Development and thyroid hormone dependence of skeletal muscle mitochondrial function towards birth.

KEY POINTS: Skeletal muscle energy requirements increase at birth but little is known regarding the development of mitochondria that provide most of the cellular energy as ATP. Thyroid hormones are known regulators of adult metabolism and are important in driving several aspects of fetal development, including muscle fibre differentiation. Mitochondrial density and the abundance of mitochondrial membrane proteins in skeletal muscle increased during late gestation. However, mitochondrial functional capacity, measured as oxygen consumption rate, increased primarily after birth. Fetal hypothyroidism resulted in significant reductions in mitochondrial function and density in skeletal muscle before birth. Mitochondrial function matures towards birth and is dependent on the presence of thyroid hormones, with potential implications for the health of pre-term and hypothyroid infants. ABSTRACT: Birth is a significant metabolic challenge with exposure to a pro-oxidant environment and the increased energy demands for neonatal survival. This study investigated the development of mitochondrial density and activity in ovine biceps femoris skeletal muscle during the perinatal period and examined the role of thyroid hormones in these processes. Muscle capacity for oxidative phosphorylation increased primarily after birth but was accompanied by prepartum increases in mitochondrial density and the abundance of electron transfer system (ETS) complexes I-IV and ATP-synthase as well as by neonatal upregulation of uncoupling proteins. This temporal disparity between prepartum maturation and neonatal upregulation of mitochondrial oxidative capacity may protect against oxidative stress associated with birth while ensuring energy availability to the neonate. Fetal thyroid hormone deficiency reduced oxidative phosphorylation and prevented the prepartum upregulation of mitochondrial density and ETS proteins in fetal skeletal muscle. Overall, the data show that mitochondrial function matures over the perinatal period and is dependent on thyroid hormones, with potential consequences for neonatal viability and adult metabolic health.

Ovine uteroplacental and fetal metabolism during and after fetal cortisol overexposure in late gestation.

Cortisol modifies fetal metabolism in preparation for delivery, but whether preterm cortisol exposure programs persisting changes in fetoplacental metabolism remains unknown. This study infused fetal sheep with saline ( n = 36) or cortisol ( n = 27) to raise fetal plasma cortisol to normal prepartum concentrations for 5 days from day 125 of gestation (term: ≈145 days). Fetal uptake and uteroplacental metabolism of glucose, oxygen, and lactate, together with fetal hepatic glucogenic capacity, were measured on the final day of infusion or 5 days later. Cortisol reduced adrenal weight and umbilical glucose uptake during infusion but increased fetal glucose concentrations, hepatic glycogen content, and hepatic glucogenic enzyme activity (fructose-1,6-bisphosphatase and glucose-6-phosphatase) and gene expression ( PC and G6PC) compared with saline infusion. Postcortisol infusion, umbilical glucose uptake, and hepatic glucose-6-phosphatase activity remained low and high, respectively, whereas fetal glucose levels normalized and hepatic glycogen was lower with higher adrenal weights than in controls. Cortisol infusion increased the proportion of total uterine glucose uptake consumed by the uteroplacental tissues, irrespective of age. Placental tracer glucose transport capacity was also increased after, but not during, cortisol infusion, without changes in placental glucose transporter gene expression. Blood lactate concentration and Pco2 were higher, whereas pH and O2 content were lower in cortisol-infused than saline-infused fetuses, although uteroplacental metabolism and fetal uptake of oxygen and lactate were unaltered. The results suggest that preterm cortisol overexposure alters fetoplacental metabolism and adrenal function subsequently with persisting increases in uteroplacental glucose consumption at the expense of the fetal supply.

A physiological increase in maternal cortisol alters uteroplacental metabolism in the pregnant ewe.

KEY POINTS: Fetal nutrient supply is dependent, in part, upon the transport capacity and metabolism of the placenta. The stress hormone, cortisol, alters metabolism in the adult and fetus but it is not known whether cortisol in the pregnant mother affects metabolism of the placenta. In this study, when cortisol concentrations were raised in pregnant sheep by infusion, proportionately more of the glucose taken up by the uterus was consumed by the uteroplacental tissues while less was transferred to the fetus, despite an increased placental glucose transport capacity. Concomitantly, the uteroplacental tissues produced lactate at a greater rate. The results show that maternal cortisol concentrations regulate uteroplacental glycolytic metabolism, producing lactate for use in utero. Prolonged increases in placental lactate production induced by cortisol overexposure may contribute to the adverse effects of maternal stress on fetal wellbeing. ABSTRACT: Fetal nutrition is determined by maternal availability, placental transport and uteroplacental metabolism of carbohydrates. Cortisol affects maternal and fetal metabolism, but whether maternal cortisol concentrations within the physiological range regulate uteroplacental carbohydrate metabolism remains unknown. This study determined the effect of maternal cortisol infusion (1.2 mg kg-1  day-1 i.v. for 5 days, n = 20) on fetal glucose, lactate and oxygen supplies in pregnant ewes on day ∼130 of pregnancy (term = 145 days). Compared to saline infusion (n = 21), cortisol infusion increased maternal, but not fetal, plasma cortisol (P < 0.05). Cortisol infusion also raised maternal insulin, glucose and lactate concentrations, and blood pH, PCO2 and HCO3- concentration. Although total uterine glucose uptake determined by Fick's principle was unaffected, a greater proportion was consumed by the uteroplacental tissues, so net fetal glucose uptake was 29% lower in cortisol-infused than control ewes (P < 0.05). Concomitantly, uteroplacental lactate production was > 2-fold greater in cortisol- than saline-treated ewes (P < 0.05), although uteroplacental O2 consumption was unaffected by maternal treatment. Materno-fetal clearance of non-metabolizable [3 H]methyl-d-glucose and placental SLC2A8 (glucose transporter 8) gene expression were also greater with cortisol treatment. Fetal plasma glucose, lactate or α-amino nitrogen concentrations were unaffected by treatment although fetal plasma fructose and hepatic lactate dehydrogenase activity were greater in cortisol- than saline-treated ewes (P < 0.05). Fetal plasma insulin levels and body weight were also unaffected by maternal treatment. During stress, cortisol-dependent regulation of uteroplacental glycolysis may allow increased maternal control over fetal nutrition and metabolism. However, when maternal cortisol concentrations are raised chronically, prolonged elevation of uteroplacental lactate production may compromise fetal wellbeing.

Placental phenotype and resource allocation to fetal growth are modified by the timing and degree of hypoxia during mouse pregnancy.

The placenta adapts its transport capacity to nutritional cues developmentally, although relatively little is known about placental transport phenotype in response to hypoxia, a major cause of fetal growth restriction. The present study determined the effects of both moderate hypoxia (13% inspired O2) between days (D)11 and D16 or D14 and D19 of pregnancy and severe hypoxia (10% inspired O2) from D14 to D19 on placental morphology, transport capacity and fetal growth on D16 and D19 (term∼D20.5), relative to normoxic mice in 21% O2. Placental morphology adapted beneficially to 13% O2; fetal capillary volume increased at both ages, exchange area increased at D16 and exchange barrier thickness reduced at D19. Exposure to 13% O2 had no effect on placental nutrient transport on D16 but increased placental uptake and clearance of (3)H-methyl-D-glucose at D19. By contrast, 10% O2 impaired fetal vascularity, increased barrier thickness and reduced placental (14)C-methylaminoisobutyric acid clearance at D19. Consequently, fetal growth was only marginally affected in 13% O2 (unchanged at D16 and -5% at D19) but was severely restricted in 10% O2 (-21% at D19). The hypoxia-induced changes in placental phenotype were accompanied by altered placental insulin-like growth factor (IGF)-2 expression and insulin/IGF signalling, as well as by maternal hypophagia depending on the timing and severity of the hypoxia. Overall, the present study shows that the mouse placenta can integrate signals of oxygen and nutrient availability, possibly through the insulin-IGF pathway, to adapt its phenotype and optimize maternal resource allocation to fetal growth during late pregnancy. It also suggests that there is a threshold between 13% and 10% inspired O2 at which these adaptations no longer occur.

Hypoxia, AMPK activation and uterine artery vasoreactivity.

Genes near adenosine monophosphate-activated protein kinase-α1 (PRKAA1) have been implicated in the greater uterine artery (UtA) blood flow and relative protection from fetal growth restriction seen in altitude-adapted Andean populations. Adenosine monophosphate-activated protein kinase (AMPK) activation vasodilates multiple vessels but whether AMPK is present in UtA or placental tissue and influences UtA vasoreactivity during normal or hypoxic pregnancy remains unknown. We studied isolated UtA and placenta from near-term C57BL/6J mice housed in normoxia (n = 8) or hypoxia (10% oxygen, n = 7-9) from day 14 to day 19, and placentas from non-labouring sea level (n = 3) or 3100 m (n = 3) women. Hypoxia increased AMPK immunostaining in near-term murine UtA and placental tissue. RT-PCR products for AMPK-α1 and -α2 isoforms and liver kinase B1 (LKB1; the upstream kinase activating AMPK) were present in murine and human placenta, and hypoxia increased LKB1 and AMPK-α1 and -α2 expression in the high- compared with low-altitude human placentas. Pharmacological AMPK activation by A769662 caused phenylephrine pre-constricted UtA from normoxic or hypoxic pregnant mice to dilate and this dilatation was partially reversed by the NOS inhibitor l-NAME. Hypoxic pregnancy sufficient to restrict fetal growth markedly augmented the UtA vasodilator effect of AMPK activation in opposition to PE constriction as the result of both NO-dependent and NO-independent mechanisms. We conclude that AMPK is activated during hypoxic pregnancy and that AMPK activation vasodilates the UtA, especially in hypoxic pregnancy. AMPK activation may be playing an adaptive role by limiting cellular energy depletion and helping to maintain utero-placental blood flow in hypoxic pregnancy.

Placental metabolism: substrate requirements and the response to stress.

The placenta is a dynamic, metabolically active organ with significant nutrient and energy requirements for growth, nutrient transfer and protein synthesis. It uses a range of substrates to meet its energy needs and has a higher rate of oxygen (O2 ) consumption than many other foetal and adult tissues. Placental metabolism varies with species and alters in response to a range of nutritional and endocrine signals of adverse environmental conditions. The placenta integrates these signals and adapts its metabolic phenotype to help maintain pregnancy and to optimize offspring fitness by diversifying the sources of carbon and nitrogen available for energy production, hormone synthesis and foeto-placental growth. The metabolic response of the placenta to adversity depends on the nature, severity and duration of the stressful challenge and on whether the insult is maternal, placental or foetal in origin. This review examines placental metabolism and its response to stresses common in pregnancy with particular emphasis on farm species like the sheep. It also considers the consequences of changes in placental metabolism for the supply of O2 and nutrients to the foetus.

Corticosterone alters materno-fetal glucose partitioning and insulin signalling in pregnant mice.

Glucocorticoids affect glucose metabolism in adults and fetuses, although their effects on materno-fetal glucose partitioning remain unknown. The present study measured maternal hepatic glucose handling and placental glucose transport together with insulin signalling in these tissues in mice drinking corticosterone either from day (D) 11 to D16 or D14 to D19 of pregnancy (term = D21). On the final day of administration, corticosterone-treated mice were hyperinsulinaemic (P < 0.05) but normoglycaemic compared to untreated controls. In maternal liver, there was no change in glycogen content or glucose 6-phosphatase activity but increased Slc2a2 glucose transporter expression in corticosterone-treated mice, on D16 only (P < 0.05). On D19, but not D16, transplacental (3) H-methyl-d-glucose clearance was reduced by 33% in corticosterone-treated dams (P < 0.05). However, when corticosterone-treated animals were pair-fed to control intake, aiming to prevent the corticosterone-induced increase in food consumption, (3) H-methyl-d-glucose clearance was similar to the controls. Depending upon gestational age, corticosterone treatment increased phosphorylation of the insulin-signalling proteins, protein kinase B (Akt) and glycogen synthase-kinase 3ß, in maternal liver (P < 0.05) but not placenta (P > 0.05). Insulin receptor and insulin-like growth factor type I receptor abundance did not differ with treatment in either tissue. Corticosterone upregulated the stress-inducible mechanistic target of rapamycin (mTOR) suppressor, Redd1, in liver (D16 and D19) and placenta (D19), in ad libitum fed animals (P < 0.05). Concomitantly, hepatic protein content and placental weight were reduced on D19 (P < 0.05), in association with altered abundance and/or phosphorylation of signalling proteins downstream of mTOR. Taken together, the data indicate that maternal glucocorticoid excess reduces fetal growth partially by altering placental glucose transport and mTOR signalling.

Dexamethasone treatment of pregnant F0 mice leads to parent of origin-specific changes in placental function of the F2 generation.

Dexamethasone treatment of F0 pregnant rodents alters F1 placental function and adult cardiometabolic phenotype. The adult phenotype is transmitted to the F2 generation without further intervention, but whether F2 placental function is altered by F0 dexamethasone treatment remains unknown. In the present study, F0 mice were untreated or received dexamethasone (0.2µgg(-1)day(-1), s.c.) over Days 11-15 or 14-18 of pregnancy (term Day 21). Depending on the period of F0 dexamethasone treatment, F1 offspring were lighter at birth or grew more slowly until weaning (P<0.05). Glucose tolerance (1gkg(-1), i.p.) of adult F1 males was abnormal. Mating F1 males exposed prenatally to dexamethasone with untreated females had no effect on F2 placental function on Day 19 of pregnancy. In contrast, when F1 females were mated with untreated males, F2 placental clearance of the amino acid analogue (14)C-methylaminoisobutyric acid was increased by 75% on Day 19 specifically in dams prenatally exposed to dexamethasone on Days 14-18 (P<0.05). Maternal plasma corticosterone was also increased, but F2 placental Slc38a4 expression was decreased in these dams (P<0.05). F0 dexamethasone treatment had no effect on F2 fetal or placental weights, regardless of lineage. Therefore, the effects of F0 dexamethasone exposure are transmitted intergenerationally to the F2 placenta via the maternal, but not paternal, line.

Prenatal cortisol exposure impairs adrenal function but not glucose metabolism in adult sheep.

Adverse environmental conditions before birth are known to programme adult metabolic and endocrine phenotypes in several species. However, whether increments in fetal cortisol concentrations of the magnitude commonly seen in these conditions can cause developmental programming remains unknown. Thus, this study investigated the outcome of physiological increases in fetal cortisol concentrations on glucose-insulin dynamics and pituitary-adrenal function in adult sheep. Compared with saline treatment, intravenous fetal cortisol infusion for 5 days in late gestation did not affect birthweight but increased lamb body weight at 1-2 weeks after birth. Adult glucose dynamics, insulin sensitivity and insulin secretion were unaffected by prenatal cortisol overexposure, assessed by glucose tolerance tests, hyperinsulinaemic-euglycaemic clamps and acute insulin administration. In contrast, prenatal cortisol infusion induced adrenal hypo-responsiveness in adulthood with significantly reduced cortisol responses to insulin-induced hypoglycaemia and exogenous adrenocorticotropic hormone (ACTH) administration relative to saline treatment. The area of adrenal cortex expressed as a percentage of the total cross-sectional area of the adult adrenal gland was also lower after prenatal cortisol than saline infusion. In adulthood, basal circulating ACTH but not cortisol concentrations were significantly higher in the cortisol than saline-treated group. The results show that cortisol overexposure before birth programmes pituitary-adrenal development with consequences for adult stress responses. Physiological variations in cortisol concentrations before birth may, therefore, have an important role in determining adult phenotypical diversity and adaptability to environmental challenges.

Real time monitoring of propofol blood concentration in ponies anaesthetized with propofol and ketamine.

This study examined the pharmacokinetics of propofol by infusion in ponies using an analyser for the rapid measurement of propofol concentrations. The analyser (Pelorus 1000; Sphere Medical Ltd., Cambridge, UK) has a measurement cycle of approximately five minutes. Ten Welsh-cross ponies (weighing 135-300 kg) undergoing minor procedures were studied after premedication with acepromazine 0.03 mg/kg and detomidine 0.015 mg/kg. Anaesthesia was induced with ketamine 2 mg/kg and diazepam 0.03 mg/kg, and maintained with an infusion of propofol at an initial rate of 0.16 mg/kg/min for the first thirty minutes, after a bolus of 0.3 mg/kg; and ketamine by infusion (20-40 µg/kg/min). Blood samples (<2 mL) were collected prior to, during and after the infusion, and on assuming standing position. Anaesthesia was uneventful; with the duration of infusion 31-89 min. Blood propofol concentrations during the infusion ranged between 1.52 and 7.65 µg/mL; pseudo-steady state concentrations 3.64-6.78 µg/mL, and concentrations on assuming standing position 0.75-1.40 µg/mL. Propofol clearance and volume of distribution were 31.4 (SD 6.1) mL/min/kg and 220.7 (132.0) mL/kg, respectively. The propofol analyser allows titration of propofol to a given concentration; and may be useful for anaesthesia in animals where kinetics are unknown; in disease states; and where intercurrent therapies affect propofol disposition.

Dietary composition programmes placental phenotype in mice.

Dietary composition during pregnancy influences fetal and adult phenotype but its effects on placental phenotype remain largely unknown. Using molecular, morphological and functional analyses, placental nutrient transfer capacity was examined in mice fed isocaloric diets containing 23%, 18% or 9% casein (C) during pregnancy. At day 16, placental transfer of glucose, but not methyl-aminoisobutyric acid (MeAIB), was greater in C18 and C9 than C23 mice, in association with increased placental expression of the glucose transporter Slc2a1/GLUT1, and the growth factor Igf2. At day 19, placental glucose transport remained high in C9 mice while MeAIB transfer was less in C18 than C23 mice, despite greater placental weights in C18 and C9 than C23 mice. Placental System A amino acid transporter expression correlated with protein intake at day 19. Relative growth of transport verses endocrine zones of the placenta was influenced by diet at both ages without changing the absolute volume of the transport surface. Fetal weight was unaffected by diet at day 16 but was reduced in C9 animals by day 19. Morphological and functional adaptations in placental phenotype, therefore, occur to optimise nutrient transfer when dietary composition is varied, even subtly. This has important implications for the intrauterine programming of life expectancy.

Adrenal glands are essential for activation of glucogenesis during undernutrition in fetal sheep near term.

In adults, the adrenal glands are essential for the metabolic response to stress, but little is known about their role in fetal metabolism. This study examined the effects of adrenalectomizing fetal sheep on glucose and oxygen metabolism in utero in fed conditions and after maternal fasting for 48 h near term. Fetal adrenalectomy (AX) had little effect on the rates of glucose and oxygen metabolism by the fetus or uteroplacental tissues in fed conditions. Endogenous glucose production was negligible in both AX and intact, sham-operated fetuses in fed conditions. Maternal fasting reduced fetal glucose levels and umbilical glucose uptake in both groups of fetuses to a similar extent but activated glucose production only in the intact fetuses. The lack of fasting-induced glucogenesis in AX fetuses was accompanied by falls in fetal glucose utilization and oxygen consumption not seen in intact controls. The circulating concentrations of cortisol and total catecholamines, and the hepatic glycogen content and activities of key gluconeogenic enzymes, were also less in AX than intact fetuses in fasted animals. Insulin concentrations were also lower in AX than intact fetuses in both nutritional states. Maternal glucose utilization and its distribution between the fetal, uteroplacental, and nonuterine maternal tissues were unaffected by fetal AX in both nutritional states. Ovine fetal adrenal glands, therefore, have little effect on basal rates of fetal glucose and oxygen metabolism but are essential for activating fetal glucogenesis in response to maternal fasting. They may also be involved in regulating insulin sensitivity in utero.

Environmental regulation of placental phenotype: implications for fetal growth.

Environmental conditions during pregnancy determine birthweight, neonatal viability and adult phenotype in human and other animals. In part, these effects may be mediated by the placenta, the principal source of nutrients for fetal development. However, little is known about the environmental regulation of placental phenotype. Generally, placental weight is reduced during suboptimal conditions like maternal malnutrition or hypoxaemia but compensatory adaptations can occur in placental nutrient transport capacity to help maintain fetal growth. In vivo studies show that transplacental glucose and amino acid transfer adapt to the prevailing conditions induced by manipulating maternal calorie intake, dietary composition and hormone exposure. These adaptations are due to changes in placental morphology, metabolism and/or abundance of specific nutrient transporters. This review examines environmental programming of placental phenotype with particular emphasis on placental nutrient transport capacity and its implications for fetal growth, mainly in rodents. It also considers the systemic, cellular and molecular mechanisms involved in signalling environmental cues to the placenta. Ultimately, the ability of the placenta to balance the competing interests of mother and fetus in resource allocation may determine not only the success of pregnancy in producing viable neonates but also the long-term health of the offspring.

Effects of Maternal Obesity On Placental Phenotype.

The incidence of obesity is rising rapidly worldwide with the consequence that more women are entering pregnancy overweight or obese. This leads to an increased incidence of clinical complications during pregnancy and of poor obstetric outcomes. The offspring of obese pregnancies are often macrosomic at birth although there is also a subset of the progeny that are growth-restricted at term. Maternal obesity during pregnancy is also associated with cardiovascular, metabolic and endocrine dysfunction in the offspring later in life. As the interface between the mother and fetus, the placenta has a central role in programming intrauterine development and is known to adapt its phenotype in response to environmental conditions such as maternal undernutrition and hypoxia. However, less is known about placental function in the abnormal metabolic and endocrine environment associated with maternal obesity during pregnancy. This review discusses the placental consequences of maternal obesity induced either naturally or experimentally by increasing maternal nutritional intake and/or changing the dietary composition. It takes a comparative, multi-species approach and focusses on placental size, morphology, nutrient transport, metabolism and endocrine function during the later stages of obese pregnancy. It also examines the interventions that have been made during pregnancy in an attempt to alleviate the more adverse impacts of maternal obesity on placental phenotype. The review highlights the potential role of adaptations in placental phenotype as a contributory factor to the pregnancy complications and changes in fetal growth and development that are associated with maternal obesity.

Glucocorticoid maturation of mitochondrial respiratory capacity in skeletal muscle before birth.

In adults, glucocorticoids act to match the supply and demand for energy during physiological challenges, partly through actions on tissue mitochondrial oxidative phosphorylation (OXPHOS) capacity. However, little is known about the role of the natural prepartum rise in fetal glucocorticoid concentrations in preparing tissues for the increased postnatal energy demands. This study examined the effect of manipulating cortisol concentrations in fetal sheep during late gestation on mitochondrial OXPHOS capacity of two skeletal muscles with different postnatal locomotive functions. Mitochondrial content, biogenesis markers, respiratory rates and expression of proteins and genes involved in the electron transfer system (ETS) and OXPHOS efficiency were measured in the biceps femoris (BF) and superficial digital flexor (SDF) of fetuses either infused with cortisol before the prepartum rise or adrenalectomised to prevent this increment. Cortisol infusion increased mitochondrial content, biogenesis markers, substrate-specific respiration rates and abundance of ETS complex I and adenine nucleotide translocator (ANT1) in a muscle-specific manner that was more pronounced in the SDF than BF. Adrenalectomy reduced mitochondrial content and expression of PGC1α and ANT1 in both muscles, and ETS complex IV abundance in the SDF near term. Uncoupling protein gene expression was unaffected by cortisol manipulations in both muscles. Gene expression of the myosin heavy chain isoform, MHCIIx, was increased by cortisol infusion and reduced by adrenalectomy in the BF alone. These findings show that cortisol has a muscle-specific role in prepartum maturation of mitochondrial OXPHOS capacity with important implications for the health of neonates born pre-term or after intrauterine glucocorticoid overexposure.

Adaptations in placental phenotype support fetal growth during undernutrition of pregnant mice.

Undernutrition during pregnancy reduces birth weight and programmes adult phenotype with consequences for life expectancy, but its effects on the phenotype of the placenta, responsible for supplying nutrients for fetal growth, remain largely unknown. Using molecular, morphological and functional analyses, placental phenotype was examined in mice during restriction of dietary intake to 80% of control from day 3 of pregnancy. At day 16, undernutrition reduced placental, but not fetal, weight in association with decreased junctional zone volume and placental expression of glucose transporter Slc2a1. At day 19, both placental and fetal weights were reduced in undernourished mice (91% and 87% of control, respectively, P < 0.01), as were the volume and surface area of the labyrinthine zone responsible for placental nutrient transfer (85% and 86%, respectively, P < 0.03). However, unidirectional materno-fetal clearance of tracer glucose was maintained and methyl-aminoisobutyric acid increased 166% (P < 0.005) per gram of undernourished placenta, relative to controls. This was associated with an 18% and 27% increased placental expression of glucose and system A amino acid transporters Slc2a1 and Slc38a2, respectively, at day 19 (P < 0.04). At both ages, undernutrition decreased expression of the placental specific transcript of the Igf2 gene by 35% (P < 0.01), although methylation of its promoter was unaffected. The placenta, therefore, adapts to help maintain fetal growth when its own growth is compromised by maternal undernutrition. Consequently, placental phenotype is responsive to environmental conditions and may help predict the risk of adult disease programmed in utero.

Physiological development of the equine fetus during late gestation.

In many species, the pattern of growth and physiological development in utero has an important role in determining not only neonatal viability but also adult phenotype and disease susceptibility. Changes in fetal development induced by a range of environmental factors including maternal nutrition, disease, placental insufficiency and social stresses have all been shown to induce adult cardiovascular and metabolic dysfunction that often lead to ill health in later life. Compared to other precocious animals, much less is known about the physiological development of the fetal horse or the longer-term impacts on its phenotype of altered development in early life because of its inaccessibility in utero, large size and long lifespan. This review summaries the available data on the normal metabolic, cardiovascular and endocrine development of the fetal horse during the second half of gestation. It also examines the responsiveness of these physiological systems to stresses such as hypoglycaemia and hypotension during late gestation. Particular emphasis is placed on the role of the equine placenta and fetal endocrine glands in mediating the changes in fetal development seen towards term and in response to nutritional and other environmental cues. The final part of the review presents the evidence that the early life environment of the horse can alter its subsequent metabolic, cardiovascular and endocrine phenotype as well as its postnatal growth and bone development. It also highlights the immediate neonatal environment as a key window of susceptibility for programming of equine phenotype. Although further studies are needed to identify the cellular and molecular mechanisms involved, developmental programming of physiological phenotype is likely to have important implications for the health and potential athletic performance of horses, particularly if born with abnormal bodyweight, premature or dysmature characteristics or produced by assisted reproductive technologies, indicative of an altered early life environment.

Placental efficiency and adaptation: endocrine regulation.

Size at birth is critical in determining life expectancy and is dependent primarily on the placental supply of nutrients. However, the fetus is not just a passive recipient of nutrients from the placenta. It exerts a significant acquisitive drive for nutrients, which acts through morphological and functional adaptations in the placenta, particularly when the genetically determined drive for fetal growth is compromised by adverse intrauterine conditions. These adaptations alter the efficiency with which the placenta supports fetal growth, which results in optimal growth for prevailing conditions in utero. This review examines placental efficiency as a means of altering fetal growth, the morphological and functional adaptations that influence placental efficiency and the endocrine regulation of these processes.

Effects of maternal dietary manipulation during different periods of pregnancy on hepatic glucogenic capacity in fetal and pregnant rats near term.

BACKGROUND AND AIM: Low birth weight is associated with an increased incidence of adult glucose intolerance, type 2 diabetes and cardiovascular disease in humans. In pregnant rats, dietary calorie or protein deprivation results in growth retarded pups, which become glucose intolerant adults with abnormal hepatic glucose metabolism and gluconeogenic enzyme activities. However, whether these abnormalities are present before birth remain unknown. METHODS AND RESULTS: This study examined the effects of manipulating dietary protein and carbohydrate intake during rat pregnancy on the fetal and maternal hepatic activities of the gluconeogenic enzymes, glucose-6-phosphatase (G6Pase) and phosphoenolpyruvate carboxykinase (PEPCK). Wistar rats were fed ad libitum with either standard chow throughout pregnancy (25% protein, 57% carbohydrate, n=6) or an isocaloric, low protein, high carbohydrate diet (LPHC, 8% protein, 81% carbohydrate) for different periods of pregnancy (early, 0-10 days, n=6; late, 10-20 days, n=7; throughout, 0-20 days, n=6) before tissue collection at day 20. The LPHC diet had no effect on fetal or placental weights, or on fetal hepatic activities of G6Pase and PEPCK in the early LPHC group. In contrast, fetuses of dams fed the LPHC diet in late or throughout pregnancy had lower body and placental weights, and higher hepatic G6Pase and PEPCK activities than controls. Maternal hepatic G6Pase activity was elevated in all LPHC groups, while maternal PEPCK activity was only increased significantly in the late LPHC group. CONCLUSIONS: Feeding a LPHC diet, particularly during late pregnancy, therefore, up-regulates fetal and maternal hepatic glucogenic capacity.