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.

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.

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.

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.

Inhibitory respiratory responses to progesterone and allopregnanolone in newborn rats chronically treated with caffeine.

KEY POINTS: In premature newborns, recurrent apnoea is systematically treated with caffeine to prevent long-term neurocognitive disorders, but a substantial percentage of apnoea persists particularly in neonates born before 28 weeks of gestation. Progesterone has been proposed as a respiratory stimulant potentially suitable for the treatment of newborn apnoea persistent to caffeine. Accordingly we asked whether acute progesterone administration reduces apnoea frequency in newborn rats treated with caffeine. Surprisingly our results show that in newborn rats treated with caffeine, administration of progesterone inhibits breathing and increases apnoea frequency. Additional experiments showed an enhanced GABAergic inhibitory drive on breathing after caffeine treatment, and that progesterone is converted to allopregnanolone (an allosteric modulator of GABAA receptors) to inhibit breathing. We conclude that combining progesterone and chronic caffeine is not an option in preterm neonates, unless the effects of allopregnanolone can be counteracted. ABSTRACT: Caffeine is the main treatment for apnoea in preterm neonates, but its interactions with other respiratory stimulants like progesterone are unknown. We tested the hypothesis that the addition of progesterone to caffeine treatments further stimulates ventilation. Newborn rats were treated with water (control) or caffeine (15 mg kg(-1)) by daily gavage between postnatal day (P)3 and P12. At P4 and P12, we measured apnoea frequency, ventilatory responses and metabolic parameters under both normoxia and hypoxia (12% O2, 20 min) following an acute administration of either saline or progesterone (4 mg kg(-1); i.p.). Progesterone injection increased the serum levels of both progesterone and its neuroactive metabolite allopregnanolone. Progesterone had no effect on ventilation in control rats under normoxia. Progesterone depressed ventilation in P12 caffeine-treated rats under normoxia and hypoxia and increased apnoea frequency in both P4 and P12 rats. Because allopregnanolone is an allosteric modulator of GABAA receptors and caffeine may enhance GABAergic inhibition in newborns, we studied the effects of the GABAA receptor antagonist bicuculline at 0, 1, 2 and 3 mg kg(-1) doses and allopregnanolone (10 mg kg(-1) dose) in P12 rats. In caffeine-treated rats, bicuculline enhanced ventilation, while allopregnanolone decreased ventilation and increased total apnoea time. Progesterone had no effect on ventilation and apnoea frequency in caffeine-treated rats injected with finasteride, which blocks the conversion of progesterone to allopregnanolone. We conclude that combining progesterone and chronic caffeine therapy is not an option for the treatment of persistent apnoea in preterm neonates, unless the effects of allopregnanolone can be counteracted.

Effects of Targeting Higher or Lower Oxygen Saturations in Centers with More Versus Less Separation between Median Saturations.

Subgroup analysis of the Canadian Oxygen Trial to compare outcomes of extremely preterm infants in centers with more versus less separation between median arterial oxygen saturations in the two target ranges. Centers with more separation observed lower rates of death or disability in the 85%-89% range than in the 91%-95% target range.

Prediction of Late Death or Disability at Age 5 Years Using a Count of 3 Neonatal Morbidities in Very Low Birth Weight Infants.

OBJECTIVE: To evaluate bronchopulmonary dysplasia (BPD), serious brain injury, and severe retinopathy of prematurity (ROP) as predictors of poor long-term outcome in very low birth weight infants. STUDY DESIGN: We examined the associations between counts of the 3 morbidities and long-term outcomes in 1514 of 1791 (85%) infants with birth weights of 500-1250 g who were enrolled in the Caffeine for Apnea of Prematurity trial from October 1999, to October 2004, had complete morbidity data, and were alive at 36 weeks postmenstrual age (PMA). BPD was defined as use of supplemental oxygen at 36 weeks PMA. Serious brain injury on cranial ultrasound included grade 3 and 4 hemorrhage, cystic periventricular leucomalacia, porencephalic cysts, or ventriculomegaly of any cause. Poor long-term outcome was death after 36 weeks PMA or survival to 5 years with 1 or more of the following disabilities: motor impairment, cognitive impairment, behavior problems, poor general health, deafness, and blindness. RESULTS: BPD, serious brain injury, and severe ROP occurred in 43%, 13%, and 6% of the infants, respectively. Each of the 3 morbidities was similarly and independently correlated with poor 5-year outcome. Rates of death or disability (95% CI) in children with none, any 1, any 2, and all 3 morbidities were 11.2% (9.0%-13.7%), 22.9% (19.6%-26.5%), 43.9% (35.5%-52.6%), and 61.5% (40.6%-79.8%), respectively. CONCLUSIONS: In very low birth weight infants who survive to 36 weeks PMA, a count of BPD, serious brain injury, and severe ROP predicts the risk of a late death or survival with disability at 5 years.

An Overview on the Respiratory Stimulant Effects of Caffeine and Progesterone on Response to Hypoxia and Apnea Frequency in Developing Rats.

The respiratory stimulant caffeine is the most frequently used xanthine (theophylline or aminophylline) for the treatment of apnea in premature infants. It decreases but does not eliminate apnea. In most cases such decreases is insufficient to prevent the use of artificial ventilation. Progesterone is a respiratory stimulant in adult mammals including human, and it decreases sleep apnea in menopausal women. Whether progesterone as an adjunct to caffeine therapy could be effective in further reducing the frequency of apnea in premature infants is not known because its respiratory effect in newborns has not been well studied. Using rat pups at different postnatal ages, we first determined whether the respiratory stimulant effects of acute caffeine (10 mg/kg, i.p.) or progesterone (4 mg/kg i.p.) are age dependent. These studies showed that caffeine enhances the ventilatory response to hypoxia in 1 and 4 days-old rats while it decreases apnea frequency in 12-days-old. In contrast, progesterone enhances the ventilatory response to hypoxia in less than 7-days-old but decreases apnea in 1-day-old rats. Preliminary experiments show that administration of progesterone (4 mg/kg i.p.) to newborn rats that are chronically treated with caffeine (mimicking its clinical uses - 7.5 mg/kg once/day by gavage) enhances the respiratory stimulant effects of caffeine. Surprisingly, acute injection of progesterone enhances apnea frequency and reduces hypoxic ventilatory response in 12-day-old rats.

Inhibition of Protein Kinases AKT and ERK1/2 Reduce the Carotid Body Chemoreceptor Response to Hypoxia in Adult Rats.

The carotid body is the main mammalian oxygen-sensing organ regulating ventilation. Despite the carotid body is subjected of extensive anatomical and functional studies, little is yet known about the molecular pathways signaling the neurotransmission and neuromodulation of the chemoreflex activity. As kinases are molecules widely involved in motioning a broad number of neural processes, here we hypothesized that pathways of protein kinase B (AKT) and extracellular signal-regulated kinases ½ (ERK1/2) are implicated in the carotid body response to hypoxia. This hypothesis was tested using the in-vitro carotid body/carotid sinus nerve preparation ("en bloc") from Sprague Dawley adult rats. Preparations were incubated for 60 min in tyrode perfusion solution (control) or containing 1 µM of LY294002 (AKT inhibitor), or 1 µM of UO-126 (ERK1/2 inhibitor). The carotid sinus nerve chemoreceptor discharge rate was recorded under baseline (perfusion solution bubbled with 5 % CO(2) balanced in O(2)) and hypoxic (perfusion solution bubbled with 5 % CO(2) balanced in N(2)) conditions. Compared to control, both inhibitors significantly decreased the normoxic and hypoxic carotid body chemoreceptor activity. LY294002- reduced carotid sinus nerve discharge rate in hypoxia by about 20 %, while UO-126 reduces the hypoxic response by 45 %. We concluded that both AKT and ERK1/2 pathways are crucial for the carotid body intracellular signaling process in response to hypoxia.

Association Between Intermittent Hypoxemia or Bradycardia and Late Death or Disability in Extremely Preterm Infants.

IMPORTANCE: Extremely preterm infants may experience intermittent hypoxemia or bradycardia for many weeks after birth. The prognosis of these events is uncertain. OBJECTIVE: To determine the association between intermittent hypoxemia or bradycardia and late death or disability. DESIGN, SETTING, AND PARTICIPANTS: Post hoc analysis of data from the inception cohort assembled for the Canadian Oxygen Trial in 25 hospitals in Canada, the United States, Argentina, Finland, Germany, and Israel, including 1019 infants with gestational ages of 23 weeks 0 days through 27 weeks 6 days who were born between December 2006 and August 2010 and survived to a postmenstrual age of 36 weeks. Follow-up assessments occurred between October 2008 and August 2012. EXPOSURES: Episodes of hypoxemia (pulse oximeter oxygen saturation <80%) or bradycardia (pulse rate <80/min) for 10 seconds or longer. Values were sampled every 10 seconds within 24 hours after birth until at least 36 weeks' postmenstrual age. MAIN OUTCOMES AND MEASURES: The primary outcome was a composite of death after 36 weeks' postmenstrual age, motor impairment, cognitive or language delay, severe hearing loss, or bilateral blindness at 18 months' corrected age. Secondary outcomes were motor impairment, cognitive or language delay, and severe retinopathy of prematurity. RESULTS: Downloaded saturation and pulse rate data were available for a median of 68.3 days (interquartile range, 56.8-86.0 days). Mean percentages of recorded time with hypoxemia for the least and most affected 10% of infants were 0.4% and 13.5%, respectively. Corresponding values for bradycardia were 0.1% and 0.3%. The primary outcome was ascertained for 972 infants and present in 414 (42.6%). Hypoxemic episodes were associated with an estimated increased risk of late death or disability at 18 months of 56.5% in the highest decile of hypoxemic exposure vs 36.9% in the lowest decile (modeled relative risk, 1.53; 95% CI, 1.21-1.94). This association was significant only for prolonged hypoxemic episodes lasting at least 1 minute (relative risk, 1.66; 95% CI, 1.35-2.05 vs for shorter episodes, relative risk, 1.01; 95% CI, 0.77-1.32). Relative risks for all secondary outcomes were similarly increased after prolonged hypoxemia. Bradycardia did not alter the prognostic value of hypoxemia. CONCLUSIONS AND RELEVANCE: Among extremely preterm infants who survived to 36 weeks' postmenstrual age, prolonged hypoxemic episodes during the first 2 to 3 months after birth were associated with adverse 18-month outcomes. If confirmed in future studies, further research on the prevention of such episodes is needed.

Gestational stress promotes pathological apneas and sex-specific disruption of respiratory control development in newborn rat.

Recurrent apneas are important causes of hospitalization and morbidity in newborns. Gestational stress (GS) compromises fetal brain development. Maternal stress and anxiety during gestation are linked to respiratory disorders in newborns; however, the mechanisms remain unknown. Here, we tested the hypothesis that repeated activation of the neuroendocrine response to stress during gestation is sufficient to disrupt the development of respiratory control and augment the occurrence of apneas in newborn rats. Pregnant dams were displaced and exposed to predator odor from days 9 to 19 of gestation. Control dams were undisturbed. Experiments were performed on male and female rats aged between 0 and 4 d old. Apnea frequency decreased with age but was consistently higher in stressed pups than controls. At day 4, GS augmented the proportion of apneas with O(2) desaturations by 12%. During acute hypoxia (12% O(2)), the reflexive increase in breathing augmented with age; however, this response was lower in stressed pups. Instability of respiratory rhythm recorded from medullary preparations decreased with age but was higher in stressed pups than controls. GS reduced medullary serotonin (5-HT) levels in newborn pups by 32%. Bath application of 5-HT and injection of 8-OH-DPAT [(±)-8-hydroxy-2-di-(n-propylamino) tetralin hydrobromide; 5-HT(1A) agonist; in vivo] reduced respiratory instability and apneas; these effects were greater in stressed pups than controls. Sex-specific effects were observed. We conclude that activation of the stress response during gestation is sufficient to disrupt respiratory control development and promote pathological apneas in newborn rats. A deficit in medullary 5-HT contributes to these effects.

Reduced hypoxic ventilatory response in newborn mice knocked-out for the progesterone receptor.

Recent studies showed that progesterone stimulates the hypoxic ventilatory response and may reduce apnoea frequency in newborn rats, but so far we still do not know by what mechanisms and whether endogenous progesterone might contribute to respiratory control in neonates. We therefore determined the role of the nuclear progesterone receptor (PR; member of the steroid receptor superfamily) by using wild-type (WT) and PR knock-out (PRKO) mice at postnatal days (P) 1, 4 and 10. We measured the hypoxic ventilatory response (14 and 12% O2, 20 min each) and apnoea frequency in both male and female mice by using whole-body plethysmography. In response to hypoxia, WT male mice had a marked hypoxic ventilatory response at P1 and P10, but not at P4. At P1 and P10, PRKO male mice had a lower hypoxic ventilatory response than WT males. Wild-type female mice had a marked hypoxic ventilatory response at P10, but not at P1 and P4. At P1 and P10, PRKO female mice had a lower hypoxic ventilatory response than WT females. In basal conditions, apnoea frequency was similar in WT and PRKO mice at P1, P4 and P10. During hypoxia, apnoea frequency was higher in WT male mice compared with PRKO male mice and WT female mice at P1. We conclude that PR is a key contributor to the hypoxic ventilatory response in newborn mice, but PR deletion does not increase the frequency of apnoea during normoxia or hypoxia.

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.

Systemic blockade of nicotinic and purinergic receptors inhibits ventilation and increases apnoea frequency in newborn rats.

We hypothesized that the combined blockade of peripheral cholinergic and purinergic receptors alters the baseline breathing pattern and respiratory responses to carotid body stimuli (hypoxia, hyperoxia and hypercapnia). Rat pups at 4 (P4) and 12 days of postnatal age (P12) received an intraperitoneal injection of either saline vehicle or hexamethonium + suramin (Hex, 1 mg kg(-1), nicotinic receptor antagonist; Sur, 40 mg kg(-1), P2X receptor antagonist; both of which act mainly on peripheral receptors). Compared with the control animals (saline-injected rats), the Hex + Sur-treated rats demonstrated the following features: (1) decreased baseline ventilation and increased frequency of apnoea and breath-by-breath irregularities, with a larger effect in the P4 than in the P12 rats; (2) a decreased peak minute ventilation and respiratory frequency response to hypoxia (fractional inspired oxygen 12%), with a greater effect in the P12 than in the P4 rats; (3) an attenuated decline of the respiratory frequency during hyperoxia (fractional inspired oxygen 50%) to a similar magnitude in rats of both ages; and (4) a decreased hypercapnic ventilatory response (fractional inspired carbon dioxide 5%) to a similar magnitude in rats of both ages. We conclude that the cholinergic nicotinic and purinergic P2X receptors are essential to maintain an adequate baseline pattern in normoxia. They also contribute, albeit not exclusively, to the hypoxic ventilatory response, with an age-specific effect, most probably linked to the cholinergic component, which might partly underlie the postnatal maturation of peripheral chemoreceptors.

Neonatal intermittent hypoxia induces persistent alteration of baroreflex in adult male rats.

Baroreflex is involved in the regulation of arterial blood pressure (BP). An increase in BP activates vagal inhibitory pathways to decrease heart rate; a concomitant decrease in sympathetic discharge reduces vascular resistance. Both responses reduce BP towards normal value. Conversely, a decrease in BP produces opposite effects to increase heart rate and vascular resistance.

Dose dependent effect of progesterone on hypoxic ventilatory response in newborn rats.

The effect of progesterone as a respiratory stimulant in newborn subjects is less known than that in adults. This study investigated the dose-response curve (0, 2, 4, and 8 mg/kg, ip) of progesterone on ventilation in non-anesthetized newborn rats at 4- and 12-days old using plethysmography. Progesterone had no effects in the regulation of normoxic ventilation. However, it enhanced the response to moderate hypoxia (FiO(2) 12%, 20 min) in 4- but not in 12-days old pups. This response was similar between the dose of 4 and 8 mg/kg. These observations suggested that progesterone enhances in age- and dose-dependent manner the hypoxic ventilatory response in newborn rats.

Impact of delivery room resuscitation on outcomes up to 18 months in very low birth weight infants.

OBJECTIVE: To examine the relationships between intensity of delivery room resuscitation and short- and long-term outcomes of very low birth weight infants enrolled in the Caffeine for Apnea of Prematurity (CAP) Trial. STUDY DESIGN: The CAP Trial enrolled 2006 infants with birthweights between 500 and 1250 g who were eligible for caffeine therapy. All levels of delivery room resuscitation were recorded in study participants. We divided infants in 4 groups of increasing intensity of resuscitation: minimal, n = 343; bag-mask ventilation, n = 372; endotracheal intubation, n = 1205; and cardiopulmonary resuscitation (chest compressions/epinephrine), n = 86. We used multivariable logistic regression models to compare outcomes across the 4 groups. RESULTS: The observed rates of death or disability, death, cerebral palsy, cognitive deficit, and hearing loss at 18 months increased with higher levels of resuscitation. Risk of bronchopulmonary dysplasia, severe retinopathy of prematurity, and brain injury also increased with higher levels of resuscitation. Adjustment for prognostic variables reduced the differences between the groups for most outcomes. Only the adjusted rates of bronchopulmonary dysplasia and severe retinopathy remained significantly higher after more intense resuscitation. CONCLUSIONS: In CAP Trial participants, the risk of death or neurodevelopmental disability at 18 months did not increase substantially with increasing intensity of delivery room resuscitation.