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.

Consequences of maternal omega-3 polyunsaturated fatty acid supplementation on respiratory function in rat pups.

KEY POINTS: Incomplete development of the neural circuits that control breathing contributes to respiratory disorders in pre-term infants. Manifestations include respiratory instability, prolonged apnoeas and poor ventilatory responses to stimuli. Based on evidence suggesting that omega-3 polyunsaturated fatty acids (n-3 PUFA) improves brain development, we determined whether n-3 PUFA supplementation (via the maternal diet) improves respiratory function in 10-11-day-old rat pups. n-3 PUFA treatment prolonged apnoea duration but augmented the relative pulmonary surface area and the ventilatory response to hypoxia. During hypoxia, the drop in body temperature measured in treated pups was 1 °C less than in controls. n-3 PUFA treatment also reduced microglia cell density in the brainstem. Although heterogeneous, the results obtained in rat pups constitute a proof of concept that n-3 PUFA supplementation can have positive effects on neonatal respiration. This includes a more sustained hypoxic ventilatory response and a decreased respiratory inhibition during laryngeal chemoreflex. ABSTRACT: Most pre-term infants present respiratory instabilities and apnoeas as a result of incomplete development of the neural circuits that control breathing. Because omega-3 polyunsaturated fatty acids (n-3 PUFA) benefit brain development, we hypothesized that n-3 PUFA supplementation (via the maternal diet) improves respiratory function in rat pups. Pups received n-3 PUFA supplementation from an enriched diet (13 g kg-1 of n-3 PUFA) administered to the mother from birth until the experiments were performed (postnatal days 10-11). Controls received a standard diet (0.3 g kg-1 of n-3 PUFA). Breathing was measured in intact pups at rest and during hypoxia (FiO2  = 0.12; 20 min) using whole body plethysmography. The duration of apnoeas induced by stimulating the laryngeal chemoreflex (LCR) was measured under anaesthesia. Lung morphology was compared between groups. Maternal n-3 PUFA supplementation effectively raised n-3 PUFA levels above control levels both in the blood and brainstem of pups. In intact, resting pups, n-3 PUFA increased the frequency and duration of apnoeas, especially in females. During hypoxia, n-3 PUFA supplemented pups hyperventilated 23% more than controls; their anapyrexic response was 1 °C less than controls. In anaesthetized pups, n-3 PUFA shortened the duration of LCR-induced apnoeas by 32%. The relative pulmonary surface area of n-3 PUFA supplemented pups was 12% higher than controls. Although n-3 PUFA supplementation augments apnoeas, there is no clear evidence of deleterious consequences on these pups. Based on the improved lung architecture and responses to respiratory challenges, this neonatal treatment appears to be beneficial to the offspring. However, further experiments are necessary to establish its overall safety.

HIF1α and physiological responses to hypoxia are correlated in mice but not in rats.

We previously reported that rats and mice that have been raised for more than 30 generations in La Paz, Bolivia (3600 m), display divergent physiological responses to high altitude, including improved respiratory and metabolic control in mice. In the present study, we asked whether these traits would also be present in response to hypoxia at sea level. To answer this question, we exposed rats (Sprague Dawley) and mice (FVB) to normoxia (21% O2) or hypoxia (15 and 12% O2) for 6 h and measured ventilation and metabolic rate (whole-body plethysmography), and expression of the transcription factor HIF-1α (ELISA and mass spectrometry) and other proteins whose expression are regulated by hypoxia (glucose transporter 1, pyruvate dehydrogenase kinase 1 and angiopoietin 2; mass spectrometry) in the brainstem. In response to hypoxia, compared with rats, mice had higher minute ventilation, lower metabolic rate and higher expression of HIF-1α in the brainstem. In mice, the expression level of HIF-1α was positively correlated with ventilation and negatively correlated with metabolic rate. In rats, the concentration of brainstem cytosolic protein decreased by 38% at 12% O2, while expression of the glucose transporter 1 increased. We conclude that mice and rats raised at sea level have divergent physiological and molecular responses to hypoxia, supporting the hypothesis that mice have innate traits that favor adaptation to altitude.

Divergent physiological responses in laboratory rats and mice raised at high altitude.

Ecological studies show that mice can be found at high altitude (HA - up to 4000 m) while rats are absent at these altitudes, and there are no data to explain this discrepancy. We used adult laboratory rats and mice that have been raised for more than 30 generations in La Paz, Bolivia (3600 m), and compared their hematocrit levels, right ventricular hypertrophy (index of pulmonary hypertension) and alveolar surface area in the lungs. We also used whole-body plethysmography, indirect calorimetry and pulse oxymetry to measure ventilation, metabolic rate (O2 consumption and CO2 production), heart rate and pulse oxymetry oxygen saturation (pO2 ,sat) under ambient conditions, and in response to exposure to sea level PO2 (32% O2=160 mmHg for 10 min) and hypoxia (18% and 15% O2=90 and 75 mmHg for 10 min each). The variables used for comparisons between species were corrected for body mass using standard allometric equations, and are termed mass-corrected variables. Under baseline, compared with rats, adult mice had similar levels of pO2 ,sat, but lower hematocrit and hemoglobin levels, reduced right ventricular hypertrophy and higher mass-corrected alveolar surface area, tidal volume and metabolic rate. In response to sea level PO2 and hypoxia, mice and rats had similar changes of ventilation, but metabolic rate decreased much more in hypoxia in mice, while pO2 ,sat remained higher in mice. We conclude that laboratory mice and rats that have been raised at HA for >30 generations have different physiological responses to altitude. These differences might explain the different altitude distribution observed in wild rats and mice.

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.

Effects of a propriety oiled mixed hay feeding system on lung function, neutrophilic airway inflammation and oxidative stress in severe asthmatic horses.

BACKGROUND: Hay feeding is considered the main triggering factor for airway obstruction and inflammation in severe equine asthma (SEA). Finding alternate strategies allowing hay feeding while controlling clinical signs of SEA is of importance. The Nutri-Foin Système is believed to decrease inhaled dust by incorporating soybean oil to mechanically processed hay. OBJECTIVES: We compared airflow obstruction and airway inflammation in horses with SEA fed oiled hay or alfalfa pellet regimen. STUDY DESIGN: Controlled trial in asthmatic research horses. METHODS: Twelve horses in exacerbation of SEA from a research herd were studied. Horses were fed either oiled treated hay (n = 6) or alfalfa pelleted hay (n = 6) for 3 months while being stabled. Lung function, bronchoalveolar lavage fluid cytology and serum antioxidant enzyme kinetics were sequentially evaluated. RESULTS: Pelleted hay and the hay treated with the Nutri-Foin Système similarly improved lung function, airway neutrophilia and serum antioxidant enzyme kinetics over time. MAIN LIMITATIONS: The small number of horses in each group. CONCLUSIONS: We conclude from this study that Nutri-Foin Système is an appropriate alternative to pelleted hay for the control of the airway obstruction in horses with SEA.

Divergent Mitochondrial Antioxidant Activities and Lung Alveolar Architecture in the Lungs of Rats and Mice at High Altitude.

Compared with mice, adult rats living at 3,600 m above sea level (SL-La Paz, Bolivia) have high hematocrit, signs of pulmonary hypertension, and low lung volume with reduced alveolar surface area. This phenotype is associated with chronic mountain sickness in humans living at high altitude (HA). We tested the hypothesis that this phenotype is associated with impaired gas exchange and oxidative stress in the lungs. We used rats and mice (3 months old) living at HA (La Paz) and SL (Quebec City, Canada) to measure arterial oxygen saturation under graded levels of hypoxia (by pulse oximetry), the alveolar surface area in lung slices and the activity of pro- (NADPH and xanthine oxidases-NOX and XO) and anti- (superoxide dismutase, and glutathione peroxidase-SOD and GPx) oxidant enzymes in cytosolic and mitochondrial lung protein extracts. HA rats have a lower arterial oxygen saturation and reduced alveolar surface area compared to HA mice and SL rats. Enzymatic activities (NOX, XO, SOD, and GPx) in the cytosol were similar between HA and SL animals, but SOD and GPx activities in the mitochondria were 2-3 times higher in HA vs. SL rats, and only marginally higher in HA mice vs. SL mice. Furthermore, the maximum activity of cytochrome oxidase-c (COX) measured in mitochondrial lung extracts was also 2 times higher in HA rats compared with SL rats, while there was only a small increase in HA mice vs. SL mice. Interestingly, compared with SL controls, alterations in lung morphology are not observed for young rats at HA (15 days after birth), and enzymatic activities are only slightly altered. These results suggest that rats living at HA have a gradual reduction of their alveolar surface area beyond the postnatal period. We can speculate that the elevation of SOD, GPx, and COX activities in the lung mitochondria are not sufficient to compensate for oxidative stress, leading to damage of the lung tissue in rats.