Day Of Hypoxia Research Articles

Cellular concentrations of plasmalogen species containing a polyunsaturated fatty acid significantly increase under hypoxia in human colorectal cancer, Caco2 cells

Plasmalogen localized in the raft of mammalian cell membranes plays a role in the storage of polyunsaturated fatty acid (PUFA), and exists to a higher extent in malignant cells that survive, and even grow in hypoxic conditions. The biosynthesis of plasmalogen in mammalian cells has been reported to depend on aerobic conditions. Using liquid chromatography-tandem mass spectrometry, we found that the intracellular concentration of plasmalogen species containing a PUFA at the sn-2-position did not change for two days from the start of hypoxic culture in human colorectal cancer-derived Caco2 cells. At the third day of hypoxia, Caco2 cells showed the average increase rate of 2.6 times in ethanolamine plasmalogen and 2.9 times in choline plasmalogen depending on the molecular species compared with those in the second day of hypoxia. In normoxic culture, there was little quantitative change in any species of both ethanolamine and choline plasmalogens for three days. The up-regulations of mRNA of Ca2+-independent phospholipase A2β and cytoplasmic phospholipase A2γ as well as the down-regulation of lysoplasmalogenase observed in hypoxia were suggested to be responsible for the increase of plasmalogen in Caco2 cells under hypoxia.

Intermittent Hypoxic Exposure Reduces Endothelial Dysfunction.

Intermittent exposure to hypoxia (IHE) increases the production of reactive oxygen and nitrogen species as well as erythropoietin (EPO), which stimulates the adaptation to intense physical activity. However, several studies suggest a protective effect of moderate hypoxia in cardiovascular disease (CVD) events. The effects of intense physical activity with IHE on oxi-inflammatory mediators and their interaction with conventional CVD risk factors were investigated. Blood samples were collected from elite athletes (control n = 6, IHE n = 6) during a 6-day IHE cycle using hypoxicator GO2 altitude. IHE was held once a day, at least 2 hours after training. In serum, hydrogen peroxide (H2O2), nitric oxide (NO), 3-nitrotyrosine (3-Nitro), proinflammatory cytokines (IL-1β and TNFα), high sensitivity C-reactive protein (hsCRP), and heat shock protein 27 (HSP27) were determined by the commercial immunoenzyme (ELISA kits) or colorimetric methods. Serum erythropoietin (EPO) level was measured by ELISA kit every day of hypoxia. IHE was found to significantly increase H2O2, NO, and HSP27 but to decrease 3NT concentrations. The changes in 3NT and HSP27 following hypoxia proved to enhance NO bioavailability and endothelial function. In the present study, the oxi-inflammatory mediators IL-1β and hsCRP increased in IHE group but they did not exceed the reference values. The serum EPO level increased on the 3rd day of IHE, then decreased on 5th day of IHE, and correlated with NO/H2O2 ratio (rs = 0.640, P < 0.05). There were no changes in haematological markers contrary to lipoproteins such as low-density lipoprotein (LDL) and non-high-density lipoprotein (non-HDL) which showed a decreasing trend in response to hypoxic exposure. The study demonstrated that IHE combined with sports activity reduced a risk of endothelial dysfunction and atherogenesis in athletes even though the oxi-inflammatory processes were enhanced. Therefore, 6-day IHE seems to be a potential therapeutic and nonpharmacological method to reduce CVD risk, especially in elite athletes participating in strenuous training.

L-Citrulline treatment alters the structure of the pulmonary circulation in hypoxic newborn pigs.

Dysregulated nitric oxide (NO) signaling contributes to chronic hypoxia (CH)-induced pulmonary hypertension (PH). NO signaling is improved and pulmonary vascular resistance (PVR) is reduced in CH piglets treated with the l-arginine-NO precursor, l-citrulline. We hypothesized that l-citrulline might cause structural changes in the pulmonary circulation that would contribute to the reduction in PVR and that the l-citrulline-induced structural changes would be accompanied by alterations in vascular endothelial growth factor (VEGF) signaling. We evaluated small pulmonary arterial (PA) wall thickness, lung capillary density, and protein abundances of VEGF, VEGFR2, and phospho (p)-VEGFR2 in PA and peripheral lung samples of piglets raised in the lab in CH (10%-12% O2 ) from the day of life (DOL) 2 until DOL 11 to 12 or raised in room air (normoxia) by the vendor and studied on arrival to the lab on DOL 11 to 12. Some CH piglets were treated with oral l-citrulline (1-1.5 g/kg/d) starting on the third day of hypoxia. PA wall thickness was 32% less and lung capillary formation was nearly doubled in l-citrulline treated than untreated CH piglets. Both of these l-citrulline-induced structural changes in the pulmonary circulation were accompanied by altered amounts of VEGF protein but not by altered amounts of either VEGFR2 or p-VEGFR2 proteins. Alterations in the structure of the pulmonary circulation in CH piglets by l-citrulline are unlikely to be mediated by overall VEGF signaling. Nonetheless, l-citrulline- induced structural changes should reduce PVR and thereby contribute to the amelioration of CH-induced PH.

Mice but not rats modulate liver mitochondrial machinery in chronic hypoxia

Mice (FVB) permanently living at high‐altitude have increased respiratory frequencies and sustained or increased metabolic rates. On the other hand, rats permanently living at high‐altitude (SD) have impaired respiratory control, high hematocrit and hemoglobin, signs of pulmonary hypertension, and reduced metabolism; all these considered to be detrimental. This is coincident with the fact that common rats are not found in natural high‐altitude environments. At sea level, we reported that mice, but nor rats, exposed to 21 days of hypoxia (12% O2) increase their metabolic rate (O2 consumption and CO2 production), similarly to other rodent species that are considered well adapted to high‐altitude. As mitochondria is the final user of O2 in metabolism, we were interested in the role of mitochondria behind this divergence in physiological adjustments. We used saponin‐permeabilized samples of liver (most energy‐consuming organ in rodents), from male adult FVB mice and SD rats after exposure to hypoxia (12% O2, for 0, 1, 7 or 21 days), to measure the mitochondrial O2 consumption rate (OCR) following the SUIT‐01 protocol in the high‐resolution respirometer O2K (OROBOROS instruments). OCR was measured with substrates activating the NADH, succinate , and fatty acid pathways of the electron transport chain (ETC). We also measured the maximum capacity of ETC by uncoupling the electron transport from the oxidative phosphorylation with CCCP. The level of activation of complexes I and II was reported as the OCR for the N or S pathway correspondingly, divided by the maximum capacity (flux control ratio).Our preliminary results show that, compared to rats, mice have significantly higher ETC maximum capacities in normoxia and hypoxia. Moreover, after 21 days of hypoxia, mice showed an increase of 43% in maximum capacity in comparison to normoxic controls, while no increase in maximum capacity was evidenced in rats. In mice, we observed that complex I is transiently hyperactivated after 1 day of hypoxia and then, its activity reduces down below control levels by day 21 of hypoxia. Contrastingly, complex II activity is reduced after one day of hypoxia, getting back to control levels by day 21 of hypoxia. Furthermore, in rats, an increased activity of complex I occurred after 21 days of hypoxia. Regardless of normoxic or hypoxic exposure, rats showed higher activation levels of complex II than mice.These results show that mice, but not rats, have the ability to modulate their liver metabolic mitochondrial machinery under chronic hypoxia. The higher and adjustable maximum capacity in mice, suggest a more powerful and plastic liver mitochondrial machinery than in rats. This might explain in part their ability to keep sustained metabolic rates under hypoxic conditions.Support or Funding InformationSupported by NSERC, the Health Respiratory Network of Québec and CIHR.

Risk factors for delirium in intensive care unit and its duration

To screen risk factors for delirium and its duration in intensive care unit (ICU) patients. 1 200 patients admitted to ICU of the Second Hospital of Shanxi Medical University from May 2017 to May 2019 were enrolled. The gender, age, anesthesia mode, duration of mechanical ventilation and hypoxia, acute physiology and chronic health evaluation II (APACHE II) score, sedative drug use, and length of ICU stay were recorded. The occurrence and duration of ICU delirium were recorded. Multivariate Logistic regression analysis and multiple linear regression analysis were used to analyze the factors with statistical significance differences between the groups for screening the risk factors for delirium and its duration in ICU patients. 397 of 1 200 patients developed delirium, the incidence of ICU delirium was 33.1%. The duration of delirium in 189 patients (47.6%) was 1.0 day, and the duration of delirium in 397 delirium patients was 2.0 (1.5, 2.5) days. (1) Analysis of risk factors for delirium: univariate analysis showed that there was no significant difference in the incidence of ICU delirium among patients with different genders or ages. The incidence of ICU delirium in patients with duration of mechanical ventilation or hypoxia 4-9 days and ≥ 10 days was higher than that in patients with ≤ 3 days. The incidence of ICU delirium of general anesthesia and internal medicine patients was higher than that of patients with lumbar anesthesia. The incidence of ICU delirium in patients with APACHE II score ≥ 20 was higher than that in patients with ≤ 10 and 11-19. The patients with length of ICU stay > 9 days had a higher ICU delirium incidence than those ≤ 8 days. Increased incidence of ICU delirium in sedative patients was found as compared with those who did not use sedatives. Multivariate Logistic regression analysis showed that APACHE II score [odds ratio (OR) = 5.491, 95% confidence interval (95%CI) was 4.361-6.913, P < 0.001], the length of ICU stay (OR = 2.679, 95%CI was 1.822-3.941, P < 0.001) and the use of sedatives (OR = 2.479, 95%CI was 1.821-3.374, P < 0.001) were risk factors for ICU delirium. (2) Analysis of risk factors of ICU delirium duration: univariate analysis showed that there was no significant difference in ICU delirium duration in patients with different genders or ages. The duration of ICU delirium in patients with duration of mechanical ventilation or hypoxia ≥ 10 days was longer than that in patients with ≤ 3 days and 4-9 days. The duration of ICU delirium in general anesthesia and non-surgical patients was higher than that in patients with spinal anesthesia. The ICU delirium duration in patients with APACHE II score ≥ 20 was longer than that in patients with ≤ 10 and 11-19. The duration of ICU delirium in patients with the length of ICU stay > 9 days was longer than that in patients with ≤ 8 days. The duration of ICU delirium in patients on sedatives was longer than those not taking sedatives. Multiple linear regression analysis showed that the duration of ICU delirium increased by an average of 0.061 days (β = 0.061, 95%CI was 0.032-0.090, P < 0.001) for each additional day of hypoxia (hypoxia duration was divided into three grades of ≤ 3, 4-9 and ≥ 10 days). For every one increase in APACHE II score (APACHE II score was divided into three grades of ≤ 10, 11-19 and ≥ 20), duration of ICU delirium extended an average of 0.058 days (β = 0.058, 95%CI was 0.048-0.068, P < 0.001). ICU delirium duration increased by an average of 0.065 days in patients with length of ICU stay > 9 days as compared with those ≤ 8 days (β = 0.065, 95%CI was 0.056-0.075, P < 0.001). On average, the duration of ICU delirium was prolonged by 0.362 days in patients on sedatives as compared with those who did not use sedatives (β = 0.362, 95%CI was 0.234-0.490, P < 0.001). APACHE II score, the length of ICU stay and the use of sedatives were common risk factors for ICU delirium and its duration. The hypoxic duration was risk factors for ICU delirium duration.

ULTRASTRUCTURAL PROPERTIES OF THE ADRENAL GLANDS DURING THE ACUTE HYPOXIA

&#x0D; &#x0D; &#x0D; The goal of the study was to study the morphofunctional properties of ultrastructural changes in the cellular and extracellular structures of the adrenal glands during hypobaric hypoxia. The materials of the study were 30 male white rats weighing 180-200 grams. Thus, the results of the conducted studies showed that morphofunctional changes under the effects of acute hypoxia, which develop in different zones of the adrenal cortex, also change the histofunctional state of the adrenal medulla. Morphometric indicators of the adrenal parenchyma increase from the 5th day of hypoxia and are characterized by the increased blood supply to the adrenal glands, which occurs both by the dilatation of capillaries and by an increase in their density.&#x0D; &#x0D; &#x0D;

Involvement of Ca2+-activated K+ channel 3.1 in hypoxia-induced pulmonary arterial hypertension and therapeutic effects of TRAM-34 in rats.

Pulmonary artery hypertension (PAH) is an incurable disease associated with the proliferation of pulmonary artery smooth muscle cells (PASMCs) and vascular remodeling. The present study examined whether TRAM-34, a highly selective blocker of calcium-activated potassium channel 3.1 (Kca3.1), can help prevent such hypertension by reducing proliferation in PASMCs. Rats were exposed to hypoxia (10% O2) for 3 weeks and treated daily with TRAM-34 intraperitoneally from the first day of hypoxia. Animals were killed and examined for vascular hypertrophy, Kca3.1 expression, and downstream signaling pathways. In addition, primary cultures of rat PASMCs were exposed to hypoxia (3% O2) or normoxia (21% O2) for 24 h in the presence of TRAM-34 or siRNA against Kca3.1. Activation of cell signaling pathways was examined using Western blot analysis. In animal experiments, hypoxia triggered significant medial hypertrophy of pulmonary arterioles and right ventricular hypertrophy, and it significantly increased pulmonary artery pressure, Kca3.1 mRNA levels and ERK/p38 MAP kinase signaling. These effects were attenuated in the presence of TRAM-34. In cell culture experiments, blocking Kca3.1 using TRAM-34 or siRNA inhibited hypoxia-induced ERK/p38 signaling. Kca3.1 may play a role in the development of PAH by activating ERK/p38 MAP kinase signaling, which may then contribute to hypoxia-induced pulmonary vascular remodeling. TRAM-34 may protect against hypoxia-induced PAH.

Changes in ghrelin, CCK, GLP-1, and peroxisome proliferator-activated receptors in a hypoxia-induced anorexia rat model.

A high-altitude environment causes appetite loss in unacclimatised humans, leading to weight reduction. Ghrelin, cholecystokinin (CCK), and glucagon like peptide-1 (GLP-1), are gut hormones involved in the regulation of food intake and energy metabolism. The liver is an important site of metabolic regulation, and together with the gut it plays a role in food intake regulation. This study intends to study the time-dependent changes occurring in plasma gut hormones, PPARα, PPARδ, and PGC1α, in the stomach and liver during hypoxia. Male Sprague Dawley rats were exposed to hypobaric hypoxia in a decompression chamber at 7620 m for different durations up to seven days. Hypoxia increased circulating ghrelin from the third day onwards while CCK and GLP-1 decreased immediately. An increase in ghrelin, ghrelin receptor protein levels, and GOAT mRNA levels in the stomach was observed. Stomach cholecystokinin receptor (CCKAR), PPARα, and PPARδ decreased. Liver CCKAR decreased during the first day of hypoxia and returned to normal levels from the third day onwards. PPARα and PGC1α expression increased while PPARδ protein levels reduced in the liver on third day. Hypoxia alters the expression of ghrelin and ghrelin receptor in the stomach, CCKAR in the liver, and PPAR and its cofactors, which might be possible role players in the contribution of gut and liver to anorexia at high altitude.

Mechanisms of Hypoxic Up-Regulation of Versican Gene Expression in Macrophages.

Hypoxia is a hallmark of many pathological tissues. Macrophages accumulate in hypoxic sites and up-regulate a range of hypoxia-inducible genes. The matrix proteoglycan versican has been identified as one such gene, but the mechanisms responsible for hypoxic induction are not fully characterised. Here we investigate the up-regulation of versican by hypoxia in primary human monocyte-derived macrophages (HMDM), and, intriguingly, show that versican mRNA is up-regulated much more highly (>600 fold) by long term hypoxia (5 days) than by 1 day of hypoxia (48 fold). We report that versican mRNA decay rates are not affected by hypoxia, demonstrating that hypoxic induction of versican mRNA is mediated by increased transcription. Deletion analysis of the promoter identified two regions required for high level promoter activity of luciferase reporter constructs in human macrophages. The hypoxia-inducible transcription factor HIF-1 has previously been implicated as a key potential regulator of versican expression in hypoxia, however our data suggest that HIF-1 up-regulation is unlikely to be principally responsible for the high levels of induction observed in HMDM. Treatment of HMDM with two distinct specific inhibitors of Phosphoinositide 3-kinase (PI3K), LY290042 and wortmannin, significantly reduced induction of versican mRNA by hypoxia and provides evidence of a role for PI3K in hypoxic up-regulation of versican expression.

Long-Lasting Changes in DNA Methylation Following Short-Term Hypoxic Exposure in Primary Hippocampal Neuronal Cultures

While the effects of hypoxia on gene expression have been investigated in the CNS to some extent, we currently do not know what role epigenetics plays in the transcription of many genes during such hypoxic stress. To start understanding the role of epigenetic changes during hypoxia, we investigated the long-term effect of hypoxia on gene expression and DNA methylation in hippocampal neuronal cells. Primary murine hippocampal neuronal cells were cultured for 7 days. Hypoxic stress of 1% O2, 5% CO2 for 24 hours was applied on Day 3, conditions we found to maximize cellular hypoxic stress response without inducing cell death. Cells were returned to normoxia for 4 days following the period of hypoxic stress. On Day 7, Methyl-Sensitive Cut Counting (MSCC) was used to identify a genome-wide methylation profile of the hippocampal cell lines to assess methylation changes resulting from hypoxia. RNA-Seq was also done on Day 7 to analyze changes in gene transcription. Phenotypic analysis showed that neuronal processes were significantly shorter after 1 day of hypoxia, but there was a catch-up growth of these processes after return to normoxia. Transcriptome profiling using RNA-Seq revealed 369 differentially expressed genes with 225 being upregulated, many of which form networks shown to affect CNS development and function. Importantly, the expression level of 59 genes could be correlated to the changes in DNA methylation in their promoter regions. CpG islands, in particular, had a strong tendency to remain hypomethylated long after hypoxic stress was removed. From this study, we conclude that short-term, sub-lethal hypoxia results in long-lasting changes to genome wide DNA methylation status and that some of these changes can be highly correlated with transcriptional modulation in a number of genes involved in functional pathways that have been previously implicated in neural growth and development.

Tissue-specific changes in fatty acid oxidation in hypoxic heart and skeletal muscle

Exposure to hypobaric hypoxia is sufficient to decrease cardiac PCr/ATP and alters skeletal muscle energetics in humans. Cellular mechanisms underlying the different metabolic responses of these tissues and the time-dependent nature of these changes are currently unknown, but altered substrate utilization and mitochondrial function may be a contributory factor. We therefore sought to investigate the effects of acute (1 day) and more sustained (7 days) hypoxia (13% O₂) on the transcription factor peroxisome proliferator-activated receptor α (PPARα) and its targets in mouse cardiac and skeletal muscle. In the heart, PPARα expression was 40% higher than in normoxia after 1 and 7 days of hypoxia. Activities of carnitine palmitoyltransferase (CPT) I and β-hydroxyacyl-CoA dehydrogenase (HOAD) were 75% and 35% lower, respectively, after 1 day of hypoxia, returning to normoxic levels after 7 days. Oxidative phosphorylation respiration rates using palmitoyl-carnitine followed a similar pattern, while respiration using pyruvate decreased. In skeletal muscle, PPARα expression and CPT I activity were 20% and 65% lower, respectively, after 1 day of hypoxia, remaining at this level after 7 days with no change in HOAD activity. Oxidative phosphorylation respiration rates using palmitoyl-carnitine were lower in skeletal muscle throughout hypoxia, while respiration using pyruvate remained unchanged. The rate of CO₂ production from palmitate oxidation was significantly lower in both tissues throughout hypoxia. Thus cardiac muscle may remain reliant on fatty acids during sustained hypoxia, while skeletal muscle decreases fatty acid oxidation and maintains pyruvate oxidation.

Interactions of acid–base balance and hematocrit regulation during environmental respiratory gas challenges in developing chicken embryos (Gallus gallus)

How the determinants of hematocrit (Hct) – alterations in mean corpuscular volume (MCV) and/or red blood cell concentration ([RBC]) – are influenced by acid–base balance adjustments across development in the chicken embryo is poorly understood. We hypothesized, based on oxygen transport needs of the embryos, that Hct will increase during 1 day of hypercapnic hypoxia (5%CO2, 15%O2) or hypoxia alone (0%CO2, 15%O2), but decrease in response to hyperoxia (0%CO2, 40%O2). Further, age-related differences in acid–base disturbances and Hct regulation may arise, because the O2 transport and hematological regulatory systems are still developing in embryonic chickens. Our studies showed that during 1 day of hypoxia (with or without hypercapnia) Hct increased through both increased MCV and [RBC] in day 15 (d15) embryo, but only through increased MCV in d17 embryo and therefore enhancement of O2 transport was age-dependent. Hypercapnia alone caused a ∼14% decrease in Hct through decreased [RBC] and therefore did not compensate for decreased blood oxygen affinity resulting from the Bohr shift. The 11% (d15) and 14% (d17) decrease in Hct during hyperoxia in advanced embryos was because of an 8% and 9% decrease, respectively, in [RBC], coupled with an associated 3% and 5% decrease in MCV. Younger, d13 embryos were able to metabolically compensate for respiratory acidosis induced by hypercapnic hypoxia, and so were more tolerant of disturbances in acid–base status induced via alterations in environmental respiratory gas composition than their more advanced counterparts. This counter-intuitive increased tolerance likely results from the relatively low M˙O2 and immature physiological functions of younger embryos.

Effects of Iron Supplementation and Depletion on Hypoxic Pulmonary Hypertension

Hypoxia is a major cause of pulmonary hypertension in respiratory disease and at high altitude. Recent work has established that the effect of hypoxia on pulmonary arterial pressure may depend on iron status, possibly acting through the transcription factor hypoxia-inducible factor, but the pathophysiological and clinical importance of this interaction is unknown. To determine whether increasing or decreasing iron availability modifies altitude-induced hypoxic pulmonary hypertension. Two randomized, double-blind, placebo-controlled protocols conducted in October-November 2008. In the first protocol, 22 healthy sea-level resident men (aged 19-60 years) were studied over 1 week of hypoxia at Cerro de Pasco, Peru (altitude 4340 m). In the second protocol, 11 high-altitude resident men (aged 30-59 years) diagnosed with chronic mountain sickness were studied over 1 month of hypoxia at Cerro de Pasco, Peru. In the first protocol, participants received intravenous infusions of Fe(III)-hydroxide sucrose (200 mg) or placebo on the third day of hypoxia. In the second protocol, patients underwent staged isovolemic venesection of 2 L of blood. Two weeks later, patients received intravenous infusions of Fe(III)-hydroxide sucrose (400 mg) or placebo, which were subsequently crossed over. Effect of varying iron availability on pulmonary artery systolic pressure (PASP) assessed by Doppler echocardiography. In the sea-level resident protocol, approximately 40% of the pulmonary hypertensive response to hypoxia was reversed by infusion of iron, which reduced PASP by 6 mm Hg (95% confidence interval [CI], 4-8 mm Hg), from 37 mm Hg (95% CI, 34-40 mm Hg) to 31 mm Hg (95% CI, 29-33 mm Hg; P = .01). In the chronic mountain sickness protocol, progressive iron deficiency induced by venesection was associated with an approximately 25% increase in PASP of 9 mm Hg (95% CI, 4-14 mm Hg), from 37 mm Hg (95% CI, 30-44 mm Hg) to 46 mm Hg (95% CI, 40-52 mm Hg; P = .003). During the subsequent crossover period, no acute effect of iron replacement on PASP was detected. Hypoxic pulmonary hypertension may be attenuated by iron supplementation and exacerbated by iron depletion. clinicaltrials.gov Identifier: NCT00952302.

L-Citrulline ameliorates chronic hypoxia-induced pulmonary hypertension in newborn piglets

Newborn piglets develop pulmonary hypertension and have diminished pulmonary vascular nitric oxide (NO) production when exposed to chronic hypoxia. NO is produced by endothelial NO synthase (eNOS) in the pulmonary vascular endothelium using l-arginine as a substrate and producing l-citrulline as a byproduct. l-Citrulline is metabolized to l-arginine by two enzymes that are colocated with eNOS in pulmonary vascular endothelial cells. The purpose of this study was to determine whether oral supplementation with l-citrulline during exposure of newborn piglets to 10 days of chronic hypoxia would prevent the development of pulmonary hypertension and increase pulmonary NO production. A total of 17 hypoxic and 17 normoxic control piglets were studied. Six of the 17 hypoxic piglets were supplemented with oral l-citrulline starting on the first day of hypoxia. l-Citrulline supplementation was provided orally twice a day. After 10 days of hypoxia or normoxia, the animals were anesthetized, hemodynamic measurements were performed, and the lungs were perfused in situ. Pulmonary arterial pressure and pulmonary vascular resistance were significantly lower in hypoxic animals treated with l-citrulline compared with untreated hypoxic animals (P < 0.001). In vivo exhaled NO production (P = 0.03) and nitrite/nitrate accumulation in the perfusate of isolated lungs (P = 0.04) were significantly higher in l-citrulline-treated hypoxic animals compared with untreated hypoxic animals. l-Citrulline supplementation ameliorated the development of pulmonary hypertension and increased NO production in piglets exposed to chronic hypoxia. We speculate that l-citrulline may benefit neonates exposed to prolonged periods of hypoxia from cardiac or pulmonary causes.

Adaptation to chronic hypoxia involves immune cell invasion and increased expression of inflammatory cytokines in rat carotid body

Exposure to chronic hypoxia (CH; 3-28 days at 380 Torr) induces adaptation in mammalian carotid body such that following CH an acute hypoxic challenge elicits an abnormally large increase in carotid sinus nerve impulse activity. The current study examines the hypothesis that CH initiates an immune response in the carotid body and that chemoreceptor hyperexcitability is dependent on the expression and action of inflammatory cytokines. CH resulted in a robust invasion of ED1(+) macrophages, which peaked on day 3 of exposure. Gene expression of proinflammatory cytokines, IL-1beta, TNFalpha, and the chemokine, monocyte chemoattractant protein-1, was increased >2-fold after 1 day of hypoxia followed by a >2-fold increase in IL-6 on day 3. After 28 days of CH, IL-6 remained elevated >5-fold, whereas expression of other cytokines recovered to normal levels. Cytokine expression was not restricted to immune cells. Studies of cultured type I cells harvested following 1 day of in vivo hypoxia showed elevated transcript levels of inflammatory cytokines. In situ hybridization studies confirmed expression of IL-6 in type I cells and also showed that CH induces IL-6 expression in supporting type II cells. Concurrent treatment of CH rats with anti-inflammatory drugs (ibuprofen or dexamethasone) blocked immune cell invasion and severely reduced CH-induced cytokine expression in carotid body. Drug treatment also blocked the development of chemoreceptor hypersensitivity in CH animals. Our findings indicate that chemoreceptor adaptation involves novel neuroimmune mechanisms, which may alter the functional phenotypes of type I cells and chemoafferent neurons.

Behavioral effects of low dissolved oxygen on the bivalve Macoma balthica

Hypoxia, a dissolved oxygen concentration (DO) below 2 mg l – 1 , is a significant stressor in many estuarine ecosystems. Many sedentary organisms, unable to move to avoid hypoxic areas, have metabolic and behavioral adaptations to hypoxic stress. We tested the effects of hypoxia on the behavior and mortality of the clam Macoma balthica, using four levels of dissolved oxygen in flow-through tanks. We used five replicates of each of four treatments: (1) Hypoxic (DO mean ± SE = 1.1 ± 0.06 mg O 2 l – 1 ), (2) Moderately hypoxic (DO 2.6 ± 0.05 mg O 2 l – 1 ), (3) Nearly normoxic (DO 3.2 ± 0.04 mg O 2 l – 1 ), (4) Normoxic (DO = 4.9 ± 0.13 mg O 2 l – 1 ). We lowered the dissolved oxygen with a novel fluidized mud-bed, designed to mimic field conditions more closely than the common practice of solely bubbling nitrogen or other gasses. This method for lowering the DO concentrations for a laboratory setup was effective, producing 1.4 l min –1 of water with a DO of 0.8 mg O 2 l – 1 throughout the experiment. The setup greatly reduced the use of compressed nitrogen and could easily be scaled up to produce more low-DO water if necessary. The lethal concentration for 50% of the M. balthica population (LC 50) was 1.7 mg O 2 l – 1 for the 28-day experimental period. M. balthica decreased its burial depth under hypoxic and moderately hypoxic (~2.5 mg O 2 l – 1 ) conditions within 72 hours of the onset of hypoxia. By the sixth day of hypoxia the burial depth had been reduced by 26 mm in the hypoxic tanks and 10 mm in the moderately hypoxic tanks. Because reduced burial depth makes the clams more vulnerable to predators, these results indicate that the sub-lethal effects of hypoxia could change the rate of predation on M. balthica in the field.

Hypoxic hypoxia as a haemostatic system-activating factor

Aimed at investigating influence of hypoxic hypoxia of different duration on haemostatic system state, the assessment of coagulogram in 152 Vistar rats 1 and 3 hours after single «lifting» to the height of 5500 m over sea level in pressure chamber and after daily 3 hours during 7 and 30 days. Activating influence of single hypoxic xypoxia was on hemostasis was revealed. While in-creasing duration of single impact , activation hemostatic system increased and anticoagulant and fibrinolytic properties of blood plasma decreased. According to the coagulogram data, prethrombotic changes developed in the form of coagulation activation, thrombocytes intake, decreased anti-thrombin III level and fibrinolytic activity on the 7-th day of hypoxia. On the 30-th day, de-creased hemostatic activity with increasing anticoagulant plasma blood reserve and restorating fibrinolytic activity.

Hypoxic stimulus alters hypothalamic AMP-activated protein kinase phosphorylation concomitant to hypophagia

Acute exposure to hypobaric hypoxia is known to decrease food intake, but the molecular mechanisms of such alteration in feeding behavior remain unknown. We tested the hypothesis that hypothalamic AMP-activated protein kinase (AMPK) phosphorylation is affected by acute exposure to hypobaric hypoxia and thus would be involved in initial anorexia. To address this issue, male rats weighing 255-270 g were either submitted to hypobaric hypoxia (H, equivalent altitude of 5,500 m), maintained under local barometric pressure conditions (N), or pair-fed an equivalent quantity of food to that consumed by H rats (PF), for 6, 24, or 48 h. Daily food intake dropped by 73% during the first day of hypoxia (P<0.01) and remained by 46% lower than in N rats thereafter (P<0.01). Hypoxia per se, as estimated by comparing experimental data between the H and PF groups, increased ob gene transcription and plasma leptin concentration. A transient increase in glucose availability occurred in the H group compared with PF animals (P<0.05). The hypoxic stimulus led to an early and transient decrease in hypothalamic AMPK and acetyl-CoA carboxylase (ACC) phosphorylation, concomitant with hypophagia and associated alterations in nutrients and hormones. An increase in NPY mRNA levels occurred from day 1, similarly in H and PF rats, and thus mainly related to food restriction alone (P<0.05). In conclusion, the present study demonstrates that hypoxia per se inhibited AMPK and ACC phosphorylation in the hypothalamus, concomitant with profound anorexia. A powerful counterregulation occurs rapidly, mediated by NPY and devoted to avoid prolonged anorexia.

Differential metabolic adaptation to acute and long‐term hypoxia in rat primary cortical astrocytes

Brain astrocytes provide structural and metabolic support to surrounding cells during ischemia. Glucose and oxygen are critical to brain function, and glucose uptake and metabolism by astrocytes are essential to their metabolic coupling to neurons. To examine astrocyte metabolic response to hypoxia, cell survival and metabolic parameters were assessed in rat primary cortical astrocytes cultured for 3 weeks in either normoxia or in either 1 day or 3 weeks sustained hypoxia (5% O2). Although cell survival and proliferation were not affected by the mildly hypoxic environment, substantial differences in glucose consumption and lactate release after either acute or prolonged hypoxia suggest that astrocyte metabolism may contribute to their adaptation. Hypoxia over a period of 1 day increased glucose uptake, lactate release, and glucose transporter 1 (GLUT1) and monocarboxylate transporter 1 (MCT1) expression, whereas hypoxia over a period of 3 weeks resulted in a decrease of all parameters. Furthermore, increased glucose uptake at 1 day of hypoxia was not inhibited by cytochalasin B suggesting the involvement of additional glucose transporters. We uncovered hypoxia-regulated expression of sodium-dependent glucose transporters (SGLT1) in astrocytes indicating a novel adaptive strategy involving both SGLT1 and GLUT1 to regulate glucose intake in response to hypoxia. Overall, these findings suggest that although increased metabolic response is required for the onset of astrocyte adaptation to hypoxia, prolonged hypoxia requires a shift to an energy conservation mode. These findings may contribute to the understanding of the relative tolerance of astrocytes to hypoxia compared with neurons and provide novel therapeutic strategies aimed at maintaining brain function in cerebral pathologies involving hypoxia.

Pulmonary vascular iNOS induction participates in the onset of chronic hypoxic pulmonary hypertension

Pathogenesis of hypoxic pulmonary hypertension is initiated by oxidative injury to the pulmonary vascular wall. Because nitric oxide (NO) can contribute to oxidative stress and because the inducible isoform of NO synthase (iNOS) is often upregulated in association with tissue injury, we hypothesized that iNOS-derived NO participates in the pulmonary vascular wall injury at the onset of hypoxic pulmonary hypertension. An effective and selective dose of an iNOS inhibitor, L-N6-(1-iminoethyl)lysine (L-NIL), for chronic peroral treatment was first determined (8 mg/l in drinking water) by measuring exhaled NO concentration and systemic arterial pressure after LPS injection under ketamine+xylazine anesthesia. A separate batch of rats was then exposed to hypoxia (10% O2) and given L-NIL or a nonselective inhibitor of all NO synthases, N(G)-nitro-L-arginine methyl ester (L-NAME, 500 mg/l), in drinking water. Both inhibitors, applied just before and during 1-wk hypoxia, equally reduced pulmonary arterial pressure (PAP) measured under ketamine+xylazine anesthesia. If hypoxia continued for 2 more wk after L-NIL treatment was discontinued, PAP was still lower than in untreated hypoxic controls. Immunostaining of lung vessels showed negligible iNOS presence in control rats, striking iNOS expression after 4 days of hypoxia, and return of iNOS immunostaining toward normally low levels after 20 days of hypoxia. Lung NO production, measured as NO concentration in exhaled air, was markedly elevated as early as on the first day of hypoxia. We conclude that transient iNOS induction in the pulmonary vascular wall at the beginning of chronic hypoxia participates in the pathogenesis of pulmonary hypertension.