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PubMed2003

Heart rate variability in rats acclimatized to high altitude.

The aims of this study were to relate heart morphology and functions changes to heart rate variability (HRV) components after acclimatization to high altitude and to define whether preadaptation to hypoxia could modulate HRV responses to acute hypoxic stress. Doppler-echocardiographic studies of the left ventricle were performed in female Wistar rats before, during, and after a 10-week exposure to moderate hypobaric hypoxia (CH rats, approximately 4000 m simulated) or normoxia (N rats, approximately 55 m). Right ventricular morphology and function and pulmonary artery pressure were evaluated using heart catheterization. Spectral analysis of HRV was studied after exposure in conscious unrestrained rats in normoxia and during acute hypoxic stress. Necropsy right ventricular hypertrophy and intraventricular and pulmonary artery hypertension were found in CH rats compared with N rats. Echocardiographic left ventricular morphology and functions were similar between the groups after exposures. Compared to the control group, CH rats had similar heart rates and HRV components when measured in normoxia. During acute hypoxic stress, HRV decreased in all rats, but less in CH rats. These results support the hypothesis that long-term mild hypoxia may moderate sympathetic activation induced by acute hypoxia and that right ventricular hypertrophy cannot be the direct cause of such a shift in sympathovagal nerve interaction during acute hypoxic stress.

Acclimatization↗
PubMed2005

Acclimatization to oxidative stress at high altitude.

Hypoxia-mediated oxidative stress has been implicated in the pathophysiology of high altitude maladaptations. To explore whether prolonged exposure to high altitude can trigger an adaptive response to oxidative stress and restore redox homeostasis in the body, the study was conducted to evaluate biochemical variables related to oxidative stress and antioxidant status in humans at sea level (190 m) and following 3- and 13- month sojourns at altitude (4,500 m). After 3 months at altitude, whole-blood thiobarbituric acid reactive substances (TBARS) were significantly higher (65.6%), nonenzymatic antioxidants like ascorbic acid and caeruloplasmin were significantly lower (41% and 22%, respectively) and plasma total antioxidant status (TAS), glutathione levels, and superoxide dismutase activity were marginally altered as compared to their basal values. After 13 months at altitude, TBARS levels regressed back to preexposure levels. Plasma total antioxidant status (TAS) improved by 21%, glutathione levels by 32.8%, and plasma bilirubin by 35.8% as compared to sea level. Average concentrations of ascorbic acid and caeruloplasmin were 18% and 37% higher as compared to the subjects studied after a 3-month stay at high altitude. In addition, there was a progressive rise in erythrocytic superoxide dismutase activity and persistent hyperurecemia. The study observed that on prolonged exposure to high altitude humans could mount an effective adaptive response to oxidative stress by activating the antioxidant defense. Hence, strengthening the antioxidant defense could be an effective strategy to prevent free-radical-mediated pathophysiological alterations and quicken acclimatization to oxidative stress.

Acclimatization↗
PubMed2005

Adaptation and acclimatization to formaldehyde in methylotrophs capable of high-concentration formaldehyde detoxification.

Formaldehyde is a highly toxic chemical common in industrial effluents, and it is also an intermediate in bacterial metabolism of one-carbon growth substrates, although its role as a bacterial growth substrate per se has not been extensively reported. This study investigated two highly formaldehyde-resistant formaldehyde utilizers, strains BIP and ROS1; the former strain has been used for industrial remediation of formaldehyde-containing effluents. The two strains were shown by means of 16S rRNA characterization to be closely related members of the genus Methylobacterium. Both strains were able to use formaldehyde, methanol and a range of multicarbon compounds as their principal growth substrate. Growth on formaldehyde was possible up to a concentration of at least 58 mM, and survival at up to 100 mM was possible after stepwise acclimatization by growth at increasing concentrations of formaldehyde. At such high concentrations of formaldehyde, the cultures underwent a period of formaldehyde removal without growth before the formaldehyde concentration fell below 60 mM, and growth could resume. Two-dimensional electrophoresis and MS characterization of formaldehyde-induced proteins in strain BIP revealed that the pathways of formaldehyde metabolism, and adaptations to methylotrophic growth, were very similar to those seen in the well-characterized methanol-utilizing methylotroph Methylobacterium extorquens AM1. Thus, it appears that many of the changes in protein expression that allow strain BIP to grow using high formaldehyde concentrations are associated with expression of the same enzymes used by M. extorquens AM1 to process formaldehyde as a metabolic intermediate during growth on methanol.

Acclimatization↗
PubMed2006

Does soil CO2 efflux acclimatize to elevated temperature and CO2 during long-term treatment of Douglas-fir seedlings?

We investigated the effects of elevated soil temperature and atmospheric CO2 on soil CO2 efflux (SCE) during the third and fourth years of study. We hypothesized that elevated temperature would stimulate SCE, and elevated CO2 would also stimulate SCE with the stimulation being greater at higher temperatures. The study was conducted in sun-lit controlled-environment chambers using Douglas-fir (Pseudotsuga menziesii) seedlings grown in reconstructed litter-soil systems. We used a randomized design with two soil temperature and two atmospheric CO2 treatments. The SCE was measured every 4 wk for 18 months. Neither elevated temperature nor CO2 stimulated SCE. Elevated CO2 increased the temperature sensitivity of SCE. During the winter, the relationship between SCE and soil moisture was negative but it was positive during the summer. The seasonal patterns in SCE were associated with seasonal changes in photosynthesis and above-ground plant growth. SCE acclimatized in the high-temperature treatment, probably because of a loss of labile soil carbon. Elevated CO2 treatment increased the temperature sensitivity of SCE, probably through an increase in substrate availability.

Acclimatization↗
PubMed1970

Urinary excretion of adrenal steroids, catecholamines and electrolytes in man, before and after acclimatization to cold in Antarctica.

1. Urine samples were collected from four men before and during test cold exposures in Melbourne, Australia, and Mawson, Antarctica. Changes in the response of body temperature to the test exposures showed that the men had acclimatized to cold at Mawson.2. Excretion rates of 17-hydroxycorticosteroids and 17-ketosteroids were significantly greater at Mawson than in Melbourne, in both the pre-exposure and exposure periods.3. Excretion rates of noradrenaline, adrenaline, sodium, potassium and creatinine did not differ significantly between Mawson and Melbourne, nor did urine flow rates.4. During the cold exposure significant increases occurred, to the same extent at Mawson as in Melbourne, in urine flow rate and in all measured urinary constituents except creatinine.

17-Hydroxycorticosteroids↗
PubMed2004

Second generation Tibetan lowlanders acclimatize to high altitude more quickly than Caucasians.

Tibetan highlanders develop at altitude peak aerobic power levels close to those of Caucasians at sea level. In order to establish whether this feature is genetic and, as a consequence, retained by Tibetan lowlanders, altitude-induced changes of peak aerobic performance were assessed in four groups of volunteers with different ethnic, altitude exposure and fitness characteristics, i.e. eight untrained second-generation Tibetans (Tib 2) born and living at 1300 m; seven altitude Sherpas living at approximately 2800-3500 m; and 10 untrained and five trained Caucasians. Measurements were carried out at sea level or at Kathmandu (1300 m, Nepal) (PRE), and after 2-4 (ALT1), 14-16 (ALT2), and 26-28 (ALT3) days at 5050 m. At ALT3, of untrained and trained Caucasians was -31% and -46%, respectively. By contrast, of Tib 2 and Sherpas was -8% and -15%, respectively. At ALT3, peak heart rate (HR(peak)) of untrained and trained Caucasians was 148 +/- 11 and 149 +/- 7 beats min(-1), respectively; blood oxygen saturation at peak exercise was 76 +/- 6% and 73 +/- 6%, and haemoglobin concentration ([Hb]) was 19.4 +/- 1.0 and 18.6 +/- 1.2 g dl(-1), respectively. Compared to Caucasians, Tib 2 and Sherpas exhibited at ALT3 higher HR(peak) (179 +/- 9 and 171 +/- 4 beats min(-1), P < 0.001), lower [Hb] (16.6 +/- 0.6 and 17.4 +/- 0.9 g dl(-1), respectively, P < 0.001), and slightly but non-significantly greater average values (82 +/- 6 and 80 +/- 7%). The above findings and the time course of adjustment of the investigated variables suggest that Tibetan lowlanders acclimatize to chronic hypoxia more quickly than Caucasians, independent of the degree of fitness of the latter.

Acclimatization↗
PubMed1995

Monitoring altitude acclimatization--a case study of an élite woman athlete.

A simple study monitoring altitude acclimatization, which is not intrusive to the athlete's training, is described. Particular attention is drawn to the change in production of lactate in response to steady state exercise, before and after altitude. The results suggest that a more thorough assessment of aerobic ability at altitude is required than that described in the British Association of Sports and Exercise Science (BASES) guidelines. It is also relevant to note that elevations in haemoglobin, promoted by altitude, can mask iron abnormalities. It is therefore recommended to assay for iron in addition to haemoglobin.

Acclimatization↗
PubMed1981

Nonshivering thermogenesis in skeletal muscle of seasonally acclimatized mice, Peromyscus.

Nonshivering thermogenesis (NST) is a major contributor to total heat production capabilities of Peromyscus and the magnitude of the NST response increases dramatically in winter-acclimatized animals. To directly assess the contribution from skeletal muscle to this NST, a hindlimb perfusion system was developed for Peromyscus. Oxygen consumption was then measured with and without norepinephrine (the mediator of NST) in freshly captured animals in summer and winter. Norepinephrine (NE) was infused at 0.001, 0.01, and 0.1 micrograms . g hindlimb muscle-1 . min-1. Vascular resistance (VR), calculated as arterial pressure divided by flow rate, increased during all NE infusions. At doses of 0.001 and 0.01, VR stabilized after approximately 10 min, but at 0.1 VR continued to rise. Resting oxygen consumption was 0.817 +/- 0.037 and 0.805 +/- 0.049 mumol O2 . g-1 . min-1 in summer (n = 8) and winter (n = 7) animals, respectively. There was no apparent increase in oxygen consumption with any dosage of NE. It appears that the increase in NST in winter animals is not due to an increased NST in skeletal muscle.

Acclimatization↗
PubMed1981

Capillary supply of skeletal muscles from acclimatized white-footed mice Peromyscus.

Winter-acclimatized white-footed mice (Peromyscus leucopus) can increase their aerobic heat production under cold stress by 70%. The possibility that changes in microvascular supply might account, in part, for some of this increased thermogenic capacity was examined in one of the primary thermogenic tissues, skeletal muscle. Capillaries were stained histochemically in four hindlimb muscles of freshly captured Peromyscus in summer and winter. Capillary density, mean fiber area, and mean capillaries in contact per muscle fiber were obtained from the soleus, plantaris, gastrocnemius, and semitendinosus. If results from all individual muscles are combined, mean fiber area is significantly smaller (8%) and mean capillary density is significantly greater (40%) in winter muscles. The mean number of capillaries in contact is not different, but the mean ratio of capillaries in contact per mean fiber area (index of potential perfusion) is significantly greater (25%) in winter muscles.

Acclimatization↗
PubMed1983

Seasonal acclimatization in American goldfinches: the role of the pectoralis muscle.

The present study attempts to assess whether the marked seasonal changes in the capacity for shivering thermogenesis in American goldfinches (Carduelis tristis) involve adjustments of metabolic pathways of the pectoralis muscles similar to those observed in mammalian muscle in response to endurance training, i.e., changes favoring increased reliance on fatty acid oxidation and decreased utilization of carbohydrate reserves. Analysis of seasonal changes in enzyme profile of the pectoralis muscle revealed that winter-acclimatized birds have significantly greater (P less than 0.05) activities of phosphorylase, phosphofructokinase, and beta-hydroxy-acyl-CoA dehydrogenase than do birds in other seasons. The activities of citrate synthase and hexokinase do not vary seasonally. These results differ fundamentally from the pattern of changes in enzyme activities associated with endurance adaptation in mammals. Furthermore no seasonal changes were observed in capacities for the oxidation of fatty acids (palmitate and linoleate) or pyruvate in either crude homogenates or isolated mitochondria of goldfinch pectoralis muscles. The oxidation of pyruvate by isolated pectoralis muscle mitochondria was inhibited (greater than 90%) by the oxidation of palmitoyl carnitine at palmitoyl carnitine concentrations as low as 50 microM. These data agree with physiological observations indicating little use of glucose by this tissue during steady-state shivering. However, the extent of this inhibition does not vary seasonally. Therefore the present study fails to document any significant seasonal change in the catabolic pathways of the pectoralis muscle that would link observed seasonal changes in capacity for shivering thermogenesis with a shift in the balance of substrate use by this tissue.

3-Hydroxyacyl CoA Dehydrogenases↗
PubMed1990

Regulation of glycolysis in the pectoralis muscles of seasonally acclimatized American goldfinches exposed to cold.

Regulation of glycolysis was assessed in winter- and summer-acclimatized goldfinches (Carduelis tristis). We exposed birds to a thermo-neutral temperature (30 degrees C), moderate cold (-15 degrees C), and severe cold (0 degrees C in an atmosphere of 21% O2-79% He), and then measured concentrations of glycogen, glycolytic intermediates, and citrate in the pectoralis muscles. Winter birds used less glycogen when exposed to moderate cold than did summer birds, confirming the carbohydrate sparing noted by Marsh and Dawson [Am. J. Physiol. 242 (Regulatory Integrative Comp. Physiol. 11): R563-R569, 1982]. However, depletion of muscle glycogen did not correlate with thermoregulatory failure in this study. Concentrations of glucose 6-phosphate and fructose 6-phosphate in the pectoralis muscles were approximately 1.9 and 0.3 mumol/g wet mass in birds exposed to thermoneutral temperatures. The levels of these intermediates fell 50-70% under conditions known to enhance flux through glycolysis as indicated by increased glucose turnover and glycogen depletion. This information identifies phosphofructokinase (PFK) as a major regulated step in glycolysis in these highly aerobic skeletal muscles. Winter birds maintained the inhibition of this step under conditions of moderate cold. However, concentrations of citrate, which have been hypothesized to be an important inhibitor of PFK, did not correlate with the observed pattern of inhibition. Therefore, if the enhanced beta-oxidative capacity of winter birds is important in the regulation of glycolysis, a mechanism other than the accumulation of citrate may be involved.

Acclimatization↗
PubMed2000

Thermal compensation of peripheral oxygen transport in skeletal muscle of seasonally acclimatized trout.

Seasonal changes in ultrastructure of locomotory muscle were quantified after acclimatization to natural temperature and photoperiod. Only modest changes were seen in the volume density (V(v)) of mitochondria in slow fibers ranging from 0.21 +/- 0.01 (summer) to 0.24 +/- 0.01 (winter), despite an increase in fiber size from 945 +/- 19 to 1,594 +/- 46 microm(2), respectively, resulting in a significantly greater total mitochondrial volume at low temperatures. In contrast, intracellular lipid stores showed a marked change with season, from a maximum V(v) of lipid droplets of 0.16 +/- 0.01 in winter, progressively declining through spring and summer to a minimum of 0.07 +/- 0.01 in autumn. For both organelles, the surface density reflected changes in V(v), indicating little modification of structure. Seasonal effects may dominate those of environmental temperature on mitochondrial separation, which in winter and spring fish at 4(o)C averaged 0.64 +/- 0.06 and 1.20 +/- 0.07 microm, respectively. The extracellular transport of oxygen also varies with season, the peak capillary density in autumn (2,851 +/- 88 mm(-2)) resulting in a minimum tissue supply (domain) area of 529 +/- 9 microm(2) per capillary. As a consequence, the predicted intracellular PO(2) ( approximately 2.5 kPa) is similar throughout the year.

Acclimatization↗
PubMed1975

Incomplete compensation of CSF [H+] in man during acclimatization to high altitude (48300 M).

This study has assessed the regulation of arterial blood and cerebrospinal fluid acid-base status in seven healthy men, at 250 m altitude and after 5 and 10-11 days sojourn at 4,300 m altitude (PaO2 = 39 mmHg day 1 to 48 mmHg day 11). We assumed that observed changes in lumbar spinal fluid acid-base status paralleled those in cisternal CSF, under these relatively steady-state conditions. Ventilatory acclimatization during the sojourn (-14 mmHg PaCO2 at day 11) was accompanied by: 1) reductions in [HCO3-] (-5 to -7 meq/1) which were similar in arterial blood and CSF; 2) substantial, yet incomplete, compensation (70-75%) of both CSF and blood pH; and 3) a level of CSF pH which was maintained significantly alkaline (+0.05 +/- 0.01) to normoxic control values. These data at 4,300 m confirmed and extended our previous findings for more moderate conditions of chronic hypoxia. It was postulated that the magnitude and time course of pH compensation in the CSF during chronic hypoxia and/or hypocapnia are determined by corresponding changes in plasma [HCO2-].

Acclimatization↗
PubMed1976

Acclimatization in a hot, humid environment: energy exchange, body temperature, and sweating.

Four trained young men, worked for 4 h/day at 43-50% of their maximum aerobic capacity for 3 days at 25 degrees C db, 18 degrees C wb and then for 10 consecutive days at 45 degrees C db, 32 degrees C wb. Their thermal status was assessed using direct calorimetry. As a group, the men showed classical acclimization responses, but there were marked individual differences. The calorimetric analysis revealed that reductions in strain were associated with minor changes in heat balance confined to the first and last hours of exposure. Events occurring within the first 4 days appeared to have little effect on body temperatures. Significant decreases in body temperature took place only when sweat and evaporation rate increased. A 10% increase in evaporation rate was accompanied by a 30% increase in sweat rate and a 200% increase in unevaporated sweat; thus, there is a wasteful overproduction of sweat. By the 10th day skin temperature was confined to the level necessary to evaporate sufficient sweat to achieve thermal balance with a fully wet body surface. The efficiency of heat transport within the body did not change with acclimatization.

Acclimatization↗
PubMed1977

Modification of renin and aldosterone response to heat by acclimatization in man.

Plasma renin activity (PRA) and aldosterone concentration (PA) increased in eight men following a brief (30--40 min) heat exposure (50 degrees C dry bulb, 25 degrees C wet bulb) with light work. Sweat loss was less than 1% body weight. Plasma cortisol concentration was unchanged or decreased. In four subjects, a standard heat test was repeated in winter and summer (natural acclimatization). The increase in PRA and PA following heat exposure was less in summer than in winter. Four other subjects were artificially acclimated by daily work periods of 90 min at 50 degrees C for 7 days (artificial acclimation). Heat-induced elevation in PRA was considerably reduced by artificial acclimation, although postheat PA was reduced in only two of the four subjects. The small degree of sweat loss under the conditions of these experiments shows that circulating renin and aldosterone levels are increased in the heat even when a significant sodium deficit is not incurred.

Acclimatization↗
PubMed1977

Effects of plasma ascorbic acid levels on heat acclimatization in man.

Thirteen male volunteers were heat acclimatized for 4 h/day for 10 consecutive days. Three to four hours before each heat exposure, four of the subjects received an oral dose of 250 ascorbic acid, five received 500 mg ascorbic acid, and the remaining four a placebo. Rectal temperature, heart rate, and sweat rate were measured hourly during exposure. Venous blood samples were collected before each administration of drug or placebo. On days 1, 2, 3, 5, 8, and 10, blood samples were also collected just prior to heat exposure and after two and four hours of exposure. In the subjects receiving ascorbic acid, total circulating plasma ascorbic acid increased over the first three or four days to a plateau level some fourfold higher than in the subjects receiving the placebo. The plateau level was the same in the subjects receiving 250 mg and 500 mg ascorbic acid. The increased ascorbic acid concentration was shown to be associated with a reduction in total sweat output, independent of rectal temperature, and a reduction in rectal temperature, independent of total sweat output. The results indicate that ascorbic acid may be effective in reducing heat strain in unacclimatized individuals.

Acclimatization↗
PubMed1978

Cellular dynamics of rats' submaxillary gland during heat acclimatization.

Male laboratory rats (Rattus norvegicus) ranging between 130 and 160 g were subjected to ambient temperatures of 34.5 degrees C from 0 to 28 days. The submaxillary gland, liver, spleen, and kidney were weighed. The acini size and the mitotic index of the acinar cells after intraperitoneal injection of vinblastine sulfate and colchicine were recorded for the submaxillary and parotid glands. The submaxillary glands showed increased growth rate over the initial 5 days, whereas the growth rate of the other organs decreased. The submaxillary gland enlargement was due to an initial hyperplasia of the acini cells reaching a maximum on the 2nd day. This was followed by hypertrophy of the Acini reaching a maximum on the l0th day. The parotid acini at control values throughout the experiment. It is postulated that the gland enlargement is effected to increase evaporative heat loss during the early stages of acclimatization prior to the lowering of heat production resulting from biochemical adaptation.

Acclimatization↗
PubMed1982

Mechanical properties of the lungs during acclimatization to altitude.

Mechanical properties of the lung were studied in nine healthy lowlanders during a 6-day sojourn at an altitude of 3,457 m. In comparison to sea-level values, it was found at altitude that 1) lung volumes measured by plethysmography including total lung capacity, vital capacity, and functional residual capacity (FRC) presented small changes not exceeding 300 ml; 2) static and dynamic lung compliances were not modified but static pressure-volume curves of lungs were shifted progressively to the left (the decrease in lung elastic recoil averaged about 2 cmH2O on days 4-6); and 3) maximal midexpiratory flow, forced expiratory volume in 1 s, and maximal expiratory and inspiratory flows were increased and, conversely, airways and pulmonary flow resistances were decreased on most days at altitude. The unchanged FRC in the face of a decreased lung recoil may be explained by an increase in thoracic blood volume at altitude, but other possible mechanisms are discussed. The decrease in resistances and increase in maximal flows may be partly explained by the decreased air density at altitude, but another contributing factor such as a bronchodilatation is also suggested. It is proposed that changes in lung mechanics at altitude may account for some of the changes in the pattern of breathing and mouth occlusion pressure (P0.1) observed during acclimatization of lowlanders to altitude.

Acclimatization↗