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The concentrations of plasma parathyroid hormone-like bioactivity and parathyroid hormone-related protein (1-86) (PTHrP) immunoreactivity were both higher in fetal pigs than in their mothers during the last 3 weeks of gestation. Both... more
The concentrations of plasma parathyroid hormone-like bioactivity and parathyroid hormone-related protein (1-86) (PTHrP) immunoreactivity were both higher in fetal pigs than in their mothers during the last 3 weeks of gestation. Both activities changed inversely with alterations in the plasma ionized calcium concentration. The data suggest that PTHrP may have a role in calcium homeostasis in the fetal pig, similar to its postulated role in sheep in the stimulation of calcium transport across the placenta.
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Research Interests: Medicine, Biological Sciences, Internal Medicine, Anoxia, Blood Glucose, and 15 moreFemale, Animals, Hypoglycemia, Cardiovascular system, Adrenocorticotropic Hormone, Fetus, Blood gas analysis, Acidosis, Lactic Acid, Catecholamines, Hemoglobins, Acute Disease, Endocrine System, hydrocortisone, and Medical and Health Sciences
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Research Interests: Endocrinology, Physiology, Medicine, Birth Weight, Biological Sciences, and 15 moreInternal Medicine, Insulin, Epinephrine, Female, Animals, Male, Hypoglycemia, Body Mass Index, Norepinephrine, Oral Hypoglycemic Agents, Age Factors, Adrenocorticotropic Hormone, Adrenal glands, hydrocortisone, and Medical and Health Sciences
This paper describes criteria used to assess maturity of the newborn foal and their clinical application to field cases of prematurity and dysmaturity. Premature and mature foals may be clearly distinguished by their behavioural and... more
This paper describes criteria used to assess maturity of the newborn foal and their clinical application to field cases of prematurity and dysmaturity. Premature and mature foals may be clearly distinguished by their behavioural and physical characteristics. Measurement of haematological parameters (mean cell volume, total white cell and differential counts), pancreatic beta cell activity (plasma glucose and insulin levels), adrenocortical-medullary function (plasma cortisol, adrenocorticotrophic hormone and catecholamines) and the renin-angiotensin system (plasma renin substrate concentrations) were found useful in evaluating the status of the newborn foal. Confirmation of the initial diagnosis can be made by response to various challenge tests eg, glucose tolerance test, short acting synthetic adrenocorticotrophic hormone (ACTH1-24) and frusemide. In the present investigation a small number of individuals appeared to be intermediate in maturity to the other two groups, indicating ...
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During late gestation in the mare, rapid fetal growth is accompanied by considerable placental growth and further invasion of the endometrium by microvilli. This growth requires extensive remodeling of the extracellular matrix (ECM). In... more
During late gestation in the mare, rapid fetal growth is accompanied by considerable placental growth and further invasion of the endometrium by microvilli. This growth requires extensive remodeling of the extracellular matrix (ECM). In early pregnancy, we know that ...
Research Interests: Biology, Medicine, Extracellular Matrix, Theriogenology, Biological Sciences, and 12 morePregnancy, Female, Animals, Fetal Growth, Amniotic Fluid, Horses, Biological markers, Parturition, Preterm Delivery, Matrix Metalloproteinase, Tissue inhibitor of metalloproteinases (TIMPs), and Medical and Health Sciences
Angiotensin-converting enzyme (ACE) has an active role in the control of blood pressure and body fluid homeostasis both before and after birth. This study investigated the ontogeny of pulmonary and renal ACE concentrations in fetal and... more
Angiotensin-converting enzyme (ACE) has an active role in the control of blood pressure and body fluid homeostasis both before and after birth. This study investigated the ontogeny of pulmonary and renal ACE concentrations in fetal and neonatal horses. Fetal pulmonary ACE concentration increased from 250 days towards term (c. 335 days). Newborn foals showed significantly higher mean concentrations of pulmonary ACE (4.40 +/- 0.62 nmol min(-1) mg protein(-1)) than both fetuses during late gestation (1.23 +/- 0.51 nmol min(-1) mg protein(-1)) and animals aged 1 day to 2 weeks of postnatal age (0.85 +/- 0.15 nmol min(-1) mg protein(-1)). Renal ACE was detected in fetal horses from 100 days of gestation but showed no developmental trend during the second half of gestation or in early postnatal life. Overall in the fetus, mean concentrations of renal ACE were also approximately 10 times lower than mean pulmonary values. Renal ACE concentration may be related to the functional immaturity of the equine kidneys. The increase in pulmonary ACE concentration seen towards term in the fetal horse may be induced by the prepartum cortisol surge that occurs very close to delivery in this species. Therefore, premature delivery in this species may interrupt the onset of ACE production in the fetal lungs and circumvent the normal maturation of the renin-angiotensin system.
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BackgroundThe fetal lung's preparation for birth consists of structural and physiologic maturation processes associated with underlying changes in gene expression. Understanding this gene expression program may help to develop... more
BackgroundThe fetal lung's preparation for birth consists of structural and physiologic maturation processes associated with underlying changes in gene expression. Understanding this gene expression program may help to develop novel therapies. Our aim was to identify novel genes up-regulated in the perinatal lung.MethodsWe used the Rae230.2 oligonucleotide array to compare gene expression in embryonic day 16 and 20 rat lungs
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Changes in the maternal nutritional environment during fetal development can influence offspring's metabolic risk in later life. Animal models have demonstrated that offspring of diet-induced obese dams develop metabolic... more
Changes in the maternal nutritional environment during fetal development can influence offspring's metabolic risk in later life. Animal models have demonstrated that offspring of diet-induced obese dams develop metabolic complications, including nonalcoholic fatty liver disease. In this study we investigated the mechanisms in young offspring that lead to the development of nonalcoholic fatty liver disease (NAFLD). Female offspring of C57BL/6J dams fed either a control or obesogenic diet were studied at 8 wk of age. We investigated the roles of oxidative stress and lipid metabolism in contributing to fatty liver in offspring. There were no differences in body weight or adiposity at 8 wk of age; however, offspring of obese dams were hyperinsulinemic. Oxidative damage markers were significantly increased in their livers, with reduced levels of the antioxidant enzyme glutathione peroxidase-1. Mitochondrial complex I and II activities were elevated, while levels of mitochondrial cyto...
Research Interests: Metabolism, Obesity, Biological Sciences, Insulin, Liver, and 15 moreMice, Female, Animals, Glutathione Peroxidase, Lipid metabolism, Fatty Liver, Homeostasis, Age Factors, Body Weight, Lipase, Glycogen, Glutamate Dehydrogenase, Adiposity, non alcoholic fatty liver disease, and Medical and Health Sciences
In mammals, the mechanisms regulating an increase in fetal arterial blood pressure with advancing gestational age remain unidentified. In all species studied to date, the prepartum increase in fetal plasma cortisol has an important role... more
In mammals, the mechanisms regulating an increase in fetal arterial blood pressure with advancing gestational age remain unidentified. In all species studied to date, the prepartum increase in fetal plasma cortisol has an important role in the maturation of physiological systems essential for neonatal survival. In the horse, the prepartum elevation in fetal cortisol and arterial blood pressure are delayed relative to other species. Hence, the mechanisms governing the ontogenic increase in arterial blood pressure in the horse fetus may mature much closer to term than in other fetal animals. In the chronically instrumented pony mare and fetus, this study investigated how changes in fetal peripheral vascular resistance, in plasma concentrations of noradrenaline, adrenaline and vasopressin, and in the maternal-to-fetal plasma concentration gradient of oxygen and glucose relate to the ontogenic changes in fetal arterial blood pressure and fetal plasma cortisol concentration as term appro...
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Low birth weight is associated with altered adipose tissue deposition and regulation of leptin production. This study determined the effects of naturally occurring variations in birth weight in pigs on postnatal growth patterns, body fat... more
Low birth weight is associated with altered adipose tissue deposition and regulation of leptin production. This study determined the effects of naturally occurring variations in birth weight in pigs on postnatal growth patterns, body fat depth and plasma leptin and other hormone concentrations. Low (< 1.47 kg) and high (> 1.53 kg) birth weight piglets were studied at 3 months (juvenile; n= 47) and 12 months of age (young adult; n= 17). At each age, arterial and venous catheters were inserted under general anaesthesia. Plasma leptin, cortisol, glucose, insulin and catecholamine concentrations were determined in basal blood samples. Body fat depth was measured by ultrasound at 12 months of age. Overall, adult fat depth was greater in low compared to high birth weight pigs and increased fat depth was associated with thinness at birth and poor early growth rates. These effects were strongest in females. Fat depth was related to current weight only in males. Compared to high birth ...
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The concentrations of plasma parathyroid hormone-like bioactivity and parathyroid hormone-related protein (1-86) (PTHrP) immunoreactivity were both higher in fetal pigs than in their mothers during the last 3 weeks of gestation. Both... more
The concentrations of plasma parathyroid hormone-like bioactivity and parathyroid hormone-related protein (1-86) (PTHrP) immunoreactivity were both higher in fetal pigs than in their mothers during the last 3 weeks of gestation. Both activities changed inversely with alterations in the plasma ionized calcium concentration. The data suggest that PTHrP may have a role in calcium homeostasis in the fetal pig, similar to its postulated role in sheep in the stimulation of calcium transport across the placenta.
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The effects of hypoinsulinaemia and altered metabolite concentrations on the fetal plasma concentrations of insulin-like growth factors (IGF) have been investigated in chronically catheterized fetal sheep made insulin deficient by... more
The effects of hypoinsulinaemia and altered metabolite concentrations on the fetal plasma concentrations of insulin-like growth factors (IGF) have been investigated in chronically catheterized fetal sheep made insulin deficient by pancreatic ablation. Fetal pancreatectomy reduced significantly the plasma IGF-1 concentration and increased plasma IGF-2 activity in comparison with the values observed in sham operated fetuses. Mean plasma IGF-1 concentrations in the sham operated and pancreatectomized fetuses were 18.6 +/- 3.1 ng/ml (n = 7) and 13.4 +/- 1.4 ng/ml (n = 13) respectively. When all the data were combined, there was a significant positive correlation between the plasma concentrations of IGF-1 and insulin in utero. The mean IGF-2 activity was 2349 +/- 83 ng/ml (n = 7) in the sham operated fetuses and 3800 +/- 532 ng/ml in the pancreatectomized animals (n = 13). Plasma IGF-2 activity was correlated positively with plasma glucose, fructose and alpha-amino nitrogen levels and in...
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To characterize propofol anaesthesia in pregnant ponies. Fourteen pony mares, at 256 ± 49 days gestation, undergoing abdominal surgery to implant fetal and maternal vascular catheters. Pre-anaesthetic medication with intravenous (IV)... more
To characterize propofol anaesthesia in pregnant ponies. Fourteen pony mares, at 256 ± 49 days gestation, undergoing abdominal surgery to implant fetal and maternal vascular catheters. Pre-anaesthetic medication with intravenous (IV) acepromazine (20 µg kg(-1)), butorphanol (20 µg kg(-1)) and detomidine (10 µg kg(-1)) was given 30 minutes before induction of anaesthesia with detomidine (10 µg kg(-1)) and ketamine (2 mg kg(-1)) IV Maternal arterial blood pressure was recorded (facial artery) throughout anaesthesia. Arterial blood gas values and plasma concentrations of glucose, lactate, cortisol and propofol were measured at 20-minute intervals. Anaesthesia was maintained with propofol infused initially at 200 µg kg(-1) minute(-1), and at 130-180 µg kg(-1) minute(-1) after 60 minutes, ventilation was controlled with oxygen and nitrous oxide to maintain PaCO2 between 5.0 and 6.0 kPa (37.6 and 45.1 mm Hg) and PaO2 between 13.3 and 20.0 kPa (100 and 150.4 mm Hg). During anaesthesia flunixin (1 mg kg(-1)), procaine penicillin (6 IU) and butorphanol 80 µg kg(-1) were given. Lactated Ringer&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;#39;s solution was infused at 10 mL kg(-1) hour(-1). Simultaneous fetal and maternal blood samples were withdrawn at 85-95 minutes. Recovery from anaesthesia was assisted. Arterial blood gas values remained within intended limits. Plasma propofol levels stabilized after 20 minutes (range 3.5-9.1 µg kg(-1)); disposition estimates were clearance 6.13 ± 1.51 L minute(-1) (mean ± SD) and volume of distribution 117.1 ± 38.9 L (mean ± SD). Plasma cortisol increased from 193 ± 43 nmol L(-1) before anaesthesia to 421 ± 96 nmol L(-1) 60 minutes after anaesthesia. Surgical conditions were excellent. Fetal umbilical venous pH, PO2 and PCO2 were 7.35 ± 0.04, 6.5 ± 0.5 kPa (49 ± 4 mm Hg) and 6.9 ± 0.5 kPa (52 ± 4 mm Hg); fetal arterial pH, PO2 and PCO2 were 7.29 ± 0.06, 3.3 ± 0.8 kPa (25 ± 6 mm Hg) and 8.7 ± 0.9 kPa (65 ± 7 mm Hg), respectively. Recovery to standing occurred at 46 ± 17 minutes, and was generally smooth. Ponies regained normal behaviour patterns immediately. Propofol anaesthesia was smooth with satisfactory cardiovascular function in both mare and fetus; we believe this to be a suitable anaesthetic technique for pregnant ponies.
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Equine umbilicus was cannulated in utero and a series of cord plasma samples removed for analysis. After steroid extraction and derivatisation, gas chromatographic-mass spectrometric (GC-MS) analysis demonstrated large differences in... more
Equine umbilicus was cannulated in utero and a series of cord plasma samples removed for analysis. After steroid extraction and derivatisation, gas chromatographic-mass spectrometric (GC-MS) analysis demonstrated large differences in steroid content between the plasma samples obtained from the umbilical artery and vein, the blood supplies leading to and from the placental surface, respectively. 3Beta-hydroxy-5,7-androstadien-17-one, dehydroepiandrosterone, pregnenolone, 3beta-hydroxy-5alpha-pregnan-20-one, 5-pregnene-3beta,20beta-diol and 5beta-pregnane-3beta,20beta-diol were identified as major constituents in extracts from umbilical arterial plasma samples, mostly as unconjugated steroids. Together with 5alpha-pregnane-3,20-dione, these steroids were identified in extracts from umbilical venous plasma samples but at significantly reduced levels to those determined in arterial plasma samples. Oestradiol-17alpha, dihydroequilin-17alpha and dihydroequilenin-17alpha were identified in extracts (mostly sulphate-conjugated) from both umbilical arterial and venous plasma samples, much larger amounts being detected in the plasma sampled from, rather than to, the placental surface. Equilin, equilenin, oestrone, oestradiol-17beta, dihydroequilin-17beta and dihydroequilenin-17beta were not detected in the present studies. Isomers of 5(10)-oestrene-3,17beta-diol together with 5(10),7-oestradiene-3,17beta-diol and its possible oxidative artifact, 5(10),7,9-oestratriene-3,17beta-diol, were tentatively identified only in sulphate-conjugated extracts from umbilical venous plasma samples. No glucuronic acid-conjugated steroids could be detected. The implications of this work in the elucidation of the biosynthetic pathways leading to both the formation of oestrogens and C18 neutral steroids at the placental surface are discussed.
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In developed societies, high-sugar and high-fat (HSHF) diets are now the norm and are increasing the rates of maternal obesity during pregnancy. In pregnant rodents, these diets lead to cardiovascular and metabolic dysfunction in their... more
In developed societies, high-sugar and high-fat (HSHF) diets are now the norm and are increasing the rates of maternal obesity during pregnancy. In pregnant rodents, these diets lead to cardiovascular and metabolic dysfunction in their adult offspring, but the intrauterine mechanisms involved remain unknown. This study shows that, relative to standard chow, HSHF feeding throughout mouse pregnancy increases maternal adiposity (+30%, P&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;lt;0.05) and reduces fetoplacental growth at d 16 (-10%, P&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;lt;0.001). At d 19, however, HSHF diet group pup weight had normalized, despite the HSHF diet group placenta remaining small and morphologically compromised. This altered fetal growth trajectory was associated with enhanced placental glucose and amino acid transfer (+35%, P&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;lt;0.001) and expression of their transporters (+40%, P&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;lt;0.024). HSHF feeding also up-regulated placental expression of fatty acid transporter protein, metabolic signaling pathways (phosphoinositol 3-kinase and mitogen-activated protein kinase), and several growth regulatory imprinted genes (Igf2, Dlk1, Snrpn, Grb10, and H19) independently of changes in DNA methylation. Obesogenic diets during pregnancy, therefore, alter maternal nutrient partitioning, partly through changes in the placental phenotype, which helps to meet fetal nutrient demands for growth near term. However, by altering provision of specific nutrients, dietary-induced placental adaptations have important roles in programming development with health implications for the offspring in later life.
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Hormones have an important role in the control of fetal growth. They act on both tissue accretion and differentiation and enable a precise and orderly pattern of growth to occur during late gestation. In part, their actions on growth may... more
Hormones have an important role in the control of fetal growth. They act on both tissue accretion and differentiation and enable a precise and orderly pattern of growth to occur during late gestation. In part, their actions on growth may be mediated by other growth factors such as the insulin-like growth factors (IGFs). Insulin stimulates fetal growth by increasing the mitotic drive and nutrient availability for tissue accretion. It has little effect on tissue differentiation. In contrast, the main effects of cortisol in utero are on tissue differentiation and maturation. Cortisol appears to act directly on the cells to alter gene transcription or post-translational processing of the gene products. Cortisol may also initiate the transition from the fetal to the adult modes of growth regulation by inducing the switch from IGF-II to IGF-I gene expression in the fetal liver. Thyroxine affects both tissue accretion and differentiation in the fetus by a combination of metabolic and non-m...
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Epidemiological findings and experimental studies in animals have shown that individual tissues and whole organ systems can be programmed in utero during critical periods of development with adverse consequences for their function in... more
Epidemiological findings and experimental studies in animals have shown that individual tissues and whole organ systems can be programmed in utero during critical periods of development with adverse consequences for their function in later life. Detailed morphometric analyses of the data have shown that certain patterns of intrauterine growth, particularly growth retardation, can be related to specific postnatal outcomes. Since hormones regulate fetal growth and the development of individual fetal tissues, they have a central role in intrauterine programming. Hormones such as insulin, insulin-like growth factors, thyroxine and the glucocorticoids act as nutritional and maturational signals and adapt fetal development to prevailing intrauterine conditions, thereby maximizing the chances of survival both in utero and at birth. However, these adaptations may have long-term sequelae. Of the hormones known to control fetal development, it is the glucocorticoids that are most likely to ca...
Research Interests: Physiology, Morphogenesis, Fetal development, Pregnancy, Humans, and 15 moreFemale, Animals, Fetal Growth, Hormones, Growth and development, Experimental Study, Enzyme, Clinical Sciences, Critical Period, Growth Factor, Glucocorticoids, Growth Retardation, Insulin Like Growth Factor, Paediatrics and reproductive medicine, and In Utero
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The insulin-like growth factors, IGF-I and IGF-II, have an important role in fetoplacental growth throughout gestation. They have metabolic, mitogenic and differentiative actions in a wide range of fetal tissues including the placenta.... more
The insulin-like growth factors, IGF-I and IGF-II, have an important role in fetoplacental growth throughout gestation. They have metabolic, mitogenic and differentiative actions in a wide range of fetal tissues including the placenta. Both Igf1and Igf2genes are expressed in fetal tissues. Expression of the Igf2gene is more abundant than Igf1 gene expression during mid to late gestation. Both IGF&amp;amp;#39;s are also present in the fetal circulations with 3-10 fold higher levels of IGF-II than IGF-1 during late gestation. Expression of the Igfgenes is developmentally regulated in a tissue specific manner and can be affected by nutritional and endocrine conditions in utero. Deletion of either Igfgene of the Igf1rgene retards fetal growth while over-expression of IGF-II leads to fetal overgrowth. In mice, placental growth is affected only by manipulation of the Igf2gene. The IGF&amp;amp;#39;s also effect the growth of individual fetal tissues and influence the uptake and utilization of nutrients by the fetal and placental tissues. Circulating concentrations and tissue expression of the IGF&amp;amp;#39;s are reduced by undernutrition and deficiency of nutritionally sensitive hormones, such as insulin, thyroxine and glucocorticoids. In general, the Igf1gene is more responsive to these stimuli than the Igf2gene. In addition, the effects of the IGFs on feto-placental growth can be amplified or attenuated by the IGF binding proteins, which are themselves regulated by nutritional and endocrine signals. The Igf2gene appears to provide the constitutive drive for intrauterine growth via its placental effects and direct paracrine actions on fetal tissue while the Igf1gene regulates fetal growth in relation to the nutrient supply.
Research Interests: Gene expression, Pregnancy, Humans, Liver, Placenta, and 15 moreFemale, Animals, Fetal Growth, Clinical Sciences, Embryonic Development, Foetus, Fetus, Gestational Age, Growth Factor, Gestation, Glucocorticoids, Insulin Like Growth Factor, hydrocortisone, Paediatrics and reproductive medicine, and In Utero
Intrauterine growth and development can impact upon the long-term health of an individual. The fetus is dependent upon the placenta for its supply of nutrients and oxygen from the mother. In turn, the functional capacity of the placenta... more
Intrauterine growth and development can impact upon the long-term health of an individual. The fetus is dependent upon the placenta for its supply of nutrients and oxygen from the mother. In turn, the functional capacity of the placenta to supply that demand is under the control of the fetal and maternal genomes. Recent evidence suggests that imprinted genes, a class of genes found in placental mammals whose expression depends on their parental origin, have multiple roles in the placenta. The imprinted genes regulate the growth and transport capacity of the placenta, thereby controlling the supply of nutrients. They may also regulate the growth rate of fetal tissues directly, thereby controlling nutrient demand by the fetus. Recent studies using mice with deletions or disruption of imprinted genes with an altered balance between placental and fetal growth and changes in placental efficiency are indicative of feto-placental signalling of fetal nutrient demand. We propose that signalling mechanisms involving growth demand signals and nutrient transporters are likely to occur and are important for fine tuning normal fetal growth.
Research Interests: Gene regulation, Genomic Imprinting, Intelligent Transport System, Fetal development, Pregnancy, and 12 morePlacenta, Mice, Functional Capacity, Female, Animals, Fetal Growth, Growth and development, Clinical Sciences, RNA-binding proteins, Growth rate, transport system, and Paediatrics and reproductive medicine
Large granulated binucleate cells (BNCs) producing placental lactogen (PL) and pregnancy-associated glycoproteins (PAG) are present in all ruminant placentae throughout pregnancy. These BNC account for 15-20% of the cells in ovine... more
Large granulated binucleate cells (BNCs) producing placental lactogen (PL) and pregnancy-associated glycoproteins (PAG) are present in all ruminant placentae throughout pregnancy. These BNC account for 15-20% of the cells in ovine trophectoderm for most of gestation but decrease in number close to term at the same time that fetal cortisol levels rise. The present study investigated the effects of cortisol on the BNC population using immunohistochemistry to count BNCs in ovine placentomes during late gestation and after experimental manipulation of the fetal cortisol level by fetal adrenalectomy and exogenous cortisol infusion. Abolition of the prepartum rise in fetal cortisol prevented the normal decline in BNC numbers towards term. Conversely, raising cortisol levels in immature fetuses to prepartum values prematurely reduced placental BNC numbers. However, a small population of BNC remained, even at the highest cortisol concentrations. When all the data were combined irrespective of treatment or gestational age, there was a significant inverse correlation between fetal plasma cortisol and the number of BNCs in the ovine placenta. These findings show that cortisol regulates the BNC population in ovine placenta during late gestation. They also have important implications for the production of PL and PAG during ovine pregnancy.