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At least 145 records · Page 8Linked to original sources
PubMed1982

[Growth of cardiac muscle cells during rat adaptation to altitude hypoxia].

The weight of the right heart ventricle in 1.5-month-old rats kept after birth in the mountains of 3400 m altitude is higher and its muscle cell cytoplasm mass is much larger compared to those in 1.5-month-old animals raised at 800 m altitude. The hypertrophy of cells is not due to their polyploidization. Only a small increase in the relative number of polyploid cells takes place under high altitude hypoxia. The weight of the right ventricle and myocyte mass in 3-month-old rats kept 1.5-3 months after the birth at 3400 m altitude also increases, although this augmentation is significantly less than in the animals grown in the mountains for 1.5 months immediately after the birth. The myocyte ploidy of adult animals adapted to hypoxia does not essentially differ from that of 1.5- and 3-month-old control rats: about 80 per cent of these cells are polyploid. Thus, the growth of cardiac myocytes under the heart hyperfunction in the case of high altitude hypoxia proceeds mainly on the ground of the stable polyploid genome, as well as normal ontogenetic growth of these cells.

Adaptation, Physiological↗
PubMed2000

Control of the unilluminated deformable mirror actuators in an altitude-conjugated adaptive optics system

Off-axis observations made with adaptive optics are severely limited by anisoplanatism errors. However, conjugating the deformable mirror to an optimal altitude can reduce these errors; it is then necessary to control, through extrapolation, actuators that are not measured by the wave-front sensor (unilluminated actuators). In this study various common extrapolation schemes are investigated, and an optimal method that achieves a significantly better performance is proposed. This extrapolation method involves a simple matrix multiplication and will be implemented in ALTAIR, the Gemini North Telescope adaptive optics system located on Mauna Kea, Hawaii. With this optimal method, the relative H-band Strehl reduction due to extrapolation errors is only 5%, 16%, and 30% when the angular distance between the guide source and the science target is 20, 40 and 60 arc sec, respectively. For a site such as Mauna Kea, these errors are largely outweighed by the increase in the size of the isoplanatic field.

Journal Article↗
PubMed2025

Whole methylomes reveal high-altitude-associated methylation at hypoxia and pigmentation genes in South American Indigenous populations.

High-altitude adaptation in Andean populations has traditionally been studied through the lens of genetic variation, with limited exploration of epigenetic mechanisms such as DNA methylation. Here, we present the first whole-methylome data comparing Indigenous populations residing in high-altitude regions of the Ecuadorian Andes to those in low-altitude Peruvian Amazon regions bordering the Andes. By leveraging whole-methylome sequencing rather than methylation arrays, we achieved an unprecedented resolution of epigenetic variation, revealing novel insights into altitude-associated adaptations. We identified significant differentially methylated regions in genes involved in hypoxia response and skin pigmentation that differ from patterns previously observed in high-altitude Tibetan individuals [Lin et al. (Genome-wide DNA methylation landscape of four Chinese populations and epigenetic variation linked to Tibetan high-altitude adaptation. Science China Life Sciences 2023;66:2354-69. https://doi.org/10.1007/s11427-022-2284-8.)]. Our findings highlight the influence that altitude-specific environmental pressures, such as hypoxia and ultraviolet radiation, can have on the epigenetic landscapes observed between human populations. Importantly, we uncovered unique regulatory methylation signatures in the hypoxia response pathways of Andean populations, underscoring a distinct epigenetic trajectory compared to other high-altitude groups. This study represents a step forward in understanding Indigenous American genomic plasticity and demonstrates the value of whole-methylome data over methylation arrays in capturing the complex interplay between epigenetics and the environment. These results support a new approach to studying altitude plasticity and underscore the critical role of epigenetics in shaping population-specific cellular responses in Indigenous communities.

UV response↗
PubMedDate not supplied

[Catalytic properties of monoamine oxidases during adaptation to altitude chamber hypoxia].

The effect of different exposures to altitude chamber hypoxia (1, 5 or 21 days) upon the catalytic properties of monoaminoxidases (MAO) of fragments of mitochondrial membranes of the Wistar rat liver, which are key enzymes in the metabolism of biogenic amines, was investigated. The MAO activity of A and B types decreased on day 5 and increased on day 21 of exposure. In addition, hypoxia modified catalytic properties of MAO which allowed the enzyme to produce oxidative deamination of nitrogen compounds that do not serve as its substrates under normal conditions. By measuring kinetic constants KM and Vmax, it was found that the enzyme affinity for serotonin increased and the rate of enzymic reaction decreased during hypoxia. The above changes of MAO catalytic properties seem to be associated with qualitative adaptation to hypoxia which triggers new metabolic pathways.

Altitude Sickness↗
PubMed2003

Patterns of control of maximum metabolic rate in humans.

In this analysis, four performance phenotypes were used to compare mechanisms of control of aerobic maximum metabolic rate (MMR): (i) untrained sedentary (US) subjects, as a reference group against which to compare (ii) power trained (PT), (iii) endurance trained (ET) and (iv) high altitude adapted native (HA) subject groups. Sprinters represented the PT group; long distance runners illustrated the ET group; and Quechuas represented the HA group. Numerous recent studies have identified contributors to control on both the adenosine triphosphate (ATP) supply side and the ATP demand side of ATP turnover. Control coefficients or c(i) values were defined as fractional change in MMR/fractional change in the capacity of any given step in ATP turnover. From the best available evidence it appears that at MMR all five of the major steps in energy delivery (namely, ventilation, pulmonary diffusion, cardiac output, tissue capillary - mitochondrial O(2) transfer, and aerobic cell metabolism per se) approach an upper functional ceiling, with control strength being distributed amongst the various O(2) flux steps. On the energy demand side, the situation is somewhat simplified since at MMR approximately 90% of O(2)-based ATP synthesis is used for actomyosin (AM) and Ca(2+) ATPases; at MMR these two ATP demand rates also appear to be near an upper functional ceiling. In consequence, at MMR the control contributions or c(i) values are rather evenly divided amongst all seven major steps in ATP supply and ATP demand pathways right to the point of fatigue. Relative to US (the reference group), in PT subjects at MMR control strength shifts towards O(2) delivery steps (ventilation, pulmonary diffusion and cardiac output). In contrast in ET and HA subjects at MMR control shifts towards the energy demand steps (AM and Ca(2+) ATPases), and more control strength is focussed on tissue level ATP supply and ATP demand. One obvious advantage of the ET and HA control pattern is improved metabolite homeostasis. Another possibility is that, with some reserve capacity in the O(2) delivery steps and control focussed on ATP turnover at the tissue level, nature has designed the ideal 'endurance machine'.

Adaptation, Physiological↗
PubMedDate not supplied

[Various individual features of human adaptation to altitude].

Two groups of young healthy men--natives of lowlands who for one year lived and worked in chronic hypoxia (Group 1 at an altitude of 1680 m with PO2 = 120 mm Hg and Group 2 at an altitude of 3650 with PO2 = 90 mm Hg) were examined. It was found that after this prolonged exposure the subjects showed a higher sensitivity of the respiration system to hypoxia, an enhanced lung ventilation and circulation, a lower gas exchange and physical work capacity. The concentration of lactic acid at rest in the Group 2 subjects was 47% higher than in the Group 1 subjects. The lactate/pyruvate ratio in the Group 2 subjects increased by 46% thus indicating an enhanced rate of anaerobic processes. A higher deficiency of buffer bases, a lower concentration of bicarbonates in blood at rest and during exercise tests of the Group 2 subjects pointed to metabolic acidosis. The subjects with a higher rate of anaerobic metabolism in a low PO2 environment displayed a diminished sensitivity of the hypoxic stimulation of respiration, an increased tolerance to the very low PAO2 and a reduced work capacity in chronic hypoxia.

Acclimatization↗
PubMed1981

Erythroid adaptation to altitude.

In May 1978, Messner and Habeler were the first to reach the summit of Mt. Everest without the use of supplemental oxygen. This feat illuminated the remarkable capacity of blood to adjust to the environment and support transport of oxygen from the lungs to the tissues despite an ambient oxygen pressure lower than that of normal mixed venous blood. It also met the exacting requirements for a true ascent of Mt. Everest set in 1935 by Frank Smythe in his book "The Spirit of the Hills". Although the conquest may seem more related to the breaking of the four minute mile than to any spirit of the hills, mountaineering has always combined emotional fulfillment with keen competition and scientific curiosity. The early mountain climbers from Petrach to Whymper were reaching for a personal spiritual experience but also were strongly influenced by priorities and first ascents. After the scaling in 1865 of Matterhorn, the last conquered peak in the Alps, a period followed during which physiologists from Bert to Hurtado provided insight into the importance of blood and lungs for oxygen transport and survival at high altitudes. The results of these studies combined with technical skill and competitive grit have permitted the current breed of mountaineers to scale successfully the most vertical mountain faces and the most lofty Himalayan peaks. These field trials of physiologic principles have also been of immense importance for our understanding of the pathophysiology of anemias and polycythemias. For whatever successes we have had in our management of patients with such disorders, we must in no small part give credit to man's eternal fascination with the top of the hills.

Altitude↗
PubMedDate not supplied

[Changes in the phospholipid and cholesterol content of rat tissues during adaptation to high altitude at different environmental temperatures].

Studies have been made on the contents of total lipids, cholesterol, phospholipids and the level of lipid peroxidation in rats adapted to a high altitude (3.200 m for 30 days) at temperatures 10 and 30 degrees C. It was shown that at lower temperature, high altitude adaptation is paralleled by more significant activation of lipid peroxidation, the decrease of phosphatidylcholine and phosphatidylethanolamine in the brain, lungs and liver, as well as by the increase of the content of phosphatidic acid and phosphatidylinositol in tissues. No negative cross-adaptation was found to hypoxic hypoxia and low temperatures.

Adaptation, Physiological↗
PubMed2001

Human genetic adaptation to high altitude.

Some 140 million persons live permanently at high altitudes (>2500 m) in North, Central and South America, East Africa, and Asia. Reviewed here are recent studies which address the question as to whether genetic adaptation to high altitude has occurred. Common to these studies are the use of the oxygen transport system and the passage of time as organizing principles, and the recognition of the multifaceted ways in which genetic factors can influence physiological processes. They differ in terms of study approach and sources of evidence for judging duration of high altitude residence. Migrant, family set, and admixture study designs have been used for comparisons within populations. These collectively demonstrate the existence of genetic influences on physiological characteristics of oxygen transport. Differences in oxygen transport-related traits between Tibetan, Andean and European populations have been interpreted as having demonstrated the existence of genetic influences on high altitude adaptation but there is not consensus as to which groups are the best-adapted. Part of the controversy lies in the kinds of evidence used to assess duration of high altitude habitation. More other information is needed for a fuller appreciation of duration of residence and also features of population history (genetic drift, gene flow) but existing data are consistent with Tibetans having lived at high altitude longer than the other groups studied. Another issue surrounds usage of the term "adaptation." The definition should be based on evolutionary biology and physiological traits linked to indices of differential fertility and/or mortality. Two examples are developed to illustrate such linkages; intrauterine growth restriction (IUGR) at high altitude and the prevalence of Chronic Mountain Sickness (CMS). Interpopulational as well as intrapopulational variation exists in these conditions which appear linked to characteristics of oxygen transport. Both adversely influence survival and appear to be less severe (IUGR) or less common (CMS) among Tibetans than other groups. Thus available evidence suggest that Tibetans are better adapted. Needed, however, are studies which are better controlled for population ancestry, especially in South America, to determine the extent to which Tibetans differ from Andean highlanders. More precise information is also needed regarding the genetic factors underlying characteristics of oxygen transport. Such studies in Tibetan, Andean and Europeans as well as other high altitude populations offers a promising avenue for clarifying the adaptive value of physiological components of oxygen transport and the extent to which such factors differ among high altitude populations.

Acclimatization↗
PubMed1983

Perspectives on functional adaptation of the high altitude native.

The major physiological processes that enable humans to attain a complete acclimatization to high altitude are briefly reviewed. The available data indicate that: (a) complete acclimatization to high altitude is associated with changes of environmentally modifiable functional traits such as lung volume but not associated with the expression of genetically controlled features such as chest size; (b) as judged by measurements of maximal aerobic power, the high altitude native has attained at high altitude an adaptation that is comparable to that attained by the low altitude native at sea level; the available information suggests that such adaptation is acquired through growth and development in an hypoxic environment; at present, however, we do not know the developmental modifications that occur within each component of the oxygen transport system, such as ventilation, pulmonary diffusion, and oxygen transport, that enable a sea level native to attain a complete functional adaptation to high altitude; and (c) at comparable altitudes among high altitude natives, there are some inter-regional differences in hemopoietic response, so that the samples derived from mining regions of the Andes are characterized by higher hemoglobin concentration than those derived from non-mining areas or the Himalayas. The source of these differences remains to be investigated.

Adaptation, Physiological↗
PubMed2002

Myocardial capillary angiogenesis and coronary flow in ischemia tolerance rat by adaptation to intermittent high altitude hypoxia.

AIM: To determine the effects of simulated intermittent high altitude hypoxia adaptation (IHA) on coronary capillary and coronary flow (CF) in rat hearts. METHODS: Model of Langendorf-perfused isolated rat hearts were used to measure CF during ischemia-reperfusion, and immunoperoxidase staining assay and computer-aid morphometry analysis were conducted to determine the myocardial capillary densities. Cyclic GMP (cGMP) level in myocardium was measured by radio-immunoassay. RESULTS: Pre-ischemia level of CF in IHA rats was higher (IHA28 13.4 mL/min+/-1.5 mL/min, IHA42 15.4 mL/min+/-2.0 mL/min, P < 0.01) than that of normoxic rats (11.0+/-0.8) mL/min, and the recovery of CF after ischemia-reperfusion was better in IHA rats. As an adaptive result, the myocardial capillary densities of the left ventricular myocardium in IHA rats were 1.5 times of those in normoxic control rats, but there was no apparent ventricular hypertrophy in IHA rats. Myocardial cGMP content (1.8+/-0.7) nmol/g in IHA rats were increased significantly compared with control rats (1.1+/-0.4) nmol/g, but cGMP level was not altered before and after ischemia-reperfusion in either group. It was also revealed that in isolated rat hearts perfused, myocardial function recovered better in IHA rats than that in normoxic control rats. CONCLUSION: IHA adaptation increased the tolerance of rat hearts against subsequent ischemia-reperfusion injury, and increase in coronary circulation and angiogenesis might be the mechanisms of myocardium protected by IHA.

Adaptation, Physiological↗
PubMed1986

[Dynamics of various characteristics of the sympathetic ganglia of animals subjected to chemical sympathectomy at high altitude].

The effect of high altitude hypoxia on the sympathetic nervous system was studied on desympathized rats. The degree of the sympathetic ganglion neurons destruction and catecholamine fluorescence were determined. The investigation showed an increase of catecholamine fluorescence in sympathetic ganglia in high altitude adaptation. 30-day administration of sympatholytic guanethidine at high altitude results in destruction of less ganglion neurons than at low altitude. At high altitude the rate of fluorescence of biogenic amines in unaffected cells remains high. After partial desympathization (7 days), the rate of neuron destruction diminishes and biogenic amines fluorescence increases along with the duration of preliminary adaptation.

Adaptation, Physiological↗