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Department of Biological and Medical Sciences
Faculty of Health and Life Sciences
+44 (0)1865 483625
My research interests are in mammalian endocrinology and the endocrine regulation of physiology and development in the fetus. Currently, my research work is focussed on two main areas:
Development and regulation of endocrine systems in the fetusThese studies have examined the bioavailability of hormones in the fetus, in particular, the glucocorticoids, thyroid hormones, leptin, insulin-like growth factors and the renin-angiotensin system. Our analyses of hormone systems in utero have included measurements of circulating concentrations, tissue metabolism and metabolic enzymes, cellular uptake mechanisms and receptor expression. These studies have demonstrated complex interactions between endocrine systems before birth and have elucidated a variety of cellular and molecular mechanisms of developmental control. Endocrine control of fetal growth, development and maturationMy research has also investigated the role of hormones in the regulation of normal fetal development. These studies have an integrative approach to systems animal biology by examining a wide variety of fetal tissues and organs, and aspects of fetal physiology, including growth, cardiovascular and renal function, nutrition and metabolism. In particular, several of these studies have established the importance of endocrine signals in fetal maturation near to delivery and in the successful transition from the intrauterine to extrauterine environment at birth. We have investigated the mechanisms of glucocorticoid action in several physiological systems, and demonstrated the important roles of other hormones, such as thyroid hormones and angiotensin II, in mediating many of the maturational effects of glucocorticoids. Overall, my research has an integrative approach to the study of mammalian endocrinology and systems animal physiology. The research findings have important implications for the understanding of normal fetal growth and development, the consequences of prematurity and fetal endocrine disorders, and the mechanisms underlying the intrauterine programming of adult (patho)physiology.
Hormones have an important role in regulating fetal development. They act as environmental signals and integrate tissue growth and differentiation with relation to nutrient availability. While hormones control the developmental fate of resources available to the fetus, the actual supply of nutrients and oxygen to the fetus depends on the placenta. However, much less is known about the role of hormones in regulating placental development, even though the placenta has a wide range of hormone receptors and produces hormones itself from early in gestation. The placenta is, therefore, exposed to hormones by autocrine, paracrine and endocrine mechanisms throughout its lifespan. It is known to adapt its phenotype in response to environmental cues and fetal demand signals, particularly when there is a disparity between the fetal genetic drive for growth and the nutrient supply. These adaptive responses help to maintain fetal growth during adverse conditions and are likely to depend, at least in part, on the hormonal milieu. This review examines the endocrine regulation of placental phenotype with particular emphasis on the glucocorticoid hormones. It focuses on the availability of placental hormone receptors and on the effects of hormones on the morphology, transport capacity and endocrine function of the placenta.
The effects of endogenous and synthetic glucocorticoids on fetal lung maturation are wellestablished, although the role of leptin in lung development before birth is unclear. This study examined mRNA and protein levels of the signalling long-form leptin receptor (Ob-Rb) in fetal ovine lungs towards term, and after experimental manipulation of glucocorticoid levels in utero by fetal cortisol infusion ormaternal dexamethasone treatment. In fetal ovine lungs, Ob-Rb protein was localised to bronchiolar epithelium, bronchial cartilage, vascular endothelium, alveolar macrophages and type II pneumocytes. Pulmonary Ob-Rb mRNA abundance increased between 100 (0.69 fractional gestational age) and 144 days (0.99) of gestation, and by 2-4-fold in response to fetal cortisol infusion and maternal dexamethasone treatment. In contrast, pulmonary Ob-Rb protein levels decreased near term and were halved by glucocorticoid treatment, without any significant change in phosphorylated signal transducer and activator of transcription-3 (pSTAT3) at Ser727, total STAT3 or the pulmonary pSTAT3: STAT3 ratio. LeptinmRNA was undetectable in fetal ovine lungs at the gestational ages studied. These findings demonstrate differential control of pulmonary Ob-Rb transcript abundance and protein translation, and/or post-translational processing, by glucocorticoids in utero. Localisation of Ob-Rb in the fetal ovine lungs, including alveolar type II pneumocytes, suggests a role for leptin signalling in the control of lung growth and maturation before birth.
The present study tested the hypothesis that overexposure to endogenous glucocorticoids in neonatal life alters the reactivity of the hypothalamic-pituitary-adrenal (HPA) axis in ponies at 1 and 2yr of age. Newborn foals received saline (0.9% NaCl, n = 8, control) or long-acting adrenocorticotropic hormone (ACTH) (Depot Synacthen 0.125mg intramuscularly twice daily, n = 9) for 5d after birth to raise cortisol concentrations 5- to 6-fold. At 1 and 2yr of age, HPA axis function was assessed by bolus administration of short-acting ACTH (1μg/kg intravenous) and insulin (0.5 U/kg intravenous) to induce hypoglycemic on separate days. Arterial blood samples were taken at 5 to 30-min intervals before and after drug administration to measure plasma ACTH and/or cortisol concentrations. There were no differences in the basal plasma ACTH or cortisol concentrations or in the cortisol response to exogenous ACTH with neonatal treatment or age. At 1 and 2yr of age, the increment in plasma ACTH but not cortisol at 60min in response to insulin-induced hypoglycemia was greater in ponies treated neonatally with ACTH than saline (P < 0.05). Neonatal cortisol overexposure induced by neonatal ACTH treatment, therefore, alters functioning of the HPA axis in adult ponies.
Antenatal synthetic glucocorticoids promote fetal maturation in pregnant women at risk of preterm delivery and their mechanism of action may involve other endocrine systems. This study investigated the effect of maternal dexamethasone treatment, at clinically relevant doses, on components of the renin-angiotensin system (RAS) in the pregnanteweandfetus.From125 days of gestation (term, 145 2 d), 10 ewes carrying single fetuses of mixed sex (3 female, 7 male) were injected twice im, at 10-11 PM, with dexamethasone (2×12 mg, n=5) or saline (n=5) at 24-hour intervals. At 10 hours after the secondinjection, maternal dexamethasone treatment increased angiotensin-converting enzyme(ACE) mRNA levels in the fetal lungs, kidneys, and heart and ACE concentration in the circulation and lungs, but not kidneys, of the fetuses. Fetal cardiac mRNA abundance of angiotensin II (AII) type 2 receptor decreased after maternal dexamethasone treatment. Between the two groups of fetuses, there were no significant differences in plasma angiotensinogen or renin concentrations; in transcript levels of renalrenin,orAIItype1or2receptorsinthelungsandkidneys;orinpulmonary,renalorcardiacprotein content of the AII receptors. In the pregnant ewes, dexamethasone administration increased pulmonary ACE and plasma angiotensinogen, and decreased plasma renin, concentrations. Some of the effects of dexamethasone treatment on the maternal and fetal RAS were associated with altered insulin and thyroid hormone activity. Changes in the local and circulating RAS induced by dexamethasone exposure in utero may contribute to the maturational and tissue-specific actions of antenatal glucocorticoid treatment.
The thyroid hormones, thyroxine (T) and triiodothyronine (T), are essential for normal growth and development of the fetus. Their bioavailability in utero depends on development of the fetal hypothalamic-pituitary-thyroid gland axis and the abundance of thyroid hormone transporters and deiodinases that influence tissue levels of bioactive hormone. Fetal T and T concentrations are also affected by gestational age, nutritional and endocrine conditions in utero, and placental permeability to maternal thyroid hormones, which varies among species with placental morphology. Thyroid hormones are required for the general accretion of fetal mass and to trigger discrete developmental events in the fetal brain and somatic tissues from early in gestation. They also promote terminal differentiation of fetal tissues closer to term and are important in mediating the prepartum maturational effects of the glucocorticoids that ensure neonatal viability. Thyroid hormones act directly through anabolic effects on fetal metabolism and the stimulation of fetal oxygen consumption. They also act indirectly by controlling the bioavailability and effectiveness of other hormones and growth factors that influence fetal development such as the catecholamines and insulin-like growth factors (IGFs). By regulating tissue accretion and differentiation near term, fetal thyroid hormones ensure activation of physiological processes essential for survival at birth such as pulmonary gas exchange, thermogenesis, hepatic glucogenesis, and cardiac adaptations. This review examines the developmental control of fetal T and T bioavailability and discusses the role of these hormones in fetal growth and development with particular emphasis on maturation of somatic tissues critical for survival immediately at birth. © 2014 Society for Endocrinology.
Introduction and methods Tragulus, the mouse deer, is considered the most primitive ruminant, with a diffuse placenta grossly quite unlike the cotyledonary type of the other ruminants. This immunocytochemical investigation of placental transporters was designed to elucidate possible mechanisms of evolution to the cotyledonary form. Results and discussion Tragulus expresses several of the major transport systems characteristic of the ruminants: the trophoblast binucleate cell (BNC) dynamics, the requirement for two isoforms, GT1 and GT3, for glucose transport, the provision of Aquaporin 3 for water control, and uterine milk and histiotrophic secretion from uterine glands. However whereas the expression of the 9kD Calcium Binding Protein (9CBP) for calcium transport in ruminants is restricted to the intercotyledonary trophoblast with its areolae, Tragulus, having no intercotyledonary area, expresses 9CBP throughout the villus trophoblast. There is some localised development of areolar-like structures in the mid term Tragulus but it is insignificant at term. The strong expression of Glucose Transporter 1 (GT1) in the BNC granules is unique to Tragulus. Conclusion Tragulus relies on essentially similar transport and BNC dynamics as the other ruminants. Thus the evolutionary pressures driving the development of the cotyledonary placenta probably lie in the increase in body size and the consequent need for a larger placental area to ensure sufficient glucose for the fetus. The delivery in Tragulus of GT1 to the maternal facing side may be this species unique solution to maintain the glucose supply. © 2014 Elsevier Ltd. All rights reserved.
First published October 19, 2010; doi:10.1152/ajpendo.00205.2010.-”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 ultilization 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.