Days Of Hypoxic Exposure Research Articles

Hypoxia impairs cellular energy allocation in the juvenile horseshoe crab Tachypleus tridentatus

Although hypoxia is a serious environmental concern for marine ecosystems globally, its biological effects on the benthic biota remain mostly unclear for some endangered species. To provide an deep understanding of the possible effects of hypoxia on the tri-spine horseshoe crab Tachypleus tridentatus, the cellular energy allocation (CEA) approach was utilized to examine the cellular responses and adaption potential of horseshoe crabs. We examined the energetic responses of T. tridentatus under low dissolved oxygen level (2 mg O2/L). The horseshoe crabs first experienced 14 days of hypoxic stress, and then recovered in a normal dissolved oxygen environment for 7 days. On the 7th and 14th day of hypoxic exposure, the levels of available energy, electron transport system activity, protein, lipids, and carbohydrates were decreased in T. tridentatus (p < 0.05). All measured parameters in the hypoxic group partially or completely recovered after seven days of re‑oxygenation, reaching a level that was significantly up-regulated (p < 0.05) compared with the 14th day and non-significantly different from the 0th day exposure (p ˃ 0.05). In conclusion, hypoxic stress has adverse effects on the energy balance of juvenile T. tridentatus, but these adverse effects can be alleviated in a short recovery period. As a result, our findings provide novel perspectives on the physiology of T. tridentatus under hypoxia acclimation, which is essential information for establishing ideal conditions for the cultivation of this endangered species.

DEVELOPMENT OF ULTRASTRUCTURAL CHANGES IN DIAPHRAGM MUSCLE FIBERS DURING PARTIAL TRACHEAL STENOSIS IN YOUNG SEXUALLY IMMATURE RATS

Introduction. The study of congenital pathology of the respiratory tract in children is of great importance for theoretical and clinical pediatric otolaryngology. Currently, in the scientific literature there are single works concerning the study of the pathogenesis and clinic of laryngomalacia. First of all, this concerns the effect of acute and chronic hypoxia on the muscles of the respiratory system, in particular, the diaphragm. The aim of thіs work is to reveal the effect of hypoxia on the development of pronounced structural and functional changes in the diaphragm muscles of sexually immature animals when modeling partial tracheal occlusion. Materials and methods. Surgical partial occlusion of the trachea was performed on in sexually immature Wistar rats; we applied electron microscopy, morphometric and statistical research methods.&#x0D; Results. The obtained data demonstrated that the muscle fibers of the diaphragm are characterized by significant structural, functional and metabolic resistance to the development of acute or chronic hypoxia due to limited lung ventilation in rats. The density of muscle fibers did not change in any of the used terms of the experiment (7 and 21 days). On the 7th day of hypoxic exposure, a change in the state of the matrix of mitochondria of muscle fibers was observed, which was accompanied by partial ultrastructural rearrangements of the organization of these organelles. At the same time, no significant changes were observed during histological studies. Electrongrams demonstrated the ultrastructural damages were mainly limited to focal reduction of myofibrils and an increase in the mitochondria's diameter and found as especially pronounced on day 21 (a state of chronic hypoxia) on the muscular component of the respiratory system in rats. These changes are accompanied by the development of dystrophic disorders in the diaphragm myofibrils. On day 21 changes in the transendothelial transport of substance molecules were also detected. This was based on establishing the fact of a significant reduction in the number of pinocytosis vesicles in the cytoplasm of endothelial cells of diaphragm hemocapillaries in animals with partial tracheal occlusion. Disruption of the structural organization of actomyosin complexes was revealed in muscle fibers due to pathological changes in the mitochondria of myofibrils. It should be noted the development of destruction or complete loss of an important ultrastructural component of muscle fibers, Z-lines. These changes were completely absent on the 7th day following the influence of partial tracheal occlusion and the development of acute hypoxia. Moreover, on day 21, partial lysis of a significant amount of myofilaments of muscle fibers was observed. In addition, the development of the process of fiber swelling was detected against the background of which the above-mentioned ultrastructural destruction of the muscular component in the diaphragm was observed. These changes indicate the need for earlier treatment of laryngomalacia in children. The delay in surgical intervention leads to the development of severe or irreversible structural changes not only in the respiratory organs, but also in their muscular system.&#x0D; Conclusion. The muscular elements of the diaphragm have the pronounced and significant resistance to the state of hypoxia under conditions of limited ventilation of the respiratory tract. Ultrastructural and morphometric data, found on the 21st day after the modeling of partial tracheal stenosis, are not only of a compensatory and adaptive in nature, but also signs of pronounced disorders in the muscle fibers of the central part of the diaphragm in test animals.

Deficits in Seizure Threshold and Other Behaviors in Adult Mice without Gross Neuroanatomic Injury after Late Gestation Transient Prenatal Hypoxia

Intrauterine hypoxia is a common cause of brain injury in children resulting in a broad spectrum of long-term neurodevelopmental sequela, including life-long disabilities that can occur even in the absence of severe neuroanatomic damage. Postnatal hypoxia-ischemia rodent models are commonly used to understand the effects of ischemia and transient hypoxia on the developing brain. Postnatal models, however, have some limitations. First, they do not test the impact of placental pathologies on outcomes from hypoxia. Second, they primarily recapitulate severe injury because they provoke substantial cell death, which is not seen in children with mild hypoxic injury. Lastly, they do not model preterm hypoxic injury. Prenatal models of hypoxia in mice may allow us to address some of these limitations to expand our understanding of developmental brain injury. The published rodent models of prenatal hypoxia employ multiple days of hypoxic exposure or complicated surgical procedures, making these models challenging to perform consistently in mice. Furthermore, large animal models suggest that transient prenatal hypoxia without ischemia is sufficient to lead to significant functional impairment to the developing brain. However, these large animal studies are resource-intensive and not readily amenable to mechanistic molecular studies. Therefore, here we characterized the effect of late gestation (embryonic day 17.5) transient prenatal hypoxia (5% inspired oxygen) on long-term anatomical and neurodevelopmental outcomes in mice. Late gestation transient prenatal hypoxia increased hypoxia-inducible factor 1 alpha protein levels (a marker of hypoxic exposure) in the fetal brain. Hypoxia exposure predisposed animals to decreased weight at postnatal day 2, which normalized by day 8. However, hypoxia did not affect gestational age at birth, litter size at birth, or pup survival. No differences in fetal brain cell death or long-term gray or white matter changes resulted from hypoxia. Animals exposed to prenatal hypoxia did have several long-term functional consequences, including sex-dichotomous changes. Hypoxia exposure was associated with a decreased seizure threshold and abnormalities in hindlimb strength and repetitive behaviors in males and females. Males exposed to hypoxia had increased anxiety-related deficits, whereas females had deficits in social interaction. Neither sex developed any motor or visual learning deficits. This study demonstrates that late gestation transient prenatal hypoxia in mice is a simple, clinically relevant paradigm for studying putative environmental and genetic modulators of the long-term effects of hypoxia on the developing brain.

Gene-environment interaction impacts on heart development and embryo survival.

Congenital heart disease (CHD) is the most common type of birth defect. In recent years, research has focussed on identifying the genetic causes of CHD. However, only a minority of CHD cases can be attributed to single gene mutations. In addition, studies have identified different environmental stressors that promote CHD, but the additive effect of genetic susceptibility and environmental factors is poorly understood. In this context, we have investigated the effects of short-term gestational hypoxia on mouse embryos genetically predisposed to heart defects. Exposure of mouse embryos heterozygous for Tbx1 or Fgfr1/Fgfr2 to hypoxia in utero increased the incidence and severity of heart defects while Nkx2-5+/- embryos died within 2 days of hypoxic exposure. We identified the molecular consequences of the interaction between Nkx2-5 and short-term gestational hypoxia, which suggest that reduced Nkx2-5 expression and a prolonged hypoxia-inducible factor 1α response together precipitate embryo death. Our study provides insight into the causes of embryo loss and variable penetrance of monogenic CHD, and raises the possibility that cases of foetal death and CHD in humans could be caused by similar gene-environment interactions.

“BEet On Alps”

PURPOSE: Skeletal muscle oxidative function is influenced by inspired O2 fraction. Previous studies in acute hypoxia have shown that dietary nitrate supplementation is able to attenuate or prevent the hypoxia-induced decrement of performance. No data have been provided during prolonged exposure to hypobaric hypoxia, a condition that affects both skeletal muscle oxidative metabolism and nitric oxide bioavailability. Aim of this study was to investigate the effects of a dietary nitrate supplementation on gastrocnemius muscle oxidative capacity during a prolonged exposure to high altitude. METHODS: At altitude (3,269m a.s.l., Casati Refuge, Italy), fourteen healthy young (29±4 yr) subjects were supplemented for three days with beetroot juice (2x70mL/day, 8.4 mmol nitrate/day [BEET-IT]) or nitrate-depleted juice (PLA) following a double-blind randomized cross-over design. As an index of gastrocnemius muscle oxidative capacity, the recovery rate of muscle oxygen consumption (mV’O2) was measured by near-infrared spectroscopy using repeated, transient arterial occlusions following a brief bout of plantar-flexion exercise. Experiments were carried out after 7-14 days of hypoxic exposure, at the end of both supplementation periods, and in normoxia. RESULTS: In normoxia, the time constant of mV’O2(13.2±4.9 s) was comparable to that observed in healthy active subjects. At altitude, the time constant of mV’O2 was significantly (p=0.01) faster in BEET-IT (9.3±3.4) vs. PLA (16.7±5.8). Plasma [nitrate] and [nitrite] were significantly higher in BEET-IT than in PLA. CONCLUSIONS: During prolonged exposure to hypobaric hypoxia, a three-day dietary nitrate supplementation accelerated the recovery kinetics of mV’O2, suggesting an improvement of muscle oxidative capacity. Future studies will have to investigate if these results are related to an increased mitochondrial efficiency and/or to a better microvascular perfusion after nitrate supplementation in hypoxia.

Tetrahydrobiopterin oral therapy recouples eNOS and ameliorates chronic hypoxia-induced pulmonary hypertension in newborn pigs.

We previously showed that newborn piglets who develop pulmonary hypertension during exposure to chronic hypoxia have diminished pulmonary vascular nitric oxide (NO) production and evidence of endothelial NO synthase (eNOS) uncoupling (Fike CD, Dikalova A, Kaplowitz MR, Cunningham G, Summar M, Aschner JL. Am J Respir Cell Mol Biol 53: 255-264, 2015). Tetrahydrobiopterin (BH4) is a cofactor that promotes eNOS coupling. Current clinical strategies typically invoke initiating treatment after the diagnosis of pulmonary hypertension, rather than prophylactically. The major purpose of this study was to determine whether starting treatment with an oral BH4 compound, sapropterin dihydrochloride (sapropterin), after the onset of pulmonary hypertension would recouple eNOS in the pulmonary vasculature and ameliorate disease progression in chronically hypoxic piglets. Normoxic (control) and hypoxic piglets were studied. Some hypoxic piglets received oral sapropterin starting on day 3 of hypoxia and continued throughout an additional 7 days of hypoxic exposure. Catheters were placed for hemodynamic measurements, and pulmonary arteries were dissected to assess eNOS dimer-to-monomer ratios (a measure of eNOS coupling), NO production, and superoxide (O2·-) generation. Although higher than in normoxic controls, pulmonary vascular resistance was lower in sapropterin-treated hypoxic piglets than in untreated hypoxic piglets. Consistent with eNOS recoupling, eNOS dimer-to-monomer ratios and NO production were greater and O2·- generation was less in pulmonary arteries from sapropterin-treated than untreated hypoxic animals. When started after disease onset, oral sapropterin treatment inhibits chronic hypoxia-induced pulmonary hypertension at least in part by recoupling eNOS in the pulmonary vasculature of newborn piglets. Rescue treatment with sapropterin may be an effective strategy to inhibit further development of pulmonary hypertension in newborn infants suffering from chronic cardiopulmonary conditions associated with episodes of prolonged hypoxia.

Rescue Treatment with L-Citrulline Inhibits Hypoxia-Induced Pulmonary Hypertension in Newborn Pigs.

Infants with cardiopulmonary disorders associated with hypoxia develop pulmonary hypertension. We previously showed that initiation of oral L-citrulline before and continued throughout hypoxic exposure improves nitric oxide (NO) production and ameliorates pulmonary hypertension in newborn piglets. Rescue treatments, initiated after the onset of pulmonary hypertension, better approximate clinical strategies. Mechanisms by which L-citrulline improves NO production merit elucidation. The objective of this study was to determine whether starting L-citrulline after the onset of pulmonary hypertension inhibits disease progression and improves NO production by recoupling endothelial NO synthase (eNOS). Hypoxic and normoxic (control) piglets were studied. Some hypoxic piglets received oral L-citrulline starting on Day 3 of hypoxia and continuing throughout the remaining 7 days of hypoxic exposure. Catheters were placed for hemodynamic measurements, and pulmonary arteries were dissected to assess NO production and eNOS dimer-to-monomer ratios (a measure of eNOS coupling). Pulmonary vascular resistance was lower in L-citrulline-treated hypoxic piglets than in untreated hypoxic piglets but was higher than in normoxic controls. NO production and eNOS dimer-to-monomer ratios were greater in pulmonary arteries from L-citrulline-treated than from untreated hypoxic animals but were lower than in normoxic controls. When started after disease onset, oral L-citrulline treatment improves NO production by recoupling eNOS and inhibits the further development of chronic hypoxia-induced pulmonary hypertension in newborn piglets. Oral L-citrulline may be a novel strategy to halt or reverse pulmonary hypertension in infants suffering from cardiopulmonary conditions associated with hypoxia.

Short-term hypoxic preconditioning improved survival following cardiac arrest and resuscitation in rats.

Cardiac arrest and resuscitation produces delayed mortality and hippocampal neuronal death in rats. Hypoxic preconditioning has been to shown to protect the brain from ischemic insults. We have previously reported that with chronic hypobaric hypoxia, the accumulation of hypoxic-inducible factor-1 alpha (HIF-1α) and its target genes was increased for the first several days of hypoxic exposure, and returned to baseline level by 3 weeks when angiogenesis is completed. In this study, we investigated the effect of short-term (3 days) and long-term (21 days) hypoxic preconditioning on recovery from cardiac arrest and resuscitation in rats. Our data showed that the overall survival rate was considerably improved in the short-term hypoxic preconditioning group compared to the non-preconditioned controls (86 %, 6/7 vs. 54 %, 7/13); however, the survival rate in the long-term hypoxic preconditioning group was decreased. Our data suggest that hypoxic preconditioning provides protection after cardiac arrest and resuscitation more likely through increased accumulation of HIF-1α and its target genes rather than through successful vascular adaptation as a result of hypoxia-induced angiogenesis.

Combined intermittent hypobaric hypoxia and muscle electro-stimulation: a method to increase circulating progenitor cell concentration?

BackgroundOur goal was to test whether short-term intermittent hypobaric hypoxia (IHH) at a level well tolerated by healthy humans could, in combination with muscle electro-stimulation (ME), mobilize circulating progenitor cells (CPC) and increase their concentration in peripheral circulation.MethodsNine healthy male subjects were subjected, as the active group (HME), to a protocol involving IHH plus ME. IHH exposure consisted of four, three-hour sessions at a barometric pressure of 540 hPa (equivalent to an altitude of 5000 m). These sessions took place on four consecutive days. ME was applied in two separate 20-minute periods during each IHH session. Blood samples were obtained from an antecubital vein on three consecutive days immediately before the experiment, and then 24 h, 48 h, 4 days, 7 days and 14 days after the last day of hypoxic exposure. Four months later a control study was carried out involving seven of the original subjects (CG), who underwent the same protocol of blood samples but without receiving any special stimulus.ResultsIn comparison with the CG the HME group showed only a non-significant increase in the number of CPC CD34+ cells on the fourth day after the combined IHH and ME treatment.ConclusionCPC levels oscillated across the study period and provide no firm evidence to support an increased CPC count after IHH plus ME, although it is not possible to know if this slight increase observed is physiologically relevant. Further studies are required to understand CPC dynamics and the physiology and physiopathology of the hypoxic stimulus.

Quercetin Reverses Hypobaric Hypoxia-Induced Hippocampal Neurodegeneration and Improves Memory Function in the Rat

Inadequate oxygen availability at high altitude causes elevated oxidative stress, resulting in hippocampal neurodegeneration and memory impairment. Though oxidative stress is known to be a major cause of neurodegeneration in hypobaric hypoxia, neuroprotective and ameliorative potential of quercetin, a flavonoid with strong antioxidant properties in reversing hypobaric hypoxia-induced memory impairment has not been studied. Four groups of male adult Sprague Dawley rats were exposed to hypobaric hypoxia for 7 days in an animal decompression chamber at an altitude of 7600 meters. Rats were supplemented with quercetin orally by gavage during 7 days of hypoxic exposure. Spatial working memory was assessed by a Morris Water Maze before and after exposure to hypobaric hypoxia. Changes in oxidative stress markers and apoptotic marker caspase 3 expression in hippocampus were assessed. Histological assessment of neurodegeneration was performed by cresyl violet and fluoro Jade B staining. Our results showed that quercetin supplementation during exposure to hypobaric hypoxia decreased reactive oxygen species levels and consequent lipid peroxidation in the hippocampus by elevating antioxidant status and free radical scavenging enzyme system. There was reduction in caspase 3 expression, and decrease in the number of pyknotic and fluoro Jade B-positive neurons in hippocampus after quercetin supplementation during hypoxic exposure. Behavioral studies showed that quercetin reversed the hypobaric hypoxia-induced memory impairment. These findings suggest that quercetin provides neuroprotection to hippocampal neurons during exposure to hypobaric hypoxia through antioxidative and anti-apoptotic mechanisms, and possesses promising therapeutic potential to ameliorate hypoxia-induced memory dysfunction.

Withania somnifera root extract ameliorates hypobaric hypoxia induced memory impairment in rats

Ethnopharmacological relevanceWithania somnifera (WS) root extract has been used traditionally in ayurvedic system of medicine as a memory enhancer and anti-stress agent. Aim of the studyTo evaluate the neuroprotective and prophylactic potential of WS root extract in ameliorating hypobaric hypoxia (HH) induced memory impairment and to explore the underlying molecular mechanism. Materials and methodsWS root extract was administered to male Sprague Dawley rats during a period of 21 days pre-exposure and 07 days exposure to a simulated altitude of 25,000ft. Spatial memory was assessed by Morris Water Maze. Neurodegeneration, corticosterone, acetylcholine (Ach) levels, acetylcholine esterase (AchE) activity, oxidative stress markers and nitric oxide (NO) concentration were assessed in the hippocampus. Synaptic and apoptotic markers were also investigated by immunoblotting. To study the role of NO in regulating corticosterone mediated signaling, the neuronal nitric oxide synthase (n-NOS) inhibitor, l-Nitro-arginine methyl ester (l-Name) and NO agonist sodium nitroprusside (SNP) were administered from 3rd to 7th day of hypoxic exposure. ResultsAdministration of WS root extract prevented HH induced memory impairment and neurodegeneration along with decreased NO, corticosterone, oxidative stress and AchE activity in hippocampal region. Inhibition of NO synthesis by administration of l-Name reduced corticosterone levels in hippocampus during hypoxic exposure while co-administration of corticosterone increased neurodegeneration. Administration of sodium nitroprusside (SNP) along with WS root extract supplementation during hypoxic exposure increased corticosterone levels and increased the number of pyknotic cells. ConclusionWS root extract ameliorated HH induced memory impairment and neurodegeneration in hippocampus through NO mediated modulation of corticosterone levels.

Erdosteine protects rat testis tissue from hypoxic injury by reducing apoptotic cell death

The purpose of this study was to examine the effects of hypobaric hypoxia on testis morphology and the effects of erdosteine on testis tissue. Caspase-3 and hypoxia-inducible factor 1α expressions were detected by immunohistochemistry. Adult male Wistar rats were placed in a hypobaric hypoxic chamber. Rats in the erdosteine group were exposed to the same conditions and treated orally with erdosteine (20 mg kg(-1) daily) at the same time from the first day of hypoxic exposure for 2 weeks. The normoxia group was evaluated as the control. The hypoxia group showed decreased height of spermatogenic epithelium in some seminiferous tubules, vacuolisation in spermatogenic epithelial cells, deterioration and gaps in the basal membrane and an increase in blood vessels in the interstitial area. The erdosteine group showed amelioration of both epithelial cell vacuolisation and basal membrane deterioration. Numbers of hypoxia-inducible factor 1α-immunostained Sertoli and Leydig cells were significantly higher in the hypoxia group than in the erdosteine group. The number of seminiferous tubules with caspase-3-immunostained germ cells was highest in the hypoxia group and decreased in the erdosteine and normoxia groups respectively. Based on these observations, erdosteine protects testis tissue from hypoxic injury by reducing apoptotic cell death.

Acetazolamide and chronic hypoxia: effects on haemorheology and pulmonary haemodynamics

We tested the effect of acetazolamide on blood mechanical properties and pulmonary vascular resistance (PVR) during chronic hypoxia. Six groups of rats were either treated or not treated with acetazolamide (curative: treated after 10 days of hypoxic exposure; preventive: treated before hypoxic exposure with 40 mg · kg(-1) · day(-1)) and either exposed or not exposed to 3 weeks of hypoxia (at altitude >5,500 m). They were then used to assess the role of acetazolamide on pulmonary artery pressure, cardiac output, blood volume, haematological and haemorheological parameters. Chronic hypoxia increased haematocrit, blood viscosity and PVR, and decreased cardiac output. Acetazolamide treatment in hypoxic rats decreased haematocrit (curative by -10% and preventive by -11%), PVR (curative by -36% and preventive by -49%) and right ventricular hypertrophy (preventive -20%), and increased cardiac output (curative by +60% and preventive by +115%). Blood viscosity was significantly decreased after curative acetazolamide treatment (-16%) and was correlated with PVR (r=0.87, p<0.05), suggesting that blood viscosity could influence pulmonary haemodynamics. The fall in pulmonary vascular hindrance (curative by -27% and preventive by -45%) after treatment suggests that acetazolamide could decrease pulmonary vessels remodelling under chronic hypoxia. The effect of acetazolamide is multifactorial by acting on erythropoiesis, pulmonary circulation, haemorheological properties and cardiac output, and could represent a pertinent treatment of chronic mountain sickness.

Corticosterone synthesis inhibitor metyrapone ameliorates chronic hypobaric hypoxia induced memory impairment in rat

Chronic exposure to hypobaric hypoxia causes oxidative stress and neurodegeneration leading to memory impairment. The present study aimed at investigating the role of corticosterone in hypoxia induced neurodegeneration and effect of metyrapone, a corticosterone synthesis inhibitor that reduces the stress induced elevation of corticosterone without affecting the basal level, in ameliorating chronic hypobaric hypoxia induced cognitive decline. Rats were exposed to simulated altitude of 25,000 ft for 0, 3, 7, 14 and 21 days to determine the temporal alterations in corticosterone and its receptors following exposure to hypobaric hypoxia. Our results showed an elevation of corticosterone in plasma and hippocampal tissue following 7 days of exposure, which declined on prolonged hypoxic exposure for 21 days. A concomitant increase in ROS and lipid peroxidation was observed along with depletion of intracellular antioxidants. Glucocorticoid and mineralocorticoid receptors were upregulated on 3 and 7 days of hypoxic exposure. Though expression of Glut1 and Glut3 were upregulated on 3 days of hypoxic exposure, sharp decline in Glut1 expression following 7 days of hypoxic exposure leads to reduced neuronal glucose uptake. Administration of metyrapone from 3rd to 7th day of hypoxic exposure to suppress hypoxia induced increase in corticosterone levels resulted in reduced oxidative damage, neurodegeneration and improvement of intracellular energy status. The metyrapone treated hypoxic animals performed better in the Morris Water Maze. Further, administration of exogenous corticosterone along with metyrapone during hypoxic exposure blunted the neuroprotective effect of metyrapone indicating a role for corticosterone in mediating hypobaric hypoxia induced neurodegeneration and memory impairment.

Chronic hypoxia stimulates an enhanced response to immune challenge without evidence of an energetic tradeoff

There is broad interest in whether there is a tradeoff between energy metabolism and immune function, and how stress affects immune function. Under hypoxic stress, maximal aerobic metabolism is limited, and other aspects of energy metabolism of animals may be altered as well. Although acute hypoxia appears to enhance certain immune responses, the effects of chronic hypoxia on immune function are largely unstudied. We tested: (1) whether chronic hypoxia affects immune function and (2) whether hypoxia affects the metabolic cost of immune function. First, flow cytometry was used to monitor the peripheral blood immunophenotype of mice over the course of 36 days of hypoxic exposure. Second, hypoxic and normoxic mice were subjected to an adaptive immune challenge via keyhole limpet hemocyanin (KLH) or to an innate immune challenge via lipopolysaccharide (LPS). The resting metabolic rates of mice in all immune challenge treatments were also measured. Although hypoxia had little effect on the peripheral blood immunophenotype, hypoxic mice challenged with KLH or LPS had enhanced immunological responses in the form of higher antibody titers or increased TNF-α production, respectively. Initially, mice exposed to hypoxia had lower metabolic rates, but this response was transitory and resting metabolic rates were normal by the end of the experiment. There was no effect of either immune challenge on resting metabolic rate, suggesting that mounting either the acute phase response or a humoral response is not as energetically expensive as previously thought. In addition, our results suggest that immune responses to chronic and acute hypoxia are concordant. Both forms of hypoxia appear to stimulate both innate and adaptive immune responses.

Interactive effects of development and hypoxia on catecholamine synthesis and cardiac function in zebrafish (Danio rerio)

The rate-limiting enzyme in the biosynthetic pathway of catecholamines is tyrosine hydroxylase (TH), the activity of which is dependent on molecular oxygen. Zebrafish (Danio rerio) possess two non-allelic TH coding genes, TH1 and TH2. A principal goal of the present study was to determine if the expression of these genes is sensitive to environmental hypoxia. Additionally, we sought to determine if catecholamine content of larvae was changed by environmental hypoxia, and whether the hearts of hypoxic larvae were equally responsive to exogenous catecholamine (norepinephrine) exposure. After 2 days of exposure to hypoxia [5-7 days post-fertilization (dpf); PO(2) = 30 Torr] TH2 mRNA expression was significantly lower and dopamine β hydroxylase (DβH) mRNA was significantly higher in whole larvae. Whole body catecholamine levels were unchanged until after 4 days of hypoxic exposure (5-9 dpf), at which time there was a significant increase in epinephrine and norepinephrine contents. Norepinephrine content was significantly elevated in the hearts of adult fish after 2 and 4 days of hypoxic exposure, and TH1 mRNA expression was increased in the kidney of both groups. After 2 or 4 days of exposure to hypoxia, larvae displayed significantly lower heart rates than normoxic fish. However, application of exogenous norepinephrine caused similar increases in heart rate in both groups. Overall, it is concluded that the mRNA expression of TH1 and TH2 is differentially affected by hypoxia exposure in larvae and adults. Also, catecholamine biosynthesis appears to be activated by 2 dpf and although whole body catecholamine levels increase during hypoxia (possibly promoting downregulation of cardiac β-adrenergic receptors), there is no accompanying decrease in the response of the heart to adrenergic stimulation.

009 Normobaric hypoxia impairs cardiac energetics and diastolic function in normal human volunteers

<h3>Background</h3> Left ventricular dysfunction is consistently observed in human heart in the first few days of hypoxic exposure, yet the cellular mechanisms underlying the dysfunction are poorly understood. We postulated that normobaric hypoxia impairs cardiac energetics leading to cardiac dysfunction. Healthy males (n=12, age 24±2) underwent 20 h of normobaric hypoxia in purpose-built hypoxia chambers. The partial pressure of oxygen during end tidal expiration (PETO2) was kept between 50 and 60 mmHg, whilst keeping peripheral oxygen saturation (SaO2) above 80%. Cardiac function was measured using magnetic resonance imaging (MRI) and echocardiography before and after hypoxic exposure. High energy phosphate metabolism was measured as the ratio of phosphocreatine to ATP (PCr/ATP) using 31Phosphorus magnetic resonance spectroscopy (MRS) before and after 20 h of hypoxia. During hypoxia, PETO₂ and SaO₂ averaged 55±1 mmHg and 83.6±0.4%, respectively. There was a 15% reduction in cardiac PCr/ATP, from 2.0±0.1 before to 1.7±0.1 after hypoxia (p&lt;0.01), and reduced diastolic function, measured as E/E9, from 6.1±0.4 to 7.5±0.7, (p&lt;0.01). Short term normobaric hypoxia led to rapid changes in cardiac energy metabolism and alterations in diastolic function in normal human hearts. Increased cardiac energy demand and reduced oxygen-limited decrease in oxidative phosphorylation may explain the low PCr/ATP and cardiac dysfunction observed after hypoxic exposure, whether in health or disease.

Two Days of Hypoxic Exposure Increased Ventilation Without Affecting Performance

The aim of this study was to test the short-term effects of using hypoxic rooms before a simulated running event. Thirteen subjects (29 +/- 4 years) lived in a hypoxic dormitory (1,800 m) for either 2 nights (n = 6) or 2 days + nights (n = 7) before performing a 1,500-m treadmill test. Performance, expired gases, and muscle electrical activity were recorded and compared with a control session performed 1 week before or after the altitude session (random order). Arterial blood samples were collected before and after altitude exposure. Arterial pH and hemoglobin concentration increased (p < 0.05) and PCO2 decreased (p < 0.05) upon exiting the room. However, these parameters returned (p < 0.05) to basal levels within a few hours. During exercise, mean ventilation (VE) was higher (p < 0.05) after 2 nights or days + nights of moderate altitude exposure (113.0 +/- 27.2 L.min) than in the control run (108.6 +/- 27.8 L.min), without any modification in performance (360 +/- 45 vs. 360 +/- 42 seconds, respectively) or muscle electrical activity. This elevated VE during the run after the hypoxic exposure was probably because of the subsistence effects of the hypoxic ventilatory response. However, from a practical point of view, although the use of a normobaric simulating altitude chamber exposure induced some hematological adaptations, these disappeared within a few hours and failed to provide any benefit during the subsequent 1,500-m run.

Impedance in Isolated Mouse Lungs for the Determination of Site of Action of Vasoactive Agents and Disease

Hypoxic pulmonary hypertension is a disease of the lung vasculature that is usually quantified by pulmonary vascular resistance (PVR). However, a more complete description of lung vascular function and right ventricular afterload is provided by pulmonary vascular impedance (PVZ) from spectral analysis of pulsatile pressure-flow relationships. We studied pulsatile pressure-flow relationships in isolated, perfused lungs of mice in normoxia, after induction of hypoxic pulmonary hypertension by 10 days of hypoxic exposure, and after the administration of the vasoactive agents sodium nitroprusside and serotonin in order to gain insight into the effects of disease and vasoactive agents on afterload. Chronic hypoxia exposure increased 0 Hz impedance (Z(0)) from 2.0 +/- 0.2 to 3.3 +/- 0.2 mmHg min/mL but decreased characteristic impedance (Z(C)) from 0.21 +/- 0.02 to 0.18 +/- 0.01 mmHg min/mL (both p < 0.05). Sodium nitroprusside only slightly decreased Z(0) but increased Z(C) in normal lungs (p < 0.05) and did not affect Z(C) and decreased Z(0) in hypertensive lungs (p < 0.05). Serotonin increased Z(C) in normal and hypertensive lungs but decreased Z(0) in hypertensive lungs (p < 0.05). There was an inverse correlation between mean pulmonary artery pressure and Z(C) in all circumstances. These findings demonstrate that vasoactive interventions can have different sites of action (i.e., proximal vs. distal segments) in the normal and chronically hypoxic pulmonary vasculature, and the pressure-dependency of Z(C) and R(W). The measurement of PVZ in isolated lungs allows for an improved understanding of the modes of action of drugs and hypoxia on the pulmonary circulation.

006 Normobaric hypoxia impairs cardiac energetics in normal human volunteers

In the first few days of hypoxic exposure, left ventricular dysfunction is consistently observed in the human heart, yet the cellular mechanisms underlying the dysfunction are poorly understood. Our hypothesis...