Response of nitric oxide pathway to L-arginine infusion at the altitude of 4,350 m

Lactobacillus delbrueckii subsp. bulgaricus Alleviates Acute Injury in Hypoxic Mice

Acute mountain sickness (AMS) is a common ailment in high-altitude areas caused by the body's inadequate adaptation to low-pressure, low-oxygen environments, leading to organ edema, oxidative stress, and impaired intestinal barrier function. The gastrointestinal tract, being the first to be affected by ischemia and hypoxia, is highly susceptible to injury. This study investigates the role of Lactobacillus delbrueckii subsp. bulgaricus in alleviating acute hypoxic-induced intestinal and tissue damage from the perspective of daily consumed lactic acid bacteria. An acute hypoxia mouse model was established to evaluate tissue injury, oxidative stress, inflammatory responses, and intestinal barrier function in various groups of mice. The results indicate that strain 4L3 significantly mitigated brain and lung edema caused by hypoxia, improved colonic tissue damage, and effectively increased the content of tight junction proteins in the ileum, reducing ileal permeability and alleviating mechanical barrier damage in the intestines due to acute hypoxia. Additionally, 4L3 helped to rebalance the intestinal microbiota. In summary, this study found that Lactobacillus delbrueckii subsp. bulgaricus strain 4L3 could alleviate acute intestinal damage caused by hypoxia, thereby reducing hypoxic stress. This suggests that probiotic lactic acid bacteria that exert beneficial effects in the intestines may alleviate acute injury under hypoxic conditions in mice, offering new insights for the prevention and treatment of AMS.

Effects of dietary N-carbamylglutamate on rumen fermentation parameters, and bacterial community diversity of Holstein dairy cows in Tibet

Introduction

The Tibetan Plateau is characterized by low temperature and hypoxia. N-carbamylglutamic acid (NCG) can increase blood oxygen saturation, and have the potential to be used to prevent the high-altitude hypoxia stress state of cows. However, its beneficial effect on the rumen microbiota of Holstein dairy cows remains unclear.

Methods

Hence, the experiments 12 multiparous (parity ranged from 2 to 7) Holstein dairy cows (413.0 ± 42 kg) were randomly assigned to 2 treatments with 6 replicates in each treatment: basal diet (CON, control group) and basal diet plus 20 g/d/cow of NCG (NCG, experiment group), respectively. To study the effects of dietary NCG supplementation on rumen microbiota of Holstein dairy cows in Tibet. The experiment lasted for 45 days, with 15 days of pre-feeding and 30 days of formal trail period.

Results

The results showed that ruminal NH₃-N concentration in NCG group was lower (p < 0.05) than that in the CON group, while molar proportion of acetic acid and total volatile fatty acid (VFA) concentration were increased (p < 0.05) with the addition of NCG. Microbial diversity increased (p < 0.05) in NCG group, with Bacteroidetes, Firmicutes, and Patescibacteria as the most abundant phyla. The KEGG pathway analysis showed that the potential function of ruminal bacteria was mainly enriched in metabolism (carbohydrates, amino acids, lipids, energy, and nucleotides) and genetic information processing (replication, repair, and translation).

Conclusion

In conclusion, NCG can improve rumen nitrogen utilization, total VFA and acetic acid production, and increase rumen microbial diversity, all of which could make the introduced Holstein dairy cows to better adapt to the harsh environment in Tibet and improve their production performance.

The Oxygen Cascade from Atmosphere to Mitochondria as a Tool to Understand the (Mal)adaptation to Hypoxia

Hypoxia is a life-threatening challenge for about 1% of the world population, as well as a contributor to high morbidity and mortality scores in patients affected by various cardiopulmonary, hematological, and circulatory diseases. However, the adaptation to hypoxia represents a failure for a relevant portion of the cases as the pathways of potential adaptation often conflict with well-being and generate diseases that in certain areas of the world still afflict up to one-third of the populations living at altitude. To help understand the mechanisms of adaptation and maladaptation, this review examines the various steps of the oxygen cascade from the atmosphere to the mitochondria distinguishing the patterns related to physiological (i.e., due to altitude) and pathological (i.e., due to a pre-existing disease) hypoxia. The aim is to assess the ability of humans to adapt to hypoxia in a multidisciplinary approach that correlates the function of genes, molecules, and cells with the physiologic and pathological outcomes. We conclude that, in most cases, it is not hypoxia by itself that generates diseases, but rather the attempts to adapt to the hypoxia condition. This underlies the paradigm shift that when adaptation to hypoxia becomes excessive, it translates into maladaptation.

N-Carbamoylglutamate Supplementation on the Digestibility, Rumen Fermentation, Milk Quality, Antioxidant Parameters, and Metabolites of Jersey Cattle in High-Altitude Areas

This study aimed to assess the impact of the dietary supplementation of N-carbamoylglutamate (NCG) on nutrient digestibility, rumen fermentation, milk quality, oxidative stress, and metabolites in the plasma and feces of Jersey cattle under high altitude with the hypoxic condition. A total of 14 healthy lactating Jersey dairy cows with similar body conditions were selected and randomly divided into 2 groups. The control group (CON group, N = 6 replicates) was fed with a conventional complete diet, whereas the experimental group (NCG group, N = 8 replicates) received 20 g/d per head NCG supplementation. The experiment lasted for 60 days, the adaptation period was 12 days, and the formal experiment period was 48 days. Except that the NCG group showed an upward trend in dry matter intake (DMI) (p = 0.09) and the fermentation parameters, the molar proportion of butyric acid tended to decrease (p = 0.08); the two groups had no significant differences (p > 0.05) in nutrients digestibility, plasma immunity, and antioxidant ability. However, compared with the CON group, the milk fat rate and blood oxygen saturation of the NCG group showed an upward trend (p = 0.09). For indexes associated with altitude stress, the contents of thyroxine, transferrin, and endothelin both decreased significantly (p < 0.05) in the NCG group. Meanwhile, heat shock protein (p = 0.07) and aldosterone (p = 0.06) also showed a downward trend. A total of 114 different metabolites were identified from feces and plasma, 42 metabolites were derived from plasma that mainly included 5 kinds of Super Class, and 72 metabolites were derived from feces that mainly included 9 kinds of Super Class. The significantly increased plasma differential metabolites were 2,5-dihydroxybenzoate and salicyluric acid, and the significantly increased fecal differential metabolites were Butenafine (fold change > 2). Pathway analysis showed that after applying NCG as a feed additive, the changes of the Jersey dairy cows mainly focused on amino acid metabolism and lipid metabolism. These results indicated that adding NCG to the diet can prevent the hypoxic stress state of lactating Jersey cows in high-altitude areas and has a tendency to improve milk quality.

Inside the Alterations of Circulating Metabolome in Antarctica: The Adaptation to Chronic Hypoxia

Although the human body may dynamically adapt to mild and brief oxygen shortages, there is a growing interest in understanding how the metabolic pathways are modified during sustained exposure to chronic hypoxia. Located at an equivalent altitude of approximately 3,800 m asl, the Concordia Station in Antarctica represents an opportunity to study the course of human adaption to mild hypoxia with reduced impact of potentially disturbing variables else than oxygen deprivation. We recruited seven healthy subjects who spent 10 months in the Concordia Station, and collected plasma samples at sea level before departure, and 90 days, 6 months, and 10 months during hypoxia. Samples were analyzed by untargeted liquid chromatography high resolution mass spectrometry to unravel how the non-polar and polar metabolomes are affected. Statistical analyses were performed by clustering the subjects into four groups according to the duration of hypoxia exposure. The non-polar metabolome revealed a modest decrease in the concentration of all the major lipid classes. By contrast, the polar metabolome showed marked alterations in several metabolic pathways, especially those related to amino acids metabolism, with a particular concern of arginine, glutamine, phenylalanine, tryptophan, and tyrosine. Remarkably, all the changes were evident since the first time point and remained unaffected by hypoxia duration (with the exception of a slight return of the non-polar metabolome after 6 months), highlighting a relative inability of the body to compensate them. Finally, we identified a few metabolic pathways that emerged as the main targets of chronic hypoxia.

Hypertensive Patients Exhibit Enhanced Thrombospondin-1 Levels at High-Altitude

Thrombospondin-1 (THBS1) levels elevate under hypoxia and have relevance in several cardiovascular disorders. The association of THBS1 with endothelial dysfunction implies its important role in hypertension. To establish the hypothesis, we screened patients with hypertension and their respective controls from the two different environmental regions. Cohort 1 was composed of Ladakhis, residing at 3500 m above sea level (ASL), whereas Cohort 2 was composed of north-Indians residing at ~200 m ASL. Clinical parameters and circulating THBS1 levels were correlated in the case–control groups of the two populations. THBS1 levels were significantly elevated in hypertension patients of both cohorts; however, the levels were distinctly enhanced in the hypertensive patients of HA as compared to normoxia (p < 0.002). The observation was supported by the receiver operating curve analysis with an area under curve of 0.7007 (0.627–0.774) demonstrating the discriminatory effect of hypobaric hypoxia on the levels as compared to normoxia (p < 0.011). Significant correlation of THBS1 and mean arterial pressure was observed with upraised positive correlations in the hypertensive highlanders as compared to the hypertensive patients from sea-level. The prevalence of differential distribution of THBS1 and CD47 genes variants, their interactions, and association with the THBS1 levels were also determined. Genotype-interactions between THBS1 rs2228263 and CD47 rs9879947 were relevant and the regression analysis highlighted the association of risk genotype-interactions with increased THBS1 levels in hypertension. Genetic studies of additional thrombospondin pathway-related genes suggest the complex role of THBS1 in the presence of its family members and the related receptor molecules at HA.

Pulmonary Hypertension in Acute and Chronic High Altitude Maladaptation Disorders

Alveolar hypoxia is the most prominent feature of high altitude environment with well-known consequences for the cardio-pulmonary system, including development of pulmonary hypertension. Pulmonary hypertension due to an exaggerated hypoxic pulmonary vasoconstriction contributes to high altitude pulmonary edema (HAPE), a life-threatening disorder, occurring at high altitudes in non-acclimatized healthy individuals. Despite a strong physiologic rationale for using vasodilators for prevention and treatment of HAPE, no systematic studies of their efficacy have been conducted to date. Calcium-channel blockers are currently recommended for drug prophylaxis in high-risk individuals with a clear history of recurrent HAPE based on the extensive clinical experience with nifedipine in HAPE prevention in susceptible individuals. Chronic exposure to hypoxia induces pulmonary vascular remodeling and development of pulmonary hypertension, which places an increased pressure load on the right ventricle leading to right heart failure. Further, pulmonary hypertension along with excessive erythrocytosis may complicate chronic mountain sickness, another high altitude maladaptation disorder. Importantly, other causes than hypoxia may potentially underlie and/or contribute to pulmonary hypertension at high altitude, such as chronic heart and lung diseases, thrombotic or embolic diseases. Extensive clinical experience with drugs in patients with pulmonary arterial hypertension suggests their potential for treatment of high altitude pulmonary hypertension. Small studies have demonstrated their efficacy in reducing pulmonary artery pressure in high altitude residents. However, no drugs have been approved to date for the therapy of chronic high altitude pulmonary hypertension. This work provides a literature review on the role of pulmonary hypertension in the pathogenesis of acute and chronic high altitude maladaptation disorders and summarizes current knowledge regarding potential treatment options.

Structural and functional alterations of nitric oxide synthase 3 due to missense variants associate with high-altitude pulmonary edema through dynamic study

The human endothelial nitric oxide synthase (NOS3) is 28 Kbp at 7q36.1 and encodes protein comprising of 1280 amino acids. Being a major source of nitric oxide, the enzyme is crucial to the vascular homeostasis and thereby to be an important pharmaceutical target. We hence have been investigating this molecule in a high-altitude disorder namely, high-altitude pulmonary edema (HAPE). We performed a genome-wide association study (GWAS) in a case-control design of sojourners that included healthy controls and HAPE patients (n = 200) each. Four NOS3 missense SNPs i.e. rs1799983 (E298D), rs3918232 (V827M), rs3918201 (R885M) and rs3918234 (Q982L), were associated significantly with HAPE (P-value < 0.05). Furthermore, extensive in silico analyses were performed to predict the detrimental effect of the four variant types and their three most relevant co-factors namely, heme, flavin adenine dinucleotide (FAD) and flavin mononucleotide (FMN) that are accountable for amendment of protein stability leading to structural de-construction. Subsequently, we validated the findings in a larger sample size of the two study groups. HAPE patients had a higher frequency of the four variants and significantly decreased levels of circulating nitric oxide (NO) (P-value < 0.001). The in silico and human subjects findings complement each other. This study explored the impact of HAPE-associated NOS3 variants with its protein structure stability and holds promise to be current and future drug targets.Communicated by Ramaswamy H. Sarma.

Exhaled Nitric Oxide Changes During Acclimatization to High Altitude: A Descriptive Study

Summerfield, Douglas T., Kirsten E. Coffman, Bryan J. Taylor, Amine N. Issa, and Bruce D. Johnson. Exhaled nitric oxide changes during acclimatization to high altitude: a descriptive study. High Alt Med Biol. 19:215-220, 2018.

AIMS

This study describes differences in the partial pressures of exhaled nitric oxide (PeNO) between subjects fully acclimatized (ACC) to 5300 m and those who have just arrived to high altitude.

METHODS

PeNO was determined in eight subjects newly exposed and nonacclimatized (non-ACC) to high altitude and compared with that in nine subjects who had ACC to high altitude for 1 month. In addition, systolic pulmonary artery pressure (sPAP) and arterial oxygen saturation (SaO₂) were measured in all participants. These measurements were repeated in the non-ACC group 5 and 9 days later.

RESULTS

PeNO levels on day 1 were significantly higher in the non-ACC versus ACC cohort (8.7 ± 3.5 vs. 3.9 ± 2.2 nmHg, p = 0.004). As the non-ACC group remained at altitude, PeNO levels fell and were not different when compared with those of the ACC group by day 9 (5.9 ± 2.4 vs. 3.9 ± 2.2 nmHg, p = 0.095). Higher sPAP was correlated with lower PeNO levels in all participants (R = -0.50, p = 0.043). PeNO levels were not correlated with SaO₂.

CONCLUSIONS

As individuals acclimatized to high altitude, PeNO levels decreased. Even after acclimatization, PeNO levels continued to play a role in pulmonary vascular tone.

Long-Term Intermittent Exposure to High Altitude Elevates Asymmetric Dimethylarginine in First Exposed Young Adults

Lüneburg, Nicole, Patricia Siques, Julio Brito, Juan José De La Cruz, Fabiola León-Velarde, Juliane Hannemann, Cristian Ibanez, and Rainer Böger. Long-term intermittent exposure to high altitude elevates asymmetric dimethylarginine in first exposed young adults. High Alt Med Biol. 18:226–233, 2017.—Hypoxia-induced dysregulation of pulmonary and cerebral circulation may be related to an impaired nitric oxide (NO) pathway. We investigated the effect of chronic intermittent hypobaric hypoxia (CIH) on metabolites of the NO pathway. We measured asymmetric and symmetric dimethylarginine (ADMA and SDMA) and monomethyl-L-arginine (L-NMMA) and assessed their associations with acclimatization in male draftees (n = 72) undergoing CIH shifts at altitude (3550 m) during 3 months. Sixteen Andean natives living at altitude (3675 m) (chronic hypobaric hypoxia [CH]) were included for comparison. In CIH, ADMA and L-NMMA plasma concentrations increased from 1.14 ± 0.04 to 1.95 ± 0.09 μmol/L (mean ± SE) and from 0.22 ± 0.07 to 0.39 ± 0.03 μmol/L, respectively, (p < 0.001 for both) after 3 months, whereas SDMA did not change. The concentrations of ADMA and L-NMMA were higher in CH (3.48 ± 0.07, 0.53 ± 0.08 μmol/L; p < 0.001) as compared with CIH. In both CIH and CH, ADMA correlated with hematocrit (r² = 0.07, p < 0.05; r² = 0.26; p < 0.01). In CIH, an association of ADMA levels with poor acclimatization status was observed. We conclude that the endogenous NO synthase inhibitors, ADMA and L-NMMA, are elevated in hypoxia. This may contribute to impaired NO production at altitude and may also be predictive of altitude-associated health impairment.

Effect of acute hypobaric hypoxia on the endothelial glycocalyx and digital reactive hyperemia in humans

Introduction: Hypoxia is associated with increased capillary permeability. This study tested whether acute hypobaric hypoxia involves degradation of the endothelial glycocalyx.

Methods: We exposed 12 subjects to acute hypobaric hypoxia (equivalent to 4500 m for 2–4 h) and measured venous blood concentrations of biomarkers reflecting endothelial and glycocalyx degradation (catecholamines, syndecan-1, soluble CD40 ligand, protein C, soluble thrombomodulin, tissue-type plasminogen activators, histone-complexed DNA fragments, and nitrite/nitrate). Endothelial function was assessed by the hyperemic response to brachial artery occlusion by peripheral arterial tonometry.

Results: Compared with normoxic baseline levels, hypoxia increased concentrations of syndecan-1 from 22 (95% confidence interval: 17–27) to 25 (19–30) ng/ml (p < 0.02) and protein C from 76 (70–83)% to 81 (74–88)% (p < 0.02). Nitrite/nitrate decreased from 23 (18–27) μM at baseline to 19 (14–24) μM and 18 (14–21) μM in hypoxia and recovery, respectively (p < 0.05). Other biomarkers remained unchanged. The post-occlusion/pre-occlusion ratio (reactive hyperemia index, RHI) decreased from 1.80 (1.52–2.07) in normoxia to 1.62 (1.28–1.96) after 2–4 h of hypobaric hypoxia and thereafter increased to 2.43 (1.99–2.86) during normoxic recovery (p < 0.01).

Conclusions: The increase in syndecan-1 and protein C suggests that acute hypobaric hypoxia produces a minor degree of glycocalyx degradation and overall cellular damage. After hypoxia RHI rebounded to higher than baseline levels suggesting improved endothelial functionality.

Differential short-term repeated forearm hyperaemic reactivity in coronary artery disease patients compared to healthy low risk participants

The hyperaemic response of the forearm is a widely used technique to assess the vascular reactivity. Little is known about the short-term reproducibility and the possible exhaustion of this response in normal or diseased states. As such, the current study was conducted to assess this phenomenon using a unique nuclear medicine- (NM-) based technique. 19 patients with coronary artery disease (CAD) undergoing NM exercise stress tests and 15 low risk (LR) participants completed 2 reactive hyperaemia tests, using a SPECT-based technique, separated by 15  min. Analyses revealed that CAD patients had lower hyperaemic responses than LR participants (P < .001), and that there was a significant group × time interaction (P < .005), such that LR participants showed a larger decrease in the reactivity (5.2 ± 0.4 to 3.6 ± 0.4) than the CAD patients (2.9 ± 0.3 to 2.6 ± 0.3). These results suggest that there is a variability, due to disease states, in the reproducibility of the hypaeremic reactivity. This needs to be taken into account in short-term repeated measure studies.

Nitric oxide in adaptation to altitude

This review summarizes published information on the levels of nitric oxide gas (NO) in the lungs and NO-derived liquid-phase molecules in the acclimatization of visitors newly arrived at altitudes of 2500 m or more and adaptation of populations whose ancestors arrived thousands of years ago. Studies of acutely exposed visitors to high altitude focus on the first 24-48 h with just a few extending to days or weeks. Among healthy visitors, NO levels in the lung, plasma, and/or red blood cells fell within 2h, but then returned toward baseline or slightly higher by 48 h and increased above baseline by 5 days. Among visitors ill with high-altitude pulmonary edema at the time of the study or in the past, NO levels were lower than those of their healthy counterparts. As for highland populations, Tibetans had NO levels in the lung, plasma, and red blood cells that were at least double and in some cases orders of magnitude greater than other populations regardless of altitude. Red blood cell-associated nitrogen oxides were more than 200 times higher. Other highland populations had generally higher levels although not to the degree shown by Tibetans. Overall, responses of those acclimatized and those presumed to be adapted are in the same direction, although the Tibetans have much larger responses. Missing are long-term data on lowlanders at altitude showing how similar they become to the Tibetan phenotype. Also missing are data on Tibetans at low altitude to see the extent to which their phenotype is a response to the immediate environment or expressed constitutively. The mechanisms causing the visitors' and the Tibetans' high levels of NO and NO-derived molecules at altitude remain unknown. Limited data suggest processes including hypoxic upregulation of NO synthase gene expression, hemoglobin-NO reactions, and genetic variation. Gains in understanding will require integrating appropriate methods and measurement techniques with indicators of adaptive function under hypoxic stress.

Endothelin receptors blockade blunts hypoxia-induced increase in PAP in humans

BACKGROUND

Activation of the endothelin-1 (ET-1) pathway may be involved in hypoxia-induced pulmonary vasoconstriction, increase in pulmonary pressure and high altitude pulmonary oedema. Thus, we investigated the effect of the ETA/ETB receptor antagonist, bosentan, on pulmonary artery systolic pressure (PASP) in healthy subjects (n = 10).

DESIGN

We used a double-blind, placebo-controlled, randomized, cross-over design to study the effects of a single oral dose of bosentan (250 mg) on PASP after 90-min-exposure to normobaric hypoxia (FiO(2) = 0.12). We measured PASP and cardiac output by echocardiography, systolic arterial blood pressure, arterial O(2) saturation (SaO(2)), and blood gases at rest and during a sub-maximal exercise.

RESULTS

PASP in normoxia at rest was 23.5 +/- 2.7 and during exercise 39.8 +/- 11.6 mmHg (P < 0.0001). During the placebo period, hypoxia induced a significant decrease in SaO(2), PaO(2) and PCO(2) and increase in pH. PASP at rest increased significantly: 32.1 +/- 3.5 mmHg (P < 0.001 vs. normoxia). Bosentan significantly blunted the hypoxia-induced increase in PASP: bosentan: 27.0 +/- 3.3 mmHg, P = 0.002 vs. placebo at rest, but not during exercise: bosentan 39.8 +/- 11.6 vs. placebo 43.0 +/- 8.5 mmHg, ns. Bosentan had no effect on the hypoxia-induced changes in blood gases, or on cardiac output and systolic arterial blood pressure, which were not modified by hypoxia.

CONCLUSION

A single oral dose of bosentan blunted an acute hypoxia-induced increase in PASP in healthy subjects, without altering cardiac output or systemic blood pressure.

Genotype at the missense G894T polymorphism (Glu298Asp) in the NOS3 gene is associated with susceptibility to acute mountain sickness

Acute mountain sickness (AMS) is a potentially serious affliction that frequently occurs in travelers to altitudes above 2500 m. The probability of developing AMS depends on environmental factors such as rate of ascent and altitude attained; however, familial clustering and recurrence rates suggest that there may be a genetic contribution to the etiology of the condition. The underlying pathophysiology of AMS is unknown, but it may involve vasogenic edema secondary to hypoxia-induced sympathetic response and endothelial dysfunction. Nitric oxide is a potent vasomodulator, and variants in the gene that encodes endothelial nitric oxide synthase (NOS3) have been shown to affect blood pressure. We tested the hypothesis that haplotypes, as determined by tagSNPs, in NOS3 would be differentially represented in individuals with and without AMS sampled at the Janai Purnima Festival at Lake Gosain Kunda, Nepal, at 4380 m. Seven SNPs were tested, and a highly significant association (p = 0.004) was found for genotypes of the commonly studied missense polymorphism Glu298Asp (rs 1799983; G/T transversion at base 894). The T allele, which previously has been associated with hypertension, was overrepresented in individuals with AMS (0.30 vs. 0.10), but not significantly when the data were corrected for multiple testing (p = 0.024). These data suggest that a variant in a gene involved in nitric oxide synthesis is a risk factor for developing AMS.

Mitochondrial nitric oxide metabolism during rat heart adaptation to high altitude: effect of sildenafil, L-NAME, and L-arginine treatments

Rats submitted to high altitude (Cerro de Pasco, Perú, 4,340 m, Po(2) = 12.2 kPa) for up to 84 days showed a physiological adaptive response with decreased body weight gain (15%), increased right ventricle weight (100%), and increased hematocrit (40%) compared with sea level animals. These classical parameters of adaptation to high altitude were accompanied by an increase in heart mitochondrial enzymes: complexes I-III activity by 34% and mitochondrial nitric oxide synthase (mtNOS) activity and expression by >75%. The hyperbolic increase for mtNOS activity during adaptation to high altitude was similar to the observed pattern for hematocrit. Hematocrit and mtNOS activity mean values correlated linearly (r(2) = 0.75, P <or= 0.05). Chronic treatment for 28 days with sildenafil (50 mg*kg(-1).day(-1)) decreased the response of mtNOS to high altitude by 25%. Conversely, N(G)-nitro-l-arginine methyl ester treatment (8.3 mg*kg(-1)*day(-1)) increased such response by 40%, whereas l-arginine treatment (106 mg*kg(-1)*day(-1)) had no effect. Nitric oxide (NO) production by mtNOS accounts for approximately 49% of total cellular NO production in sea level rats and for approximately 54% in rats exposed to high altitude for 84 days. It is concluded that mtNOS is a substantial source of cardiac NO, a factor in the adaptive response to sustained heart hypoxia that is susceptible to be modified by pharmacological treatments.

Plasma and placental nitric oxide levels in women with and without pre-eclampsia living at different altitudes

OBJECTIVE

To investigate the nitric oxide (NO) levels in the plasma and the placentas of pregnant women with pre-eclampsia and women without pre-eclampsia, and to determine the effect of high or low altitude of residence.

METHODS

NO was determined by chemoluminescence and group comparisons were performed.

RESULTS

Women with pre-eclampsia (n=63) had higher plasma NO levels (38.6+/-17.44 vs 30.6+/-12.44 micromol/L, P=0.004) and higher placental NO levels (38.5+/-17.0 vs 24.3+/-7.16 ng/mg protein, P<0.05) compared with women without pre-eclampsia. A similar trend was found when comparisons were made according to altitude of residence. NO levels were significantly higher in the plasma of pre-eclamptic women living at sea level (41.11+/-18.78 vs 28.96+/-9.57 micromol/L, P=0.003), and in the placentas of women living at high altitude (39.51+/-16.98 vs 21.91+/-6.64 ng/mg protein, P<0.0001).

CONCLUSION

Women with pre-eclampsia had higher plasma and placental NO levels and the differences were associated with altitude of residence.

High altitude and oxidative stress

Exposure to high altitude, which is associated with decreased oxygen pressure, could result in oxidative/reductive stress, enhanced generation of reactive oxygen and nitrogen species (RONS), and related oxidative damage to lipids, proteins, and DNA. The severity of oxidative challenge is related to the degree of altitude. A wide range of RONS generating systems are activated during exposure to high altitude, including the mitochondrial electron transport chain, xanthine oxidase, and nitric oxide synthase. High altitude appears to weaken the enzymatic and non-enzymatic antioxidant systems, and increased nutritional uptake of antioxidant vitamins are beneficial to reduce the altitude-induced oxidative damage. The pattern of high altitude exposure-associated oxidative damage resembles ischemia/reperfusion injury. The adaptive process to this oxidative challenge requires a relatively long period of time. Physical exercise or an enhanced level of physical activity at high altitude, exacerbates the extent of the oxidative challenge. Therefore, special attention is necessary to curb the degree of oxidative stress.

L-arginine supplementation enhances exhaled NO, breath condensate VEGF, and headache at 4,342 m

We examined the effect of dietary supplementation with L-arginine on breath condensate VEGF, exhaled nitric oxide (NO), plasma erythropoietin, symptoms of acute mountain sickness, and respiratory related sensations at 4,342 m through the course of 24 h in seven healthy male subjects. Serum L-arginine levels increased in treated subjects at time 0, 8, and 24 h compared with placebo, indicating the effectiveness of our treatment. L-arginine had no significant effect on overall Lake Louise scores compared with placebo. However, there was a significant increase in headache within the L-arginine treatment group at 12 h compared with time 0, a change not seen in the placebo condition between these two time points. There was a trend (p = 0.087) toward greater exhaled NO and significant increases in breath condensate VEGF with L-arginine treatment, but no L-arginine effect on serum EPO. These results suggest that L-arginine supplementation increases HIF-1 stabilization in the lung, possibly through a NO-dependent pathway. In total, our observations indicate that L-arginine supplementation is not beneficial in the prophylactic treatment of AMS.

Evidence of a decrease in nitric oxide-storage molecules following acute hypoxia and/or hypobaria, by means of chemiluminescence analysis

Nitrate, nitrite, and other nitroso compounds (NOxs) had been proposed as possible nitric oxide (NO) storage molecules. The present work examines, by means of chemiluminescence analysis, changes in NOx serum levels in rats 1 h before and 24, 48, and 72 h after exposure to acute hypobaric hypoxia (HH; barometric pressure [P(B)] 225 mmHg, oxygen partial pressure [PO2] 48 mmHg), normobaric hypoxia (NH; P(B) 716 mmHg [Jaén city], PO2 48 mmHg), hypobaric normoxia (HN; P(B) 225 mmHg, PO2 150 mmHg), and normobaric normoxia (NN; P(B) 716 mmHg, PO2 150 mmHg) the latter as a control group. Results show a decrease in NOx levels, which reached significance 24 h after exposure in HH animals, 4 h after exposure in the HN and NH groups, and persisted after 48 h of exposure in the HN group. NOx determinations were also performed in brain (cerebral cortex, hippocampus, decorticated brain [basal ganglia-brainstem] and cerebellum), liver, kidney, lung, and heart homogenates, 72 h after the experiment, to detect persistent effects when serum NOx levels had returned to basal values. Only in cerebellum (HN group) and hippocampus (HN and NH groups) were NOx levels significantly lower than in controls. We conclude that not only acute hypobaric hypoxia but also either hypobaria or hypoxia alone induce changes in NOx serum levels. Moreover, all three episodes involve a decrease in NOxs, greater and longer-lasting in hypoxia alone than in hypobaria and hypoxia together. The exhaustion of these NO-storage molecules could be critical when, as during a hypoxic episode, the L-arginine/NOS pathway is impaired.

Heart mitochondrial nitric oxide synthase is upregulated in male rats exposed to high altitude (4,340 m)

Male rats exposed for 21 days to high altitude (4,340 m) responded with arrest of weight gain and increased hematocrit and testosterone levels. High altitude significantly (58%) increased heart mitochondrial nitric oxide (NO) synthase (mtNOS) activity, whereas heart cytosolic endothelial NOS (eNOS) and liver mtNOS were not affected. Western blot analysis found heart mitochondria reacting only with anti-inducible NOS (iNOS) antibodies, whereas the postmitochondrial fraction reacted with anti-iNOS and anti-eNOS antibodies. In vitro-measured NOS activities allowed the estimation of cardiomyocyte capacity for NO production, a value that increased from 57% (sea level) to 79 nmol NO.min(-1).g heart(-1) (4,340 m). The contribution of mtNOS to total cell NO production increased from 62% (sea level) to 71% (4340 m). Heart mtNOS activity showed a linear relationship with hematocrit and a biphasic quadratic association with estradiol and testosterone. Multivariate analysis showed that exposure to high altitude linearly associates with hematocrit and heart mtNOS activity, and that testosterone-to-estradiol ratio and heart weight were not linearly associated with mtNOS activity. We conclude that high altitude triggers a physiological adaptive response that upregulates heart mtNOS activity and is associated in an opposed manner with the serum levels of testosterone and estradiol.

Sildenafil inhibits altitude-induced hypoxemia and pulmonary hypertension

Exposure to high altitude induces pulmonary hypertension that may lead to life-threatening conditions. In a randomized, double-blind, placebo-controlled study, the effects of oral sildenafil on altitude-induced pulmonary hypertension and gas exchange in normal subjects were examined. Twelve subjects (sildenafil [SIL] n = 6; placebo [PLA] n = 6) were exposed for 6 days at 4,350 m. Treatment (3 x 40 mg/day) was started 6 to 8 hours after arrival from sea level to high altitude and maintained for 6 days. Systolic pulmonary artery pressure (echocardiography) increased at high altitude before treatment (+29% versus sea level, p < 0.01), then normalized in SIL (-6% versus sea level, NS) and remained elevated in PLA (+21% versus sea level, p < 0.05). Pulmonary acceleration time decreased by 27% in PLA versus 6% in SIL (p < 0.01). Cardiac output and systemic blood pressures increased at high altitude then decreased similarly in both groups. Pa(O(2)) was higher and alveolar-arterial difference in O(2) lower in SIL than in PLA at rest and exercise (p < 0.05). The altitude-induced decrease in maximal O(2) consumption was smaller in SIL than in PLA (p < 0.05). Sildenafil protects against the development of altitude-induced pulmonary hypertension and improves gas exchange, limiting the altitude-induced hypoxemia and decrease in exercise performance.

Expression of nitrergic system and protein nitration in adult rat brains submitted to acute hypobaric hypoxia

Changes in the nitric oxide (NO) system of the rat cerebral cortex were investigated by immunohistochemistry, immunoblotting, and NO synthase (NOS) activity assays in adult rats submitted for 30 min to hypoxia, in a hypobaric chamber at a simulated altitude of 38,000 ft (11000 m) (154.9 mm Hg). The cerebral cortex was studied after different survival times, 0 and 24 h, 5, 8, 15, and 30 days of reoxygenation. This situation led to morphological alterations in the large type I interneurons, as well as immunoreactive changes in the appearance and number of the small neurons (type II), both containing neuronal NOS (nNOS). Some of these small neurons showed immunoreactive cytoplasm and short processes; others, the more numerous during all reoxygenation periods, contained the immunoreactive product mainly related to a perinuclear ring. Ultrastructurally, these small neurons exhibited changes in nuclear structures as in the shape of the nuclear membrane, in the distribution of heterochromatin, and in the nucleolar morphology. The reaction product for nitrotyrosine, as a marker of protein nitration, showed modifications in distribution of the immunoreactive product. No expression was found for inducible NOS (iNOS). All these modifications were accompanied by increased nNOS and nitrotyrosine production as demonstrated by Western blotting and calcium-dependent activity, returning to control conditions after 30 days of reoxygenation, suggesting a reversible NO mechanism of action.

Interaction between reactive oxygen species and nitric oxide in the microvascular response to systemic hypoxia

Systemic hypoxia results in oxidative stress due to a change in the reactive oxygen species (ROS)-nitric oxide (NO) balance. These experiments explored two mechanisms for the altered ROS-NO balance: 1) decreased NO synthesis by NO synthase due to limited O(2) substrate availability and 2) increased superoxide generation. ROS levels and leukocyte adherence in mesenteric venules of rats during hypoxia were studied in the absence and presence of an NO donor [spermine NONOate (SNO)] and of the NO precursor L-arginine. We hypothesized that if the lower NO levels during hypoxia were due to O(2) substrate limitation, L-arginine would not prevent hypoxia-induced microvascular responses. Graded hypoxia (produced by breathing 15, 10, and 7.5% O(2)) increased both ROS (123 +/- 6, 148 +/- 11, and 167 +/- 3% of control) and leukocyte adherence. ROS levels during breathing of 10 and 7.5% O(2) were significantly attenuated by SNO (105 +/- 6 and 108 +/- 3%, respectively) and L-arginine (117 +/- 5 and 115 +/- 2%, respectively). Both interventions reduced leukocyte adherence by similar degrees. The fact that the effects of L-arginine were similar to those of SNO does not support the idea that NO generation is impaired in hypoxia and suggests that tissue NO levels are depleted by the increased ROS during hypoxia.