Regulation of glucocorticoid receptor mRNA and heat shock protein 70 mRNA in the developing sheep brain

Maternal psychosocial stress during early gestation impairs fetal structural brain development in sheep

Maternal stress, especially during early pregnancy, predisposes offspring to neuropsychiatric disorders. We hypothesized that maternal psychosocial stress (MPS) during pregnancy affects fetal structural neurodevelopment depending on the gestational age of exposure. Fetal sheep brains were harvested at 130 days gestation (dG, term 150 dG) from ewes frequently isolated from flock-mates during early gestation (first and second trimester; n = 10) or late gestation (third trimester; n = 10), or from control flock-mates (n = 8). Immunohistochemistry for formation of neuronal processes, myelination, synaptic density, cell proliferation and programed cell death was performed on brain tissue sections. Sections of the cortical gray matter, the hippocampal CA3 region and the superficial, subcortical and deep white matter were examined morphometrically. Stress effects depended on the brain region and time of exposure. Stress during early gestation but not during late gestation reduced the amount of neuronal processes in the cerebral cortex and hippocampus by 36.9 ± 10.1% (p < 0.05, mean ± SEM) and 36.9 ± 15.8% (p < 0.05), respectively, accompanied by a decrease in synaptic density in the cerebral cortex and hippocampus by 39.8 ± 23.1% (p < 0.05) and 32.9 ± 13.4% (p < 0.01). Myelination was decreased in white matter layers on average by 44.8 ± 11.7% (p < 0.05) accompanied by reduced (glial) cell proliferation in the deep white matter by 83.6 ± 12.4% (p < 0.05). In contrast, stress during the third trimester had no effect in any brain region. Chronic MPS during the first and second trimester induced prolonged effects on neuronal network and myelin formation which might contribute to disturbed neurobehavioral, cognitive and motor development in offspring of stressed mothers.Lay summaryMany women are exposed to stressful events during pregnancy. Maternal stress especially during early pregnancy predisposes for offspring's neuropsychiatric disorders. In our sheep study, we show that disturbance of fetal brain development is a potential mechanism and is worst during 1st and 2nd trimester.

Proteomics-driven analysis of ovine whey colostrum

The aim of this study was to shed light in to the complexity of the ovine colostrum proteome, with a specific focus on the low abundance proteins. The ovine colostrum is characterized by a few dominating proteins, as the immunoglobulins, but it also contains less represented protein species, equally important for the correct development of neonates. Ovine colostrum, collected immediately after lambing, was separated by 1D SDS-PAGE. Proteins bands were digested with trypsin and the resulting peptides were analyzed by LC-MS/MS. On the basis of the Swiss-Prot database, a total of 343 unique proteins were identified. To our knowledge, this study represents the most comprehensive analysis of ovine colostrum proteome.

Prenatal xenobiotic exposure and intrauterine hypothalamus-pituitary-adrenal axis programming alteration

The hypothalamic-pituitary-adrenal (HPA) axis is one of the most important neuroendocrine axes and plays an important role in stress defense responses before and after birth. Prenatal exposure to xenobiotics, including environmental toxins (such as smoke, sulfur dioxide and carbon monoxide), drugs (such as synthetic glucocorticoids), and foods and beverage categories (such as ethanol and caffeine), affects fetal development indirectly by changing the maternal status or damaging the placenta. Certain xenobiotics (such as caffeine, ethanol and dexamethasone) may also affect the fetus directly by crossing the placenta into the fetus due to their lipophilic properties and lower molecular weights. All of these factors probably result in intrauterine programming alteration of the HPA axis, which showed a low basal activity but hypersensitivity to chronic stress. These alterations will, therefore, increase the susceptibility to adult neuropsychiatric (such as depression and schizophrenia) and metabolic diseases (such as hypertension, diabetes and non-alcoholic fatty liver disease). The "over-exposure of fetuses to maternal glucocorticoids" may be the main initiation factor by which the fetal HPA axis programming is altered. Meantime, xenobiotics can directly induce abnormal epigenetic modifications and expression on the important fetal genes (such as hippocampal glucocorticoid receptor, adrenal steroidogenic acute regulatory protein, et al) or damage by in situ oxidative metabolism of fetal adrenals, which may also be contributed to the programming alteration of fetal HPA axis.

Glucocorticoids and fetal programming part 2: Mechanisms

The lifelong health of an individual is shaped during critical periods of development. The fetus is particularly susceptible to internal and external stimuli, many of which can alter developmental trajectories and subsequent susceptibility to disease. Glucocorticoids are critical in normal development of the fetus, as they are involved in the growth and maturation of many organ systems. The surge in fetal glucocorticoid levels that occurs in most mammalian species over the last few days of pregnancy is an important developmental switch leading to fundamental changes in gene regulation in many organs, including the brain. These changes are important for the transition to postnatal life. Exposure of the fetus to increased levels of glucocorticoids, resulting from maternal stress or treatment with synthetic glucocorticoids, can lead to long-term 'programming' of hypothalamic-pituitary-adrenal function and behaviours. Glucocorticoids act at multiple levels within the fetal brain. Growing evidence indicates that they can exert powerful effects on the epigenome, including on DNA methylation, histone acetylation and microRNA, to influence gene expression. Such influences probably represent a critical component of the 'programming' process, and might be partly responsible for the transgenerational effects of antenatal glucocorticoid exposure on neurologic, cardiovascular and metabolic function.

Context modulates outcome of perinatal glucocorticoid action in the brain

Prematurely born infants may be at risk, because of inadequate maturation of tissues. If there are signs of preterm birth, it has become common practice therefore to treat either antenatally the mother or postnatally the infant with glucocorticoids to accelerate tissue development, particularly of the lung. However, this life-saving early glucocorticoid treatment was found to increase the risk of adverse outcome in later life. In one animal study, the authors reported a 25% shorter lifespan of rats treated as newborns with the synthetic glucocorticoid dexamethasone, but so far this finding has not been replicated. After a brief clinical introduction, we discuss studies in rodents designed to examine how perinatal glucocorticoid action affects the developing brain. It appears that the perinatal action of the glucocorticoid depends on the context and the timing as well as the type of administered steroid. The type of steroid is important because the endogenous glucocorticoids cortisol and corticosterone bind to two distinct receptor populations, i.e., mineralocorticoid and glucocorticoid receptors (GR), while synthetic glucocorticoids predominantly bind to the GR. In addition, if given antenatally hydrocortisone is inactivated in the placenta by 11β-HSD type 2, and dexamethasone is not. With respect to timing, the outcome of glucocorticoid effects is different in early vs. late phases of brain development. The context refers to the environmental input that can affect the susceptibility to glucocorticoid action in the newborn rodent brain; early handling of pups and maternal care obliterate effects of post-natal dexamethasone treatment. Context also refers to coping with environmental conditions in later life, for which the individual may have been programed epigenetically by early-life experience. This knowledge of determinants affecting the outcome of perinatal glucocorticoid exposure may have clinical implications for the treatment of prematurely born infants.

Glucocorticoid programming of the fetal male hippocampal epigenome

The late-gestation surge in fetal plasma cortisol is critical for maturation of fetal organ systems. As a result, synthetic glucocorticoids (sGCs) are administered to pregnant women at risk of delivering preterm. However, animal studies have shown that fetal exposure to sGC results in increased risk of behavioral, endocrine, and metabolic abnormalities in offspring. Here, we test the hypothesis that prenatal GC exposure resulting from the fetal cortisol surge or after sGC exposure results in promoter-specific epigenetic changes in the hippocampus. Fetal guinea pig hippocampi were collected before (gestational day [GD52]) and after (GD65) the fetal plasma cortisol surge (Term∼GD67) and 24 hours after (GD52) and 14 days after (GD65) two repeat courses of maternal sGC (betamethasone) treatment (n = 3-4/gp). We identified extensive genome-wide alterations in promoter methylation in late fetal development (coincident with the fetal cortisol surge), whereby the majority of the affected promoters exhibited hypomethylation. Fetuses exposed to sGC in late gestation exhibited substantial differences in DNA methylation and histone h3 lysine 9 (H3K9) acetylation in specific gene promoters; 24 hours after the sGC treatment, the majority of genes affected were hypomethylated or hyperacetylated. However, 14 days after sGC exposure these differences did not persist, whereas other promoters became hypermethylated or hyperacetylated. These data support the hypothesis that the fetal GC surge is responsible, in part, for significant variations in genome-wide promoter methylation and that prenatal sGC treatment profoundly changes the epigenetic landscape, affecting both DNA methylation and H3K9 acetylation. This is important given the widespread use of sGC in the management of women in preterm labor.

The role of cortisol in chronic binge alcohol-induced cerebellar injury: Ovine model

Women who drink alcohol during pregnancy are at high risk of giving birth to children with neurodevelopmental disorders. Previous reports from our laboratory have shown that third trimester equivalent binge alcohol exposure at a dose of 1.75 g/kg/day results in significant fetal cerebellar Purkinje cell loss in fetal sheep and that both maternal and fetal adrenocorticotropin (ACTH) and cortisol levels are elevated in response to alcohol treatment. In this study, we hypothesized that repeated elevations in cortisol from chronic binge alcohol are responsible at least in part for fetal neuronal deficits. Animals were divided into four treatment groups: normal control, pair-fed saline control, alcohol and cortisol. The magnitude of elevation in cortisol in response to alcohol was mimicked in the cortisol group by infusing pregnant ewes with hydrocortisone for 6 h on each day of the experiment, and administering saline during the first hour in lieu of alcohol. The experiment was conducted on three consecutive days followed by four days without treatment beginning on gestational day (GD) 109 until GD 132. Peak maternal blood alcohol concentration in the alcohol group was 239 ± 7 mg/dl. The fetal brains were collected and processed for stereological cell counting on GD 133. The estimated total number of fetal cerebellar Purkinje cells, the reference volume and the Purkinje cell density were not altered in response to glucocorticoid infusion in the absence of alcohol. These results suggest that glucocorticoids independently during the third trimester equivalent may not produce fetal cerebellar Purkinje cell loss. However, the elevations in cortisol along with other changes induced by alcohol could together lead to brain injury seen in the fetal alcohol spectrum disorders.

Role of the hypothalamic-pituitary-adrenal axis in developmental programming of health and disease

Adverse environments during the fetal and neonatal development period may permanently program physiology and metabolism, and lead to increased risk of diseases in later life. Programming of the hypothalamic-pituitary-adrenal (HPA) axis is one of the key mechanisms that contribute to altered metabolism and response to stress. Programming of the HPA axis often involves epigenetic modification of the glucocorticoid receptor (GR) gene promoter, which influences tissue-specific GR expression patterns and response to stimuli. This review summarizes the current state of research on the HPA axis and programming of health and disease in the adult, focusing on the epigenetic regulation of GR gene expression patterns in response to fetal and neonatal stress. Aberrant GR gene expression patterns in the developing brain may have a significant negative impact on protection of the immature brain against hypoxic-ischemic encephalopathy in the critical period of development during and immediately after birth.

Antenatal corticosteroids: a risk factor for the development of chronic disease

Preterm birth remains a major health issue worldwide. Since the 1990s, women at risk for preterm birth received a single course of exogenous antenatal corticosteroids (ACSs) to facilitate fetal lung maturity. More recently, repeated or multiple courses of ACS have been supported to provide continued fetal maturity support for women with continued risk of preterm birth. However, exogenous ACS reduces birth weight which, in turn, is associated with adverse adult outcomes such as coronary heart disease, stroke, hypertension, and type 2 diabetes. The long-term effects of ACS exposure on HPA axis activity and neurological function are well documented in animal studies, and it appears that ACS, regardless of dose exposure, is capable of affecting fetal HPA axis development causing permanent changes in the HPA axis that persists through life and is manifested by chronic illness and behavioral changes. The challenge in human studies is to demonstrate whether an intervention such as ACS administration in pregnancy contributes to developmental programming and how this is manifested in later life.

Prenatal synthetic glucocorticoid exposure alters hypothalamic-pituitary-adrenal regulation and pregnancy outcomes in mature female guinea pigs

Preterm delivery occurs in approximately 10% of all pregnancies. Prenatal exposure to synthetic glucocorticoids (sGCs) reduces the incidence of respiratory distress syndrome (RDS) in these babies. Therefore, administration of multiple courses of sGCs became common practice. Animal and human studies have demonstrated that multiple courses of sGCs can have long-term effects. While the majority of animal studies have been undertaken in male offspring, it is emerging that there are profound sex differences in the consequences of prenatal sGC exposure. To our knowledge, no studies have determined the effects of prenatal sGC exposure on hypothalamic-pituitary-adrenal (HPA) axis function in female offspring while accounting for reproductive cycle status, or determined if there are effects on pregnancy parameters. Pregnant guinea pigs were administered three courses of betamethasone (Beta), dexamethasone (Dex) or vehicle on gestational days 40/41, 50/51 and 60/61. In adulthood (age range: postnatal days 126-165), basal and activated HPA axis function were assessed at various stages of the reproductive cycle. The female offspring were then mated and underwent an undisturbed pregnancy. Females were killed in the luteal phase of the reproductive cycle following litter weaning, and molecular analysis undertaken. In the luteal phase, Beta-exposed females exhibited significantly lower basal salivary cortisol levels (P < 0.05). Dex-exposed females also exhibited significantly lower basal salivary cortisol levels during the luteal phase (P < 0.05), but increased basal salivary cortisol levels during the ostrous phase (P < 0.01). The Beta-exposed females exhibited increased glucocorticoid receptor (GR) mRNA expression in the CA1/2 region of the hippocampus (P < 0.05) and MC2R mRNA in the adrenal cortex (P < 0.05). The Dex-exposed animals exhibited higher hippocampal GR and mineralocorticoid receptor (MR) mRNA levels (P < 0.05). Beta-exposed females showed reduced fecundity (P < 0.05). In Dex-exposed females there was a lower male to female sex ratio. In conclusion, prenatal sGC exposure affects HPA axis activity, in a cycle-dependent manner, and long-term reproductive success. The clinical implications of the findings on endocrine function and pregnancy in females are profound and further follow-up is warranted in human cohorts. Furthermore, we have shown there are considerable difference in phenotypes between the Beta- and Dex-exposed females and the specific endocrine and maternal outcome is contingent on the specific sGCs administered during pregnancy.

Effects of intrauterine exposure to synthetic glucocorticoids on fetal, newborn, and infant hypothalamic-pituitary-adrenal axis function in humans: a systematic review

BACKGROUND

Synthetic glucocorticoids are commonly used in reproductive medicine. Fetal organ systems are highly sensitive to changes in the intrauterine environment, including overexposure to glucocorticoids. Structural and functional alterations resulting from such changes may persist throughout life and have been associated with diverse diseases. One system that could be particularly sensitive to fetal glucocorticoid overexposure is the hypothalamic-pituitary-adrenal (hpa) axis. Many human studies have investigated this possibility, but a systematic review to identify consistent, emergent findings is lacking.

METHODS

We systematically review 49 human studies, assessing the effects of intrauterine exposure to synthetic glucocorticoids on fetal, neonate, and infant hpa function.

RESULTS

Study quality varied considerably, but the main findings held true after restricting the analyses to higher-quality studies: intrauterine exposure to synthetic glucocorticoids reduces offspring hpa activity under unstimulated conditions after pain but not pharmacological challenge. Although reduced unstimulated hpa function appears to recover within the first 2 wk postpartum, blunted hpa reactivity to pain is likely to persist throughout the first 4 months of life. There is some evidence that the magnitude of the effects is correlated with the total amount of glucocorticoids administered and varies with the time interval between glucocorticoid exposure and hpa assessment.

CONCLUSIONS

This systematic review has allowed the demonstration of the way in which intrauterine exposure to various regimens of synthetic glucocorticoids affects various forms of hpa function. As such, it guides future studies in terms of which variables need to be focused on in order to further strengthen the understanding of such therapy, whilst continuing to profit from its clinical benefits.

Development of a method of measuring cellular stress in cattle and sheep

In the current studies, flow cytometric methods were used to demonstrate that heat shock protein (hsp) 70 is constitutively expressed in ovine and bovine leukocytes but that the level of expression varies considerably between different leukocyte types and between species. We also show that expression of hsp70 is upregulated in response to an in vitro heat shock treatment. The optimal temperature for heat shock of leukocytes from sheep and cattle is 43.5 degrees C. In sheep and cattle, the relative susceptibility of leukocyte type to upregulation of hsp70 expression, as assayed as percent positive cells, by in vitro heat shock was cell type specific. Best results were obtained from fresh samples; after storage at room temperature for 24h upregulation was highly variable between animals and less than in fresh samples. These studies demonstrate that evaluation of leukocyte hsp70 expression by flow cytometry is a robust, reproducible method for use in the evaluation of cellular stress responses in cattle and sheep. The application of the methods described may be a valuable tool in assessing in vivo stress responses in livestock species.

Fetal fornix transection and gestation length in sheep

Experiments in several species indicate that the hippocampus influences hypothalamo-pituitary-adrenal (HPA) axis function. In fetal sheep, simultaneous ACTH and cortisol rises over the last 30 days of gestation peak at term and are necessary for birth. We hypothesized that if the fetal hippocampal formation is functional in late gestation, loss of hippocampal input to the HPA axis following fetal fornix transection would change gestation length in comparison to controls. At 118-121 days of gestation (dG), stereotaxic technique was used in fetal sheep to sham transect (SHAM; n = 8) or transect (FXTX; n = 6) the dorsal fornix at the level of the hippocampal commissure. No differences were found between SHAM and FXTX fetuses in daily hormone profiles over the last week of gestation or in gestation length (148.0 +/- 1.2 vs. 149.0 +/- 0.4 dG, respectively). We conclude that the fetal hippocampus is immature in late gestation and we speculate that an immature hippocampus is necessary for the loss of negative feedback control that gives rise to the long term, simultaneous increases in ACTH and cortisol that are indispensable for labor and delivery at term in sheep.

Fetal programming of hypothalamo-pituitary-adrenal function: prenatal stress and glucocorticoids

Prenatal stress (PS) and maternal exposure to exogenous glucocorticoids can lead to permanent modification of hypothalamo-pituitary-adrenal (HPA) function and stress-related behaviour. Both of these manipulations lead to increased fetal exposure to glucocorticoids. Glucocorticoids are essential for many aspects of normal brain development, but exposure of the fetal brain to an excess of glucocorticoids can have life-long effects on neuroendocrine function. Both endogenous glucocorticoid and synthetic glucocorticoid exposure have a number of rapid effects in the fetal brain, including modification of neurotransmitter systems and transcriptional machinery. Such fetal exposure permanently alters HPA function in prepubertal, postpubertal and ageing offspring, in a sex-dependent manner. Prenatal stress and exogenous glucocorticoid manipulation also lead to the modification of behaviour, brain and organ morphology, as well as altered regulation of other endocrine systems. It is also becoming increasingly apparent that the timing of exposure to PS or synthetic glucocorticoids has tremendous effects on the nature of the phenotypic outcome. Permanent changes in endocrine function will ultimately impact on health in both human and animal populations.

Central regulation of the hypothalamic-pituitary-adrenal axis during fetal development in the Guinea-pig

We have previously shown that the foetal guinea-pig hypothalamic-pituitary-adrenal (HPA) axis is activated near the time of parturition and that this is associated with changes in limbic glucocorticoid receptors (GR) and mineralocorticoid receptors. In the present study, we hypothesized that the foetal hypothalamic paraventricular nucleus (PVN) and pituitary contribute significantly to foetal HPA drive but that these areas remain sensitive to negative feedback by circulating glucocorticoids in late gestation. However, we observed decreased corticotrophin-releasing hormone mRNA expression in the PVN and decreased pro-opiomelanocortin (POMC) mRNA levels in the anterior pituitary with advanced gestational age. The reduction in POMC mRNA expression was likely the result of negative feedback via circulating glucocorticoids because GR mRNA was unchanged during development in the foetal pituitary. Furthermore, we found that maternally administered glucocorticoids significantly decreased foetal pituitary POMC mRNA expression in a dose-dependent manner at gestational day (gd) 62 with male foetuses being more sensitive to these effects. These findings show that the foetal HPA axis remains highly sensitive to glucocorticoid feedback even as plasma adrenocorticotropic hormone and cortisol levels are elevated at the end of gestation.

RETRACTED: Maternal adversity, glucocorticoids and programming of neuroendocrine function and behaviour

The fetus may be exposed to increased endogenous glucocorticoid or synthetic glucocorticoid in late gestation. Approximately 7% of pregnant women in Europe and North America are treated with synthetic glucocorticoid to promote lung maturation in fetuses at risk of preterm delivery. Very little is known about the mechanisms by which synthetic glucocorticoid or prenatal stress influence neurodevelopment in the human, or whether specific time windows of increased sensitivity exist. Glucocorticoids are essential for many aspects of normal brain development, but exposure of the fetal brain to excess glucocorticoid can have life-long effects on neuroendocrine function and behaviour. Both endogenous glucocorticoid and synthetic glucocorticoid exposure have a number of rapid effects in the fetal brain, including modification of neurotransmitter systems and transcriptional machinery. Such fetal exposure permanently alters hypothalamo-pituitary-adrenal (HPA) function in prepubertal, postpubertal and aging offspring, in a sex-dependent manner. Prenatal glucocorticoid manipulation also leads to modification of behaviour, brain and organ morphology, as well as altered regulation of other endocrine systems. Permanent changes in endocrine function will impact on health, since elevated cumulative exposure to endogenous glucocorticoid is linked to the premature onset of pathologies associated with aging.

Fetal glucocorticoid exposure and hypothalamo-pituitary-adrenal (HPA) function after birth

The fetus may be exposed to increased endogenous glucocorticoid or synthetic glucocorticoid in late gestation. Indeed, 7-10% of pregnant women in Europe and North America are treated with synthetic glucocorticoid to promote lung maturation in fetuses at risk of preterm delivery. Such therapy is effective in reducing respiratory complications. However, very little is known about the mechanisms by which synthetic glucocorticoid or prenatal stress influence neurodevelopment in the human, or whether specific time windows of increased sensitivity exist. Glucocorticoids are essential for many aspects of normal brain development. However, there is growing evidence that exposure of the fetal brain to excess glucocorticoid can have lifelong effects on neuroendocrine function and behavior. We have shown that both endogenous glucocorticoid and synthetic glucocorticoid exposure has a number of rapid effects in the fetal brain in late gestation, including modification of neurotransmitter systems and transcriptional machinery. Such fetal exposure permanently alters hypothalamo-pituitary-adrenal (HPA) function in prepubertal, postpubertal, and aging offspring, in a sex-dependent manner. These effects are linked to changes in central glucocorticoid feedback machinery after birth. Prenatal glucocorticoid manipulation also leads to modification of HPA-associated behaviors, brain and organ morphology, as well as altered regulation of other endocrine systems. Permanent changes in endocrine function will have a long-term impact on health, since elevated cumulative exposure to endogenous glucocorticoid is linked to the premature onset of pathologies associated with aging.

Programming of the hypothalamo-pituitary-adrenal axis: serotonergic involvement

The ability of the early environment to programme the developing hypothalamo-pituitary-adrenal (HPA) axis has been reported in several animal species. There is considerable evidence that a similar process can occur in the human, and that long-term alterations in HPA function are associated with altered susceptibility to disease in later life. The phenotype of HPA function following early manipulation depends on the timing and intensity of the manipulation as well as the gender of the fetus/neonate. There is considerable interplay between the developing HPA and the reproductive axes and emerging evidence indicates that this interaction is modified by early environmental manipulation. Studies are rapidly unravelling the mechanisms that underlie developmental programming of the HPA axis. In this context, the serotonergic system has been identified as a primary system involved in this process. Understanding the mechanisms involved in neuroendocrine programming will facilitate the development of interventions aimed at reversing or ameliorating the impact of an adverse intrauterine environment.

Glucocorticoids, hypothalamo-pituitary-adrenal (HPA) development, and life after birth

Approximately 10% of women in North America are treated with synthetic glucocorticoid (sGC) between 24 and 32 weeks of pregnancy (term approximately 40 weeks), to promote lung maturation in fetuses at risk of preterm delivery. Such therapy is highly effective in reducing the frequency of respiratory complications, and as a result, repeated course treatment has become widespread. Nothing is known about the impact of repeated sGC treatment on neuroendocrine development in the human, or if specific time windows of increased sensitivity exist. Glucocorticoids are essential for many aspects of normal brain development. However, there is growing evidence from a number of species, that exposure of the fetal brain to excess glucocorticoid can have life-long effects on behaviour and neuroendocrine function. We have shown that exposure of fetuses to sGC in late gestation permanently alters HPA function in pre-pubertal, post-pubertal, and aging offspring, in a sex-dependent manner. These effects are linked to changes in central glucocorticoid feedback. Prenatal glucocorticoid exposure also leads to modification of HPA-associated behaviours and organ morphology, as well as altered regulation of other neuroendocrine systems. Permanent changes in HPA function will have a long-term impact on health, since elevated cumulative exposure to endogenous glucocorticoid has been linked to the premature onset of pathologies associated with aging.

Effects of fetal ovine adrenalectomy on sympathetic and baroreflex responses at birth

Studies were performed to test the hypothesis that the absence of adrenal glucocorticoids late in gestation alters sympathetic and baroreflex responses before and immediately after birth. Fetal sheep at 130-131 days gestation (term 145 days) were subjected to bilateral adrenalectomy before the normal prepartum increase in plasma cortisol levels. One group of fetuses (n = 5) received physiological cortisol replacement with a continuous infusion of hydrocortisone (2 mg x day(-1) x kg(-1) for 10 days), whereas the other group received 0.9% NaCl vehicle (n = 5). All animals underwent a second surgery 48 h before the study for placement of a renal nerve recording electrode. Heart rate (HR), mean arterial blood pressure (MABP), renal sympathetic nerve activity (RSNA), and baroreflex control of HR and RSNA were studied before and after cesarean section delivery. At the time of study (140-141 days gestation), fetal plasma cortisol concentration was undetectable in adrenalectomized (ADX) fetuses and 58 +/- 9 ng/ml in animals receiving cortisol replacement (ADX + F). Fetal and newborn MABP was significantly greater in ADX + F relative to ADX animals. One hour after delivery, MABP increased 13 +/- 3 mmHg and RSNA increased 91 +/- 12% above fetal values in ADX + F (both P < 0.05) but remained unchanged in ADX lambs. The midpoint pressures of the fetal HR and RSNA baroreflex function curves were significantly greater in ADX + F (54 +/- 3 and 56 +/- 3 mmHg for HR and RSNA curves, respectively) than ADX fetuses (45 +/- 2 and 46 +/- 3 mmHg). After delivery, the baroreflex curves reset toward higher pressure in ADX + F but not ADX lambs. These results suggest that adrenal glucocorticoids contribute to cardiovascular regulation in the late-gestation fetus and newborn by modulating arterial baroreflex function and sympathetic activity.

Maternal undernutrition in early gestation alters molecular regulation of the hypothalamic-pituitary-adrenal axis in the ovine fetus

We have demonstrated previously that plasma adrenocorticotropin hormone and cortisol responses to exogenous and endogenous stimuli are reduced in fetuses of mildly undernourished ewes. In the present study, we examined the molecular regulation of fetal hypothalamic-pituitary-adrenal (HPA) axis function at 127-130 days gestation (dGA) following 15% reduction in maternal nutrition between 0 and 70 dGA. Using in situ hybridization, we found that corticotropin releasing hormone (CRH) mRNA expression in the hypothalamic paraventricular nucleus (PVN) was lower in fetuses from nutrient restricted ewes than in controls. Restricted fetuses also had greater levels of mRNA encoding preproenkephalin (PENK) and magnocellular arginine vasopressin (AVP) in the PVN. Expression of oxytocin mRNA and parvocellular AVP mRNA in the PVN and pro-opiomelanocortin mRNA in the pituitary were unchanged. Glucocorticoid receptor mRNA expression was unaltered at the PVN, but was reduced (> 40%) in the anterior pituitary of restricted fetuses. Northern blot analysis demonstrated that levels of adrenal P450scc mRNA and P450(C17) mRNA were not different between the groups. We conclude that the reduction in HPA function reported previously is mediated, at least in part, by a decrease in expression of CRH mRNA and increase in PENK mRNA in the PVN.

Glucocorticoid programming of pituitary-adrenal function: mechanisms and physiological consequences

Increasing epidemiological evidence supports the notion that adverse events in fetal life permanently alter the structure and physiology of the adult offspring, a phenomenon dubbed 'fetal programming'. In particular, low weight or thinness at birth in humans is associated with an increased risk of cardiovascular and metabolic disorders as well as neuroendocrine dysfunction in adult life. Glucocorticoid administration during pregnancy is well-documented to both reduce offspring birth weight and alter the maturation of organs (hence their use to accelerate fetal lung maturation in premature labour). Here data are reviewed which show, in rodents and other models, that antenatal exposure to endogenous or exogenous glucocorticoids reduces offspring birth weight and produces permanent hypertension, hyperglycaemia, hyperinsulinaemia, altered behaviour and neuroendocrine responses throughout the lifespan. Processes underlying fetal programming include determination of the 'set point' of the hypothalamic-pituitary-adrenal (HPA) axis and of tissue glucocorticoid receptor (GR) expression. Similar HPA axis hyperreactivity occurs in lower birth weight humans and may be an early manifestation of the 'low birth weight' phenotype.

Antenatal glucocorticoids and the developing brain: mechanisms of action

Glucocorticoids are critical for normal brain development. There is no doubt that prenatal treatment with synthetic glucocorticoid affords great benefit to the preterm infant. However, animal studies, now carried out in many species, indicate that there may be some long-term physiological costs of early exposure to excess glucocorticoid, and that these appear sex-dependent. Further, the effects may not become apparent until later life. Given the dynamics of corticosteroid receptor systems in late gestation, it is likely that there are critical windows of development when specific regions of the brain are more sensitive to the influence of synthetic glucocorticoid. Once such windows have been identified it will be possible to target prenatal treatments, so as to maximize benefit and reduce risk of long-term effects. Notwithstanding, the data reviewed below indicate that caution should be exercised in the use of multiple course glucocorticoid therapy during pregnancy.