Development of the ACTH and corticosterone response to acute hypoxia in the neonatal rat

The effects of sleep restriction during abstinence on oxycodone seeking: Sex-dependent moderating effects of behavioral and hypothalamic-pituitary-adrenal axis-related phenotypes

During opioid use and abstinence, sleep disturbances are common and are thought to exacerbate drug craving. In this study, we tested the hypothesis that sleep restriction during abstinence from oxycodone self-administration would increase drug seeking during extinction and footshock reinstatement tests. We also performed behavioral phenotyping to determine if individual variation in responses to stressors and/or pain are associated with oxycodone seeking during abstinence, as stress, pain and sleep disturbance are often co-occurring phenomena. Sleep restriction during abstinence did not have selective effects on oxycodone seeking for either sex in extinction and footshock reinstatement tests. Some phenotypes were associated with drug seeking; these associations differed by sex and type of drug seeking assessment. In female rats, pain-related phenotypes were related to high levels of drug seeking during the initial extinction session. In male rats, lower anxiety-like behavior in the open field was associated with greater drug seeking, although this effect was lost when correcting for oxycodone intake. Adrenal sensitivity prior to oxycodone exposure was positively associated with footshock reinstatement in females. This work identifies sex-dependent relationships between HPA axis function and opioid seeking, indicating that HPA axis function could be a therapeutic target for the treatment of opioid use disorder, with tailored approaches based on sex. Sleep disturbance during abstinence did not appear to be a major contributing factor to opioid seeking.

The relationship between hypoxia exposure and circulating cortisol levels in social and solitary African mole-rats: An initial report

Hypoxemia from exposure to intermittent and/or acute environmental hypoxia (lower oxygen concentration) is a severe stressor for many animal species. The response to hypoxia of the hypothalamic-pituitary-adrenal axis (HPA-axis), which culminates in the release of glucocorticoids, has been well-studied in hypoxia-intolerant surface-dwelling mammals. Several group-living (social) subterranean species, including most African mole-rats, are hypoxia-tolerant, likely due to regular exposure to intermittent hypoxia in their underground burrows. Conversely, solitary mole-rat species, lack many adaptive mechanisms, making them less hypoxia-tolerant than the social genera. To date, the release of glucocorticoids in response to hypoxia has not been measured in hypoxia-tolerant mammalian species. Consequently, this study exposed three social African mole-rat species and two solitary mole-rat species to normoxia, or acute hypoxia and then measured their respective plasma glucocorticoid (cortisol) concentrations. Social mole-rats had lower plasma cortisol concentrations under normoxia than the solitary genera. Furthermore, individuals of all three of the social mole-rat species exhibited significantly increased plasma cortisol concentrations after hypoxia, similar to those of hypoxia-intolerant surface-dwelling species. By contrast, individuals of the two solitary species had a reduced plasma cortisol response to acute hypoxia, possibly due to increased plasma cortisol under normoxia. If placed in perspective with other closely related surface-dwelling species, the regular exposure of the social African mole-rats to hypoxia may have reduced the basal levels of the components for the adaptive mechanisms associated with hypoxia exposure, including circulating cortisol levels. Similarly, the influence of body mass on plasma cortisol levels cannot be ignored. This study demonstrates that both hypoxia-tolerant rodents and hypoxia-intolerant terrestrial laboratory-bred rodents may possess similar HPA-axis responses from exposure to hypoxia. Further research is required to confirm the results from this pilot study and to further confirm how the cortisol concentrations may influence responses to hypoxia in African mole-rat.

Sleep restriction during opioid abstinence affects the hypothalamic-pituitary-adrenal (HPA) axis in male and female rats

Hypothalamic-pituitary-adrenal (HPA) axis dynamics are disrupted by opioids and may be involved in substance abuse; this persists during withdrawal and abstinence and is associated with co-morbid sleep disruption leading to vulnerability to relapse. We hypothesized that chronic sleep restriction (SR) alters the HPA axis diurnal rhythm and the sexually dimorphic response to acute stressor during opioid abstinence. We developed a rat model to evaluate the effect of persistent sleep loss during opioid abstinence on HPA axis dynamics in male and female rats. Plasma ACTH and corticosterone were measured diurnally and in response to acute restraint stress in rats Before (control) compared to During subsequent opioid abstinence without or with SR. Abstinence, regardless of sleep state, led to an increase in plasma ACTH and corticosterone in the morning in males. There was a tendency for higher PM plasma ACTH during abstinence in SR males (p = 0.076). ACTH and corticosterone responses to restraint were reduced in male SR rats whereas there was a failure to achieve the post-restraint nadir in female SR rats. There was no effect of the treatments or interventions on adrenal weight normalized to body weight. SR resulted in a dramatic increase in hypothalamic PVN AVP mRNA and plasma copeptin in male but not female rats. This corresponded to the attenuation of the HPA axis stress response in SR males during opioid abstinence. We have identified a potentially unique, sexually dimorphic role for magnocellular vasopressin in the control of the HPA axis during opioid abstinence and sleep restriction.

Role of CRF and the hypothalamic-pituitary-adrenal axis in stroke: revisiting temporal considerations and targeting a new generation of therapeutics

Ischaemic neurovascular stroke represents a leading cause of death in the developed world. Preclinical and human epidemiological evidence implicates the corticotropin-releasing factor (CRF) family of neuropeptides as mediators of acute neurovascular injury pathology. Preclinical investigations of the role of CRF, CRF receptors and CRF-dependent activation of the hypothalamic-pituitary-adrenal (HPA) axis have pointed toward a tissue-specific and temporal relationship between activation of these pathways and physiological outcomes. Based on the literature, the major phases of ischaemic stroke aetiology may be separated into an acute phase in which CRF and anti-inflammatory stress signalling are beneficial and a chronic phase in which these contribute to neural degeneration, toxicity and apoptotic signalling. Significant gaps in knowledge remain regarding the pathway, temporality and systemic impact of CRF signalling and stress biology in neurovascular injury progression. Heterogeneity among experimental designs poses a challenge to defining the apparent reciprocal relationship between neurological injury and stress metabolism. Despite these challenges, it is our opinion that the elucidated temporality may be best matched with an antibody against CRF with a half-life of days to weeks as opposed to minutes to hours as with small-molecule CRF receptor antagonists. This state-of-the-art review will take a multipronged approach to explore the expected potential benefit of a CRF antibody by modulating CRF and corticotropin-releasing factor receptor 1 signalling, glucocorticoids and autonomic nervous system activity. Additionally, this review compares the modulation of CRF and HPA axis activity in neuropsychiatric diseases and their counterpart outcomes post-stroke and assess lessons learned from antibody therapies in neurodegenerative diseases.

Reprogramming of glucocorticoid receptor function by hypoxia

Here, we investigate the impact of hypoxia on the hepatic response of glucocorticoid receptor (GR) to dexamethasone (DEX) in mice via RNA-sequencing. Hypoxia causes three types of reprogramming of GR: (i) much weaker induction of classical GR-responsive genes by DEX in hypoxia, (ii) a number of genes is induced by DEX specifically in hypoxia, and (iii) hypoxia induces a group of genes via activation of the hypothalamic-pituitary-adrenal (HPA) axis. Transcriptional profiles are reflected by changed GR DNA-binding as measured by ChIP sequencing. The HPA axis is induced by hypothalamic HIF1α and HIF2α activation and leads to GR-dependent lipolysis and ketogenesis. Acute inflammation, induced by lipopolysaccharide, is prevented by DEX in normoxia but not during hypoxia, and this is attributed to HPA axis activation by hypoxia. We unfold new physiological pathways that have consequences for patients suffering from GC resistance.

Glucocorticoid Receptor Antagonist Alters Corticosterone and Receptor-sensitive mRNAs in the Hypoxic Neonatal Rat

Hypoxia, a common stressor with preterm birth, increases morbidity and mortality associated with prematurity. Glucocorticoids (GCs) are administered to the preterm infant to improve oxygenation; prolonged use of GCs remains controversial. We evaluated a selective glucocorticoid receptor (GR) antagonist (CORT113176) in our neonatal rat model of human prematurity to assess how fasting and hypoxia-induced increases in neonatal corticosterone affects endogenous hormones and endocrine pancreas function. Neonatal rat pups at postnatal day (PD) 2, PD8, and PD15 were pretreated with CORT113176 and, after 60 minutes of separation and fasting, exposed to hypoxia (8% O2) or control (normoxia) for 30 or 60 minutes while fasting was continued. Plasma corticosterone, ACTH, glucose, and insulin were measured and fasting Homeostatic Model Assessment of Insulin Resistance was calculated. Glucocorticoid and insulin receptor-sensitive gene mRNAs were analyzed in liver, muscle, and adipose to evaluate target tissue biomarkers. CORT113176 pretreatment augmented baseline and hypoxia-induced increases in corticosterone and attenuated hypoxia-induced increases in insulin resistance at PD2. Normoxic and hypoxic stress increased the hepatic GR-sensitive gene mRNAs, Gilz and Per1; this was eliminated by pretreatment with CORT113176. CORT113176 pretreatment decreased baseline insulin receptor-sensitive gene mRNAs Akt2, Irs1, Pik3r1, and Srebp1c at PD2. We show that CORT113176 variably augments the stress-induced increases in corticosterone concentrations (attenuation of negative feedback) and that GR is critical for hepatic responses to stress in the hypoxic neonate. We also propose that measurement of Gilz and Per1 mRNA expression may be useful to evaluate the effectiveness of GR antagonism.

Hyperoxia Leads to Transient Endocrine Alterations in the Neonatal Rat During Postnatal Development

Introduction: High oxygen concentrations have been identified as one factor contributing to the pathogenesis of the retinopathia of prematurity, chronic lung disease of the preterm infant and preterm brain injury. Preterm infants also show short- and long-term alterations of the endocrine system. If hyperoxia is one pathogenetic factor has not been investigated yet. With regard to the high prevalence of neurodevelopmental impairments in preterm infants, the hypothalamus-pituitary-thyroid (HPT) axis, the hypothalamus-pituitary-adrenal (HPA) axis and the hypothalamus-pituitary-somatotropic (HPS) axis are of special interest due to their important role in neurodevelopment. Objective: The aim of this study was to investigate the effect of hyperoxia on the endocrine system in the neonatal rat by analyzing the activities of the HPT, HPA and HPS axes, respectively. Methods: Three-days old Wistar rats were exposed to hyperoxia (oxygen 80%, 48 h). On postnatal day 5 (P5) and P11, transcript levels of thyroid-stimulating hormone (TSH), proopiomelanocortin and growth hormone (GH) were analyzed in pituitary sections by in situ hybridization. Serologic quantification of TSH and thyroxine (T4), adrenocorticotropic hormone and GH were performed by Multiplex analysis and Enzyme-linked Immunosorbent Assay. Results: At P5, significantly lower GH levels were observed in pituitaries (mRNA) and in sera of rats exposed to hyperoxia. Serum TSH was significantly elevated without changes in T4. Conclusion: This is the first study demonstrating transient endocrine alterations following hyperoxia in the neonatal rat making oxygen a possible contributor to the pathogenesis of endocrine alterations seen in preterm infants. Considering the detrimental multi-organ effects of hyperoxia on the immature organism, a rational use of therapeutic oxygen in the treatrnent of preterm infants is of utmost importance.

Insulin and glucose responses to hypoxia in male and female neonatal rats: Effects of the androgen receptor antagonist flutamide

Hypoxia is common with preterm birth and may lead to long-term effects on adult pancreatic endocrine function and insulin sensitivity. This phenomenon may be sexually dimorphic due to the hypoxia-induced augmentation of the neonatal androgen surge in male newborns. We evaluated this phenomenon by pretreating neonatal rats on postnatal days (PD) 1, 6, 13, or 20 with flutamide (a nonsteroidal androgen receptor antagonist) at a standard or a high dose (10 or 50 mg/kg) compared to vehicle control. One day later, neonatal rats were exposed to either acute normoxic or hypoxic separation (fasting) for 90 min, and blood was sampled for the measurement of insulin and glucose and the calculation of HOMA-IR as an index of insulin resistance. During normoxic and hypoxic separation (fasting), flutamide increased insulin secretion in PD2, PD7, and PD14 pups, high dose flutamide attenuated insulin secretion, and high dose flutamide attenuated the increase in HOMA-IR due to hypoxia. Our studies suggest a unique role of the androgen receptor in the control of neonatal pancreatic function, possibly by blocking a direct effect of neonatal testosterone or in response to indirect regulatory effects of androgens on insulin sensitivity.

Corticosterone, Adrenal, and the Pituitary-Gonadal Axis in Neonatal Rats: Effect of Maternal Separation and Hypoxia

Hypoxia, a common stressor in prematurity, leads to sexually dimorphic, short- and long-term effects on the adult hypothalamic-pituitary-adrenal (HPA) and hypothalamic-pituitary-gonadal (HPG) axes. We hypothesized that these effects are due to stress-induced increases in testosterone during early postnatal life. We evaluated this phenomenon by systematically assessing the short-term effects of normoxic or hypoxic separation on male and female pups at birth, postnatal hours (H) 2, 4, and 8, and postnatal days (PD) 2 to 7. Our findings were (a) hypoxic separation led to a large increase in plasma corticosterone from 4H-PD4, (b) neither normoxic nor hypoxic separation affected critical adrenal steroidogenic pathway genes; however, a significant decrease in baseline Cyp11a1, Mc2r, Mrap, and Star adrenal expression during the first week of neonatal life confirmed the start of the adrenal stress hyporesponsive period, (c) a luteinizing hormone/follicle-stimulating hormone-independent increase in plasma testosterone occurred in normoxic and hypoxic separated male pups at birth, (d) testicular Cyp11a1, Lhcgr, and Star expression was high at birth and decreased thereafter suggesting a hyporesponsive period in the testes, and (e) elevated estrogen in the early neonatal period occurred independently of gonadotropin stimulation. We conclude that a large corticosterone response to hypoxia during the first 5 days of life occurs as an adaptation to neonatal stress, that the testosterone surge during the first hours after birth occurs independently of gonadotropins but is associated with upregulation of the steroidogenic pathway genes in the testes, and that high postnatal estrogen production also occurs independently of gonadotropins.

T-cell Receptor Excision Circles in Newborns with Heart Defects

In the fetus, the cardiac neural crest gives rise to both the thymus and the conotruncus of the heart. In newborn screening for severe T-cell lymphopenia neonates with congenital heart defects may be detected. In this study, we investigated the occurrence of T-cell lymphopenia in neonates with or without 22q11.2 deletion syndrome (del) suffering from heart defects. This retrospective cohort study included 125 patients with heart defects. T-cell receptor excision circles (TRECs), a measure for T-cell lymphopenia, were quantified by RT-PCR using stored newborn screening blood spots. Three patient groups were compared: non-conotruncal defects (n = 57), conotruncal defects (n = 42), and 22q11.2 del with conotruncal defects (n = 26). Significantly lower TREC values were detected in patients with 22q11.2 del and conotruncal heart defects compared to those with non-syndromic conotruncal (p < 0.001) and non-conotruncal (p < 0.001) defects. In contrast, no significant difference was found between patients with non-syndromic conotruncal and non-conotruncal heart defects (p = 0.152). Low TREC levels were obtained in neonates treated with heart surgery/intervention within 2 weeks after birth and in those with a fatal outcome (p = 0.02) independent of patient group. A correlation was found between low TREC numbers and oxygen saturation, SpO₂ below 95% (p = 0.017). The SpO₂ was significantly lower in the non-syndromic conotruncal group compared to non-conotruncal (p < 0.001) and 22q11.2 del group (p = 0.015). No correlation was found between low neonatal TRECs and infections needing hospitalization later in life (p = 0.135). Patients with 22q11.2 del and conotruncal defects have significantly lower TREC levels compared to patients with heart defects without this syndrome.

The effects of flutamide on the neonatal rat hypothalamic-pituitary-adrenal and gonadal axes in response to hypoxia

Hypoxia is common with preterm birth and may lead to long-term effects on the adult hypothalamic-pituitary-adrenal (HPA) axis that are sexually dimorphic due to neonatal androgens. Although the adult rat adrenal does not express appreciable CYP17 activity, the neonatal rat adrenal may synthesize androgens that could be a critical local factor in the development of adrenal function. We evaluated these phenomena by pretreating the neonatal rats on postnatal days (PD) 1, 6, 13, 20 with flutamide (a nonsteroidal androgen receptor antagonist) at a standard or a high dose (10 mg/kg or 50 mg/kg) compared to vehicle control. One day later, neonatal rats were exposed to acute hypoxia and blood was sampled. We found that (a) in PD2 pups, flutamide augmented corticosterone responses in a sexually dimorphic pattern and without an increase in ACTH, (b) PD7 and PD14 pups had the smallest corticosterone response to hypoxia (c) PD21 pups had an adult-like corticosterone response to hypoxia that was sexually dimorphic, (d) flutamide attenuated ACTH responses in PD7 hypoxic pups, and (e) high-dose flutamide suppressed the HPA axis, FSH, and estradiol. Flutamide demonstrated mixed antagonist and agonist effects that changed during the first three weeks of neonatal life. We conclude that the use of flutamide in neonatal rats to evaluate androgen-induced programming of subsequent adult behavior is not optimal. However, our studies suggest neonatal androgens play a role in regulation of adrenal function that is sexually dimorphic and changes during early development.

A Long-Acting Neutralizing Monoclonal ACTH Antibody Blocks Corticosterone and Adrenal Gene Responses in Neonatal Rats

The control of steroidogenesis in the neonatal adrenal gland is of great clinical interest. We have previously demonstrated that the postnatal day (PD) 2 rat exhibits a large plasma corticosterone response to hypoxia in the absence of an increase in plasma ACTH measured by RIA, whereas the corticosterone response to exogenous ACTH is intact. By PD8, the corticosterone response to hypoxia is clearly ACTH-dependent. We hypothesized that this apparently ACTH-independent response to hypoxia in the newborn rat is due to an increase in a bioactive, nonimmunoassayable form of ACTH. To evaluate this phenomenon, we pretreated neonatal rats with a novel, specific, neutralizing anti-ACTH antibody (ALD1611) (20 mg/kg or 1 mg/kg IP) on the morning of PD1, PD7, and PD14. Twenty-four hours later, we measured hypoxia- or ACTH-stimulated plasma ACTH and corticosterone. For long-term effects, ALD1611 was given on PD1 and pups were studied on PD8 and PD15. Pretreatment with ALD1611 significantly decreased baseline corticosterone and completely blocked the corticosterone response to hypoxia and exogenous ACTH stimulation at all ages. The effect of 1 mg/kg ALD1611 on PD1 had dissipated by PD15. The decrease in corticosterone in ALD1611-treated pups was associated with decreases in baseline and hypoxia- and ACTH-stimulated adrenal Ldlr, Mrap, and Star mRNA expression at all ages. The adrenal response to hypoxia in the newborn rat is ACTH-dependent, suggesting the release of nonimmunoassayable, biologically active forms of ACTH. ALD1611 is useful as a tool to attenuate stress-induced, ACTH-dependent adrenal steroidogenesis in vivo.

Hypoxia Inducible Factor Expression and Angiogenesis - Analysis in the Pituitary Gland and Patterns of Death

BACKGROUND/AIM

We investigated the expression of angiogenesis and hypoxia markers in the adenohypophysis and neurohypophysis of patients who died from various acute or chronic diseases.

MATERIALS AND METHODS

Paraffin-embedded material of pituitary glands (97 patients) was investigated immunohistochemically for vascular density (CD31) and the expression of vascular endothelial growth factor (VEGF) and of hypoxia inducible factors HIF1α and HIF2α.

RESULTS

Vascular density, and HIF1α/HIF2α reactivity is directly related with VEGF expression in the pituitary gland, suggesting that the HIF pathway may regulate the vascular density and blood flow in the gland under hypoxic conditions. HIF2α appears to be a key regulator in neurohypophysis, whilst in adenohypophysis HIF1α and HIF2α are equally expressed. Chronic conditions, including alcoholism and substance abuse, seem to activate the HIF pathway in both neuro- and adeno-hypophysis.

CONCLUSION

The HIF pathway has an important role in regulating vascular density and blood flow in the pituitary gland.

Programming of the Adult HPA Axis After Neonatal Separation and Environmental Stress in Male and Female Rats

Maternal separation, hypoxia, and hypothermia are common stressors in the premature neonate. Using our rat model of human prematurity, we evaluated sexual dimorphisms in the long-term effects of these neonatal stressors on behavior of the hypothalamic-pituitary-adrenal (HPA) axis in adult rats. Neonatal rats were exposed daily on postnatal days 2 to 6 to maternal separation with normoxia, with hypoxia allowing spontaneous hypothermia, with hypothermia per se, and with hypoxia while maintaining isothermia with external heat. The major findings were that (a) prior maternal-neonatal separation during the first week of postnatal life attenuated the plasma ACTH and corticosterone response to restraint stress in adult male but not female rats, (b) prior neonatal hypothermia augmented the plasma ACTH and corticosterone response to restraint stress in adult male rats, but not female rats, and (c) changes in hypothalamic, pituitary, and adrenal mRNA expression did not account for most of these HPA axis effects. Most of the programming effects on adult HPA axis was attributed to prior maternal-neonatal separation alone (with normoxia) because the addition of hypoxia with spontaneous hypothermia, hypothermia per se, and hypoxia while preventing hypothermia during maternal-neonatal separation had minimal effects on the HPA axis. These results may inform strategies to prevent sexually dimorphic sequelae of neonatal stress including those due to medical interventions.

Effect of a melanocortin type 2 receptor (MC2R) antagonist on the corticosterone response to hypoxia and ACTH stimulation in the neonatal rat

The adrenal stress response in the neonatal rat shifts from ACTH-independent to ACTH-dependent between postnatal days 2 (PD2) and 8 (PD8). This may be due to an increase in an endogenous, bioactive, nonimmunoreactive ligand to the melanocortin type 2 receptor (MC2R). GPS1574 is a newly described MC2R antagonist that we have shown to be effective in vitro. Further experimentation with GPS1574 would allow better insight into this seemingly ACTH-independent steroidogenic response in neonates. We evaluated the acute corticosterone response to hypoxia or ACTH injection following pretreatment with GPS1574 (32 mg/kg) or vehicle for GPS1574 in PD2, PD8, and PD15 rat pups. Pretreatment with GPS1574 decreased baseline corticosterone in PD2 pups but increased baseline corticosterone in PD8 and PD15 pups. GPS1574 did not attenuate the corticosterone response to hypoxia in PD2 pups and augmented the corticosterone response in PD8 and PD15 pups. GPS1574 augmented the corticosterone response to ACTH in PD2 and PD15 pups but had no significant impact on the response in PD8 pups. Baseline adrenal Mrap and Star mRNA increased from PD2 to PD15, whereas Mrap2 mRNA expression was low and did not change with age. The data suggest that GPS1574 is not a pure MC2R antagonist, but rather acts as a biasing agonist/antagonist. Its ability to attenuate or augment the adrenal response may depend on the ambient plasma ACTH concentration and/or developmental changes in early transduction steroidogenic pathway genes.

The integration of multiple signaling pathways provides for bidirectional control of CRHR1 gene transcription in rat pituitary cell during hypoxia

Hypoxia upregulates hypothalamic corticotrophin releasing hormone (CRH) and its receptor type-1 (CRHR1) expression and activates the HPA axis and induces hypoxic sickness and behavioral change. The transcriptional mechanism by which hypoxia differently regulates CRHR1 expression remains unclear. Here we report hypoxia time-dependently induced biphasic expression of CRHR1mRNA in rat pituitary during different physiological status. Short exposure of gestational dams to hypoxia reduced CRHR1mRNA in the pituitary of P1-P14 male rat offspring. A short- and prolonged-hypoxia evoked biphasic response of CRHR1mRNA characterized initially by decreases and subsequently by persistent increases, mediated by a rapid negative feedback via CRHR1 signaling and positive transcriptional control via NF-κB, respectively. Further analysis of CRHR1 promoter in cultured primary anterior pituitary and AtT20 cells showed that c-Jun/AP-1 delivered negative while HIF-1α and NF-κB delivered positive control of transcription at CRHR1 promoter. The negative and positive inputs are integrated by hypoxic initiation and duration in CRHR1 transcription.

Insulin sensitivity, leptin, adiponectin, resistin, and testosterone in adult male and female rats after maternal-neonatal separation and environmental stress

Care of premature infants often requires parental and caregiver separation, particularly during hypoxic and hypothermic episodes. We have established a neonatal rat model of human prematurity involving maternal-neonatal separation and hypoxia with spontaneous hypothermia prevented by external heat. Adults previously exposed to these neonatal stressors show a sex difference in the insulin and glucose response to arginine stimulation suggesting a state of insulin resistance. The current study used this cohort of adult rats to evaluate insulin resistance [homeostatic model assessment of insulin resistance (HOMA-IR)], plasma adipokines (reflecting insulin resistance states), and testosterone. The major findings were that daily maternal-neonatal separation led to an increase in body weight and HOMA-IR in adult male and female rats and increased plasma leptin in adult male rats only; neither prior neonatal hypoxia (without or with body temperature control) nor neonatal hypothermia altered subsequent adult HOMA-IR or plasma adiponectin. Adult male-female differences in plasma leptin were lost with prior exposure to neonatal hypoxia or hypothermia; male-female differences in resistin were lost in the adults that were exposed to hypoxia and spontaneous hypothermia as neonates. Exposure of neonates to daily hypoxia without spontaneous hypothermia led to a decrease in plasma testosterone in adult male rats. We conclude that neonatal stressors result in subsequent adult sex-dependent increases in insulin resistance and adipokines and that our rat model of prematurity with hypoxia without hypothermia alters adult testosterone dynamics.

Multiple beneficial effects of melanocortin MC4 receptor agonists in experimental neurodegenerative disorders: Therapeutic perspectives

Melanocortin peptides induce neuroprotection in acute and chronic experimental neurodegenerative conditions. Melanocortins likewise counteract systemic responses to brain injuries. Furthermore, they promote neurogenesis by activating critical signaling pathways. Melanocortin-induced long-lasting improvement in synaptic activity and neurological performance, including learning and memory, sensory-motor orientation and coordinated limb use, has been consistently observed in experimental models of acute and chronic neurodegeneration. Evidence indicates that the neuroprotective and neurogenic effects of melanocortins, as well as the protection against systemic responses to a brain injury, are mediated by brain melanocortin 4 (MC₄) receptors, through an involvement of the vagus nerve. Here we discuss the targets and mechanisms underlying the multiple beneficial effects recently observed in animal models of neurodegeneration. We comment on the potential clinical usefulness of melanocortin MC₄ receptor agonists as neuroprotective and neuroregenerative agents in ischemic stroke, subarachnoid hemorrhage, traumatic brain injury, spinal cord injury, and Alzheimer's disease.

Sex differences in adult rat insulin and glucose responses to arginine: programming effects of neonatal separation, hypoxia, and hypothermia

Acute neonatal hypoxia, a common stressor, causes a spontaneous decrease in body temperature which may be protective. There is consensus that hypothermia should be prevented during acute hypoxia in the human neonate; however, this may be an additional stress with negative consequences. We hypothesize that maintaining body temperature during hypoxia in the first week of postnatal life alters the subsequent insulin, glucose, and glucagon secretion in adult rats. Rat pups were separated from their dam daily from postnatal days (PD) 2-6 for the following 90 min experimental treatments: (1) normoxic separation (control), (2) hypoxia (8% O2) allowing spontaneous hypothermia, (3) normoxic hypothermia with external cold, and (4) exposure to 8% O2 while maintaining body temperature using external heat. An additional normoxic non-separated control group was performed to determine if separation per se changed the adult phenotype. Plasma insulin, glucose, and glucagon responses to arginine stimulation were evaluated from PD105 to PD133. Maternal separation (compared to non-separated neonates) had more pronounced effects on the adult response to arginine compared to the hypoxic, hypothermic, and hypoxic-isothermic neonatal treatments. Adult males exposed to neonatal maternal separation had augmented insulin and glucose responses to arginine compared to unseparated controls. Additionally, neonatal treatment had a significant effect on body weight gain; adults exposed to neonatal maternal separation were significantly heavier. Female adults had significantly smaller insulin and glucose responses to arginine regardless of neonatal treatment. Neonatal maternal separation during the first week of life significantly altered adult beta-cell function in a sexually dimorphic manner.

Effect of Novel Melanocortin Type 2 Receptor Antagonists on the Corticosterone Response to ACTH in the Neonatal Rat Adrenal Gland In Vivo and In Vitro

Stress-induced increases in neonatal corticosterone demonstrate a unique shift from ACTH independence to ACTH dependence between postnatal day 2 (PD2) and day 8 (PD8) in newborn rats. This shift could be due to the binding of a bioactive, non--immunoreactive plasma ligand to the adrenocortical melanocortin 2 receptor (MC2R) (ACTH receptor). A potent MC2R antagonist would be useful to evaluate this phenomenon in the neonate. Therefore, we investigated the acute corticosterone response to ACTH(1-39) injection in rat pups pretreated with newly developed MC2R antagonists (GPS1573 and GPS1574), which have not been tested in vivo. The doses used in vivo were based on their in vitro potency, with GP1573 being more potent than GPS1574. GPS1573 (PD2 and PD8), GPS1574 (PD2 only), or vehicle were injected intraperitoneally (ip) 10 min before baseline sampling. Then, 0.001 mg/kg of ACTH(1-39) was injected ip, and subsequent blood samples obtained for the measurement of plasma corticosterone. Pretreatment of PD2 pups with GPS1573 demonstrated augmentation, rather than inhibition, of the corticosterone response to ACTH. In PD8 pups, pretreatment with 0.1 mg/kg GPS1573, but not 4 mg/kg, augmented the corticosterone response to ACTH. Pretreatment with GPS1574 attenuated the plasma corticosterone response to ACTH at 30 min in PD2 pups. The activity of these two compounds in vivo do not match their potency in vitro, with GPS1573 leading to a small augmentation of the corticosterone response to ACTH in vivo while GPS1574 resulted in inhibition.

Pharmacological stimulation of hypoxia inducible factor-1α facilitates the corticosterone response to a mild acute stressor

While both glucocorticoids (the principal output of the hypothalamic-pituitary-adrenal axis) and oxidative stress have been implicated in outcomes due to an excessive or prolonged stress response, the precise mechanisms linking these two systems remain poorly elucidated. One potential mediator between the hypothalamic-pituitary-adrenal axis and oxidative stress is the hypoxia inducible factor-1 (HIF-1) pathway. HIF-1 is an oxygen-responsive transcription factor with diverse effects including changes in cellular metabolism. The experiments in this manuscript sought to determine if pharmacological stimulation of HIF-1α via administration of dimethyloxalylglycine (DMOG) would facilitate the corticosterone response to a mild acute stressor. DMOG administration significantly increased plasma corticosterone 5 min after an acute airpuff without changing baseline plasma corticosterone or plasma corticosterone level two hours post-startle. DMOG administration also reduced hippocampal gene expression of the pro-translocation co-chaperone for the glucocorticoid receptor, FKBP4, two hours after airpuff startle. At this same two-hour time point, hippocampal expression of FKBP5, an anti-translocation co-chaperone of the glucocorticoid receptor, in the DMOG-treated group was also positively correlated with plasma corticosterone levels. These data indicate that there is significant crosstalk between the hypothalamic-pituitary-axis and the HIF-1 pathway and extend the current knowledge of glucocorticoid and hypoxia interactions in an ethologically relevant stress model.

Renin knockout rat: control of adrenal aldosterone and corticosterone synthesis in vitro and adrenal gene expression

The classic renin-angiotensin system is partly responsible for controlling aldosterone secretion from the adrenal cortex via the peptide angiotensin II (ANG II). In addition, there is a local adrenocortical renin-angiotensin system that may be involved in the control of aldosterone synthesis in the zona glomerulosa (ZG). To characterize the long-term control of adrenal steroidogenesis, we utilized adrenal glands from renin knockout (KO) rats and compared steroidogenesis in vitro and steroidogenic enzyme expression to wild-type (WT) controls (Dahl S rat). Adrenal capsules (ZG; aldosterone production) and subcapsules [zona reticularis/fasciculata (ZFR); corticosterone production] were separately dispersed and studied in vitro. Plasma renin activity and ANG II concentrations were extremely low in the KO rats. Basal and cAMP-stimulated aldosterone production was significantly reduced in renin KO ZG cells, whereas corticosterone production was not different between WT and KO ZFR cells. As expected, adrenal renin mRNA expression was lower in the renin KO compared with the WT rat. Real-time PCR and immunohistochemical analysis showed a significant decrease in P450aldo (Cyp11b2) mRNA and protein expression in the ZG from the renin KO rat. The reduction in aldosterone synthesis in the ZG of the renin KO adrenal seems to be accounted for by a specific decrease in P450aldo and may be due to the absence of chronic stimulation of the ZG by circulating ANG II or to a reduction in locally released ANG II within the adrenal gland.

Adrenocortical sensitivity to ACTH in neonatal rats: correlation of corticosterone responses and adrenal cAMP content

A coordinated hypothalamic-pituitary-adrenal axis response is important for the survival of newborns during stress. We have previously shown that prior to postnatal day (PD) 5, neonatal rats exposed to hypoxia (one of the most common stressors effecting premature neonates) exhibit a large corticosterone response with a minimal increase in immunoassayable plasma ACTH and without a detectable increase in adrenal cAMP content (the critical second messenger). To explore the phenomenon of ACTH-stimulated steroidogenesis in the neonate, we investigated the adrenal response to exogenous ACTH in the normoxic neonatal rat. Rat pups at PD2 and PD8 were injected intraperitoneally with porcine ACTH at low, moderate, or high doses (1, 4, or 20 μg/kg body wt). Trunk blood and whole adrenal glands were collected at baseline (before injection) and 15, 30, or 60 min after the injection. ACTH stimulated corticosterone release in PD2 and PD8 pups. In PD2 pups, plasma corticosterone at baseline and during the response to ACTH injection was greater than values measured in PD8 pups, despite lower adrenal cAMP content in PD2 pups. Specifically, the low and moderate physiological ACTH doses produced a large corticosterone response in PD2 pups without a change in adrenal cAMP content. At extremely high, pharmacological levels of plasma ACTH in PD2 pups (exceeding 3,000 pg/ml), an increase in adrenal cAMP was measured. We conclude that physiological increases in plasma ACTH may stimulate adrenal steroidogenesis in PD2 pups through a non-cAMP-mediated pathway.

Programming of the hypothalamic-pituitary-adrenal axis by neonatal intermittent hypoxia: effects on adult male ACTH and corticosterone responses are stress specific

Intermittent hypoxia (IH) is an animal model of apnea-induced hypoxia, a common stressor in the premature neonate. Neonatal stressors may have long-term programming effects in the adult. We hypothesized that neonatal exposure to IH leads to significant changes in basal and stress-induced hypothalamic-pituitary-adrenal (HPA) axis function in the adult male rat. Rat pups were exposed to normoxia (control) or 6 approximately 30-second cycles of IH (5% or 10% inspired O₂) daily on postnatal days 2-6. At approximately 100 days of age, we assessed the diurnal rhythm of plasma corticosterone and stress-induced plasma ACTH and corticosterone responses, as well as mRNA expression of pertinent genes within the HPA axis. Basal diurnal rhythm of plasma corticosterone concentrations in the adult rat were not affected by prior exposure to neonatal IH. Adults exposed to 10% IH as neonates exhibited an augmented peak ACTH response and a prolonged corticosterone response to restraint stress; however, HPA axis responses to insulin-induced hypoglycemia were not augmented in adults exposed to neonatal IH. Pituitary Pomc, Crhr1, Nr3c1, Nr3c2, Avpr1b, and Hif1a mRNA expression was decreased in adults exposed to neonatal 10% IH. Expression of pertinent hypothalamic and adrenal mRNAs was not affected by neonatal IH. We conclude that exposure to neonatal 10% IH programs the adult HPA axis to hyperrespond to acute stimuli in a stressor-specific manner.

Adrenal insufficiency is prevalent in HbE/β-thalassaemia paediatric patients irrespective of their clinical severity and transfusion requirement

OBJECTIVES

Transfusion dependency is known to cause endocrinopathies in patients with thalassaemia such as adrenal insufficiency, because transfusion-related iron overload is injurious to endocrine organs. Children with HbE/ß-thalassaemia vary greatly in red cell transfusion requirement and some are transfusion dependent (TD), whereas others are nontransfusion dependent (NTD). Because iron overload is thought to be the primary cause of adrenal insufficiency, TD children with HbE/ß-thalassaemia are considered likely candidates for the development of adrenal insufficiency, while the adrenal function of NTD children is generally considered to be normal. As yet, the prevalence of adrenal insufficiency among children with NTD HbE/β-thalassaemia is not known. The present study was performed to (i) assess the prevalence of adrenal insufficiency in children with both TD and NTD HbE/β-thalassaemia and to evaluate whether there is any difference in the prevalence of adrenal insufficiency between both groups and (ii) determine the type of adrenal insufficiency (primary or secondary).

METHODS

We investigated the prevalence of adrenal insufficiency among TD (n = 42) and NTD (n = 43) children with HbE/β-thalassaemia by assessing morning serum cortisol levels, and we distinguished between primary and secondary adrenal insufficiency by assessing the cortisol responses following the 1- and 250-μg ACTH stimulation tests.

RESULTS

The prevalence of adrenal insufficiency among TD and NTD children with HbE/β-thalassaemia was 50% and 53·5%, respectively. By using the 250-μg ACTH stimulation test, at least 39% and 23·5% were diagnosed with adrenal gland hypofunction in TD and NTD children, respectively.

CONCLUSION

This is the first study to show that adrenal insufficiency is common among all children with HbE/β-thalassaemia, irrespective of their transfusion history or requirement. Our findings have important implications for the clinical management of these children.

Adrenocortical control in the neonatal rat: ACTH- and cAMP-independent corticosterone production during hypoxia

We have previously demonstrated that the neonatal corticosterone response to acute hypoxia shifts from ACTH independence to ACTH dependence between postnatal days two (PD2) and eight (PD8). Cyclic AMP (cAMP) is the obligatory intracellular second messenger of ACTH action, and we hypothesized that corticosterone production in neonatal rats shifts from a cAMP-independent mechanism to cAMP-dependent mechanism between PD2 and PD8. Plasma ACTH and corticosterone and adrenal cAMP and cGMP responses to acute severe hypoxia (8% O₂ for 5, 10, 20, 30, and 180 min) were measured in neonatal rats at PD2, PD8, and PD15. Plasma ACTH and corticosterone were measured by radioimmunoassay, and adrenal cAMP and cGMP were measured by ELISA. Plasma corticosterone-binding globulin (CBG) was measured in normoxic pups by ELISA. The largest corticosterone response was observed in PD2 pups, despite only a small increase in plasma ACTH that was not sustained. The PD2 ACTH-independent increase in corticosterone occurred with no change in adrenal cAMP or cGMP content. Plasma CBG concentration was lowest in PD2 pups. Large corticosterone responses were measured during the first 30 min of hypoxia. Differences in corticosterone responses between PD2 and PD8 pups cannot be attributed to changes in plasma protein binding capacity, and the PD2 corticosterone response is consistent with a nongenomic mechanism of action. We conclude that the sustained corticosterone response to hypoxia in PD2 pups occurs with small and transient ACTH responses and independently of increases in adrenal cAMP or cGMP.

Effects of age on ACTH, corticosterone, glucose, insulin, and mRNA levels during intermittent hypoxia in the neonatal rat

Apnea, the temporary cessation of respiratory airflow, is a common cause of intermittent hypoxia (IH) in premature infants. We hypothesized that IH elicits a stress response and alters glucose homeostasis in the neonatal rat. Rat pups were studied on postnatal day (PD) 2, 8, 10, 12, and 14. Pups were exposed to normoxia (control) or six cycles consisting of 30-s exposures to hypoxia (FiO2 = 3%) over a 60-min period. Blood samples were obtained at baseline, after the third cycle (~30 min), and after the sixth cycle (~60 min). Tissue samples were collected following the sixth cycle. Plasma ACTH, corticosterone, glucose, and insulin were analyzed at all ages. Hypothalamic, pituitary, and adrenal mRNA expression was evaluated by quantitative PCR in PD2, PD8, and PD12 pups. Exposure to IH elicited significant increases in plasma ACTH and corticosterone at all ages studied. The largest increase in corticosterone occurred in PD2 pups, despite only a very small increase in plasma ACTH. This ACTH-independent increase in corticosterone in PD2 pups was associated with increases in adrenal Ldlr and Star mRNA expression. Additionally, IH caused hyperglycemia and hyperinsulinemia at all ages. We conclude that IH elicits a significant pituitary-adrenal response and significantly alters glucose homeostasis. Furthermore, the quantitative and qualitative characteristics of these responses depend on developmental age.

Circadian rhythm of salivary cortisol in infants with congenital heart disease

Children with congenital heart disease (CHD) have associated extracardiac co-morbidities at the time of surgery and during ongoing growth and development. Perioperative events include disrupted glucose homeostasis, capillary leak, and fluid retention. The hypothalamic-pituitary-adrenal (HPA) axis has an important role in homeostasis in that the secretion of cortisol contributes to the response to stress, glucose regulation, blood volume control, and immune regulation. We investigated the diurnal rhythm of the HPA axis in infants with CHD by measuring salivary cortisol in the morning (0600-0900 h-circadian peak) and evening (2100-2400 h-circadian nadir). Twenty-nine infants aged 12 weeks to 1 year were included: 16 with acyanotic disease (SpO₂ ≥ 90 %) and 13 with cyanotic disease (SpO2 < 90 %). Morning salivary cortisol was similar between the two groups [acyanotic 7.0 nmol/L (1.8-23.1); cyanotic 9.7 nmol/L (0.9-15.6); p = 0.68]. Evening salivary cortisol was similar between the two groups [acyanotic 0.9 nmol/L (0.2-8.5); cyanotic 1.4 nmol/L (0.5-14.9); p = 0.32]. Both cyanotic and acyanotic groups demonstrated an intact diurnal rhythm. In conclusion, chronic hypoxia secondary to cyanotic CHD does not affect the circadian rhythm of the HPA axis. By 12 weeks of age, infants with hypoxia secondary to cyanotic CHD have a normal cortisol diurnal rhythm.

Melanocortins as potential therapeutic agents in severe hypoxic conditions

Melanocortin peptides with the adrenocorticotropin/melanocyte-stimulating hormone (ACTH/MSH) sequences and synthetic analogs have protective and life-saving effects in experimental conditions of circulatory shock, myocardial ischemia, ischemic stroke, traumatic brain injury, respiratory arrest, renal ischemia, intestinal ischemia and testicular ischemia, as well as in experimental heart transplantation. Moreover, melanocortins improve functional recovery and stimulate neurogenesis in experimental models of cerebral ischemia. These beneficial effects of ACTH/MSH-like peptides are mostly mediated by brain melanocortin MC(3)/MC(4) receptors, whose activation triggers protective pathways that counteract the main ischemia/reperfusion-related mechanisms of damage. Induction of signaling pathways and other molecular regulators of neural stem/progenitor cell proliferation, differentiation and integration seems to be the key mechanism of neurogenesis stimulation. Synthesis of stable and highly selective agonists at MC(3) and MC(4) receptors could provide the potential for development of a new class of drugs for a novel approach to management of severe ischemic diseases.

Effects of body temperature maintenance on glucose, insulin, and corticosterone responses to acute hypoxia in the neonatal rat

One of the biggest challenges of premature birth is acute hypoxia. Hypothermia during acute hypoxic periods may be beneficial. We hypothesized that prevention of hypothermia during neonatal hypoxia disrupts glucose homeostasis and places additional metabolic challenges on the neonate. Pups at PD2 and PD8 were exposed to 8% O2 for 3 h, during which they were allowed to either spontaneously cool or were kept isothermic. There was also a time control group that was subjected to normoxia and kept isothermic. Plasma glucose, insulin, C-peptide, corticosterone, and catecholamines were measured from samples collected at baseline, 1 h, 2 h, and 3 h. In postnatal day 2 (PD2) rats, hypoxia alone resulted in no change in plasma glucose by 1 h, an increase by 2 h, and a subsequent decrease below baseline values by 3 h. Hypoxia with isothermia in PD2 rats elicited a large increase in plasma insulin at 1 h. In PD8 rats, hypoxia with isothermia resulted in an initial increase in plasma glucose, but by 3 h, glucose had decreased significantly to below baseline levels. Hypoxia with and without isothermia elicited an increase in plasma corticosterone at both ages and an increase in plasma epinephrine in PD8 rats. We conclude that the insulin response to hypoxia in PD8 rats is associated with an increase in glucose similar to an adult; however, insulin responses to hypoxia in PD2 rats were driven by something other than glucose. Prevention of hypothermia during hypoxia further disrupts glucose homeostasis and increases metabolic challenges.

Age and sex differences in the ventilatory response to hypoxia and hypercapnia in awake neonatal, pre-pubertal and young adult rats

There is evidence for a "sensitive period" in respiratory development in rats around postnatal age (P) 12-13d. Little is known about sex differences during that time. The purpose of this study was to assess the effect of sex on breathing development, specifically around the "sensitive period". We used whole-body plethysmography to study breathing in normoxic, hypoxic and hypercapnic gases in non-anesthetized male and female neonatal rats from P10 to P15, juvenile (P30) and young adult (P90) rats. Compared to other neonatal ages, P12-13 male rats had significantly lower ventilation during normoxia, hypoxia, and hypercapnia. Compared to age-matched females, P12-13 male rats had lower ventilation in normoxia and hypoxia and a lower O(2) saturation during hypoxia. Circulating estradiol was greater in P12-13 male vs. female rats. Estradiol and ventilatory responses to hypoxia and hypercapnia were negatively correlated in neonatal male, but not female rats. Our results suggest that P10-15 includes a critical developmental period in male but not female rats.

Effect of animal facility construction on basal hypothalamic-pituitary-adrenal and renin-aldosterone activity in the rat

Although loud noise and intense vibration are known to alter the behavior and phenotype of laboratory animals, little is known about the effects of nearby construction. We studied the effect of a nearby construction project on the classic stress hormones ACTH, corticosterone, renin, and aldosterone in rats residing in a barrier animal facility before, for the first 3 months of a construction project, and at 1 month after all construction was completed. During some of the construction, noise and vibrations were not obvious to investigators inside the animal rooms. Body weight matched for age was not altered by nearby construction. During nearby construction, plasma ACTH, corticosterone, and aldosterone were approximately doubled compared with those of pre- and postconstruction levels. Expression of CRH mRNA in the paraventricular nucleus of the hypothalamus, CRH receptor and POMC mRNA in the anterior pituitary, and most mRNAs for steroidogenic genes in the adrenal gland were not significantly changed during construction. We conclude that nearby construction can cause a stress response without long-term effects on hypothalamic-pituitary-adrenal axis gene expression and body weight.

Adrenocorticotropic hormone and corticosterone responses to acute hypoxia in the neonatal rat: effects of body temperature maintenance

The corticosterone response to acute hypoxia in neonatal rats develops in the 1st wk of life, with a shift from ACTH independence to ACTH dependence. Acute hypoxia also leads to hypothermia, which may be protective. There is little information about the endocrine effects of body temperature maintenance during periods of neonatal hypoxia. We hypothesized that prevention of hypothermia during neonatal hypoxia would augment the adrenocortical stress response. Rat pups separated from their dams were studied at postnatal days 2 and 8 ( PD2 and PD8). In one group of pups, body temperature was allowed to spontaneously decrease during a 30-min prehypoxia period. Pups were then exposed to 8% O2 for 3 h and allowed to become spontaneously hypothermic or externally warmed (via servo-controlled heat) to maintain isothermia. In another group, external warming was used to maintain isothermia during the prehypoxia period, and then hypoxia with or without isothermia was applied. Plasma ACTH and corticosterone and mRNA expression of genes for upstream proteins involved in the steroidogenic pathway were measured. Maintenance of isothermia during the prehypoxia period increased baseline plasma ACTH at both ages. Hypothermic hypoxia caused an increase in plasma corticosterone; this response was augmented by isothermia at PD2, when the response was ACTH-independent, and at PD8, when the response was ACTH-dependent. In PD8 rats, isothermia also augmented the plasma ACTH response to hypoxia. We conclude that maintenance of isothermia augments the adrenocortical response to acute hypoxia in the neonate. Prevention of hypothermia may increase the stress response during neonatal hypoxia, becoming more pronounced with increased age.

Effect of high-dose total body irradiation on ACTH, corticosterone, and catecholamines in the rat

Total body irradiation (TBI) or partial body irradiation is a distinct risk of accidental, wartime, or terrorist events. Total body irradiation is also used as conditioning therapy before hematopoietic stem cell transplantation. This therapy can result in injury to multiple tissues and might result in death as a result of multiorgan failure. The hypothalamic-pituitary-adrenal (HPA) axis could play a causative role in those injuries, in addition to being activated under conditions of stress. In a rat model of TBI, we have established that radiation nephropathy is a significant lethal complication, which is caused by hypertension and uremia. The current study assessed HPA axis function in rats undergoing TBI. Using a head-shielded model of TBI, we found an enhanced response to corticotropin-releasing hormone (CRH) in vitro in pituitaries from irradiated compared with nonirradiated rats at both 8 and 70 days after 10-Gy single fraction TBI. At 70, but not 8 days, plasma adrenocorticotrophic hormone (ACTH) and corticosterone levels were increased significantly in irradiated compared with nonirradiated rats. Plasma aldosterone was not affected by TBI at either time point, whereas plasma renin activity was decreased in irradiated rats at 8 days. Basal and stimulated adrenal steroid synthesis in vitro was not affected by TBI. In addition, plasma epinephrine was decreased at 70 days after TBI. The hypothalamic expression of CRH messenger RNA (mRNA) and hippocampal expression of glucocorticoid receptor mRNA were unchanged by irradiation. We conclude that the hypertension of radiation nephropathy is not aldosterone or catecholamine-dependent but that there is an abscopal activation of the HPA axis after 10 Gy TBI. This activation was attributable at least partially to enhanced pituitary ACTH production.

Stress and adrenergic function: HIF1α, a potential regulatory switch

Stress elicits adrenal epinephrine and cortisol release into the bloodstream to initiate physiological and behavioral responses to counter and overcome stress, the classic "fight or flight" response (Cannon and De La Paz, Am J Physiol 28:64-70, 1911). Stress and the stress hormone epinephrine also contribute to the pathophysiology of illness, e.g., behavioral disorders, cardiovascular disease, and immune dysfunction. Epinephrine itself is regulated by stress through its biosynthesis by phenylethanolamine N-methyltransferase (PNMT, EC 2.1.1.28). Single and repeated immobilization (IMMO) stress in rats stimulates adrenal PNMT mRNA and protein expression via the transcription factors, Egr-1 and Sp1. Moderate hypoxic stress increases PNMT promoter-driven gene expression and endogenous PNMT mRNA and protein in PC12 cells. Induction is initiated through cAMP and PLC signaling, with PKA, PKC, PI3K, ERK1/2 MAPK, and p38 MAPK continuing downstream signal transduction, followed by activation of HIF1α, Egr-1, and Sp1. While functional Egr-1 and Sp1 binding sites exist within the proximal PNMT promoter, a putative hypoxia response element is a weak HIF binding site. Yet, HIF1α overexpression increases PNMT promoter-driven luciferase activity and endogenous PNMT. When the Egr-1 or Sp1 sites are mutated, HIF1α does not stimulate the PNMT promoter. siRNA knock down of Egr-1 or Sp1 prevents promoter activation while siRNA knock down of HIF1α inhibits Egr-1 and Sp1 induction. Findings suggest that hypoxia activates the PNMT gene indirectly via HIF1α stimulation of Egr-1 and Sp1. Thus, for stress-induced illnesses where adrenergic dysfunction is implicated, HIF1α may be an "on-off" switch regulating adrenergic responses to stress and a potential target for therapeutic intervention.

Cardiac and plasma lipid profiles in response to acute hypoxia in neonatal and young adult rats

Background

The physiological and biochemical responses to acute hypoxia have not been fully characterized in neonates. Fatty acids and lipids play an important role in most aspects of cardiac function.

Methods

We performed comprehensive lipid profiling analysis to survey the changes that occur in heart tissue and plasma of neonatal and young adult rats exposed to hypoxia for 2 h, and following 2 h of recovery from hypoxia.

Results

Cardiac and plasma concentrations of short-chain acylcarnitines, and most plasma long-chain fatty acids, were decreased in hypoxic neonates. Following recovery from hypoxia, concentrations of propionylcarnitine, palmitoylcarnitine, stearoylcarnitine were increased in neonatal hearts, while oleylcarnitine and linoleylcarnitine concentrations were increased in neonatal plasma. The concentrations of long-chain fatty acids and long-chain acylcarnitines were increased in the hearts and plasma of hypoxic young adult rats; these metabolites returned to baseline values following recovery from hypoxia.

Conclusion

There are differential effects of acute hypoxia on cardiac and plasma lipid profiles with maturation from the neonate to the young adult rat. Changes to neonatal cardiac and plasma lipid profiles during hypoxia likely allowed for greater metabolic and physiologic flexibility and increased chances for survival. Persistent alterations in the neonatal cardiac lipid profile following recovery from hypoxia may play a role in the development of rhythm disturbances.