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PubMed2003

An increased expression of nucleolin is associated with a physiological nucleolar segregation.

Nucleolar segregation is the most striking cellular phenotypic feature of cold-acclimatized carp and depicts the cyclical reprogramming that the physiology of the fish undergoes between summer and winter, where a clear differential expression of some nucleolar related genes occurs. We characterized carp nucleolin, a nucleolar protein involved in multiple steps of ribosome biogenesis, and evaluated its expression upon fish acclimatization. We show that the carp cDNA deduced amino acid sequence exhibits the same tripartite structural organization found in other species. Nevertheless, we observed that nucleolin mRNA expression was strongly induced in the cold-adapted carp as was the nuclear protein content, assessed by immunocytochemistry in liver sections. The physiological up-regulation of nucleolin in the cold-acclimatized carp, where rRNA transcription and processing are depressed concomitantly with the nucleolus segregation, is consistent with the notion that nucleolin plays a fundamental role in repressing rRNA synthesis.

Acclimatization↗
PubMed2006

White blood cell and hormonal responses to 4300 m altitude before and after intermittent altitude exposure.

Recent studies have demonstrated that brief daily IAE (intermittent altitude exposure) was equally as effective as continuous altitude residence in inducing physiological adaptations consistent with altitude acclimatization. Although the positive benefits of IAE have been clearly defined, the potential negative consequences of IAE on health, specifically the immune system, remain undefined. The present study determined the effects of IAE on WBC (white blood cell) and hormonal responses during rest and exercise at 4300 m altitude. Six lowlanders (age, 23+/-2 years; body weight, 77+/-6 kg; values are means+/-S.E.M.) completed a VO(2)max (maximal O(2) uptake) and submaximal cycle ergometer test during a 30-h SL (sea level) exposure and during a 30 h exposure to 4300 m altitude-equivalent once before (PreIAE) and once after (PostIAE) a 3-week period of IAE (4 hxday(-1), 5 daysxweek(-1), 4300 m). The submaximal cycle ergometer test consisted of two consecutive 15-min work bouts at 40% and 70% of altitude-specific VO(2)max. Blood samples were obtained at rest and during both exercise work bouts for measurements of WBC count, leucocyte subset counts, cortisol, adrenaline (epinephrine) and noradrenaline (norepinephrine). WBC, neutrophil and lymphocyte counts increased significantly (P<0.05) during rest and exercise from SL to PreIAE and decreased (P<0.05) during rest and exercise from PreIAE to PostIAE. Monocyte counts decreased (P<0.05) during rest and exercise from PreIAE to PostIAE, but eosinophil and basophil counts did not change. Cortisol, adrenaline and noradrenaline did not change during rest or exercise from SL to PreIAE or PostIAE, but all increased significantly (P<0.05) from rest during the two work bouts. In conclusion, this type of IAE stimulus did not induce a hormonal stress response and did no harm in terms of activation of the immune system at altitude, as measured by WBC and leucocyte subset counts. This method of pre-acclimatization can therefore be highly recommended for inducing altitude acclimatization without the 'altitude residency' requirement.

Acclimatization↗
PubMed1992

Muscular adaptations at extreme altitude: metabolic implications during exercise.

Residence at extreme altitude results in pronounced reductions in muscle mass and the cross-sectional area of the slow and fast twitch fibre types. The reductions in muscle contractile proteins appear not to be accompanied by significant alterations in the proportion of the major fibre types and consequently in the myosin heavy chain isozymes. Acclimatization to extreme altitude is also accompanied by a marked reduction in mitochondrial potential that occurs regardless of activity status. At least during mountaineering expeditions, the maximal activity of cytosolic enzymes involved in anaerobic function appear to be unaffected. In contrast, extreme hypobaric hypoxia with low exercise appears to result in loss of the activities of cytosolic enzymes. The attenuation of glycolysis during exercise accompanying acclimatization does not appear to be due to adaptations in fibre size, capillarization or mitochondrial potential. Rather, evidence from both acclimatization and training at sea level suggests that a depressed blood epinephrine concentration is involved.

Acclimatization↗
PubMed1992

A practical approach to altitude training: where to live and train for optimal performance enhancement.

Altitude training may improve performance by a number of mechanisms. Acclimatization may improve both oxygen delivery and extraction. Hypoxic exercise may increase the training stimulus thus magnifying the effects of endurance training. Conversely, high altitude decreases VO2max and reduces the workloads at which training occurs. At altitude, base training is performed at a slower velocity and lower oxygen uptake (lower absolute workload) compared to sea level, though heart rate is similar and lactate is higher (probably greater relative workload). Interval workouts are performed at a lower absolute workload at altitude and are associated with lower peak heart rates and blood lactate concentrations. Red cell volume is increased during altitude training, as long as iron stores are normal. We suggest that for performance at altitude, acclimatization and/or hypoxic exercise is preferable; for performance at sea level, living at altitude (acclimatization) with sea level training may be the optimal strategy. However neither approach is a substitute for a carefully designed training program including appropriate rest and nutrition.

Acclimatization↗
PubMed1986

Effect of changes in dietary energy intake and environmental temperature on heat tolerance in the fowl.

The improvement in heat tolerance acquired during the acclimatization of laying hens to intermittent heat stress was lost or considerably reduced when energy intake increased following the addition of maize oil to the diet. The oxygen consumption (VO2) of acclimatised hens increased after the addition of maize oil to the diet. Reducing the environmental temperature (Ta) from 30 degrees to 10 degrees C prevented the development of acclimatization if the heat stress commenced soon after the change of Ta; if the heat stress commenced 5 weeks after the change of Ta acclimatization took place normally. Reducing the Ta from 30 degrees to 10 degrees C resulted in an increased VO2 and food intake. The administration of triiodothyronine increased VO2 and reduced the heat tolerance of acclimatised hens. It is concluded that heat tolerance, despite being reinforced by regular exposure to heat stress, remains susceptible to changes in energy metabolism brought about by dietary or environmental means.

Acclimatization↗
PubMed2004

Altitude and endurance training.

The benefits of living and training at altitude (HiHi) for an improved altitude performance of athletes are clear, but controlled studies for an improved sea-level performance are controversial. The reasons for not having a positive effect of HiHi include: (1) the acclimatization effect may have been insufficient for elite athletes to stimulate an increase in red cell mass/haemoglobin mass because of too low an altitude (< 2000-2200 m) and/or too short an altitude training period (<3-4 weeks); (2) the training effect at altitude may have been compromised due to insufficient training stimuli for enhancing the function of the neuromuscular and cardiovascular systems; and (3) enhanced stress with possible overtraining symptoms and an increased frequency of infections. Moreover, the effects of hypoxia in the brain may influence both training intensity and physiological responses during training at altitude. Thus, interrupting hypoxic exposure by training in normoxia may be a key factor in avoiding or minimizing the noxious effects that are known to occur in chronic hypoxia. When comparing HiHi and HiLo (living high and training low), it is obvious that both can induce a positive acclimatization effect and increase the oxygen transport capacity of blood, at least in 'responders', if certain prerequisites are met. The minimum dose to attain a haematological acclimatization effect is > 12 h a day for at least 3 weeks at an altitude or simulated altitude of 2100-2500 m. Exposure to hypoxia appears to have some positive transfer effects on subsequent training in normoxia during and after HiLo. The increased oxygen transport capacity of blood allows training at higher intensity during and after HiLo in subsequent normoxia, thereby increasing the potential to improve some neuromuscular and cardiovascular determinants of endurance performance. The effects of hypoxic training and intermittent short-term severe hypoxia at rest are not yet clear and they require further study.

Acclimatization↗
PubMed1995

Exercise in the heat: strategies to minimize the adverse effects on performance.

Exercise in the heat is usually associated with reduced performance; both dehydration and hyperthermia adversely affect mental and physical performance. For athletes from temperate climates, the negative effects of heat had humidity can be attenuated by a period of acclimatization. This requires up to 10-14 days. Endurance-trained individuals already show some of the adaptations that accompany acclimatization, but further adaptation occurs with training in the heat. Prior dehydration has a negative effect even on exercise of short duration where sweat losses are small. The athlete must begin exercise fully hydrated and regular ingestion of fluids is beneficial where the exercise duration exceeds 40 min. Dilute carbohydrate-electrolyte (sodium) drinks are best for fluid replacement and also supply some substrate for the exercising muscles. Post-exercise rehydration requires electrolyte as well as volume replacement. In extreme conditions, neither acclimatization nor fluid replacement will allow hard exercise to be performed without some risk of heat illness.

Acclimatization↗
PubMed2006

The role of zooxanthellae in the thermal tolerance of corals: a 'nugget of hope' for coral reefs in an era of climate change.

The ability of coral reefs to survive the projected increases in temperature due to global warming will depend largely on the ability of corals to adapt or acclimatize to increased temperature extremes over the next few decades. Many coral species are highly sensitive to temperature stress and the number of stress (bleaching) episodes has increased in recent decades. We investigated the acclimatization potential of Acropora millepora, a common and widespread Indo-Pacific hard coral species, through transplantation and experimental manipulation. We show that adult corals, at least in some circumstances, are capable of acquiring increased thermal tolerance and that the increased tolerance is a direct result of a change in the symbiont type dominating their tissues from Symbiodinium type C to D. Our data suggest that the change in symbiont type in our experiment was due to a shuffling of existing types already present in coral tissues, not through exogenous uptake from the environment. The level of increased tolerance gained by the corals changing their dominant symbiont type to D (the most thermally resistant type known) is around 1-1.5 degrees C. This is the first study to show that thermal acclimatization is causally related to symbiont type and provides new insight into the ecological advantage of corals harbouring mixed algal populations. While this increase is of huge ecological significance for many coral species, in the absence of other mechanisms of thermal acclimatization/adaptation, it may not be sufficient to survive climate change under predicted sea surface temperature scenarios over the next 100 years. However, it may be enough to 'buy time' while greenhouse reduction measures are put in place.

Acclimatization↗
PubMed2003

Sympathetic neural overactivity in healthy humans after prolonged exposure to hypobaric hypoxia.

Acute exposure to hypoxia causes chemoreflex activation of the sympathetic nervous system. During acclimatization to high altitude hypoxia, arterial oxygen content recovers, but it is unknown to what degree sympathetic activation is maintained or normalized during prolonged exposure to hypoxia. We therefore measured sympathetic nerve activity directly by peroneal microneurography in eight healthy volunteers (24 +/- 2 years of age) after 4 weeks at an altitude of 5260 m (Chacaltaya, Bolivian Andes) and at sea level (Copenhagen). The subjects acclimatized well to altitude, but in every subject sympathetic nerve activity was highly elevated at altitude vs. sea level (48 +/- 5 vs. 16 +/- 3 bursts min(-1), respectively, P < 0.05), coinciding with increased mean arterial blood pressure (87 +/- 3 vs. 77 +/- 2 mmHg, respectively, P < 0.05). To examine the underlying mechanisms, we administered oxygen (to eliminate chemoreflex activation) and saline (to reduce cardiopulmonary baroreflex deactivation). These interventions had minor effects on sympathetic activity (48 +/- 5 vs. 38 +/- 4 bursts min(-1), control vs. oxygen + saline, respectively, P < 0.05). Moreover, sympathetic activity was still markedly elevated (37 +/- 5 bursts min(-1)) when subjects were re-studied under normobaric, normoxic and hypervolaemic conditions 3 days after return to sea level. In conclusion, acclimatization to high altitude hypoxia is accompanied by a striking and long-lasting sympathetic overactivity. Surprisingly, chemoreflex activation by hypoxia and baroreflex deactivation by dehydration together could account for only a small part of this response, leaving the major underlying mechanisms unexplained.

Acclimatization↗
PubMed1976

Influence of long-term intermittent exposures to hypoxia on decompression-induced pulmonary haemorrhage.

Healthy male rats were acclimatized by being placed in a decompression chamber at a simulated altitude of 18 000 feet (5486 m) for three hours daily for 84 days. The altitude acclimatized rats paired with unacclimatized rats were rapidly decompressed together. The range of decompression was performed from on atmospheric pressure to an ambient pressure of 30 mmHg in 0-2 seconds. It was found that in control rats, 14 of 20 lung (70%) exhibited pulmonary haemorrhage following rapid decompression. In altitude acclimatized rats, however, only 6 of 20 (30%) revealed decompression-induced haemorrhage. The difference was statistically significant. The present findings indicate that long-term intermittent exposures to hypoxia might increase the resistance of pulmonary tissue to rapid decompression, resulting in a decrease in frequency and severity of pulmonary haemorrhage. The possible mechanism of such a phenomenon is discussed.

Acclimatization↗
PubMed1983

Metabolic adjustments of small passerine birds for migration and cold.

Passerines (members of the order Passeriformes such as finches, chickadees, jays, and warblers) are predominantly small birds characterized by relatively intense metabolic rates. Members of this group breeding at middle or high latitudes may either evade winter cold by migration or enhance their resistance to it by acclimatization. We review the energetic consequences associated with these two modes of response. Despite their apparent dissimilarity, migration and winter acclimatization both depend on substantial aerobic endurance, and both involve extensive power outputs by the flight muscles in locomotion or shivering. Such power outputs entail extensive deposition and catabolism of fat. Information available on these processes and their control in passerine birds is discussed. Knowledge of them is still in a formative stage, but it is already clear that aerobic capacity of passerines is stable at a high level throughout the year. However, changes are observed in the activity of certain enzymes involved in the catabolism of fats and carbohydrates. Full interpretation of these findings must await additional research. Nevertheless it is evident that the complex processes of migration and winter acclimatization are intimately linked with the metabolic properties of the highly aerobic skeletal muscle contained within the flight apparatus of passerines.

Acclimatization↗
PubMed1986

Thermal and metabolic adaptation to first cold-water immersion in juvenile penguins.

Juvenile king and macaroni penguins are terrestrial seabirds and must face an intensive and prolonged energetic demand during their passage from shore to marine life in cold subantarctic seawater. Evidence for progressive thermal adaptation was sought by measurement of metabolic rate (MR) and body (Tb) and skin (Tsk) temperatures in unrestrained, fully immersed penguins. Steady-state responses obtained after the 3rd h of immersion in never-immersed (NI) penguins were compared with those of penguins acclimatized to seawater temperature (A). NI macaroni penguins, unlike NI king penguins, showed a fall in Tb on their first immersion but, once acclimatized, were able to maintain their homeothermy due to an increase (greater than 3.2 W/kg) in regulatory thermogenesis. In NI king penguins, during a simulation of seawater adaptation by 10 successive immersions, MR at 7 degrees C water temperature (Tw) rose from 6.0 to 9.4 W/kg (becoming 3-5 times higher than in air), whereas Tb rose from 37.6 to 38.4 degrees C. In both species occurrence of peak MR at much lower Tw, progressive increase in thermogenesis capacity, and lower conductance in water after adaptation to marine life (28 and 36% less in A king and macaroni penguins, respectively) showed that the passage from shore to marine life consisted of a true cold acclimatization.

Acclimatization↗
PubMed1997

High altitude-induced changes in alpha1-adrenergic receptors and Ins(1,4,5)P3 responses in cerebral arteries.

In response to high-altitude long-term hypoxemia, the cerebral arteries of fetal and adult sheep show decreased contractile responses to norepinephrine (NE) and other agonists. To test the hypothesis that hypoxia-induced developmental and vessel specific cerebral artery contractility changes are mediated, in part, by changes in alpha1-adrenergic receptor (alpha1-AR) density and/or NE-induced inositol 1,4,5-trisphosphate [Ins(1,4,5)P3] responses, we performed the following study. In common carotid (Com) and main branch cerebral (MBC) arteries from normoxic adult ewes and near-term fetuses and those acclimatized to high altitude (3,820 m), we quantified alpha1-AR density (maximal binding in fmol/mg protein) and affinity (dissociation constant in nM) with the alpha1-AR antagonist [3H]prazosin. In addition, we quantified NE-induced Ins(1,4,5)P3 responses in these arteries. With long-term hypoxemia, alpha1-AR density in fetal and adult Com decreased 75% (from 113 +/- 18 to 28 +/- 5 fmol/mg protein) and 66% (from 54 +/- 3 to 18 +/- 4 fmol/mg protein), respectively, from normoxic control values. alpha1-AR density of the fetal and adult MBC decreased 76% (from 47 +/- 4 to 11 +/- 1 fmol/mg protein) and 61% (from 23 +/- 3 to 9 +/- 3 fmol/mg protein), respectively, from controls. In hypoxemic adult Com, the NE-induced Ins(1,4,5)P3 response decreased 51% (from 309 +/- 38 to 151 +/- 24%) from the control value. In fetal and adult MBC, long-term hypoxemia was associated with decreases of 35% (from 345 +/- 40 to 225 +/- 30%) and 44% (from 355 +/- 55 to 199 +/- 16%), respectively, from control values. We conclude that in the adult Com and MBC vessels, acclimatization to high-altitude, long-term hypoxemia was associated with significant decreases in both alpha1-AR density values and Ins(1,4,5)P3 responses to NE. Similarly, in the fetal MBC arteries, high-altitude hypoxemia was associated with marked attenuation of both alpha1-AR density and NE-induced Ins(1,4,5)P3 responses. The magnitude of decreases in NE-induced Ins(1,4,5)P3 responses in these vessels correlated fairly well with the decreases in alpha1-AR density. These findings suggest that changes in noradrenergic receptor-second messenger coupling may play a role in altered cerebrovascular tone in association with high-altitude acclimatization and other forms of long-term hypoxia in both fetus and adult.

Acclimatization↗
PubMed2000

Hematological changes and athletic performance in horses in response to high altitude (3,800 m).

This study had two goals: 1) measure hematologic changes with high-altitude acclimatization in horses; and 2) assess the effect of 9 days at high altitude on subsequent athletic performance at low altitude. Six horses performed standardized exercise tests on a dirt track (before and during time at altitude) and treadmill (pre- and postaltitude exposure). Resting and immediate postexercise blood samples were measured for blood volume, lactate, red cell number, packed cell volume, and 2,3-diphosphoglycerate (DPG) concentrations at 225 m, over a 9-day period at 3,800 m, and shortly after returning to 225 m. Acclimatization produced increases in total red cell volume (38.2 +/- 2.4 to 48.1 +/- 2.9 ml/kg, P = 0.004) and DPG/hemoglobin concentrations (19.4 +/- 1.7 increased to 29.4 +/- 0. 4 micromol/g, P = 0.004). Two performance variables, heart rate recovery postexercise and lactate recovery, were faster after acclimatization.

2,3-Diphosphoglycerate↗
PubMed1976

Acclimization in a hot, humid environment: cardiovascular adjustments.

Four trained young men worked for 4 h/day at 40-50% of their maximum aerobic capacity first 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. This portion of the study was mainly concerned with central circulatory changes during acclimatization. The central circulatory adaptation to work in heat could be divided into four distinct phases: phase I (day 1) was characterized by a progressive fall in stroke volume (SV) during heat exposure but cardiac output (CO) was maintained above control values by high heart rates. Phase II (days 2 and 3) was marked by increases in SV ande decreases in heart rate but with little change in CO from phase I. During phase III (days 4-8 of acclimatization), CO increased due to increases in SV. Phase IV (days 6-8) was associated with decreases in rectal and skin temperature towards control levels. SV and HR both decline in this phase so that CO was not elevated greatly above control levels. The results indicated that central circulatory and temperature regulating events are not casually associated in acclimatization.

Acclimatization↗
PubMed1976

Ventilatory control in peripheral chemoreceptor-denervated ponies during chronic hypoxemia.

The present study was designed to provide further insight into the role of the carotid and aortic chemoreceptors in ventilatory (VE) acclimatization during sojourn at altitude. Measurements were made: 1) on 10 ponies near sea level (SL, 740 Torr) under normal conditions, 2) on 6 of these at SL following chemoreceptor denervation (CD), and 3) subsequently on all 10 during 4 days of hypobaric hypoxia (PaO2 = 40-47 Torr). CD resulteo in hypoventilation at SL (deltaPaCO2 = d8 Torr, P less than 0.05), and it prevented hyperventilation normally observed with injection of NaCN and acute exposure to hypoxia (less than 1 h). In contrast, hyperventilation was evident in normal ponies during acute hypoxia (deltaPaCO2 = -6.7 Torr). Ventilation increased in both groups between the 2nd and 8th h of hypoxia (deltaPaCO2 from 1 h = -4 Torr, P less than 0.05). This change, a common characteristic of acclimatization, persisted throughout 4 days of hypoxia in the normal ponies. However, in the CD ponies this change was evident consistently only through the 12th h and after the 44 h hyperventilation was no longer evident. We conclude that the peripheral chemoreceptors are essential in ponies for normal VE acclimatization to this degree of hypoxemia. Two additional findings in CD ponies suggest the presence of a CNS inhibitory influence on the VE control center during chronic hypoxemia. First, acute hyperoxygenation on the 4th day of hypoxemia induced hyperventilation (deltaPaCO2 = -5 Torr, P less than 0.05). Second, again on the 4th day and during hyperoxygenation, VE responsiveness to CO2 and doxapram HCl was greater than at sea level.

Acclimatization↗
PubMed1977

Recurrent heat exposure: enzymatic responses in resting and exercising men.

Heat acclimatization was induced in a group of healthy male test subjects by repetitive treadmill walking (5.6 km-h-1, 49 degrees/27 degrees C dry/wet bulb, 90 min-day-1, 7 days). A second group of men, paired for maximal O2 consumption and body weight, remained sedentary under identical environmental conditions. Total plasma protein increased significantly after 45 (P less than 0.05) and 90 (P less than 0.025) min of exercise on the first day of heat exposure, yet after 7 days no increments occurred. Even after heat acclimatization was achieved (day 7), plasma levels of creatine phosphokinase increased during the 90-min walk in the heat (time O vs. 90, P less than 0.025), as was also the case on day 1 (P less than 0.05). Levels of lactate dehydrogenase, glutamate-oxaloacetate transaminase, and glutamate-pyruvate transaminase were not significantly affected by exercise in the heat either before or after heat acclimatization. No correlations could be drawn between base-line enzyme levels and state of physical conditioning.

Acclimatization↗
PubMed1978

Pulse rate-rectal temperature relationships during prolonged work.

Forty-six industrial workers performed a total of 653 1-h work bouts over a wide range of work rates )142-273 W/m2) and environmental temperatures (11-35 degrees C corrected effective temperature) in the summer and winter seasons. Simultaneous measurements of heart rates and rectal temperatures were made at the end of each work period, and the relationship between heart rate and rectal temperature was computed with standard multiple linear regression techniques. The overall regression equation is: heart rate (beats/min) = 29.3 (beats/min. degrees C) x rectal temperature (degrees C) - 988.6 (beats/min). The relationship is significantly altered by work rate and job- and season-acquired acclimatization of the subjects. These data suggest that the average heart rates of industrial workers during prolonged work can be predicted from rectal temperatures with a reasonable degree of confidence if the degree of acclimatization and work rates are known. For a rectal temperature of 38.0 degrees C the expected heart rate during prolonged work ranges from 109 beats/min in acclimatized men working at low rates to 143 for unacclimatized men working at heavy rates.

Acclimatization↗