Prenatal Glucocorticoid Exposure Research Articles

Altered vascular contractility in adult female rats with hypertension programmed by prenatal glucocorticoid exposure

Excessive exposure to glucocorticoids during gestation reduces birth weight and induces permanent hypertension in adulthood. The mechanisms underlying this programmed elevation of blood pressure have not been established. We hypothesised that prenatal glucocorticoid exposure may lead to vascular dysfunction in adulthood. Pregnant rats received dexamethasone (Dex) (100 microg/kg, s.c.) or vehicle (control) daily throughout pregnancy. Blood pressure was elevated (students t-test, unpaired; P < 0.05) in adult female offspring (aged 12-16 weeks) of Dex-treated mothers (148.0 +/- 3.6 mmHg, n=10) compared with the control group (138.0 +/- 2.5 mmHg, n=8). Vascular responsiveness in aortae and mesenteric arteries was differentially affected by prenatal Dex: aortae were less responsive to angiotensin II, whereas mesenteric arteries were more responsive to norepinephrine, vasopressin and potassium (mesenteric arteries respond poorly to angiotensin II in vitro). Acetylcholine-mediated, endothelium-dependent relaxation was similar in both groups. Prenatal exposure to Dex had no effect on blood pressure or aldosterone response to acute (15 min, i.v.) infusion of angiotensin II (75 ng/kg per min). In contrast, chronic (2-week, s.c.) infusion of angiotensin II (100 ng/kg per min) produced a greater elevation (P < 0.05) of blood pressure in Dex-treated rats (150.0 +/- 3.6 mmHg) than in controls (135.3 +/- 5.4 mmHg), and aldosterone levels were higher in Dex-treated animals. There was no angiotensin II-induced medial hypertrophy/hyperplasia in mesenteric arteries from Dex-treated rats. These results indicate that vascular function is altered in a region-specific manner in rats with glucocorticoid-programmed hypertension. Despite a striking increase in mesenteric artery contraction in Dex-treated rats, in vivo studies suggest that abnormalities of the renin-angiotensin-aldosterone system, rather than enhanced vascular contractility, may be responsible for the elevation of blood pressure in these animals.

Prenatal glucocorticoid exposure affects learning and vulnerability of cholinergic neurons

Prenatal treatment with synthetic glucocorticoids is commonly used as a treatment for women at risk of preterm delivery. However, little is known about the life-long consequences of these treatments on the fetus. In the present study, we evaluated cognitive function as well as susceptibility of cholinergic neurons to 192IgG-saporin immunolesion in adult rats after prenatal glucocorticoid treatment. Morris water maze results revealed a significant difference in learning and memory function in adult rats that were prenatally exposed to dexamethasone, and further cognitive deficits after 192IgG-saporin exposure. Choline acetyl transferase activity was decreased in the cortex of dexamethasone-treated rats compared with controls. In addition, rats prenatally exposed to either dexa, or betamethasone revealed a dramatic decrease in choline acetyl transferase activity compared to control rats after 192IgG-saporin lesion. We report behavioral and biochemical evidence for altered cognitive function and increased susceptibility of cholinergic neurons to 192IgG-saporin in adult rats after prenatal glucocorticoid treatment. Taken together, these results suggest that prenatal treatment with dexamethasone could affect cognitive functions and render cholinergic neurons more vulnerable to challenges later in life.

Sex-Specific Effects of Prenatal Low-Protein and Carbenoxolone Exposure on Renal Angiotensin Receptor Expression in Rats

Experimental models have shown the developing cardiovascular and renal systems to be sensitive to mild shifts in maternal nutrition, leading to altered function and risk of disease in adult life. The offspring of Wistar rats fed a low-protein diet during pregnancy exhibit a reduced nephron number and hypertension in postnatal life, providing a useful tool to examine the mechanistic basis of programming. Evidence indicates that upregulation of the renin-angiotensin system plays an important role, in particular through receptor-mediated changes in angiotensin II activity. However, although programmed hypertension has proven dependent on maternal glucocorticoids, there appear to be conflicting effects of prenatal low-protein and glucocorticoid exposure on postnatal angiotensin receptor expression. This study aimed to resolve this issue by comparing the effects of low-protein and glucocorticoid exposures on postnatal nephron number and angiotensin receptor expression. In addition, this study examined the modulation of prenatal treatment effects by postnatal inhibition of type 1 angiotensin receptor. The data demonstrates that whereas prenatal low-protein and glucocorticoid exposure have a similar effect in reducing nephron number, there are age- and gender-related differences in their effects on postnatal angiotensin receptor expression. In addition, this study provides novel evidence of a substantial upregulation of type 2 angiotensin receptor expression in low-protein- and glucocorticoid-exposed female offspring at 20 weeks of age, with implications for subsequent renal remodeling and function. Despite being targeted to the postnephrogenic period, inhibition of type 1 angiotensin receptor had an inhibitory effect on renal and somatic growth, additionally indicating its unsuitability during early life.

Cognitive dysfunctions in children – to which extent is they caused by pre- and perinatal stress?

Attention Deficit and Hyperactivity Disorder (ADHD) is the most common neurodevelopmental disorder with prevalence around 5% and with behavioural problems within three domains: inattention, hyperactivity and impulsivity. Many attempts have been made to formulate a single theory of ADHD. Yet, little progress has been made towards elucidating its pathophysiology. Imbalance in the dopamine system is believed to influence cognitive functions, e.g. executive functions, working memory and motor functions, leading to the behavioural problems. Numerous studies in children with ADHD have demonstrated that psycho stimulants have a positive effect on the behaviour. A range of family, adoptation and twin studies has provided compelling evidence that genetic factors contribute to the expression of the ADHD symptoms. Molecular-genetic studies have shown polymorphism in several genes involved in dopamine transmission, e.g., D4 receptor and dopamine transporter. The reduced volume of several brain regions in children with ADHD, also indicate an early influence on brain development. However, there are also a number of studies reporting increased incidence of ADHD in preterm children and in children with perinatal complications, as well as after maternal smoking during pregnancy. Hence, there is indirect evidence that also perinatal factors may influence early brain development and later development of executive functions. The mechanisms of this prenatal programming of the immature brain are unknown. One plausible mechanism, induced by stress, could be via the glucocorticoids, which exert a wide spectrum of effects, ranging from sub cellular reorganisation to neurone-neurone and neurone-glia interaction. Based on rodent experiments, sustained elevation or reduction of these hormones during the foetal period can permanently modify brain structure and function. An important persisting abnormality following prenatal glucocorticoid exposure is reduced expression of glucocorticoid receptor and mineralocorticoid receptor mRNAs in the prefrontal cortex and hippocampus.

Prenatal glucocorticoid exposure and physiological programming of adult disease

Prenatal glucocorticoid exposure and physiological programming of adult disease

Glucocorticoid Programming

Epidemiological evidence suggests that an adverse fetal environment permanently programs physiology, leading to increased risks of cardiovascular, metabolic, and neuroendocrine disorders in adulthood. Prenatal glucocorticoid excess or stress might link fetal maturation and adult pathophysiology. In a variety of animal models, prenatal glucocorticoid exposure or inhibition of 11beta-hydroxysteroid dehydrogenase type 2 (11beta-HSD2), the fetoplacental "barrier" to maternal glucocorticoids, reduces birth weight and causes permanent hypertension, hyperglycemia, and increased hypothalamic-pituitary-adrenal axis (HPA) activity and behavior resembling anxiety. In humans, 11beta-HSD2 gene mutations cause low birth weight and reduced placental 11beta-HSD2 activity associated with intrauterine growth retardation. Low birth weight babies have higher plasma cortisol levels throughout adult life, indicating HPA programming. The molecular mechanisms may reflect permanent changes in the expression of specific transcription factors; key is the glucocorticoid receptor itself. Differential programming of the glucocorticoid receptor in different tissues reflects effects upon one or more of the multiple tissue-specific alternate first exons/promoters of the glucocorticoid receptor gene. Overall, the data suggest that either pharmacological or physiological exposure to excess glucocorticoids prenatally programs pathologies in adult life.

Prenatal glucocorticoid exposure and postnatal adaptation in premature newborn baboons ventilated for six days

Objective Renal and cardiovascular function is improved during the first 24 hours of life in preterm ventilated baboons exposed to prenatal betamethasone (BETA). We hypothesized BETA-induced effects would be sustained through day 6 of life. Study design Pregnant baboons received saline or BETA (6 mg) 48 and 24 hours before preterm delivery at 125 days' gestation. The newborn baboons were ventilated for 6 days, and assessed for renal, cardiovascular, and endocrine function. Results Mean arterial blood pressure (MAP) and glomerular filtration rate (GFR) values 24 hours after delivery were higher in the BETA group. Kidney Na, K-ATPase activity was higher in the BETA group by day 6. All other measures were similar in both groups by day 6. Conclusion Prenatal BETA exposure in the premature baboon: (1) increases MAP and GFR on day 1 without measurable effects by day 6 and (2) increases kidney Na, K-ATPase activity.

Prenatal glucocorticoid exposure alters hypothalamic-pituitary-adrenal function and blood pressure in mature male guinea pigs.

Pregnant guinea pigs were treated with dexamethasone (1 mg kg(-1)) or vehicle on days 40-41, 50-51 and 60-61 of gestation, after which animals delivered normally. Adult male offspring were catheterized at 145 days of age and subjected to tests of hypothalamic-pituitary-adrenal (HPA) axis function in basal and activated states. Animals exposed to dexamethasone in utero (mat-dex) exhibited increased hippocampus-to-brain weight ratio, increased adrenal-to-body weight ratio and increased mean arterial pressure. There were no effects on gestation length, birth weight and postnatal growth. There were no overall differences in diurnal plasma adrenocorticotropic hormone (ACTH) and cortisol profiles, though there were subtle differences during the subjective afternoon between control and mat-dex offspring. A significant decrease in initial ACTH suppression was observed following dexamethasone injection in mat-dex offspring compared to control offspring. Molecular analysis revealed significantly increased MR mRNA expression in the limbic system and particularly in the dentate gyrus in mat-dex offspring. In the anterior pituitary, both pro-opiomelanocortin (POMC) and glucocorticoid receptor (GR) mRNA levels were significantly elevated in mat-dex offspring. In conclusion, (1) repeated prenatal treatment with synthetic glucocorticoid (sGC) permanently programmes organ growth, blood pressure and HPA regulation in mature male offspring and these changes involve modification of corticosteroid receptor expression in the brain and pituitary; (2) the effects of prenatal sGC exposure on HPA function appear to change as a function of age, indicating the importance of investigating HPA and cardiovascular outcome at multiple time points throughout life.

Endocrine mechanisms of intrauterine programming.

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 cause tissue programming in utero. They are growth inhibitory and affect the development of all the tissues and organ systems most at risk of postnatal pathophysiology when fetal growth is impaired. Their concentrations in utero are also elevated by all the nutritional and other challenges known to have programming effects. Glucocorticoids act at cellular and molecular levels to alter cell function by changing the expression of receptors, enzymes, ion channels and transporters. They also alter various growth factors, cytoarchitectural proteins, binding proteins and components of the intracellular signalling pathways. Glucocorticoids act, directly, on genes and, indirectly, through changes in the bioavailability of other hormones. These glucocorticoid-induced endocrine changes may be transient or persist into postnatal life with consequences for tissue growth and development both before and after birth. In the long term, prenatal glucocorticoid exposure can permanently reset endocrine systems, such as the somatotrophic and hypothalamic-pituitary-adrenal axes, which, in turn, may contribute to the pathogenesis of adult disease. Endocrine changes may, therefore, be both the cause and the consequence of intrauterine programming.

Glucocorticoids and sex-dependent development of brain glucocorticoid and mineralocorticoid receptors.

We have previously shown that repeated antenatal synthetic glucocorticoid exposure has sex-specific effects on hypothalamic-pituitary-adrenal development in the fetal and adult guinea pig. However, little is known about the mechanisms that underlie these sex-specific outcomes. In the current study we demonstrated that glucocorticoid receptors (GR) and mineralocorticoid receptors (MR) exhibit sex differences in their temporal and spatial expression during fetal and early postnatal life. During development, we observed decreased GR mRNA in the paraventricular nucleus, decreased MR mRNA and MR protein in the hippocampus, and increased GR mRNA and GR protein in the hippocampus. We have also shown that on gestational d 50, maternally administered betamethasone (BETA) reduces fetal plasma ACTH and cortisol concentrations. BETA significantly affected hippocampal MR protein expression, and this effect was greatest in males. BETA was unable to autoregulate GR protein during fetal life, indicating that regulation of brain corticosteroid receptors is fundamentally different in fetal compared with adult life. The sex differences in the pattern of GR and MR expression during development may indicate different windows of vulnerability to prenatal glucocorticoid exposure in fetal life.

Effects of prenatal glucocorticoid exposure on cardiac calreticulin and calsequestrin protein expression during early development and in adulthood.

Overexpression of the conserved Ca(2+)-binding proteins calreticulin and calsequestrin impairs cardiac function, leading to premature death. Calreticulin is vital for embryonic development, but also impairs glucocorticoid action. Glucocorticoid overexposure during late fetal life causes intra-uterine growth retardation and programmed hypertension in adulthood. To determine whether intra-uterine growth retardation or programmed hypertension was associated with altered calreticulin or calsequestrin expression, effects of prenatal glucocorticoid overexposure (maternal dexamethasone treatment on days 15-21 of pregnancy) were examined during fetal life and postnatal development until adulthood (24 weeks). Dexamethasone (100 or 200 microg/kg of maternal body weight) was administered via osmotic pump. Calreticulin was detected as a 55 kDa band and calsequestrin as 55 and 63 kDa bands in 21 day fetal hearts. Only the 55 kDa calsequestrin band was detected postnatally. Prenatal glucocorticoid overexposure at the higher dose decreased calreticulin protein expression (26%; P <0.05) but increased calsequestrin protein expression, both 55 and 63 kDa bands, by 87% ( P <0.01) and 78% ( P <0.01); only the 55 kDa calsequestrin band was increased at the lower dose (66%; P <0.05). Offspring of dams treated at the lower dexamethasone dose were studied further. In control offspring, cardiac calreticulin protein expression declined between 2 and 3 weeks of age, and remained suppressed until adulthood. Cardiac calsequestrin protein expression increased 2-fold between fetal day 21 and postnatal day 1 and continued to increase until adulthood, at which time it was 3.4-fold higher ( P <0.001). Prenatal dexamethasone exposure minimally affected postnatal calsequestrin protein expression, but the postnatal decline in calreticulin protein expression was abrogated and calreticulin protein expression in adulthood was 2.2-fold increased ( P <0.001) compared with adult controls. In view of the known associations between cardiac calreticulin overexpression and impaired cardiac function, targeted up-regulation of calreticulin may contribute to the increased risk of adult heart disease introduced as a result of prenatal overexposure to glucocorticoids.

Repeated maternal glucocorticoid administration and the developing liver in fetal sheep.

Prenatal glucocorticoid exposure has been associated with a reduction in birth weight and postnatal alterations in glucose homeostasis and hypothalamic-pituitary-adrenal (HPA) axis function. The mechanisms underlying these responses are unknown, although changes in fetal hepatic development may play an important role. The fetal liver produces key regulators of fuel metabolism and of the developing HPA axis that are altered by glucocorticoids. The local availability of glucocorticoids is regulated, in part, by corticosteroid-binding protein (CBG), glucocorticoid receptors (GR) and by the enzyme 11beta-hydroxysteroid dehydrogenase (11betaHSD), but the effects of maternal glucocorticoid administration on the expression of these genes in the fetal liver are unknown. 11betaHSD1 is the predominant form of this enzyme present in the liver and is responsible for the conversion of cortisone to cortisol. To determine if prenatal glucocorticoid exposure alters fetal hepatic regulation of CBG, 11betaHSD1 and GRs, we treated pregnant ewes with betamethasone (0.5 mg/kg) intramuscularly at 104, 111 and 118 days of gestation (term 150 days). Animals were killed at 125 or 146 days of gestation. Maternal betamethasone administration did not alter mean cord plasma glucose but significantly decreased cord plasma insulin levels (P<0.05) at 125 days of gestation. At 146 days of gestation, cord plasma glucose levels were significantly increased without alterations in insulin levels following maternal betamethasone treatment (P<0.05). Maternal betamethasone administration resulted in a significant increase in fetal hepatic 11betaHSD1 mRNA and protein levels at 125 days of gestation (P<0.05). CBG mRNA levels were significantly elevated over control at 125 days although levels of CBG protein were not significantly different. GR protein levels were not statistically different at either 125 or 146 days of gestation following glucocorticoid administration. These data suggest that prenatal betamethasone exposure in the ovine fetus results in alterations in cord glucose and insulin levels as well as alterations in hepatic 11betaHSD1 mRNA and protein expression. These changes in 11betaHSD1 increase the potential to generate local cortisol from circulating cortisone. We speculate that this could affect expression of glucocorticoid-dependent hepatic enzymes involved with the regulation of glucose production and HPA responsiveness.

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∼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.

Is prenatal glucocorticoid administration another origin of adult disease?

1. The intra-uterine environment is now believed to play a major role in the origin of many adult diseases. Illnesses in which there is significant 'programming' before the time of birth include hypertension, diabetes, coronary heart disease and stroke. Acting on a genetic predisposition, intra-uterine triggers appear to programme the individual's metabolism and endocrine milieu and, after birth, these risk factors are then either amplified or minimized by environmental influences. The triggers operative during fetal life that have been studied most extensively are undernutrition and glucocorticoid exposure. 2. Over the past decade, a series of studies in sheep have focused on the perinatal and life-long consequences of glucocorticoid exposure in mid- to late-pregnancy. These studies in the sheep model have shown that maternal injections with glucocorticoids, in a manner similar to clinical treatment for women at risk of preterm birth, enhance fetal lung maturation, but were also associated with developmental and other functional alterations that are of concern. With weekly doses to the mother, there is restricted fetal growth, delayed myelination of the central nervous system, altered blood pressure soon after birth and increased insulin response to glucose challenge in early adulthood. If the glucocorticoids are given to the fetus by ultrasound-guided intramuscular injection, rather than to the mother, the effects on lung maturation are similar, but growth is spared and blood pressure after birth is unaltered. Increased insulin response to glucose challenge occurs in early adulthood with glucocorticoid by either route and is independent of growth restriction. 3. The findings in experimental animals are supported by studies of children in the Western Australian Preterm Infant Follow-up Study. Multivariate analyses have shown that increasing the number of glucocorticoid exposures, for the purpose of enhancing lung maturation prior to preterm birth, is associated with reduced birthweight and behavioural disorders at 3 years of age. 4. The results of these animal and clinical studies provide further support for a role of prenatal glucocorticoid exposure in triggering predisposition to adult disease. Further exploration of these models is expected to uncover the mechanisms and lead to effective strategies that may underpin clinical interventions.

Prenatal glucocorticoid exposure and risk for cerebral palsy among low birth weight children

Prenatal glucocorticoid exposure and risk for cerebral palsy among low birth weight children

Prenatal glucocorticoid exposure and risk for cerebral palsy among low birth weight children

Prenatal glucocorticoid exposure and risk for cerebral palsy among low birth weight children

Programming effects in sheep of prenatal growth restriction and glucocorticoid exposure.

Our aim was to determine the postnatal effects of single and repeated glucocorticoid injections during late gestation. Repeated (104, 111, 118, 125 days) or single (104 days) injections of betamethasone or saline were given to the ewe or by ultrasound guided injection to the fetus (term 150 days). Lambs were born spontaneously and studied at 3 and 6 mo and 1 yr of age. Arterial pressure was measured at each age, and we performed intravenous glucose tolerance tests at 6 mo and 1 yr. Repeated maternal, but not single maternal or fetal, betamethasone injections prolonged gestation, reduced weight at birth and 3 mo, and was associated with low arterial pressure at 3 mo but not at 6 mo and 1 yr. Glucose metabolism was altered in all betamethasone treatment groups, regardless of the number or route of injections. Our data demonstrate that glucocorticoid-induced fetal growth restriction is associated with a transient reduction in postnatal arterial pressure, but glucocorticoid exposure with or without growth restriction alters glucose metabolism.

Prenatal glucocorticoid programming of brain corticosteroid receptors and corticotrophin-releasing hormone: possible implications for behaviour.

Glucocorticoids may underlie the association between low birth weight and adult disorders such as hypertension, type 2 diabetes and affective dysfunction. We investigated the behavioural and molecular consequences of two paradigms of prenatal dexamethasone administration in rats. Rats received dexamethasone (100 microg/kg per day) throughout pregnancy (DEX1-3), in the last third of pregnancy only (DEX3) or vehicle. Both dexamethasone treatments reduced birth weight, only DEX1-3 offspring had reduced body weight in adulthood. In adult offspring, both prenatal dexamethasone paradigms reduced exploratory behaviour in an open field. In contrast, only DEX3 reduced exploration in an elevated plus-maze and impaired behavioural responses and learning in a forced-swim test. This behavioural inhibition may reflect increased baseline corticotrophin-releasing hormone mRNA levels (30% higher) in the central nucleus of the amygdala in both dexamethasone-exposed groups. Adult DEX3 offspring also showed increased corticotrophin-releasing hormone mRNA with unaltered glucocorticoid receptor mRNA in the hypothalamic paraventricular nucleus and reduced hippocampal glucocorticoid- and mineralocorticoid receptor mRNA expression, suggesting reduced hippocampal sensitivity to glucocorticoid suppression of the stress axis. In contrast, DEX1-3 rats had no changes in hippocampal corticosteroid receptors, but showed increased mRNA levels for both receptors in the basolateral nucleus of the amygdala. From this data we suggest that prenatal glucocorticoid exposure programs behavioural inhibition perhaps via increased amygdalar corticotrophin-releasing hormone levels, while DEX3 also impairs coping and learning in aversive situations, possibly via altered hippocampal corticosteroid receptor levels. Overexposure to glucocorticoids, especially late in gestation, may explain the link between reduced early growth and adult affective dysfunction.

Prenatal Glucocorticoid Modifies Hypothalamo-Pituitary-Adrenal Regulation in Prepubertal Guinea Pigs

We hypothesized that exposure to synthetic glucocorticoid during rapid brain growth (d50–52, birth = 68 days) in fetal guinea pigs modifies hypothalamo-pituitary-adrenal (HPA) function after birth, and that this involves changes in central corticosteroid receptor regulation. On the basis of our previous studies, we proposed that this effect is sex-specific. Pregnant guinea pigs were treated with dexamethasone (1 mg/kg) or vehicle on d50–51 of gestation, and juvenile offspring were euthanized at rest or following isolation stress on postnatal day 18. Dexamethasone increased the length of gestation (1.5 days) and altered body and organ (brain, heart, adrenal) growth. Resting plasma cortisol concentrations were significantly elevated in young male, but not female guinea pigs exposed to dexamethasone as fetuses. In female offspring born to dexamethasone-treated mothers, cortisol responses to isolation stress were attenuated. In males, elevated basal cortisol levels were not increased further by isolation. In the brain, hippocampal glucocorticoid receptor (GR) mRNA levels were significantly lower (10–25%) in females exposed to dexamethasone in utero. In contrast, GR mRNA levels were elevated (10–20%) in males from this prenatal treatment group. Mineralocorticoid receptor mRNA in the limbic system and GR mRNA levels in the pars distalis were unaffected. Pro-opiomelanocortin mRNA was significantly lower (30%) in the male pars intermedia following dexamethasone exposure. In conclusion, prenatal glucocorticoid exposure affects growth and HPA function as well as limbic and hypothalamic GR expression in juvenile offspring, and these effects are highly sex-specific.

5′-Heterogeneity of Glucocorticoid Receptor Messenger RNA Is Tissue Specific: Differential Regulation of Variant Transcripts by Early-Life Events

Glucocorticoid receptor (GR) gene expression is regulated in a complex tissue-specific manner, notably by early-life environmental events that program tissue GR levels. We have identified and characterized several new rat GR mRNAs. All encode a common protein, but differ in their 5'-leader sequences as a consequence of alternate splicing of, potentially, 11 different exon 1 sequences. Most are located in a 3-kb CpG island, upstream of exon 2, that exhibits substantial promoter activity in transfected cells. Ribonuclease (RNase) protection analysis demonstrated significant levels of six alternate exons 1 in vivo in rat, with differences between liver, hippocampus, and thymus reflecting tissue-specific differences in promoter activity. Two of the alternate exons 1 (exons 1(6) and 1(10)) were expressed in all tissues examined, together present in 77-87% of total GR mRNA. The remaining GR transcripts contained tissue-specific alternate first exons. Importantly, tissue-specific first exon usage was altered by perinatal environmental manipulations. Postnatal handling, which permanently increases GR in the hippocampus, causing attenuation of stress responses, selectively elevated GR mRNA containing the hippocampus-specific exon 1(7). Prenatal glucocorticoid exposure, which increases hepatic GR expression and produces adult hyperglycemia, decreased the proportion of hepatic GR mRNA containing the predominant exon 1(10), suggesting an increase in a minor exon 1 variant. Such tissue specificity of promoter usage allows differential GR regulation and programming.