Gestational hypoxia alone or combined with restraint sensitizes the hypothalamic–pituitary–adrenal axis and induces anxiety-like behavior in adult male rat offspring

We have reported that hypoxia affects the hypothalamic–pituitary–adrenal (HPA) axis and behavior by driving the expression of central corticotropin-releasing hormone (CRH) and its receptors in adult mammals, and this effect is modulated by other factors. Here, we address whether or not intermittent hypoxia (IH) or restraint (R) or a combination of both (IH+R) during gestation would result in differential alteration of the HPA axis and behavior of the adult male offspring. Gravid rats were exposed to IH in a hypobaric chamber (10.8% O₂, altitude of 5 km), R, or both, daily for 4 h for 21 days. Control parameters were set at sea level (20.9% O₂). All the stressors significantly and differentially increased CRH and corticotropin-releasing factor receptor type 1 (CRHR1) expression but decreased corticotropin-releasing factor receptor type 2 (CRHR2) in the paraventricular nucleus of the hypothalamus (PVN), enhanced CRHR1 mRNA and CRHR2 mRNA expression in the anterior pituitary, and increased plasma adrenocorticotropic hormone (ACTH) and corticosterone (CORT) levels and adrenal weight in adult male offspring aged 120 days. Furthermore, norepinephrine (NE) and dopamine (DA) levels significantly increased in the locus coeruleus (LC), while the percentage of entries into the open arms of the elevated-plus maze test (EPM) markedly declined. In all the above effects, the combination-induced effect was stronger than each stressor alone. Confocal imaging showed a rich colocalization of CRHR1 with CRH or urocortin I (Ucn I), and CRHR2 with CRH or urocortin III (Ucn III) in the PVN, and CRHR1 with CRH in the LC in EPM-tested groups. In conclusion, IH or R alone or both in combination during gestation sensitize the HPA axis and induce anxiety-like behavior of the adult male offspring, and the combined effects are significantly great than IH or R alone. The CRH-NE neural circuit between the PVN and LC through CRH receptor driving might partly be involved in the effects. The differential colocalization of CRH with CRHR1 might be the neural basis of these effects.     

Corticotropin releasing hormone and proopiomelanocortin involvement in the cutaneous response to stress

The skin is a known target organ for the proopiomelanocortin (POMC)-derived neuropeptides alpha-melanocyte stimulating hormone (alpha-MSH), beta-endorphin, and ACTH and also a source of these peptides. Skin expression levels of the POMC gene and POMC/corticotropin releasing hormone (CRH) peptides are not static but are determined by such factors as the physiological changes associated with hair cycle (highest in anagen phase), ultraviolet radiation (UVR) exposure, immune cytokine release, or the presence of cutaneous pathology. Among the cytokines, the proinflammatory interleukin-1 produces important upregulation of cutaneous levels of POMC mRNA, POMC peptides, and MSH receptors; UVR also stimulates expression of all the components of the CRH/POMC system including expression of the corresponding receptors. Molecular characterization of the cutaneous POMC gene shows mRNA forms similar to those found in the pituitary, which are expressed together with shorter variants. The receptors for POMC peptides expressed in the skin are functional and include MC1, MC5 and mu-opiate, although most predominant are those of the MC1 class recognizing MSH and ACTH. Receptors for CRH are also present in the skin. Because expression of, for example, the MC1 receptor is stimulated in a similar dose-dependent manner by UVR, cytokines, MSH peptides or melanin precursors, actions of the ligand peptides represent a stochastic (predictable) nonspecific response to environmental/endogenous stresses. The powerful effects of POMC peptides and probably CRH on the skin pigmentary, immune, and adnexal systems are consistent with stress-neutralizing activity addressed at maintaining skin integrity to restrict disruptions of internal homeostasis. Hence, cutaneous expression of the CRH/POMC system is highly organized, encoding mediators and receptors similar to the hypothalamic-pituitary-adrenal (HPA) axis. This CRH/POMC skin system appears to generate a function analogous to the HPA axis, that in the skin is expressed as a highly localized response which neutralizes noxious stimuli and attendant immune reactions.     

Hypothalamus-pituitary-adrenal modifications consequent to chronic stress exposure in an experimental model of depression in rats

The modifications in the hypothalamus-pituitary-adrenal (HPA) axis function induced by repeated unavoidable stress exposure, according to a standardized procedure used for inducing an experimental model of depression, were studied. Rats exposed to this procedure show hyporeactivity to both pleasurable and aversive stimuli and this condition is antagonized by the repeated administration of classical antidepressant drugs. We also studied whether imipramine administration during stress exposure would interfere with the possible modifications in the HPA axis. Rats were exposed to a 4-week stress procedure with and without imipramine treatment and then tested for escape, as compared with non-stressed control animals. Twenty-four hours later all rats were bled through a tail nick for plasma corticosterone measurement before and after dexamethasone (10 microg/kg) or corticotropin-releasing hormone (CRH, 1 microg/kg) administration. Rats were then killed, adrenals and thymus weighed, brain areas dissected out and frozen for glucocorticoid receptors (GRs) and corticotropin-releasing hormone receptor 1 (CRHR1) immunoblotting and for the assessment of hypothalamic corticotropin-releasing hormone levels. RESULTS: Rats exposed to a 4-week unavoidable stress showed escape deficit and their basal plasma corticosterone levels were higher than those of control animals. Moreover, they had decreased response to dexamethasone administration, adrenal hypertrophy, and decreased GR expression in the hippocampus, hypothalamus, medial prefrontal cortex and pituitary. No significant modifications in CRHR1 expression were observed in the pituitary nor in different discrete brain areas. CRH levels in the hypothalamus and the plasma corticosterone response to CRH administration were found to be higher in stressed rats than in controls. Imipramine treatment offset all the behavioral and neurochemical stress-induced modifications. In conclusion, the present results strengthen the assumption that the escape/avoidance behavioral deficit induced by inescapable stress exposure is accompanied by steadily increased HPA activity, and that imipramine effect is strongly related to a normalization of HPA axis activity.     

Hypothalamo-pituitary-adrenocortical dysregulation in aging F344/Brown-Norway F1 hybrid rats

Hypothalamo-pituitary-adrenocortical (HPA) axis aging was studied in young (3 mo), middle aged (15 mo) and aged (30 mo) F344/Brown Norway hybrid rats. This strain was selected to obviate HPA-relevant pathologies found in other aging models. Aged, unstressed rats showed enhanced central HPA drive, marked by elevated ACTH release and decreased pituitary proopiomelanocortin and corticotropin-releasing factor receptor 1 (CRH-R1) mRNAs. Acute corticosterone responses to spatial novelty were exacerbated in aged rats; however, responses to restraint or hypoxia were not affected. Chronic stress exposure also differentially increased HPA drive in aged animals, marked by elevated paraventricular nucleus CRH peptide levels and pituitary proopiomelanocortin mRNA. Plasma ACTH and pituitary POMC and CRH-R1 mRNA expression in middle-aged rats were intermediate those of young and aged animals. Middle-aged animals responded to chronic stress with disproportionate increases in CRH mRNA levels, and increased corticosterone secretion following hypoxia but not novelty. The results suggest a gradual increase in HPA tone across the aging process, culminating in marked hyperresponsivity to both acute and chronic stress in senescence.     

Chronic subcutaneous leptin infusion diminishes the responsiveness of the hypothalamic-pituitary-adrenal (HPA) axis in female rhesus monkeys

The fat derived protein leptin has its anorexic action through a number of neuropeptides including an upregulation of corticotropin releasing hormone (CRH) expression in the hypothalamus. However, the influence of leptin on these neuropeptides may be different during stress. The present study used ovariectomized female rhesus monkeys (n=8) to further define the effect of leptin on HPA responsivity. To accomplish this, we assessed the effects of constant leptin infusion on cortisol and ACTH secretion in both a predictable and unpredictable situation as well as in response to dexamethasone suppression-CRH stimulation test. We hypothesized that leptin would attenuate the increase in cortisol and ACTH to a novel, unpredictable situation and would enhance glucocorticoid negative feedback and diminish the response to CRH. Animals were assessed under control placebo conditions and during a 28 day infusion with recombinant human leptin (6 microg/kg/day, SC). Within each treatment condition, HPA responsivity was assessed during no estradiol replacement and acute estradiol replacement that produced serum concentrations of approximately 40 pg/ml. However, the results indicated that neither estradiol alone or in combination with leptin had any consistent effect on the outcome measures. Compared to the control condition, leptin had no effect on the cortisol diurnal rhythm; however, evening but not morning plasma ACTH concentrations were significantly lower during leptin infusion. In contrast, the response in plasma cortisol and ACTH to an unpredictable situation was significantly attenuated by chronic leptin infusion. Furthermore, leptin enhanced glucocorticoid negative feedback and blunted CRH-induced increase in both cortisol and ACTH. Taken together, these data suggest that in the female monkey, leptin has little effect on basal cortisol. However, when the HPA axis is activated, leptin attenuates the neuroendocrine response by enhancing glucocorticoid negative feedback. These data underscore the potential importance of leptin in maintaining homeostasis through its diverse interaction with the HPA axis.     

Association study of corticotropin-releasing hormone receptor1 gene polymorphisms and antidepressant response in major depressive disorders

Hypothalamic-pituitary-adrenal (HPA) axis appears to play a key role in the pathogenesis of major depressive disorders (MDD). Treatment of certain selective serotonin reuptake inhibitors (SSRIs) has been shown to reduce the activity of corticotropin-releasing hormone (CRH) neurons and may contribute to their therapeutic action. It has been proposed that the downregulation of CRH activity is final and common step of antidepressant treatment. In this study, we tested whether the polymorphisms of three sites (rs1876828, rs242939 and rs242941) in corticotropin-releasing hormone receptor1 (CRHR1) gene are related to 6 weeks fluoxetine antidepressant effect in 127 Han Chinese patients with MDD. The results show that the rs242941 G/G genotype and homozygous GAG haplotype of the three single-nucleotide polymorphisms (SNPs) are associated with fluoxetine therapeutic response in MDD patients of high-anxiety (HA). The results support the idea that the CRHR1 gene is likely to be involved in the antidepressant response in MDD.     

Effects of treadmill exercise on hypoactivity of the hypothalamo-pituitary-adrenal axis induced by chronic administration of corticosterone in rats

The stress response alters behavior, autonomic function and secretion of multiple hormones, including CRF, ACTH, and glucocorticoid, through the HPA axis. Consecutive stress exposures lead to HPA axis dysregulation such as hyperactivity in Alzheimer's disease and depression, and hypoactivity in post-traumatic stress disorder. In the present study, we established a model of hypoactivated HPA axis in rat through chronic administration of corticosterone (40 mg/kg, s.c.) for 19 consecutive days. In this model, CRF mRNA expression in the hypothalamus and ACTH levels in serum were significantly decreased by chronic administration of corticosterone. In addition, the effect of treadmill exercise was investigated in our hypoactivated HPA axis rat model. Treadmill exercise recovered the dysregulated hypoactivity of the HPA axis induced by corticosterone administration for 19 days. The results of the present study suggest that treadmill exercise may aid recovery of hypoactivated HPA axis dysregulation in psychological diseases such as post-traumatic stress disorder.     

Anxiety-like behavior in the elevated-plus maze tests and enhanced IL-1β, IL-6, NADPH oxidase-1, and iNOS mRNAs in the hippocampus during early stage of adjuvant arthritis in rats

We studied anxiety-like behavior in the elevated plus-maze (EPM) tests in male Lewis rats on days 2 and 4 of adjuvant arthritis (AA). In plasma we analyzed C-reactive protein (CRP), albumin, ACTH, corticosterone, in the hippocampus the mRNA expression of interleukin-1β (IL-1β), interleukin-6 (IL-6), corticotrophin releasing factor (CRH), NADPH oxidases NOX1 and NOX2, and inducible NO-synthase (iNOS). EPM tests showed a higher anxiety index in AA rats on days 2 and 4 and reduction of total entries. On days 2 and 4 we found reduced plasma albumin, enhanced CRP, ACTH and corticosterone, and in the hippocampus enhanced mRNA for NOX1 and IL-1β in AA rats, on day 4 we found enhanced mRNAs for iNOS and IL-6, and reduced mRNA for CRH. The mRNA for NOX2 did not change on any experimental day. These results suggest enhanced anxiety, as well as locomotor impairment during the early phase of AA that correlate with enhanced mRNA expressions of parameters of oxidative stress NOX1, iNOS, and inflammatory cytokines IL-1β and IL-6 in the hippocampus.     

The effect of confinement during lactation on the hypothalamic-pituitary-adrenal axis and behaviour of primiparous sows

Commercial sows are typically confined in crates before and during parturition and remain there throughout lactation. In various animal species including non-lactating pigs, confinement over similar periods leads to adaptive changes in the HPA axis, consistent with chronic stress. To investigate evidence for chronic stress in lactating sows, primiparous sows (gilts) were kept in behaviourally confining crates with straw bedding (CS, n = 8) or without bedding (C, n = 8) or in larger strawed pens (PS, n = 16) between 5 days before parturition until 29 days postpartum (piglets were weaned on day 28). Behavioural and physiological recordings (Plasma ACTH and cortisol) were taken at intervals (baseline), and CRH injections were given on five occasions (days 2, 8, 15, 22 and 29 postpartum). The PS gilts spent more time in substrate-directed behaviour and lying ventrally, and less time lying laterally and sitting than the two crated treatments (C and CS) throughout lactation. Baseline plasma ACTH and cortisol levels showed no treatment differences, although we confirmed that a diurnal pattern exists, with morning (1000 h) cortisol being higher than later in the day. CRH challenge tests suggested changes in the HPA axis, consistent with chronic stress, by the end of the lactation period. Cortisol response to CRH tended to be higher in CS than PS across all days, and by day 29 cortisol response to CRH was significantly higher in CS compared to PS and tended to be higher in C than PS. Cortisol/ACTH ratio following CRH challenge also tended to be higher in the crate treatments (C and CS) by day 29. These data suggest that prolonged confinement in farrowing crates may have a negative impact on sow welfare.     

Association of CRHR1 and CRHR2 with major depressive disorder and panic disorder in a Japanese population

Major depressive disorder (MDD) and panic disorder (PD) are common and disabling medical disorders with stress and genetic components. Dysregulation of the stress response of the hypothalamic-pituitary-adrenal axis, including the corticotrophin-releasing hormone (CRH) signaling via primary receptors (CRHR1 and CRHR2), is considered to play a major role for onset and recurrence in MDD and PD. To confirm the association of CRHR1 and CRHR2 with MDD and PD, we investigated 12 single nucleotide polymorphisms (SNPs) (rs4076452, rs7209436, rs110402, rs242924, rs242940, and rs173365 for CRHR1 and rs4722999, rs3779250, rs2267710, rs1076292, rs2284217, and rs226771 for CRHR2) in MDD patients (n = 173), PD patients (n = 180), and healthy controls (n = 285). The SNP rs110402 and rs242924 in the CRHR1 gene and the rs3779250 in the CRHR2 gene were associated with MDD. The SNP rs242924 in the CRHR1 gene was also associated with PD. The T-A-T-G-G haplotype consisting of rs7209436 and rs173365 in CRHR1 was positively associated with MDD. The T-A haplotype consisting of rs7209436 and rs110402 in CRHR1 was positively associated with MDD. The C-C haplotype consisting of rs4722999 and rs37790 in CRHR1 was associated with PD. These results provide support for an association of CRHR1 and CRHR2 with MDD and PD.     

Effect of naloxone-precipitated morphine withdrawal on CRH and vasopressin mRNA expression in the rat hypothalamic paraventricular nucleus

Morphine withdrawal is characterized by an increase in the hypothalamus-pituitary-adrenocortical (HPA) axis activity. Here, by means of in situ hybridization, the changes in CRH and vasopressin (AVP) mRNAs have been analysed within the rat hypothalamic paraventricular nucleus (PVN) during morphine dependence and after naloxone-precipitated morphine withdrawal. CRH and AVP mRNA expression were analysed 30 min following administration of saline or naloxone to control groups and to morphine dependent rats. The data for in situ hybridization analysis of PVN neurons show that there were no changes in the total size of labelled area for CRH or AVP mRNA during morphine withdrawal, indicating that dependence on morphine does not involve alterations in the number of neurons expressing CRH or AVP mRNA. However, levels of mRNA encoding for CRH were decreased in the PVN during morphine dependence and withdrawal. By contrast, injection of saline or naloxone to morphine dependent rats did not affect the intensity of AVM mRNA expression. All these findings are discussed in term of cellular events that couple morphine dependence-increased HPA axis activity with changes in gene expression in selective neurons of the PVN.     

Periodic maternal deprivation induces gender-dependent alterations in behavioral and neuroendocrine responses to emotional stress in adult rats.

There is evidence that stressful events during the neonatal "stress hyporesponsive period" may influence both emotional behavior and the maturation of the hypothalamic-pituitary-adrenal (HPA) axis in rats. We tested whether periodic maternal deprivation (180 min daily on postnatal days 3-10, PMD) caused chronic changes in emotional behavior and HPA axis activity in either male or female adult rats, or both. In addition, HPA secretory responses to human/rat corticotropin-releasing factor (CRH, 50 ng/kg i.v.) were determined in the adult males. In the elevated plus-maze test, adult (4-5 months of age) PMD-treated animals of both sexes displayed increased anxiety-related behavior compared to control rats. This was indicated by a reduction in the number of entries (male: 70% reduction, p < 0.01; female: 31% reduction, p < 0.01) and amount of time spent on the open arms (male: 86% reduction, p < 0.01; female: 40% reduction, NS). Neuroendocrine parameters were also altered in PMD-treated rats in a gender-dependent manner. Whereas basal plasma adrenocorticotropin (ACTH) and corticosterone levels did not differ significantly between PMD and control groups of either sex, the ACTH response to elevated plus-maze exposure, a predominantly emotional stressor, was higher in male (p < 0.01), but not female, PMD animals than in the respective controls. In contrast, PMD had no effect on behavioral (duration of struggling) or HPA axis responses to forced swimming (90 s, 19 degrees C), a complex and predominantly physical stressor, in either male or female rats. In response to CRH stimulation, PMD-treated males did not show differences in the ACTH secretion compared to controls, indicating alterations in HPA axis regulation at a suprapituitary level. Thus, PMD caused long-term changes in the emotional behavior of adult rats of both sexes, although to a differing degree in males and females, whereas it appeared to cause predominantly alterations in the HPA axis response in males, depending on the characteristics of the stressor used.     

Gene‐based SNP genetic association study of the corticotropin‐releasing hormone receptor‐2 (CRHR2) in major depression

An increasing amount of data suggests that affective disorders are related to dysregulation of the hypothalamic‐pituitary‐adrenal (HPA) axis, the stress‐response system. Corticotropin‐releasing hormone receptor‐2 (CRHR2)‐deficient mice display a stress‐sensitive and anxiety‐like phenotype suggesting that the CRHR2 is a plausible functional candidate gene influencing the reactivity of the HPA axis and therefore the liability to develop affective disorders. In this study, a gene‐based single nucleotide polymorphism (SNP) map of the corticotropin‐releasing hormone receptor 2 (CRHR2) was constructed containing one synonymous cSNP in exon 10, two intronic SNPs, and two SNPs in the 5′ upstream regulatory region. No significant difference in allele or genotype frequency was found for four out of the five SNPs between Belgian unipolar (UP) patients and age‐, gender‐, and ethnicity‐matched controls. The cSNP did show allelic and genotypic association with borderline significance (P = 0.04). However, a replication study of this cSNP in a bipolar sample of Belgian origin and a Swedish UP sample did not show significant differences in allele and genotype frequencies. © 2002 Wiley‐Liss, Inc.     

Antenatal glucocorticoids blunt the functioning of the hypothalamic-pituitary-adrenal axis of neonates and disturb some behaviors in juveniles

Antenatal glucocorticoids are highly effective in preventing respiratory distress of premature babies but can induce physiological and behavioral disturbances in young infants as well as in animals. Therefore, the hypothalamic-pituitary-adrenal (HPA) axis of rat neonates, and the consequences on behavioral development of offspring have been studied after five antenatal injections of dexamethasone (DEX) or vehicle. DEX decreased offspring body weight at birth, and significantly delayed the normal growth for the first 3 weeks of life. This paralleled diminished behavioral performances measured on postnatal day 3 (righting reflex) and postnatal day 10 (grasping test). Circulating levels of adrenocorticotrophin (ACTH) and corticosterone were significantly decreased on postnatal day 1 and this was related to a diminution of HPA axis activity shown by the decrease of central expression of corticotropin releasing hormone (CRH) mRNA, immunoreactive content in paraventricular neurons (PVN) and in the median eminence endings were significantly decreased. On the other hand, expression of another secretagogue of ACTH, arginine vasopressin (AVP), was differently affected in the PVN parvocellular neurons of offspring of the DEX group since AVP mRNA increased whereas immunoreactive content of the PVN parvocellular neurons was lowered. Simultaneously, the co-production of AVP and CRH in PVN neurons was stimulated. This can support the view that antenatal DEX reached the fetus and produced some damage which did not parallel that induced by prenatal stress of the pregnant females, especially the low body weight of offspring. The harmful consequence of antenatal DEX treatment was not restrictively due to the blunting of the HPA axis but also to the low body weight, which disturbed behavioral performances for the first weeks of life and could participate in other disorders in adult life.     

Erratum: Association of CRHR1 and CRHR2 with major depressive disorder and panic disorder in a Japanese population

Major depressive disorder (MDD) and panic disorder (PD) are common and disabling medical disorders with stress and genetic components. Dysregulation of the stress response of the hypothalamic–pituitary–adrenal axis, including the corticotrophin‐releasing hormone (CRH) signaling via primary receptors (CRHR1 and CRHR2), is considered to play a major role for onset and recurrence in MDD and PD. To confirm the association of CRHR1 and CRHR2 with MDD and PD, we investigated 12 single nucleotide polymorphisms (SNPs) (rs4076452, rs7209436, rs110402, rs242924, rs242940, and rs173365 for CRHR1 and rs4722999, rs3779250, rs2267710, rs1076292, rs2284217, and rs226771 for CRHR2) in MDD patients (n = 173), PD patients (n = 180), and healthy controls (n = 285). The SNP rs110402 and rs242924 in the CRHR1 gene and the rs3779250 in the CRHR2 gene were associated with MDD. The SNP rs242924 in the CRHR1 gene was also associated with PD. The T–A–T–G–G haplotype consisting of rs7209436 and rs173365 in CRHR1 was positively associated with MDD. The T–A haplotype consisting of rs7209436 and rs110402 in CRHR1 was positively associated with MDD. The C–C haplotype consisting of rs4722999 and rs3779250 in CRHR2 was associated with PD. These results provide support for an association of CRHR1 and CRHR2 with MDD and PD. © 2012 Wiley Periodicals, Inc.     

Corticotropin-releasing hormone receptor 1 coexists with endothelin-1 and modulates its mRNA expression and release in rat paraventricular nucleus during hypoxia

To determine whether corticotropin-releasing hormone receptor 1 (CRHR1) coexists with endothelin-1 (ET-1) in rat paraventricular nucleus (PVN), ET-1 expression and its regulation by CRH and CRHR1 under hypoxia, rats were exposed to simulated continuous hypoxia at 5 km altitude (CH5km, equal to 10.8% O(2)) in a hypobaric chamber for 1, 2, 5, 10, 15 or 25 days. ET-1, CRH, and its mRNA were measured using radioimmunoassay (RIA), immunohistochemistry, and in situ hybridization. The coexistence of ET-1 and CRHR1 was identified by confocal immunofluorescence. The results showed that CH5km caused a significant decrease of ET-1 level in PVN at 5 days, but decreased CRH on days 1 and 2 while it increased on days 5 and 10. CH5km induced ET-1 mRNA upregulation and ET-1 decrease at 5 days, the effects were completely reversed by treatment with five-daily-injections of a CRHR1 antagonist (butyl-[2,5-dimethyl-7-(2,4,6-trimethylphenyl)-7H-pyrrolo[2,3-d] pyrimidin-4-yl]-ethylamine: CP-154,526). Also, this treatment significantly reversed the CH5km-induced increase in CRH and CRHmRNA in PVN at 5 days. Moreover we found that the changes in expression of ET-1 and CRHR1 induced by CH5km were co-localized in parvocellular PVN cells. In conclusion, CRHR1 coexists with ET-1 in parvocellular PVN, continuous hypoxia stimulates ET-1 and ET-1mRNA as well as CRH and CRHmRNA, and CRHR1 evidently modulates ET-1 release and ET-1mRNA activation caused by continuous hypoxia.     

Estrogen modifies stress response of catecholamine biosynthetic enzyme genes and cardiovascular system in ovariectomized female rats

Estrogen is likely involved in the gender specific differences in coping with stress. Activation of catecholamine (CA) biosynthetic enzyme gene expression in central and peripheral CA systems plays a key role in response to stress and in regulation of the cardiovascular system. Here we examined whether estradiol can modulate response of hypothalamic-pituitary-adrenal axis (HPA), gene expression of enzymes related to CA biosynthesis in several noradrenergic locations, tetrahydrobiopterin (BH4) concentration and blood pressure (BP) in response to immobilization stress (IMO) of ovariectomized female rats. Rats were injected with 25 mug/kg estradiol benzoate (EB) or sesame oil once daily for 16 days and subsequently exposed to two hours of IMO. The IMO triggered elevation in plasma ACTH was lessened in EB-pretreated animals. However, estradiol did not alter the IMO-elicited rise of tyrosine hydroxylase mRNA levels in adrenal medulla (AM) and in the nucleus of solitary track (NTS) compared with controls. The response of GTP cyclohydrolase I (GTPCH) mRNA in AM to IMO was also similar in both groups. Several responses to IMO in EB-treated rats were reversed. Instead of IMO-elicited elevation in dopamine beta-hydroxylase mRNA levels in the locus coeruleus, GTPCH mRNA and BH4 levels in the NTS, they were reduced by IMO. In a parallel experiment, BP was monitored during restraint stress. The elevation of BP in response to single or repeated restraint stress was sustained during 2 h in controls and reduced after 70 min stress in EB treated rats. One month after withdrawal of EB treatment, the BP response to restraint was similar to that of rats which never received EB. The results demonstrate that estrogen can modulate responses to stress affecting HPA axis, CA biosynthesis, in central and peripheral noradrenergic systems, and BP.     

Effect of maternal nutrient restriction in early gestation on responses of the hypothalamic-pituitary-adrenal axis to acute isocapnic hypoxaemia in late gestation fetal sheep

Epidemiological and experimental evidence suggests that maternal undernutrition during pregnancy may alter development of fetal organ systems. We have demonstrated previously that fetal hypothalamic-pituitary-adrenal (HPA) axis responses to exogenous corticotropin-releasing hormone (CRH) + arginine vasopressin (AVP), or adrenocorticotrophin hormone (ACTH), are reduced in fetuses of mildly undernourished ewes. To examine these effects further we tested HPA axis responses to acute isocapnic hypoxaemia in fetal sheep at 114-129 days gestation (dGA), following 15% reduction in maternal nutritional intake between 0 and 70 dGA. Fetuses from control (C) and nutrient-restricted (R) ewes were chronically catheterised and plasma ACTH and cortisol responses were determined at 114-115, 120-123 and 126-129 dGA during hypoxaemia (1 h) induced by lowering the maternal inspired O2 fraction (FI,O2). Basal plasma cortisol concentrations and HPA axis responses at 114-115 and 120-123 dGA did not differ between C and R fetuses. At 126-129 dGA, both plasma ACTH (P < 0.01) and cortisol (P < 0.05) responses were smaller in R fetuses compared to C fetuses. Fetal blood gas status, fetal body weight, body proportions and organ weights did not differ between the groups. We conclude that mild maternal undernutrition alters development of the fetal HPA axis producing a reduction in pituitary and adrenal responsiveness to endogenous stimuli.