Loss of testosterone induces postprandial insulin resistance and increases the expression of the hepatic antioxidant flavin-containing monooxygenases in mice exposed to intermittent hypoxia.

AIM: We tested the hypothesis that low testosterone alters the effects of intermittent hypoxia (IH) on glucose homeostasis, hepatic oxidative stress, and transcriptomic profile in male mice. METHODS: We used sham-operated or orchiectomized (ORX) mice exposed to normoxia (Nx) or IH for 2 weeks. We performed fasting insulin and glucose tolerance tests and assessed fasting and postprandial insulin resistance with the HOMA-IR. The activity of hepatic prooxidant (NADPH oxidase-NOX), antioxidant enzymes (superoxide dismutase, catalase, and glutathione peroxidase-SOD, Cat, GPx), lipid peroxidation (MDA concentration), and the total concentration of glutathione (GSH) were measured under postprandial conditions. mRNA sequencing and pathway enrichment analyses were used to identify hepatic genes underlying the interactions between IH and testosterone. RESULTS: In Sham mice, IH improves fasting insulin sensitivity and glucose tolerance, while there are no effects of IH in ORX mice. In ORX mice, IH induces postprandial hyperinsulinemia, insulin resistance, and a prooxidant profile of enzyme activity (low SOD activity) without altering hepatic MDA and GSH content. ORX and IH altered the expression of genes involved in oxidoreductase activities, cytochromes-dependent pathways, and glutathione metabolism. Among the genes upregulated in ORX-IH mice, the flavin-containing monooxygenases (FMO) are particularly relevant since these are potent hepatic antioxidants that could help prevent overt oxidative stress in ORX-IH mice. CONCLUSION: Low levels of testosterone in male mice exposed to IH induce post-prandial hyperinsulinemia and insulin resistance and determine the mechanisms by which the liver handles IH-induced oxidative stress.

Orchiectomy exacerbates sleep-disordered breathing induced by intermittent hypoxia in mice.

We tested the hypothesis that low testosterone levels alter the regulation of breathing in mice exposed to intermittent hypoxia (IH). We used orchiectomized (ORX) or control (Sham-operated) mice exposed to normoxia or IH (12 h/day, 10 cycles/h, 6% O2) for 14 days. Breathing was measured by whole-body plethysmography to asses the stability of the breathing pattern (frequency distribution of total cycle time - Ttot) and the frequency and duration of spontaneous and post-sigh apneas (PSA). We characterized sighs as inducing one (S1) or more (S2) apnea and determined the sigh parameters (volume, peak inspiratory and expiratory flows, cycle times) associated with PSA. IH increased the frequency and duration of PSA and the proportion of S1 and S2 sighs. The PSA frequency was mostly related to the sigh expiratory time. The effects of IH on PSA frequency were amplified in ORX-IH mice. Our experiments using ORX support the hypothesis that testosterone is involved in the regulation of breathing in mice following IH.

The ultrasound-based cardiac output monitoring is a useful tool to define baseline hemodynamic parameters in healthy permanent residents at high altitude: results of a monocentric pilot study.

Previous studies on the cardiac data of healthy permanent residents living in high-altitude regions such as Tibet and the Andes have yielded inconsistent findings and significant disparities. These discrepancies can be mainly attributed to the invasive methods conventionally used for parameter evaluation. However, with the introduction of cutting-edge ultrasound technology, there is now an innovative approach to addressing and reconciling these variations. In this pilot study, we employed an ultrasound-based cardiac output monitoring (USCOM) device to evaluate cardiac output and related hemodynamic variables in a group of 20 healthy high-altitude Andean residents (comprising 10 men and 10 women) aged between 26 and 35 years old. The monocentric study was carried out in La Paz, Bolivia, located between at an altitude of 3,600-4,000 m. A total of 60 hemodynamic measurements were evaluated, accounting for three technical replicates per subject. Our results showed strong intrasubject reproducibility and revealed important differences related to both sex and hemodynamic parameters in highlanders compared to individuals residing at sea level. We conclude that USCOM represents a highly reliable technology for performing hemodynamic measurements in high-altitude residents. Our preliminary findings underscore the need for larger studies, encompassing larger sample sizes, specifically tailored to gender considerations, and extendable to broader highland populations. These findings have special significant implications for the management of hemodynamics in intensive care and postoperative settings, warranting further comprehensive research efforts.

Erythropoietin Produces a Dual Effect on Carotid Body Chemoreception in Male Rats.

Erythropoietin (EPO) regulates respiration under conditions of normoxia and hypoxia through interaction with the respiratory centers of the brainstem. Here we investigate the dose-dependent impact of EPO in the CB response to hypoxia and hypercapnia. We show, in isolated "en bloc" carotid body (CB) preparations containing the carotid sinus nerve (CSN) from adult male Sprague Dawley rats, that EPO acts as a stimulator of CSN activity in response to hypoxia at concentrations below 0.5 IU/ml. Under hypercapnic conditions, EPO did not influence the CSN response. EPO concentrations above 0.5 IU/ml decreased the response of the CSN to both hypoxia and hypercapnia, reaching complete inhibition at 2 IU/ml. The inhibitory action of high-dose EPO on the CSN activity might result from an increase in nitric oxide (NO) production. Accordingly, CB preparations were incubated with 2 IU/ml EPO and the unspecific NO synthase inhibitor (L-NAME), or the neuronal-specific NO synthase inhibitor (7NI). Both NO inhibitors fully restored the CSN activity in response to hypoxia and hypercapnia in presence of EPO. Our results show that EPO activates the CB response to hypoxia when its concentration does not exceed the threshold at which NO inhibitors masks EPO's action.

Lung oxidative stress and transcriptional regulations induced by estradiol and intermittent hypoxia.

We determined the effects of chronic intermittent hypoxia (CIH) and estradiol (E2) on oxidative stress and gene expression in the lungs. Female Sprague-Dawley rats were left intact (sham) or ovariectomized (OVX) and implanted with pumps delivering vehicle or E2 (0.5 mg/kg/day). Two weeks following surgery, the rats were exposed to room air (RA) or CIH for 7 days (10% O2, 10 cycles/hour, 8 h/day). Lung samples were used to measure the activities of pro- (NADPH and xanthine oxidases) and antioxidant (superoxide dismutase, catalase and glutathione peroxidase) enzymes, and concentrations of advanced oxidation of protein products (AOPP). We determined gene expression with an RNA microarray and enrichment analysis of differentially expressed genes. In rats exposed to RA, OVX and E2 supplementation increased pro- and antioxidant activities and AOPP concentration. In rats exposed to CIH, AOPP concentration, pro- and antioxidant enzymes activities increased in sham, did not changed in OVX-Veh rats, and were reduced in OVX-E2 rats. In rats exposed to RA, genes involved in extracellular matrix were up-regulated by OVX and down-regulated by E2, while E2 up-regulated genes involved in cell mobility/adherence and leukocytes migration. OVX downregulated expression of roughly 200 olfactory receptor genes without effect of E2. CIH altered gene expression in sham and OVX-E2, but not in OVX-Veh rats. Enrichment analysis confirmed the antioxidant effects of E2 under CIH. There are important interactions between ovarian hormones and CIH that can be relevant to better understand the consequences of sleep apnea (i.e. CIH) on the occurrence of lung pathologies in women.

Metabolic responses to intermittent hypoxia are regulated by sex and estradiol in mice.

The roles of sex and sex-hormones on the metabolic consequences of intermittent hypoxia (IH, a reliable model of sleep apnea) are unknown. We used intact male or female mice and ovariectomized (OVX) females treated with vehicle (Veh) or estradiol (E2) and exposed to normoxia (Nx) or IH (6% O2, 10 cycles/h, 12 h/day, 2 wk). Mice were then fasted for 6 h, and we measured fasting glucose and insulin levels and performed insulin or glucose tolerance tests (ITT or GTT). We also assessed liver concentrations of glycogen, triglycerides (TGs), and expression levels of genes involved in aerobic or anaerobic metabolism. In males, IH lowered fasting levels of glucose and insulin, slightly improved glucose tolerance, but altered glucose tolerance in females. In OVX-Veh females, IH reduced fasting glucose and insulin levels and strongly impaired glucose tolerance. E2 supplementation reversed these effects and improved homeostasis model assessment of ß-cell function (HOMA-ß), a marker of pancreatic glucose-induced insulin released. IH decreased liver TG concentration in males and slightly increased glycogen in OVX-Veh females. Liver expression of glycolytic (Ldha) and mitochondrial (citrate synthase, Pdha1) genes was reduced by IH in males and in OVX-Veh females, but not in intact or OVX-E2 females. We conclude that 1) IH reduced fasting levels of glycemia in males and in ovariectomized females. 2) IH improves glucose tolerance only in males. 3) In females IH decreased glucose tolerance, this effect was amplified by ovariectomy, and reversed by E2 supplementation. 4) During IH exposures, E2 supplementation appears to improve pancreatic ß cells functions.NEW & NOTEWORTHY We assessed fasting glycemic control, and tolerance to insulin and glucose in male and female mice exposed to intermittent hypoxia. IH improves glucose tolerance in males but had opposite effects in females. This response was amplified following ovariectomy in females and prevented by estradiol supplementation. Metabolic consequences of IH differ between males and females and are regulated by estradiol in female mice.

Progesterone decreases apnoea and reduces oxidative stress induced by chronic intermittent hypoxia in ovariectomized female rats.

NEW FINDINGS: What is the central question of this study? Does progesterone reduce the effect of chronic intermittent hypoxia (CIH) on arterial blood pressure, respiratory control and oxidative stress in the central nervous system in ovariectomized rats? What is the main finding and its importance? Progesterone does not prevent the elevation of arterial blood pressure in rats exposed to CIH, but normalizes respiratory control, and reduces cerebral oxidative stress. This study draws focus to a potential role of progesterone and the consequences of sleep apnoea in menopausal women. ABSTRACT: We tested the hypothesis that progesterone (Prog) reduces the effect of chronic intermittent hypoxia (CIH) on arterial blood pressure, respiratory chemoreflexes and oxidative stress in the central nervous system. Ovariectomized female rats were implanted with osmotic pumps delivering vehicle (Veh) or Prog (4 mg kg-1  day-1 ). Two weeks following the surgery, rats were exposed to room air (Air) or CIH (7 days, 10% O2 , 10 cycles h-1 , 8 h day-1 ). We studied three groups: Veh-Air, Veh-CIH and Prog-CIH. After the CIH exposures, we measured the mean arterial pressure (MAP; tail cuff) and assessed the frequency of apnoeas at rest and ventilatory responses to hypoxia and hypercapnia (whole body plethysmography). The activities of the pro-oxidant enzyme NADPH oxidase (NOX) and antioxidant enzymes superoxide dismutase (SOD; in mitochondrial and cytosolic fractions) and glutathione peroxidase (GPx), as well as the concentration of malondialdehyde (MDA), a marker of lipid peroxidation, were measured in brain cortex and brainstem samples. CIH exposure increased the MAP, the frequency of apnoeas, and the respiratory frequency response to hypoxia and hypercapnia. Prog did not prevent the CIH-induced elevation in MAP, but it reduced the CIH-induced frequency of apnoeas and increased hypoxic and hypercapnic ventilatory responses. In the brain cortex, CIH increased NOX activity, and decreased the cytosolic and mitochondrial SOD activities. These effects were prevented by Prog. NOX activity was increased by CIH in the brainstem, and this was also blocked by Prog. The study draws focus to the links between ovarian hormones and the consequences of sleep apnoea in women.

Erythropoietin and caffeine exert similar protective impact against neonatal intermittent hypoxia: Apnea of prematurity and sex dimorphism.

Apnea of prematurity (AoP) is associated with severe and repeated episodes of arterial oxygen desaturation (intermittent hypoxia - IH), which in turn increases the number of apneas. So far, there is no data addressing whether IH leads to sex-specific respiratory consequences, neither if drugs targeting AoP are more effective in males or females. We used rat pups for investigating whether IH-mediated increase of apneas is sex-specific. We also tested whether caffeine (treatment of choice of AoP), erythropoietin (Epo - a neuroprotective factor and potent respiratory stimulant), and combination of both (caffeine+Epo) prevent the IH-mediated formation of apneas in a sex-dependent manner. Newborn rats exposed to IH (21% - 10% FIO2-8 h a day - 10 cycles per hour) during postnatal days (P) 3-10 were used in this work. Animals were administered drug vehicle, Epo, caffeine and Epo + caffeine (daily from P3 to P10) gavage. At P10 the frequency of apneas at rest (as an index of respiratory dysfunction induced by IH), and respiratory parameters were measured by plethysmography. Our results showed that IH significantly increases the number of apneas in male but not in female rat pups. Moreover, caffeine and Epo in males similarly prevented the increase of apneas induced by IH, and the administration of both drugs together did not provide a cumulative beneficial effect. No impact of drugs was evidenced in females. Apart from apneas, IH increased the normoxic basal ventilation (ventilation at rest) of male animals, and treatments did not prevent such alteration. Besides, no IH- nor treatment-mediated modulation of basal ventilation was found in the basal ventilation of female animals. Analysis of the activity of pro- and antioxidative molecules revealed that IH induces oxidative stress in the brainstem of male and female animals and that all tested treatments similarly prevented such oxidative imbalance in pups of both sexes. We concluded that neonatal IH and the treatments tested to prevent its respiratory consequences are sex-specific. The mechanics associated with such prevention are directly linked with the prevention of oxidative stress and the maturation of the brain. These findings are relevant to understanding better the AoP disorder and for proposing Epo as a new therapeutical tool.

Targeting progesterone receptors in newborn males and females: From the animal model to a new perspective for the treatment of apnea of prematurity?

The steroid hormone progesterone is well-known for its role in neuroprotection, in the pre- and postnatal brain development, and is also recognized as a potent respiratory stimulant that reduces the frequency of sleep apnea in adult female subjects. Over the past few years, we have used newborn rats or mice to provide convincing evidence that the respiratory effect of progesterone involves a balance between excitation mediated by progesterone receptors, and an inhibition due to the fast conversion of progesterone to allopregnanolone, a positive allosteric modulator of GABAA receptors. This review focuses on the sex- and age- specific roles of nuclear and membrane progesterone receptors (nPR or mPR), and highlight the clinical potential of these receptors for the treatment of apnea of prematurity. We present original data showing that in newborn rats, selective nPR or mPR agonists are more efficient to reduce apnea frequency at postnatal days 12 than at postnatal day 1, and appear more efficient in males than in females. Furthermore, new results obtained by using intra-cisternal injection of specific siRNA targeting mPRα, mPRß (two mPR with high brain expression) or nPR suggest that mPRß regulates the stability of the breathing pattern in males, while effects of nPR appear in females. While several important questions remain to be addressed before a safe clinical use could be proposed, these results highlight the potential role of these drugs as complementary, and sex-specific tools for the treatment of apnea in preterm neonates.

Roles of oestradiol receptor alpha and beta against hypertension and brain mitochondrial dysfunction under intermittent hypoxia in female rats.

AIM: Chronic intermittent hypoxia (CIH) induces systemic (hypertension) and central alterations (mitochondrial dysfunction underlying cognitive deficits). We hypothesized that agonists of oestradiol receptors (ER) α and ß prevent CIH-induced hypertension and brain mitochondrial dysfunction. METHODS: Ovariectomized female rats were implanted with osmotic pumps delivering vehicle (Veh), the ERα agonist propylpyraoletriol (PPT - 30 µg/kg/day) or the ERß agonist diarylpropionitril (DPN - 100 µg/kg/day). Animals were exposed to CIH (21%-10% FI O2 - 10 cycles/hour - 8 hours/day - 7 days) or normoxia. Arterial blood pressure was measured after CIH or normoxia exposures. Mitochondrial respiration and H2 O2 production were measured in brain cortex with high-resolution respirometry, as well as activity of complex I and IV of the electron transport chain, citrate synthase, pyruvate, and lactate dehydrogenase (PDH and LDH). RESULTS: Propylpyraoletriol but not DPN prevented the rise of arterial pressure induced by CIH. CIH exposures decreased O2 consumption, complex I activity, and increased H2 O2 production. CIH had no effect on citrate synthase activity, but decreased PDH activity and increased LDH activity indicating higher anaerobic glycolysis. Propylpyraoletriol and DPN treatments prevented all these alterations. CONCLUSIONS: We conclude that in OVX female rats, the ERα agonist prevents from CIH-induced hypertension while both ERα and ERß agonists prevent the brain mitochondrial dysfunction and metabolic switch induced by CIH. These findings may have implications for menopausal women suffering of sleep apnoea regarding hormonal therapy.

Protective roles of estradiol against vascular oxidative stress in ovariectomized female rats exposed to normoxia or intermittent hypoxia.

AIM: We tested the hypothesis that estradiol (E2 ) reduces aortic oxidative stress and endothelial dysfunction in ovariectomized (OVX) female rats exposed to room air (RA) or chronic intermittent hypoxia (CIH). METHODS: We used intact or OVX female rats treated with vehicle or E2 (0.5 mg/kg/d) and exposed to RA or CIH (21%-10% O2 , 10 cycles/h, 8 h/d) for 7 or 35 days, and measured the arterial pressure, heart rate and plasma endothelin-1 levels. We also measured in thoracic aortic samples, the activities of the pro-oxidant enzymes NADPH (NOX) and xanthine oxidase (XO), the antioxidant enzymes superoxide dismutase, catalase, glutathione peroxidase and the advanced oxidation protein products (AOPP-oxidative stress marker). Finally, we used aortic rings to assess the contractile response to phenylephrine and the vasodilatory response to acetylcholine. RESULTS: After 7 or 35 days of CIH, E2 supplementation reduced arterial pressure. E2 reduced plasma endothelin-1 levels after 7 days of CIH, but not after 35 days. Ovariectomy, but not CIH for 7 days, increased aortic oxidative stress and E2 treatment prevented this effect. Remarkably, in animals exposed to RA, this was achieved by a reduction in NOX and XO activities, but in animals exposed to CIH this was achieved by increased catalase activity. In OVX female rats exposed to CIH for 7 days, E2 supplementation improved the NO-mediated vasodilation. After 35 days of CIH, enzymatic activities, AOPP and aortic reactivity were similar in all groups. CONCLUSION: E2 -based therapy could help prevent the vascular consequences of CIH in apneic women.

Role of Estradiol Receptor Beta (ERß) on Arterial Pressure, Respiratory Chemoreflex and Mitochondrial Function in Young and Aged Female Mice.

We tested the hypothesis that ERß is involved in respiratory control in female mice. We used young adult (5-6 months-old) and aged (17-18 months-old) ERßKO or wild-type controls (WT) female mice to assess arterial blood pressure (via a tail-cuff sensor) and indices of respiratory pattern (sighs and apneas - recorded by whole body plethysmography at rest). We also measured respiratory parameters at rest and in response to brief (<10 min) exposure to hypoxia (12% O2) or hypercapnia (5% CO2). Because ERß is localized in mitochondria, and because estradiol and ERß agonist increase mitochondrial O2 consumption, we assessed the mitochondrial respiration (with a high-resolution oxygraph system) and the in vitro activity of the complex I of the electron transfer chain in samples of brain cortex in aged wild-type and ERßKO female mice. Compared to young WT mice, young ERßKO mice had elevated arterial blood pressure, but similar ventilatory responses to hypoxia and hypercapnia. In old ERßKO female mice compared to old WT mice, the arterial blood pressure was lower, the frequency of sighs was higher and the frequency of apneas was lower, and the hypoxic and hypercapnic ventilatory responses were reduced. In old ERßKO mice mitochondrial respiration and complex I activities in the brain cortex were lower than in WT mice. We conclude that ERß has age-specific effects on vascular and respiratory functions in female mice.

Sex-based differences in apnoea of prematurity: A retrospective cohort study.

NEW FINDINGS: What is the central question of the study? Is there a sex-based difference in the incidence of apnoea of prematurity and the success or failure of caffeine therapy in preterm infants? What is the main finding and its importance? Our data show that females received fewer days of caffeine treatment than males. This was most noticeable in infants born between 260/7 and 276/7  weeks of gestational age. These results highlight the importance of considering sex in clinical and basic research investigating the pathophysiology of apnoea of prematurity. ABSTRACT: This retrospective cohort study assessed whether sex influences the occurrence of apnoea of prematurity (AOP) in preterm infants. The analysis included a cohort of 24,387 preterm infants born between the gestational ages (GA) of 240/7 and 336/7  weeks that were admitted to tertiary neonatal care units participating in the Canadian Neonatal Network from January 2011 to December 2015. Of those, 13,983 (57%) were diagnosed with AOP. More females were diagnosed with AOP than males, but the difference in the male/female ratio was marginal (P = 0.058). The majority (89%) of infants diagnosed with AOP received caffeine (89% of males; 89% of females). By using the discontinuation of caffeine therapy as a proxy for the resolution of significant AOP, data analysis showed that females born before 336/7 weeks of GA stopped caffeine treatment earlier than males whether the caffeine was discontinued before 34 or 37 weeks of GA. Consequently, females had fewer days of caffeine therapy than males, especially infants born between 260/7 and 276/7  weeks (P < 0.004), 280/7 and 296/7  weeks (P < 0.03), and 320/7 and 336/7  weeks of GA (P < 0.04). Similar trends were observed when the corrected GA at discontinuation of caffeine was used. Given that AOP is indicative of an immature respiratory system, our data suggest that the maturation of the respiratory system might occur more rapidly in females than males. We conclude that sex needs to be considered in future studies on AOP.

Respiratory regulation by steroids in newborn rats: a sex-specific balance between allopregnanolone and progesterone receptors.

NEW FINDINGS: What is the central question of this study? What are the contributions of allopregnanolone, the neuroactive metabolite of progesterone, and nuclear (nPR) and membrane (mPR) progesterone receptors to the respiratory effect of progesterone in newborn rats? What is the main finding and its importance? Acute progesterone injection increases the apnoea frequency, whereas finasteride (which blocks the conversion of progesterone to allopregnanolone) reduces apnoea frequency. An nPR agonist decreases apnoea frequency in males and an mPR agonist decreases apnoea frequency in males and females. Chronic injection of progesterone decreases the frequency of apnoea more efficiently in males than in females. We tested the hypothesis that the effects of progesterone on apnoea frequency in newborn rats are the result of a balance between its neuroactive metabolite, allopregnanolone (GABAA receptor modulator), and progesterone receptors. We used male and female rats between 10 and 12 days of age and recorded respiratory and metabolic parameters (whole-body plethysmography), and assessed the frequency and duration of apnoeas in normoxia. We tested the effects of a single injection of progesterone (4 mg kg-1 , i.p.), finasteride (10 mg kg-1 , i.p.; a 5α-reductase antagonist, which blocks the conversion of progesterone to allopregnanolone), finasteride plus progesterone, or agonists of the nuclear or membrane progesterone receptors (R5020 or Org-od-02-0, 4 mg kg-1 ). To test the hypothesis that chronic exposure to progesterone reduces the frequency of apnoeas, we used male and female rats treated daily with progesterone between postnatal days 3 and 12. The acute injection of progesterone reduced minute ventilation and metabolic rate and increased the frequency of apnoeas. Finasteride decreased the frequency of apnoeas, and finasteride plus progesterone did not increase apnoea frequency but decreased minute ventilation in female rats. Although R5020 decreased apnoea frequency only in males, Org-od-02-0 decreased apnoea frequency in males and females and decreased respiratory frequency in females. Chronic progesterone treatment reduced apnoea frequency more efficiently in males than in females, but in females (not in males) an acute injection of caffeine (the gold standard for the treatment of apnoea in preterm neonates) further reduced apnoea frequency. Apnoea frequency in newborn rats is, in part, determined by a sex-specific balance between allopregnanolone, GABAA receptors and progesterone receptors.

Estradiol Protects Against Cardiorespiratory Dysfunctions and Oxidative Stress in Intermittent Hypoxia.

Study Objectives: We tested the hypothesis that estradiol (E2) protects against cardiorespiratory disorders and oxidative stress induced by chronic intermittent hypoxia (CIH) in adult female rats. Methods: Sprague-Dawley female rats (230-250 g) were ovariectomized and implanted with osmotic pumps delivering vehicle or E2 (0.5 mg/kg/d). After 14 days of recovery, the rats were exposed to CIH (21%-10% O2: 8 h/d, 10 cycles per hour) or room air (RA). After 7 days of CIH or RA exposure, we measured arterial pressures (tail cuff), metabolic rate (indirect calorimetry), minute ventilation, the frequency of sighs and apneas at rest, and ventilatory responses to hypoxia and hypercapnia (whole body plethysmography). We collected the cerebral cortex, brainstem, and adrenal glands to measure the activity of NADPH and xanthine oxidase (pro-oxidant enzymes), glutathione peroxidase, and the mitochondrial and cytosolic superoxide dismutase (antioxidant enzymes) and measured lipid peroxidation and advanced oxidation protein products (markers of oxidative stress). Results: CIH increased arterial pressure, the frequency of apnea at rest, and the hypoxic and hypercapnic ventilatory responses and reduced metabolic rate. CIH also increased oxidant enzyme activities and decreased antioxidant activity in the cortex. E2 treatment reduced body weight and prevented the effects of CIH. Conclusions: E2 prevents cardiorespiratory disorders and oxidative stress induced by CIH. These observations may help to better understand the underlying mechanisms linking menopause and occurrence of sleep apnea in women and highlight a potential advantage of hormone therapy.

Sex-specific respiratory effects of acute and chronic caffeine administration in newborn rats.

Caffeine is widely used for the treatment of apnea of prematurity (AoP) but whether this effect varies with sex is unknown. To shed some light on this question, we present a summary of data obtained on the effects of caffeine on the respiratory chemoreflexes and apnea frequency in 1- and 12-days old male and female rats. Caffeine was either administered as a single acute injection (10mg/kg, i.p.) or for 10 consecutive days (7.5mg/kg/day between 3 and 12days of life by gavage, simulating its clinical use). Acute caffeine had little effects on breathing in 1-day old male and female rats. In 12-days old female rats caffeine reduced the response to hypercapnia (not hypoxia) compared to males. During the steady state of hypoxia females had a lower frequency of apneas than males, and acute injection of caffeine decreased the frequency of apnea, suppressing the differences between males and females. In 12-days old rats chronic administration of caffeine stimulated basal breathing and decreased the frequency of apnea similarly in males and females. In response to hypoxia, chronic caffeine administration also masked the difference in respiratory frequency between males and females observed in control rats. Female rats had lower frequency of apnea than males with or without caffeine treatment. These observations indicate that sex influences the respiratory responses to caffeine and this effect seems to depend on the modality of administration (acute vs chronic) and environmental oxygen (normoxia vs hypoxia).

Ovarian steroids act as respiratory stimulant and antioxidant against the causes and consequences of sleep-apnea in women.

Evidence supports the importance of ovarian hormones as potential tools against sleep apneas in women. On one hand, progesterone is largely acknowledged as being a respiratory stimulant that reduces the frequency of apneas, but the underlying mechanisms remain poorly understood. Recent studies in mice showed that the respiratory effects of progesterone are mediated by at least two classes of progesterone receptors, including the nuclear (nPR) and membrane receptors (mPR). Some of these receptors (nPR) have sex-specific effects on the frequency of apneas recorded during sleep in mice, while mPRß acts in males as well as in females. Moreover, sleep apnea is a condition that induces an "oxidative stress" response in several tissues, and this contributes to the deleterious consequences of sleep apneas, including the development of hypertension. While estradiol is recognized as an antioxidant hormone, its potential protective role has remained mostly ignored in the field. We will review recent data supporting an antioxidant role of estradiol in female rats exposed to intermittent hypoxia, a reliable animal model of sleep apnea. Since estradiol has two main receptors (ERα and ERß) we will discuss their relative implications, and present new data showing a key role for ERα to prevent the hypertension induced by intermittent hypoxia. Overall this review highlights the fact that ovarian hormones could potentially be used as efficient tools against the causes (i.e. instabilities of the respiratory control system) and consequences (oxidative stress) of sleep apnea.

Respiratory responses to progesterone and allopregnanolone following chronic caffeine treatment in newborn female rats.

We recently showed that in 12-day-old male rats exposed to caffeine for 10 consecutive days, progesterone inhibits the respiratory response to hypoxia and increases apnea frequency (Uppari et al., 2016). This was partly due to a higher inhibitory response of GABAa receptor to allopregnanolone, the neuroactive metabolite of progesterone. In the present study, we addressed whether similar effects occur in females. We used newborn female rats daily gavaged with water (control) or caffeine (15mg/kg) between the postnatal (P) days 3-12. At P12, we recorded ventilation, metabolic rate, and apnea frequency and duration in normoxia and in response to moderate hypoxia, following an intraperitonial injection of progesterone (4mg/kg) or allopregnanolone (10mg/kg). In control rats, progesterone had no effect on breathing in normoxia and in hypoxia, and in rats treated with caffeine it decreased the initial increase in respiratory frequency in hypoxia. In both groups, allopregnalone decreased breathing frequency in normoxia and in hypoxia and increased the frequency of apnea in normoxia in control rats and in rats treated with caffeine. Injection of bicuculline (a specific GABAa receptor antagonist) prevented the inhibitory effects of allopregnanolone on breathing in both groups. These data indicate that chronic caffeine treatment unmasked an inhibitory effect of progesterone on the hypoxic response but this was weaker than in males, and contrasting to what was observed in male rats (Uppari et al., 2016), GABAa receptors are not significantly affected by chronic caffeine treatment in newborn female rats.

Efficient breathing at neonatal ages: A sex and Epo-dependent issue.

During postnatal life, the respiratory control system undergoes intense development and is highly responsive to stimuli emerging from the environment. In fact, interruption of breathing prevents gas exchange and results in systemic hypoxia that, if prolonged, can lead to cardio-respiratory failure or sudden infant death. Moreover, in newborns and infants, respiratory disorders related to neural control dysfunction show significant sexual dimorphism with a higher prevalence in males. To this day, the therapeutic tools available to alleviate these respiratory disorders remain limited. Furthermore, the factors explaining the sexual dimorphism in newborns and during infancy remain unknown. Erythropoietin (Epo) was originally discovered as a cytokine able to increase the production of red blood cells upon conditions of reduced oxygen availability. We now know that Epo is a cytokine also secreted by neurons and astrocytes that protects the brain during trauma or hypoxic stress in a sex dependent manner. In this novel line of research, our previous studies demonstrated at adult ages that cerebral Epo acts as a respiratory stimulant in rodents and humans. These results provided a strong rationale for exploring the role of cerebral Epo in neuronal respiratory control during postnatal development. The objective of this review is to summarize our recent findings showing that cerebral Epo is a potent sex-specific respiratory stimulant at neonatal ages. Keeping in mind that Epo is routinely and safely administrated in newborn humans for anemia and neonatal asphyxia, we predict that our research provides the basis necessary to promote the clinical use of Epo against neonatal respiratory disorders related to neural control dysfunction.