregnancy and peak lactation, the adaptive changes in glutamine metabolism by the small intestine, kidneys and skeletal muscle of hindlimb are similar; however, the liver appears to release glutamine during late pregnancy, but to utilize glutamine during peak lactation.

The metabolism of acetone in the pregnant rat

The administration of a single dose of acetone (100 mg/kg bw) to virgin and 21-day pregnant rats resulted in the appearance of relatively high concentrations of 1,2-propanediol, acetol and methylglyoxal in plasma and liver. In the fetuses no methylglyoxal was detectable. The acetone metabolism curves tend to indicate that the capacity for acetone disposal may be enhanced in the 48 hr-fasted pregnant rat, thus enabling the animal to re-use acetone metabolically, possibly for accelerated gluconeogenesis.

Mitochondrial alterations in embryos exposed to B-hydroxybutyrate in whole embryo culture

The ketone body B-hydroxybutyrate (B-OHB) produces malformations and ultrastructural alterations in mitochondria of mouse embryos exposed for 24 hours to the compound in whole embryo culture. The present study was conducted to establish the time-course of the mitochondrial changes to determine whether the changes are reversible, and to relate these changes to the malformations produced by the compound. Since mitochondria also play a key role in the metabolism of ketone bodies, the capacity of the early somite embryo to metabolize B-OHB was investigated in an effort to link the morphological alterations in the mitochondria to a biochemical process. Early somite embryos were cultured 4, 8, or 24 hours in the presence of 32 mM DL-B-OHB and then cultured for an additional 24 hours in control serum. Finally, embryonic tissue during the teratogenic period was assessed for its capability to oxidize B-OHB using D-(3-14C)-B-OHB. The treated embryos showed progressive alterations in the mitochondria, beginning at 4 hours with a loss of matrix density and culminating at 24 hours with high-amplitude swelling, complete loss of matrix density, and disappearance of cristae. These alterations were reversible following removal of the embryos after 24 hours of exposure to B-OHB and culturing for an additional 24 hours in control serum. Metabolism studies demonstrated that the early somite embryo possesses a limited capacity to oxidatively metabolize B-OHB. The biochemical implications of these findings are discussed with respect to the possible role of ketone bodies in the mechanism of diabetes-induced congenital malformations.

Similar metabolic response to acute ethanol intake in pregnant and non-pregnant rats either fed or fasted

Plasma ethanol concentration 3 hr after its oral administration (3 g/kg body wt) did not differ in 20 day pregnant rats with virgin controls, and in both groups values were higher when studied after 24 hr fasted than when fed. In fed animals, blood glucose and liver glycogen concentrations were lower in pregnant than in virgin rats, whereas ethanol intake in both groups enhanced blood glucose levels, it reduced liver glycogen content only in virgins. In fetuses, maternal ethanol intake enhanced blood glucose levels. In fasted animals, ethanol intake decreased blood glucose levels in pregnant and virgin animals but did not affect these levels in fetuses. Ethanol intake enhanced beta-hydroxybutyrate/acetoacetate ratio similarly in blood of pregnant and virgin rats when either fed or fasted, and it produced the same change in fetuses from fasted mothers. Results indicate that the metabolic response to acute ethanol does not differ between pregnant and non-pregnant animals, and it is proposed that fetuses passively follow the metabolic changes occurring in their mothers after receiving ethanol.

Fetal fuels. VII. Ketone bodies inhibit synthesis of purines in fetal rat brain

Maternal starvation in late gestation results in ketonemia and a lowered DNA content in fetal rat brain. Because purines are needed for formation of new RNA and DNA, we examined the de novo pathway for purine biosynthesis in fetal rat brain slices by measuring the incorporation of [14C]formate into [14C]adenine. Maternal starvation days 18-20 resulted in a slight but nonsignificant fall in purine biosynthesis from 0.230 +/- 0.006 to 0.216 +/- 0.006 mumol X g-1 X 2 h-1. Graded concentrations of DL-3-hydroxybutyrate (3OHB) produced a progressive inhibition of formate incorporation in fetal brain slices, and rates of purine biosynthesis in the presence of 5.4 mM 3OHB were significantly lower (P less than 0.01) in fetal brain slices from both fed and starved mothers, i.e., 0.199 +/- 0.006 and 0.189 +/- 0.006 mumol X g-1 X 2 h-1, respectively. Acetoacetate caused an inhibition similar in magnitude to 3OHB. That 3OHB did not act via a protein biosynthetic step was evidenced by unimpaired biosynthesis of purines and sustained 3OHB inhibition in the presence of 1 mM cycloheximide. Unlike the de novo pathway, the salvage pathway measured by incorporation of [8-14C]adenine into labeled nucleotides was not significantly inhibited even by supraphysiological levels of 3OHB (21.6 mM). Serial measurements of the de novo and salvage pathways in neonatal brain slices showed a maintenance of salvage activity during the first 2 wk but a progressive fall in activity of the de novo pathway. Thus ketone bodies could act to restrain the synthesis of purine nucleotide building blocks for new cell formation in fetal but not in neonatal rat brain.

Acetoacetate utilization by human placental mitochondria

It has been shown that mitochondria from human placenta incubated in the presence of 2-oxoglutarate or its precursors utilize acetoacetate at the rate about I nmol/min/mg protein. Utilization of acetoacetate is completely inhibited by arsenite. Mitochondria from human placental tissue show activity of 3-oxoacid-CoA transferase and acetoacetyl-CoA thiolase. It is proposed that acetoacetate utilization by placental mitochondria proceeds via the conversion to acetoacetyl-CoA catalysed by 3-oxoacid-CoA transferase, and then to acetyl-CoA, catalysed by acetoacetyl-CoA thiolase.

Characterization of rat placental TRH-like material and the ontogeny of placental and fetal brain TRH

TRH immunological and biological activity was characterized in rat placental extracts. Placentae were extracted sequentially with 2 N acetic acid and glacial acetic acid. The lyophilized residues were further extracted with 90 per cent methanol, and the extracts were then dried, and reextracted with distilled water. When a 100 000 g supernatant fraction of this extract was utilized for characterization, TRH extracted from the placenta was found to be similar to synthetic TRH by four criteria: parallelism of immunoassay inhibition curves, similarity of elution volumes after Sephadex G-10 chromatography, TRH biological activity (TSH release from rat pituitaries in vitro), and identity on high-pressure liquid chromatography. Between the 16th and 20th day of gestation, placental TRH activity increased nearly threefold, from 10.9 +/- 3.0 to 29.7 +/- 3.7 pg/mg protein. Changes of a similar magnitude were apparent in the fetal brain (6.0 +/- 0.5 to 18.9 +/- 2.4 pg/mg protein). Our studies suggest that TRH activity in the rat placenta increases with gestational age in a pattern similar to that described previously for certain placental protein hormones and developmental changes in fetal brain TRH.

Fetal fuels VI. Metabolism of alpha-ketoisocaproic acid in fetal rat brain

The metabolic regulation of alpha-ketoisocaproic acid was studied in fetal brain from rats. Starvation of the mother for days 18-20 did not alter CO2 evolution from alpha-ketoisocaproic acid in fetal brain slices but significantly diminished the incorporation of the branched-chain keto acids into leucine. When fetal brain slices from starved mothers were exposed to graded concentrations of labeled alpha-ketoisocaproic acid (0.05-2.5 mM), over 70% of the labeled products were consistently represented by leucine and less than 30% by CO2. Both beta-hydroxybutyrate and pyruvate, alone and in combination, diminished the amount of 14CO2 that evolved from alpha-ketoisocaproic acid-1-14C, but had no effect on the conversion of the keto acid to labeled leucine. It is concluded that exogenous alpha-ketoisocaproic acid is preferentially converted to leucine by fetal brain slices independent of the nutritional state of the mother. During maternal starvation, beta-hydroxybutyrate, by restraining irreversible decarboxylation of alpha-ketoisocaproic acid, could act to salvage the keto acid for conversion to leucine. Thus alpha-ketoisocaproic acid metabolism in the fetal brain may be regulated in part by altered metabolic functions in this structure and in part by changing components in circulating fuel mixtures reaching the fetus from the starved mother.

Placental permeability and energy metabolism enzymes in fetuses of lipemic rats

A model of maternal lipemia without hyperglycemia, in the rat, produced by high-fat feedings, was developed to study the effects of and abnormal maternal lipid homeostasis on placental transport of nutrients and possible alterations of key enzymes of energy metabolism in the liver and brain of the fetuses. Pregnant rats fed lower concentrations of fat served as controls. All studies were carried out in dams and fetuses one day prior to delivery. The dietary treatment of the dams and fetuses produced in the fetuses ketonemia as well as lipemia. Following a bolus of 14C-3-0-methyl-D-glucose to the dams, the levels of the tracer remained higher in the blood and brain of lipemic than in control fetuses. By contrast, there was a decrease in the fluxes of 14C-alpha-amino-isobutyric acid in the fetuses of lipemic dams as compared to controls. Among enzymes of energy metabolism, fetal liver glucose-6-phosphatase and succinic dehydrogenase were enhanced by lipemia. Fetal brain glucose-6-phosphatase was depressed. Thus, lipemia, as occurring in poorly controlled maternal diabetes, may be a factor in determining the access to the fetus of essential, neutral amino acids and alter the normal activity of energy metabolism enzymes in the fetus.

Effect of short term fasting on plasma composition of lactating rats

The effects of a 24-h fast upon plasma and blood components of the lactating rat on day 20 after parturition have been determined. Body weight decrease observed with fasting was more marked in nursing dams than in controls. The changes observed agree with a limited use of lipidic resources, exhaustion of liver glycogen and considerable utilization of amino acids as energetic - as well as gluconeogenetic - substrates. Blood and plasma glucose were maintained in fasted dams at a level comparable with that of controls. The actual variations observed in the plasma aminogram were limited, showing a remarkable maintenance of the dam's own amino-acid homeostasis.

Fetal fuels. IV. Regulation of branched-chain amino and keto acid metabolism in fetal brain

The regulation of branched-chain amino and keto acid metabolism was examined in fetal rat brains at 20 days gestation. When fetal brain slices were incubated with [1-14C]leucine, graded concentrations of beta-hydroxybutyrate or acetoacetate resulted in a progressive rise in labeled alpha-ketoisocaproic acid accompanied by a fall in 14CO2, whereas the sum of these products remained unchanged. These reciprocal relationships were maintained when leucine concentrations were varied from 0.4 to 4 mM. Increasing concentrations of glucose or pyruvate enhanced the formation of both 14CO2 and alpha-ketoisocaproic acid from [1-14C]leucine, but resulted in a progressive decrease in the conversion of alpha-ketoisocaproic acid to 14CO2. That glucose and ketone bodies probably acted via separate mechanisms was suggested by a further inhibition of alpha-ketoisocaproic acid decarboxylation whenever beta-hydroxybutyrate was added. When mothers were starved from days 18-20, a threefold rise in circulating branched-chain keto acids was reflected concordantly in the fetus and was attended by a significant enhancement of leucine transaminase activity in fetal brain. Because levels of circulating ketone bodies reported during maternal starvation were maximally effective in diminishing the conversion of alpha-ketoisocaproic acid to 14CO4, it is suggested that the inhibitory effects of beta-hydroxybutyrate on the critical dehydrogenase step in branched-chain keto acid metabolism in fetal brain could restrain oxidation of maternally derived alpha-ketoisocaproic acid, thereby permitting salvage for reversible transamination to leucine.

Glucose homeostasis during the perinatal period in normal rats and rats with a glycogen storage disorder

The fetal rat mobilizes liver glycogen during parturition for use as a glucose source until the onset of gluconeogenesis at 2 h after birth. A rat strain (NZR/Mh) unable to mobilize liver glycogen because of a phosphorylase b kinase deficiency has been used to assess the importance of liver glycogen in glucose homeostasis of the newborn. In normal rats the mean blood glucose concentration of the fetus measured at various times up to 24 h after natural birth ranged between 3.7 and 5.4 mM. In contrast, fetuses of the affected rats were hypoglycemic before birth (2.02 +/- 0.15 mM), and by 1 h after birth the blood glucose had decreased to 0.74 +/- 0.14 mM. Concentrations increased by 4 h to 1.48 +/- 0.17 mM and by 24 h reached values not significantly different from the normal newborn rats. Changes in plasma insulin over the perinatal period were similar in both groups although concentrations were always significantly lower in the affected rts. The findings demonstrate the crucial role of the fetal liver glycogen store in the maintenance of normoglycemia in the newborn. The normal rat does not develop hypoglycemia when born naturally and left with the mother after birth (in contrast to other studies in which the newborn were taken by cesarian delivery 1 d prematurely and kept in an artificial environment without food). The rats with the glycogen storage disorder experienced severe hypoglycemia without any apparent effects, which raises questions concerning alternative fuels available to and utilized by the newborn.

Carbohydrate metabolism in pregnancy XVI: longitudinal estimates of the effects of pregnancy on D-(63H) glucose and D-(6-14C) glucose turnovers during fasting in the rat

We measured blood glucose concentrations and glucose turnover rates in 24 hr fasted, conscious, unrestrained pregnant rats and nongravid controls on days 18, 19, and 20 of gestation. Turnover measurements were secured with simultaneous equilibrium infusions of D-(6-3H) and D-(6-14C) glucose so that gluconeogenic recycling could also be determined. "Steady state" values for blood glucose in the mother after 24 hr of fasting did not significantly differ on each of the days, and these concentrations were significantly lower than the values in 24 hr fasted nongravid rats. At 18 days gestation, glucose turnover did not differ from nongravid values. By contrast, values for glucose turnover after 24 hr fasting increased significantly and progressively in the 19 and 20 day pregnant rats. The increase in turnover correlated with the increasing growth of the conceptus. The ratio between D-(6-14C) glucose and D-(6-3H) turnover remained constant (and the same as in the nongravid rats) during all 3 days of gestation suggesting that rates of glucose recycling remained unaltered. These longitudinal studies indicate that the factors contributing to the pattern of "accelerated starvation" during dietary deprivation in pregnancy may vary as pregnancy progresses. The exaggerated lowering of blood glucose which accompanies fasting occurs before total glucose turnover increases. This could provide a potential mechanism for conserving maternal glucose. Since transplacental transfer of glucose is concentration-dependent, the early establishment of a lower "steady state" for circulating glucose could diminish the magnitude of loss of this key nutrient to the fetus.

Nitrogen retention during late gestation in the rat in response to marginal zinc intake

This study was conducted to characterize nitrogen retention in response to marginal dietary zinc during gestation. Long-Evans rats were randomly assigned to one of two dietary groups on day 1 of gestation. The dams were fed a basal diet supplemented with either restricted or control levels of zinc. Feces and urine were collected for 24 h on day 20 of pregnancy, and their nitrogen and zinc contents were determined. Urinary and fecal nitrogen excretions were similar for zinc-restricted and control dams, whereas fecal zinc excretions were depressed by feeding the zinc-restricted diet. Mean zinc and nitrogen retentions were negative for the zinc-restricted and positive for the control groups. Multiple stepwise regression analysis showed that nitrogen retention on day 20 depended on both dietary nitrogen and zinc intakes. Zinc-restricted offspring weighed 12% less and the maternal plasma zinc concentrations were reduced by 66% when compared with the control group values on day 22. Marginal dietary zinc and the associated anorexia limited fetal growth without causing excessive nitrogen excretion or severe weight loss.

Congenital malformations: the possible role of diabetes care outside pregnancy

A consecutive and prospective series comprising 949 newborn infants of diabetic mothers treated during pregnancy and delivery in the period 1966--1977 has been analysed. The malformation rate was 8.2%. As compared to infants of mothers (White classes B-F alone) controlled outside pregnancy elsewhere, the rate of malformations was significantly reduced (from 14.1 to 7.4%) in fants whose mothers attended two hospitals specializing in the treatment and ambulatory control of diabetics. For diabetics not controlled at a diabetic centre outside pregnancy the malformation rate was 9% in classes B + C and 19.4% in classes D + F, compared to 6.2 and 8.5%, respectively, for those who were controlled. The rates of malformation (total as well as severe alone) were significantly reduced in infants of White's classes D + F, and insignificantly reduced in classes B + C (in class A no comparison could be made). The findings indicate that poor diabetic control outside pregnancy is teratogenic, although the 'disastrous malformation factor' of diabetes appears not to be totally dependent on the degree of compensation of the disbetic metabolism, as measured by the variables usually applied.