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PubMed1976

[Changes in serum proteins,-iron and -copper in swimmers before and after altitude training (author's transl)].

Fifteen male swimmers (mean age 19.3 +/- 2.1 years) were subjected to a standard 120 min swimming exercise test: a) before, and b) after 5 weeks of intensive training at middle altitude (2000 m). At rest, serum levels of alpha2-macroglobulin, transferrin and copper were elevated in swimmers as compared to untrained subjects. After the altitude training program, significant increases of the parameters of iron and copper metabolism, as well as of alpha2HS-glycoprotein and beta1A-globulin were observed. After the first exercise test (a), a significant rise in serum alpha1-acid glycoprotein, alpha1-antitrypsin, hemopexin, alpha2-macroglobulin, ceruloplasmin, transferrin, iron, copper and alpha2-HS-glycoprotein was noted. The same 120 min-exercise test after the altitude training (b) led to only small changes, especially as concerns the parameters of iron metabolism. The characteristic immediate and long-lasting changes in serum proteins and heavy metals in swimmers and the effects of training in middle altitude on the answer of the organism to swimming exercise with respect to the mentioned biochemical parameters are discussed.

Adult↗
PubMed1991

Glucoregulatory hormones in man at high altitude.

Concentrations of glucose, lactic acid, free fatty acid (FFA), insulin, cortisol and growth hormone (GH) in the blood were monitored in 15 euglycaemic men (sojourners, SJ) at sea level (SL) and while at altitudes of 3500 m and 5080 m, in acclimatised low landers (ALL) and in high altitude natives (HAN). In SJ, blood glucose and insulin concentrations showed a significant increase on the 3rd and 7th day after arrival at high altitude (HA), thereafter returning to sea level values and remaining the same during the entire period of their stay at 3500 m. Subsequently, on arrival at higher altitude (5080 m) the glucose concentrations again showed an increase over the preceding values and returned to SL values on day 41 while at 5080 m. A significant increase in cortisol concentrations was seen on day 3 after arrival at HA and the increased levels were maintained until day 21 at 3500 m. The cortisol concentrations on day 30 after arrival at 5080 m came down to SL values and remained unchanged thereafter. No appreciable change in GH and FFA was seen during the sojourn at HA. On the other hand, blood lactic acid concentration decreased significantly. There was no difference between the fasting glucose concentrations in ALL at 3500 m and in HAN at 3500 m and 4200 m compared to values of SJ at SL, whereas ALL at 4200 m had higher glucose values. Concentrations of plasma insulin and GH in ALL and HAN were higher than the values of SJ at SL, whereas cortisol values did not show any difference. These observations indicated that at HA the glucose values were high for the insulin concentration observed and might have been due to increased secretion of GH by the pituitary gland.

Adaptation, Physiological↗
PubMed1979

The effect of various stimulated altitudes on the turnover of norepinephrine and dopamine in the central nervous system of rats.

The elimination rate constant, half-life and turnover time of dopamine (DA) and norepinephrine (NE) were determined, after inhibiting their biosynthesis by alpha-methyl-para-tyrosine (alpha MT), in the hypothalamus, striatum and the remainder of the brain of rats exposed to different degrees of hypobaric hypoxia, corresponding to altitudes of 1,800, 3,800, 5,200 and 7,000 meters. The effects varied as a function of the degree of hypoxia and the brain region studied. The turnover time of NE in the hypothalamus remained unchanged, regardless of the altitude, while in the rest of the brain the rate constant of neurotransmitter elimination decreased inversely as a linear function of the degree of hypoxia. On the contrary, the changes of the DA turnover time in the striatum and the rest of the brain, were biphasic, being accelerated by moderate altitudes (1,800 m) and retarded by the two highest simulated altitudes studied as a function of hypoxia. The differential effects of hypoxia on NE and DA turnovers are attributed to different sensitivities of the respective enzyme systems.

Altitude↗
PubMed1995

Fluid distribution and tissue thickness changes in 29 men during 1 week at moderate altitude (2,315 m).

To quantify fluid distribution at a moderate altitude (2,315 m) 29 male subjects were studied with respect to tissue thickness changes [front (forehead), sternum, tibia], changes of total body water, changes of plasma volume, total protein concentrations (TPC), colloid osmotic pressure (COP), and electrolytes. Tissue thickness at the forehead showed a significant increase from 4.14 mm to 4.41 mm 48 h after ascent to the Rudolfshuette (2,315 m) (P < 0.05). At 96 h after ascent the tissue thickness at the tibia was decreased to 1.33 mm compared to the control value of 1.59 mm (P < 0.01). Body mass increased from 75.5 kg (control) to 76.2 kg on the last day (P < 0.05) and body water from 44.21 to 45.01 during the week (P < 0.01). The accumulation fluid in the upper part of the body was paralleled by a decrease in TPC and COP. At 48 h after the ascent COP dropped from 29.5 mmHg to 27.5 mmHg (P < 0.01). After 96 h at moderate altitude COP was still significantly decreased compared to the control level. At 1.5 h after the return from the Rudolf-shuette in Saalfelden (744 m) COP was back to the control values. The TPC also showed an initial drop from 7.75 g.dl-1 to 7.48 g.dl-1 after 48 h at altitude and remained below the control value during the whole week (P < 0.01). It seems from our study that even with exposure to moderate altitude measurable fluid shifts to the upper part of the body occurred which were detected by our ultrasound method.

Acclimatization↗
PubMed1987

Oxygen transfer properties and dimensions of red blood cells in high-altitude camelids, dromedary camel and goat.

To estimate the advantage of the small red blood cells (RBC) of high-altitude camelids for O2 transfer, the kinetics of O2 uptake into and release from the RBC obtained from llama, vicuña and alpaca were investigated at 37 degrees C with a stopped-flow technique. O2 transfer conductance of RBC (G) was estimated from the rate of O2 saturation change and the corresponding O2 pressure difference between medium and hemoglobin. For comparison, O2 kinetics for the RBC of a low-altitude camelid (dromedary camel) and the pygmy goat were determined and previously measured values for human RBC were used. O2 transfer of RBC was found to be strongly influenced by extracellular diffusion, except with O2 release into dithionite solutions of sufficiently high concentration (greater than 30 mM). The G values measured in these 'standard' conditions, Gst (in mmol X min-1 X Torr-1 X (ml RBC)-1) were: high-altitude camelids, 0.58 (averaged for llama, alpaca and vicuña since there were no significant interspecific differences); camel 0.42; goat, 0.42; man, 0.39. The differences can in part be attributed to expected effects of the size and shape of the RBC (volume, surface area, mean thickness), as well as to the intracellular O2 diffusivity which depends on the concentration of cellular hemoglobin. The high Gst of RBC of high-altitude camelids may be considered to enhance O2 transfer in lungs and tissues. But the O2 transfer conductance of blood, theta, equal to Gst multiplied by hematocrit (in mmol X min-1 X Torr-1 X (ml blood)-1), was only slightly higher as compared to other species: 0.20 (llama, alpaca, vicuña), 0.14 (camel), 0.18 (goat), 0.17 (man).

Altitude↗
PubMed1990

Pulmonary vascular disease in a rabbit at high altitude.

A male weanling rabbit of the New Zealand White strain, born and living at an altitude of 3800 m in La Paz, Bolivia, developed right ventricular hypertrophy. This was found to be associated with growth of vascular smooth muscle cells in the intima of pulmonary arterioles, and contrasted with muscularization of the walls of pulmonary arterioles, without extension into the intima, found in a healthy, high-altitude control rabbit of the same strain. A low-altitude control showed no such muscularization. It is concluded that alveolar hypoxia, acting directly or through an intermediate agent, is a growth factor for vascular smooth muscle cells in pulmonary arterioles. This is the first report of pulmonary vascular disease due to high altitude in rabbits.

Altitude↗
PubMed1992

Mast cells in the human lung at high altitude.

Mast cell densities in the lung were measured in five native highlanders of La Paz (3600 m) and in one lowlander dying from high-altitude pulmonary oedema (HAPO) at 3440 m. Two of the highlanders were Mestizos with normal pulmonary arteries and the others were Aymara Indians with muscular remodelling of their pulmonary vasculature. The aim of the investigation was to determine if accumulation of mast cells in the lung at high altitude (HA) is related to alveolar hypoxia alone, to a combination of hypoxia and muscularization of the pulmonary arterial tree, or to oedema of the lung. The lungs of four lowlanders were used as normoxic controls. The results showed that the mast cell density of the two Mestizos was in the normal range of lowlanders (0.6-8.8 cells/mm2). In the Aymara Indians the mast cell counts were raised (25.6-26.0 cells/mm2). In the lowlander dying from HAPO the mast cell count was greatly raised to 70.1 cells/mm2 lung tissue. The results show that in native highlanders an accumulation of mast cells in the lung is not related to hypoxia alone but to a combination of hypoxia and muscular remodelling of the pulmonary arteries. However, the most potent cause of increased mast cell density in the lung at high altitude appears to be high-altitude pulmonary oedema.

Adult↗
PubMed2003

Pressure breathing in fighter aircraft for G accelerations and loss of cabin pressurization at altitude--a brief review.

PURPOSE: The purpose of this brief review is to outline the past and present use of pressure breathing, not by patients but by fighter pilots. SOURCE: Of the historical and recent references quoted, most are from aviation-medicine journals that are not often readily available to anesthesiologists. PRINCIPAL FINDINGS: Pressure breathing at moderate levels of airway pressure gave World War II fighter pilots a tactical altitude advantage. With today's fast and highly maneuverable jet fighters, very much higher airway pressures of the order of 8.0 kPa (identical with 60 mmHg) are used. They are used in conjunction with a counterpressure thoracic vest and an anti-G suit for the abdomen and lower body. Pressurization is activated automatically in response to +Gz accelerations, and to a potentially catastrophic loss of cabin pressurization at altitude. During +Gz accelerations, pressure breathing has been shown to maintain cerebral perfusion by raising the systemic arterial pressure, so increasing the level of G-tolerance that is afforded by the use of anti-G suits and seat tilt-back angles alone. This leaves the pilot less reliant on rigorous, and potentially distracting, straining maneuvers. With loss of cabin pressurization at altitude, pressure breathing of 100% oxygen at high airway pressures enables the pilot's alveolar PO(2) to be maintained at a safe level during emergency descent. CONCLUSION: Introduced in military aviation, pressure breathing for G-tolerance and pressure breathing for altitude presented as concepts that may be of general physiological interest to many anesthesiologists.

Acceleration↗
PubMed2006

Is BMR repeatable in deer mice? Organ mass correlates and the effects of cold acclimation and natal altitude.

Basal metabolic rate (BMR) is probably the most studied aspect of energy metabolism in vertebrate endotherms. Numerous papers have explored its mass allometry, phylogenetic and ecological relationships, and ontogeny. Implicit in many of these studies (and explicit in some) is the view that BMR responds to selection, which requires repeatability and heritability. However, BMR is highly plastic in response to numerous behavioral and environmental factors and there are surprisingly few data on its repeatability. Moreover, the mechanistic underpinnings of variation in BMR are unclear, despite considerable research. We studied BMR repeatability in deer mice (Peromyscus maniculatus) across intervals of 30-60 days, and also examined the influence of birth altitude (3,800 m versus 340 m) and temperature acclimation (to approximately 5 or approximately 20 degrees C) on BMR, and the relationship between BMR and organ size. Neither acclimation temperature nor natal altitude alone influenced BMR, but the combination of birth at high altitude and cold acclimation significantly increased BMR. Few visceral organ masses were correlated to BMR and most were inconsistent across natal altitudes and acclimation temperatures, indicating that no single organ 'controls' variation in BMR. In several treatment groups, the mass of the 'running motor' (combined musculoskeletal mass) was negatively correlated to BMR and the summed mass of visceral organs was positively correlated to BMR. We found no repeatability of BMR in any treatment group. That finding-in sharp contrast to high repeatability of BMR in several other small endotherms-suggests little potential for direct selection to drive BMR evolution in deer mice.

Acclimatization↗
PubMed2003

Oxygen transport in blood at high altitude: role of the hemoglobin-oxygen affinity and impact of the phenomena related to hemoglobin allosterism and red cell function.

Altitude hypoxia is a major challenge to the blood O2 transport system, and adjustments of the blood-O2 affinity might contribute significantly to hypoxia adaptation. In principle, lowering the blood-O2 affinity is advantageous because it lowers the circulatory load required to assure adequate tissue oxygenation up to a threshold corresponding to about 5,000 m altitude, whereas at higher altitudes an increased blood-O2 affinity appears more advantageous. However, the rather contradictory experimental evidence raises the question whether other factors superimpose on the apparent changes of the blood-O2 affinity. The most important of these are as follows: (1) absolute temperature and temperature gradients within the body; (2) the intracapillary Bohr effect; (3) the red cell population heterogeneity in terms of O2 affinity; (4) control of altitude alkalosis; (5) the possible role of hemoglobin as a carrier of the vasodilator nitric oxide; (6) the effect of varied red cell transit times through the capillaries.

Allosteric Regulation↗
PubMed2004

Effect of a high-altitude expedition to a Himalayan peak (Pumori, 7,161 m) on plasma and erythrocyte antioxidant profile.

The effects of a high-altitude exposure were studied in six mountaineers who spent 3 weeks at an altitude range between 5,250 and 7,161 m after 1 week in an acclimatization trek (2,800-5,250 m). Blood drawn from the antecubital vein was collected at sea level 1 day before and 1 day after the expedition to analyse some haematological variables [haemoglobin (Hb), haematocrit (Htc) and red blood cell (RBC) count], erythrocyte antioxidant enzyme activity [superoxide dismutase (SOD), glutathione peroxidase (GPx) and glutathione reductase (Gr)] and membrane fatty acid profile [mono-unsaturated fatty acids (MUFA), polyunsaturated fatty acids (PUFA), saturated fatty acids (SFA), trans fatty acids (TRANS)]. Moreover, total antioxidant status (TAS), thiobarbituric acid reactive substances (TBARS), thiol protein groups (SH), SOD, GPx and Gr were measured in plasma. High-altitude exposure induced polycythaemia, with significant increases in RBC count (5.26%), Hb concentration (4.83%) and Htc (6.26%). Furthermore, a significant increase in plasma TBARS, SOD and Gr was observed after the expedition, whereas SH, TAS and GPx decreased. Erythrocyte glutathione-cycle-related antioxidant enzyme activity was upregulated, whereas SOD activity was maintained after the expedition. In addition, despite the unchanged (MUFA+PUFA)/SFA ratio, the membrane erythrocyte fatty acid content showed a significant increase in PUFAs and a decrease in TRANS, suggesting enhanced membrane fluidity. In conclusion, it seems that high-altitude exposure, besides quantitative variations in RBC expression, induced plasma oxidative stress and damage, and significant changes in erythrocyte components, namely in antioxidant enzyme activity and membrane fatty acid profile that might modify RBC functionality.

Adaptation, Physiological↗
PubMed2000

Effects of hypobaric hypoxia on vascular endothelial growth factor and the acute phase response in subjects who are susceptible to high-altitude pulmonary oedema.

In order to investigate whether vascular endothelial growth factor (VEGF) and inflammatory pathways are activated during acute hypobaric hypoxia in subjects who are susceptible to high-altitude pulmonary oedema (HAPE-S), seven HAPE-S and five control subjects were exposed to simulated altitude corresponding to 4000 m in a hypobaric chamber for 1 day. Peripheral venous blood was taken at 450 m (Zürich level) and at 4000 m, and levels of erythropoietin (EPO), VEGF, interleukin-6 (IL-6) and the acute-phase proteins complement C3 (C3), alpha1-antitrypsin (alpha1AT), transferrin (Tf) and C-reactive protein (CRP) were measured. Peripheral arterial oxygen saturation (SaO2) was recorded. Chest radiography was performed before and immediately after the experiment. EPO increased during altitude exposure, correlating with SaO2, in both groups (r = -0.86, P < 0.001). Venous serum VEGF did not show any elevation despite a marked decrease in SaO2 in the HAPE-S subjects [mean (SD) HAPE-S: 69.6 (9.1)%; controls: 78.7 (5.2)%]. C3 and alpha1AT levels increased in HAPE-S during hypobaric hypoxia [from 0.94 (0.11) g/l to 1.07 (0.13) g/l, and from 1.16 (0.08) g/l to 1.49 (0.27) g/l, respectively; P < 0.05], but remained within the clinical reference ranges. No significant elevations of IL-6, Tf or CRP were observed in either group. The post-exposure chest radiography revealed no signs of oedema. We conclude that VEGF is not up-regulated in HAPE-S and thus does not seem to increase critically pulmonary vascular permeability during the 1st day at high altitude. Furthermore, our data provide evidence against a clinically relevant inflammation in the initial phase of exposure to hypoxia in HAPE-S, although C3 and alpha1AT are mildly induced.

Acute-Phase Proteins↗
PubMed1997

General and local cold responses in humans after 2 weeks at high altitude.

To investigate the effects of a short-term high altitude residence (2 weeks between 4150 m and 6885 m in the Andes) on the general and local cold responses after descent, 11 subjects were submitted both to a whole body standard cold air test (SCAT, dry bulb temperature = 1 degree C, 2 h, nude, at rest) and to a local cold water test of the right upper limb (CWT, 5 degrees C, 5 min) both before and after the expedition. Compared to before the expedition, a lower systolic blood pressure was observed after the high altitude residence [130.00 (SEM 3.35) mm Hg vs 140.40 (SEM 4.74) mm Hg at the end of CWT, P < 0.05] whereas no significant change either in diastolic blood pressure or in heart rate was found. All skin temperatures of the right upper limb were lowered (P < 0.05). During SCAT, body temperatures were unchanged (rectal and mean skin temperature, Tsk) but metabolic heat production was slightly but significantly diminished [110 (SEM 4) W.m-2 vs 125 (SEM 3) W.m-2, P < 0.05] and heat debt increased [11.37 (SEM 1.11) kJ.kg-1 vs 9.30 (SEM 2.30) kJ.kg-1, P < 0.05]. Moreover, the time of onset of continuous shivering (d) was shortened [8.20 (SEM 1.90) min vs 17.30 (SEM 3.60) min, P < 0.05] and the level of Tsk observed at (d) was higher [25.70 (SEM 0.80) degrees C vs 23.57 (SEM 0.78) degrees C, P < 0.05] suggesting an increase in the sensitivity of the thermoregulatory system despite the slight decreased shivering activity observed. It was concluded that general and local cold tolerance were modified by a short-term residence at altitude and that the changes observed were not in accordance with general or (and) local cold adaptation. In contrast, high altitude sojourn could be a risk factor for frostbite of the extremities.

Altitude↗
PubMed1998

Implications of moderate altitude training for sea-level endurance in elite distance runners.

Elite distance runners participated in one of two studies designed to investigate the effects of moderate altitude training (inspiratory partial pressure of oxygen approximately 115-125 mmHg) on submaximal, maximal and supramaximal exercise performance following return to sea-level. Study 1 (New Mexico, USA) involved 14 subjects who were assigned to a 4-week altitude training camp (1500-2000 m) whilst 9 performance-matched subjects continued with an identical training programme at sea-level (CON). Ten EXP subjects who trained at 1640 m and 19 CON subjects also participated in study 2 (Krugersdorp, South Africa). Selected metabolic and cardiorespiratory parameters were determined with the subjects at rest and during exercise 21 days prior to (PRE) and 10 and 20 days following their return to sea-level (POST). Whole blood lactate decreased by 23% (P < 0.05 vs PRE) during submaximal exercise in the EXP group only after 20 days at sea-level (study 1). However, the lactate threshold and other measures of running economy remained unchanged. Similarly, supramaximal performance during a standardised track session did not change. Study 2 demonstrated that hypoxia per se did not alter performance. In contrast, in the EXP group supramaximal running velocity decreased by 2% (P < 0.05) after 20 days at sea-level. Both studies were characterised by a 50% increase in the frequency of upper respiratory and gastrointestinal tract infections during the altitude sojourns, and two male subjects were diagnosed with infectious mononucleosis following their return to sea-level (study 1). Group mean plasma glutamine concentrations at rest decreased by 19% or 143 (74) microM (P < 0.001) after 3 weeks at altitude, which may have been implicated in the increased incidence of infectious illness.

Adult↗
PubMed1999

"Live high, train low" does not change the total haemoglobin mass of male endurance athletes sleeping at a simulated altitude of 3000 m for 23 nights.

The purpose of this study was to document the effect of 23 days of "live high, train low" on the haemoglobin mass of endurance athletes. Thirteen male subjects from either cycling, triathlon or cross-country skiing backgrounds participated in the study. Six subjects (HIGH) spent 8-10 h per night in a "nitrogen house" at a simulated altitude of 3000 m in normobaric hypoxia, whilst control subjects slept at near sea level (CONTROL, n = 7). Athletes logged their daily training sessions, which were conducted at 600 m. Total haemoglobin mass (as measured using the CO-rebreathing technique) did not change when measured before (D1 or D2) and after (D28) 23 nights of hypoxic exposure [HIGH 990 (127) vs 972 (97) g and CONTROL 1042 (133) vs 1033 (138) g, before and after simulated altitude exposure, respectively]. Nor was there any difference in the substantial array of reticulocyte parameters measured using automated flow cytometry prior to commencing the study (D1), after 6 (D10) and 15 (D19) nights of simulated altitude, or 1 day after leaving the nitrogen house (D28) when HIGH and CONTROL groups were compared. We conclude that red blood cell production is not stimulated in male endurance athletes who spend 23 nights at a simulated altitude of 3000 m.

Adult↗
PubMed2001

Effect of human exposure to altitude on muscle endurance during isometric contractions.

The aim of this study was to evaluate the influence of exposure to altitude on muscle endurance during isometric contractions. Six sedentary subjects were studied. Surface electromyograph (sEMG) activity was recorded from the right biceps brachii (BB) during exhausting isometric exercise at 80% maximal voluntary contraction. Experiments were performed before, during and 6 months after a 12 day stay at the EV-K2 laboratory (Nepal, 5,050 m above sea level). From the sEMG signals from BB, the median frequencies (fmed) were computed for consecutive 1 s epochs. The sEMG was also analysed using a non-linear tool, the recurrence quantification analysis, and the percentage of determinism (%DET) was then calculated. The haemoglobin saturation significantly decreased at altitude. The mean (SD) BB endurance time decreased from 22.4 (4) s to 18.3 (4.7) s (P < 0.05). After exposure to altitude a significant variation in fmed and %DET slopes was observed. We concluded that during the first period of acclimatisation at altitude there was an impairment of isometric muscle endurance performance and there was also evidence of a modified myoelectric activity pattern suggesting a greater fatigability of the neuromuscular system.

Adult↗
PubMed2005

Antifungal activities of actinomycete strains associated with high-altitude sagebrush rhizosphere.

The antifungal-producing potential of actinomycete populations from the rhizosphere of low-altitude sagebrush, Artemisia tridentata, has been examined. In a continued investigation of new sources of antifungal-producing microorganisms, this study examined the antifungal-producing potential of actinomycetes from the rhizosphere of high-altitude A. tridentata. With high-altitude sagebrush, rhizosphere soil actinomycete numbers were one to four orders of magnitude higher than those found in nonrhizosphere bulk soils and different from those found with the low-altitude plants. A total of 122 actinomycete isolates was screened against nine fungal species and six bacterial species for the production of antimicrobial compounds. Four rhizosphere isolates, Streptomyces amakusaensis, S. coeruleorubidus, S. hawaiiensis and S. scabies, showed broad-spectrum antifungal activity against three or more fungal species in plate assays. In liquid antagonism assays, mycelium production by Aspergillus niger was reduced by up to 50% by two of the actinomycete isolates. These results demonstrate the potential of rhizosphere microbiology in the search for new antimicrobials.

Actinobacteria↗
PubMed2006

Effect of altitude on the primary products of photosynthesis and the associated enzymes in barley and wheat.

There is little information available on the primary products of photosynthesis and the change in the activity of the associated enzymes with altitude. We studied the same in varieties of barley and wheat grown at 1300 (low altitude, LA) and 4200 m (high altitude, HA) elevations above mean sea level in the western Himalayas. Plants at both the locations had similar photosynthetic rates, leaf water potential and the chlorophyll fluorescence kinetics. The short-term radio-labelling experiments in leaves showed appearance of (14)CO(2) in phosphoglyceric acid and sugar phosphates in plants at both the LA and HA, suggesting a major role of ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) in CO(2) fixation in the plants at two altitudes, whereas the appearance of labelled carbon in aspartate (Asp) and glutamate (Glu) at HA suggested a role of phosphoenolpyruvate carboxylase (PEPCase) in photosynthesis metabolism. Plants at HA had significantly higher activities of PEPCase, carboxylase and oxygenase activity of Rubisco, aspartate aminotransferase (AspAT), and glutamine synthetase (GS). However, the activities of malate dehydrogenase, NAD-malic enzyme and citrate synthase were similar at the two locations. Such an altered metabolism at HA suggested that PEPCase probably captured CO(2) directly from the atmosphere and/or that generated metabolically e.g. from photorespiration at HA. Higher oxygenase activity at HA suggests high photorespiratory activity. OAA thus produced could be additionally channelised for Asp synthesis using Glu as a source of ammonia. Higher GS activity ensures higher assimilation rate of NH(3) and the synthesis of Glu through GS-GOGAT (glutamine:2-oxoglutarate aminotransferase) pathway, also as supported by the appearance of radiolabel in Glu at HA. Enhanced PEPCase activity coupled with higher activities of AspAT and GS suggests a role in conserving C and N in the HA environment.

Altitude↗