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PubMed2005

In vitro effect of hydrostatic pressure exposure on hydroxyl radical production in fish red muscle.

The effects of hydrostatic pressure on reactive oxygen species (ROS) production have been studied in vitro on fish red muscle fibres. In the eel, Anguilla anguilla, previous studies have shown that hydrostatic pressure acclimatization improves oxidative phosphorylation efficiency together with a supposed concomitant decrease in electron leak and ROS production. In order to test the hypothesis of an electron leak decrease under pressure, hydroxyl radical (HO*) production and oxygen consumption were measured on fish red muscle fibres directly exposed to hydrostatic pressure. Experiments were performed under two conditions--atmospheric pressure and hydrostatic pressure (16.1 MPa)--on eel and trout (which exhibit low- and high-pressure sensitivity, respectively). This work has permitted, first, the validation of an indirect HO* measurement (in vitro) on fish red muscle and the documentation of reference values for fish. Second, at atmospheric pressure, results show higher oxygen consumption for trout (+40%) than for eel which is accompanied by higher HO* production (+90%); in addition, both species present a positive relationship between HO* production and oxygen consumption. Hydrostatic pressure exposure reverses this relationship for eel but not for trout. These preliminary results only partially verify the proposed hypothesis and further experiments are needed.

Acclimatization↗
PubMed1997

Gas exchange at extreme altitude: results from the British 40th Anniversary Everest Expedition.

Since Messner and Habeler climbed to the summit of Mount Everest (8,848 m) without oxygen in 1978, there has been controversy between scientists trying to explain this feat. Field studies have suggested better respiratory performance than that found during a simulated climb in a hypobaric chamber, but the lack of data at extreme altitude has hampered the debate. We measured arterial oxygen saturation (Sa,O2) and alveolar partial pressure of oxygen (PA,O2) in nine subjects as they climbed from 3,500 to 8,000 m. Four of the climbers reached 8,000 m and one reached the summit. We also tested the effects of breathing supplementary oxygen on Sa,O2 at 6,550 and 8,000 m. At all altitudes tested, we found that both PA,O2 and Sa,O2 were higher than expected from low pressure chamber studies. We also found that standard rates of supplementary oxygen (2 L x min(-1)) were insufficient to restore Sa,O2 above 90% at 8,000 m. The respiratory performance of climbers at extreme altitude is better than expected from sea-level chamber studies, which may, in part, explain why humans can reach the summit (8,848 m) without added oxygen. The better performance is likely to be due to more appropriate acclimatization.

Acclimatization↗
PubMed2004

Regulation of membrane fatty acid composition by temperature in mutants of Arabidopsis with alterations in membrane lipid composition.

BACKGROUND: A wide range of cellular responses occur when plants are exposed to elevated temperature, including adjustments in the unsaturation level of membrane fatty acids. Although membrane bound desaturase enzymes mediate these adjustments, it is unknown how they are regulated to achieve these specific membrane compositions. Furthermore, the precise roles that different membrane fatty acid compositions play in photosynthesis are only beginning to be understood. To explore the regulation of the membrane composition and photosynthetic function in response to temperature, we examined the effect of temperature in a collection of mutants with altered membrane lipid fatty acid composition. RESULTS: In agreement with previous studies in other species, the level of unsaturation of membrane fatty acids in Arabidopsis was inversely correlated with growth temperature. The time required for the membrane fatty acids to attain the composition observed at elevated temperature was consistent with the timing required for the synthesis of new fatty acids. Comparisons of temperature-induced fatty acid alterations in membranes were made among several Arabidopsis lines including wild-type Columbia, and the compositional mutants, fad5, fad6, act1 and double mutants, fad7 fad8 and act1 fad6. The results revealed key changes that occur in response to elevated temperature regardless of the specific mutations in the glycerolipid pathway, including marked decreases in trienoic fatty acids and consistent increases in unsaturated 16:0 and in dienoic 18:2 levels. Fluorescence measurements of various mutants indicated that photosynthetic stability as well as whole plant growth at elevated temperature is influenced by certain membrane fatty acid compositions. CONCLUSIONS: The results of this study support the premise that defined proportions of saturated and unsaturated fatty acids in membrane lipids are required for photosynthetic thermostability and acclimation to elevated temperature. The results also suggest that changes in the membrane fatty acid composition brought about in response to temperature are regulated in such a way so as to achieve highly similar unsaturation levels despite mutations that alter the membrane composition prior to a high-temperature exposure. The results from examination of the mutant lines also suggest that interorganellar transfer of fatty acids are involved in mediating temperature-induced membrane alterations, and reveal steps in the fatty acid unsaturation pathway that appear to have key roles in the acclimatization of membranes to high temperature.

Acclimatization↗
PubMed1986

High altitude cerebral edema.

Acute mountain sickness (AMS) is usually a benign and self-limited illness that befalls previously healthy individuals who ascend rapidly to high altitude without sufficient acclimatization. In its more severe forms, AMS can progress to a life-threatening condition in which pulmonary or cerebral edema can occur singly or in concert. High altitude cerebral edema (HACE) is a little-known clinical entity that manifests itself by a perplexing array of both generalized and localized neurological symptoms and signs. Furthermore, the development of HACE in climbers offers a unique experimental situation in which to examine the effects of hypoxia on the central nervous system. The epidemiology and clinical picture of HACE are reviewed. In addition, the pathology and predominant pathophysiological mechanisms postulated to explain HACE are examined, and the present recommendations for the prevention and treatment of this dangerous and unusual form of brain swelling are discussed.

Acclimatization↗
PubMed1987

Effect of high altitude on the visual evoked responses in humans on Mt. Everest.

Cerebral visual evoked potentials (VEPs) were collected over a 1-year period from the summer of 1983 through the summer of 1984 from 16 members of the American Ultima Thule Everest Expedition at sea level and at altitudes of 7,100 ft, 16,800 ft, and 21,300 ft. VEPs in response to 100 unilateral LED flashes were processed by a modified Nicolet CA-1000 computer of average transients with an analysis time of 250 ms and were recorded by an X-Y plotter. Readings of oxygen saturation, tetrapolar impedance pulmonary plethysmography, and clinical signs and symptoms of acute mountain sickness (AMS) were recorded. The latency of the major waves of the VEPs increased on initial arrival at higher altitude and returned toward base line over time with acclimatization. There were more acute latency changes in individuals who suffered from symptoms of AMS, which reversed with amelioration of symptoms.

Acclimatization↗
PubMed2004

Local action of exogenous nitric oxide (NO) on the skin blood flow of rock pigeons (Columba livia) is affected by acclimation and skin site.

We studied the blood flow over dorsal and abdominal, non-brooding patch skin of two groups of pigeons: one group was thermally acclimated to cold (winter-acclimatized, WAC) while the other group was acclimated to a mesic environment (thermally non-challenged, NOC). Two bilateral patches at the measurement sites were treated simultaneously with a gel containing sodium nitrate and ascorbic acid, to generate nitric oxide (NO), and a vehicle gel. Blood flow was measured by laser Doppler velocimetry. Changes induced by these treatments were calculated against basic blood flow values for the corresponding patch. The results showed that the basic blood flow over the abdominal skin patches at room temperature was higher than over the dorsal skin in both acclimation states, but comparison revealed a sustainably higher level of basic skin blood flow in the WAC pigeons. The local response to exogenous NO was non-uniform over the two skin areas measured, and a specific vasodilatory action on the abdominal microvessels was recorded in the NOC pigeons. Abdominal vasodilatation in the WAC pigeons seemed to involve other mechanisms as well as local NO-dependent ones, among which the role of cold-induced vasodilatation (CIVD) is discussed here. Interestingly, the dorsal skin seemed to be less responsive to the action of NO, irrespective of the acclimation state. Our results show that acclimation state and skin site affect the action of exogenous NO on local skin blood flow, and we suggest that the differences reflect acclimation-induced changes in the vascularity of the skin and in its sensitivity to thermal stimuli and that the roles of the abdominal and dorsal skin are different with respect to environmental changes.

Acclimatization↗
PubMed2006

Mitochondrial mechanisms of cold adaptation in cod (Gadus morhua L.) populations from different climatic zones.

Adjustments in mitochondrial properties and capacities are crucial in acclimatization to seasonal cold as well as in evolutionary cold adaptation of marine ectotherms. To examine whether gene expression mechanisms contribute to different settings of aerobic capacities in populations of cod (Gadus morhua) along a latitudinal cline, maximum activities of key enzymes of mitochondrial metabolism and their respective mRNA levels were compared in white muscle and liver of cold (4 degrees C) and warm (10 degrees C) acclimated individuals from cod populations of the North Sea and the Barents Sea, respectively. In white muscle, cold acclimation caused a parallel increase in citrate synthase (CS) and in cytochrome c oxidase (COX) activities, but with a much larger effect in the cold eurythermal Arctic population. In liver, cold acclimation was accompanied by increments in CS activities, but differences between populations were minor. Overall COX activities in liver were not affected by cold acclimation, but were higher in the cold adapted population. In both populations increments in muscle CS capacities were tightly correlated with elevated mRNA levels, suggesting transcriptional control of citrate synthase levels in muscle. In liver, CS mRNA levels differed between populations but were not affected by cold acclimation, so that post-transcriptional control may contribute to elevated functional levels in this tissue. Mitochondrial-encoded COX2 mRNA levels were not limiting for functional activities in both tissues, in favour of post-transcriptional control or limitations by other transcripts of the COX complex. Altogether, the differentiation in gene expression between both populations was more strongly expressed at 4 degrees C. The comparison of functional levels and transcript levels may reflect genetic differentiation at functional sites, in line with genetic differences between the two populations previously established by non-coding genetic markers.

Acclimatization↗
PubMed2001

Seasonal change in the capacity for supercooling by neonatal painted turtles.

Hatchlings of the North American painted turtle (Chrysemys picta) typically spend their first winter of life inside the shallow, subterranean nest where they completed incubation the preceding summer. This facet of their natural history commonly causes neonates in northerly populations to be exposed in mid-winter to ice and cold, which many animals survive by remaining unfrozen and supercooled. We measured the limit of supercooling in samples of turtles taken shortly after hatching and in other samples after 2 months of acclimation (or acclimatization) to a reduced temperature in the laboratory or field. Animals initially had only a limited capacity for supercooling, but they acquired an ability to undergo deeper supercooling during the course of acclimation. The gut of most turtles was packed with particles of soil and eggshell shortly after hatching, but not after acclimation. Thus, the relatively high limit of supercooling for turtles in the days immediately after hatching may have resulted from the ingestion of soil (and associated nucleating agents) by the animals as they were freeing themselves from their eggshell, whereas the relatively low limit of supercooling attained by acclimated turtles may have resulted from their purging their gut of its contents. Parallels may, therefore, exist between the natural-history strategy expressed by hatchling painted turtles and that expressed by numerous terrestrial arthropods that withstand the cold of winter by sustaining a state of supercooling.

Acclimatization↗
PubMed2002

Adaptive thermogenesis in hummingbirds.

The occurrence of non-shivering thermogenesis in birds has long been a controversial issue. Although birds are endothermic vertebrates, sharing with mammals (placental mammals and marsupials) a common ancestor, they do not possess brown adipose tissue or a similar type of tissue, unlike their mammalian counterparts. Some bird species are, however, able to withstand very low ambient temperatures (-70 degrees C) or undergo periods of heterothermia, and there is now good experimental evidence showing that non-shivering thermogenesis may indeed occur in birds under such conditions. The skeletal muscles of birds, particularly the flight muscles, occupy a significant fraction (approximately 30 %) of the total body mass, and recent results have shown that they are likely to be the main sites for non-shivering thermogenesis. The precise mechanisms involved in adaptive thermogenesis in birds are still not fully understood. The translocation of Ca(2+) between intracellular compartments and the cystosol mediated by the sarcoplasmic reticulum Ca(2+)-ATPase, uncoupled from ATP synthesis, is one mechanism whereby chemi-osmotic energy can be converted into heat, and it has been proposed as one of the possible mechanisms underlying non-shivering thermogenesis in birds on the basis of data obtained mainly from ducklings acclimatized to cold conditions. The recent characterization of an uncoupling protein homolog in avian skeletal muscle and the expression of its mRNA at different stages of the torpor/rewarming cycle of hummingbirds indicate that it has the potential to function as an uncoupling protein and could play a thermogenic role during rewarming in these birds.

Acclimatization↗
PubMed1979

[Role of brown adipose tissue in the thermal response to chlorpromazine in rats during cold exposure (author's transl)].

Significance of the intercapsular brown adipose tissue (IBAT) in the thermal response to chlorpromazine (CPZ) during acute and chronic cold exposure was studied in rats. Adult male Wistar-Imamichi rats were exposed to 4 degrees C for 1 (cold-exposed) or 30 days (cold-acclimated). Intraperitoneal injection of 10 mg/kg CPZ caused a more marked and lasted hypothermia in acute cold-exposed rats as compared with that seen in control or in cold-acclimatized rats. Hypothermia induced by CPZ was unaffected by removal of IBAT either in control or acute cold-exposed rats. But in cold-acclimated rats, the removal of IBAT potentiated the hypothermia by CPZ. The relative weight of IBAT in cold-acclimated rats was about 3 times heavier than that in control and acute cold-exposed rats. CPZ had no effect on the relative weight of IBAT in all groups examined. Total lipids in IBAT showed no significant changes following CPZ administration in rats of all groups. In acute cold-exposed rats, serum FFA level progressively decreased after CPZ injection. The noradrenaline concentration in IBAT increased after chronic cold exposure and CPZ suppressed this elevation. The results suggest that the thermogenesis related sympathetic activity in the IBAT plays a mediatory role in thermal response to CPZ during cold acclimation.

Acclimatization↗
PubMed2006

American Chestnut [Castanea dentata (Marsh.) Borkh].

The key to successful transformation of American chestnut is having the correct combination of explant tissue, selectable and scorable markers, and a reliable regeneration system. Rapidly dividing somatic embryos, growing as proembryogenic masses, are a suitable tissue; the bar gene is a suitable selectable marker in conjunction with 1.0 to 10 mg/L phosphirothricin (PPT); and the mgfp5-ER gene is an effective nondestructive scorable marker. We have also found that the more gently the somatic embryos are treated during the inoculation and co-cultivation steps, the higher the transformation efficiency. The average transformation efficiency that can be expected using the described protocol is approx 20 stable and embryogenic transformation events/g of somatic embryo tissue. Cell line and batch-to-batch deviations both upward and downward should be expected. Finally, somatic embryos can be induced to form shoots, which can then be micropropagated and acclimatized.

Acclimatization↗
PubMed1996

Introduction of retired breeder F344/DuCrj rats for aging research.

Male retired breeder F344/DuCrj rats of 17 months of age were purchased in three lots and maintained for aging studies until 25 months of age. These rats were compared with male virgin rats of the same strain for survival percentage, body weight and food consumption. In the retired breeders, decrease in body weight and low food consumption were noted after delivery, and one or two months were required for these parameters to return to the delivery level. After recovery, the body weight and food consumption as well as survival percentage in the retired breeders were similar to those in virgins. From our results, we consider that it takes one to two months to acclimatize aged rats.

Acclimatization↗
PubMed2005

Influence of moderate altitude on blood lactate and heart rate in a standardized exercise test in healthy volunteers.

Nineteen healthy volunteers were exposed to a standardized exercise test at sea level (SLa), at an altitude of 1700 m before (1700a) and after a moderate 10-day mountain training (1700b), with a final control four weeks later at sea level (SLb). Vital signs, blood lactate and arterial oxygen saturation were determined prior, during or after the exercise test. Whereas systolic blood pressure and heart rate at rest did not change substantially, diastolic blood pressure decreased at the final control (SLb, p<0.05) and oxygen saturation was significantly lower at 1700 m (1700a, 1700b, p<0.01). Lactate at rest increased from 1.16 (SLa) to 1.97 (1700a) mmol/l after acute exposure followed by a slight reduction after adaptation (p<0.05). The mean maximum lactate levels were as follows: 6.03, 10.56, 6.22 and 8.75 (p<0.01). The mean maximum performance increased during the study (225.6, 223.3, 231.6, 248.1 Watt, p<0.01). Lactate versus workload curves did not show a marked shift to the right. No significant changes of maximum heart rates during the exercise test were found. In conclusion, a sojourn at 1700 m provokes an increase of lactate levels with subsequent reduction after acclimatization and has a significant positive impact on the mean maximum performance after moderate mountain training.

Acclimatization↗
PubMed1996

Elevation of serum cholesterol at high altitude and its relationship to hematocrit.

The positive relationship between hematocrit and serum cholesterol may be due to dilution. Accordingly, high hematocrits would yield reduced serum pools for dilution of cholesterol, thus producing higher levels. To test this effect, the relationships between hematocrit and cholesterol were evaluated at low-altitude and high-altitude clinics. Retrospective chart reviews were conducted at Madison, WI (264 m) and Leadville, CO (3105 m) to identify family practice patients who underwent hematocrit and serum cholesterol determinations on the same day. We excluded patients with medical conditions or on medications that affect cholesterol, patients with high glucose and triglyceride levels, and patients with extreme cholesterol levels. Remaining patients (153 in each altitude group) were matched by age and sex. The mean hematocrits and cholesterol levels were compared using analysis of variance. The linear relationships between hematocrit and cholesterol were compared using analysis of covariance. The mean hematocrit was significantly higher at high altitude (47.5% versus 41.3%; p < 0.0005) as were the mean serum cholesterol (190 mg/dL versus 177 mg/dL; p < 0.002) and the low-density lipoprotein:high-density lipoprotein ratio (2.80 versus 2.27; p < 0.05). Whereas a significant, positive relationship existed between hematocrit and cholesterol at low altitude (2.15 mg/dL per %; p < 0.002), no such relationship was found at high altitude. Hematocrit and serum cholesterol were elevated for family practice patients living at high altitudes. Differences exist between altitudes in the relationship between hematocrit and cholesterol. Acclimatization to high altitude and its resultant erythropoiesis may increase serum cholesterol levels. Consequently, relocation to a high altitude may increase the risk of arteriosclerotic cardiovascular disease.

Acclimatization↗
PubMed1991

[Functional differentiation of thermoregulation, with particular references to seasonal variation of whole body sweat rate of exercising man].

We investigated the seasonal variation of sweating response during exercise. Four adult healthy men repeated a moderate bicycle exercise (60 watts) in a climatic chamber of an ambient temperature of 30 degrees C (relative humidity, 45%) in winter, spring, summer, and fall. In summer, sweat rate immediately increased as soon as the exercise started, whereas in winter in a few minutes. The mean sweat rate during exercise was significantly different between winter and summer. The transient reduction of the Tsk was observed at the beginning of the exercise in winter. The Tsk decreased in proportion to increasing of sweat rate in each season. Significantly negative correlations were found between sweat rate and the rate of change of Tsk during exercise in each season. The slope and intercept of regression line were significantly different between winter and summer. The index of sweating was made available for the relative value, changing rate against annual mean value of total sweat loss (delta SR, %). The relative value rather than the absolute value (i.e., expressed as g.m-2.h-1) corrected well with skin temperature. It is suggested that the present results may reflect adapted changes in the thermoregulatory mechanisms to seasonal acclimatization. Moreover, the fall in skin temperature during exercise may be not due to increased evaporative cooling, but may be the result of vasoconstriction probably caused by non-thermal factors.

Acclimatization↗
PubMed2002

Observations on normal body temperatures in Vietnamese and Japanese in Vietnam.

The observations described in this paper were made during a study of the effects of tropical climate upon Vietnamese and Japanese. We measured rectal and skin temperatures every 10 min for 26 hrs in 6 Vietnamese and 6 Japanese. The experiments have been conducted for 2 hot months, June and July 1999 and 2000 in Hanoi, Vietnam. The ambient temperatures ranged from 33 to 36 degrees C. The results obtained are summarized as follows: 1) Skin temperatures at thigh, forearm and hand during the daytime were significantly higher in the Vietnamese subjects than in the Japanese ones. It would be physiological reactions to warm ambient temperatures, which is advantageous for dissipation of body heat. 2) The average rectal temperature during the daytime is significantly higher in the Vietnamese than in the Japanese, while significantly lower at night. 3) Average range of oscillation of rectal temperature was 1.26 degrees C in the Vietnamese, which was clearly greater than in the Japanese. The higher core temperature, which was actively regulated under warm temperature, seemed of adaptive significance, resulting in the reduction of water consumption like camels in the desert. A greater range of oscillation in tropical Vietnamese people might have ecological significance for efficient acclimatization in the warm environment, suggesting that the setpoint of core temperature could show a greater range of oscillation.

Acclimatization↗
PubMed2005

Effects of short-term exercise in the heat on thermoregulation, blood parameters, sweat secretion and sweat composition of tropic-dwelling subjects.

This study investigates the effects of a short-term aerobic training program in a hot environment on thermoregulation, blood parameters, sweat secretion and composition in tropic-dwellers who have been exposed to passive heat. Sixteen healthy Malaysian-Malay male volunteers underwent heat acclimation (HA) by exercising on a bicycle ergometer at 60% of VO2max for 60 min each day in a hot environment (Ta: 31.1+/-0.1 degrees C, rh: 70.0+/-4.4%) for 14 days. All parameters mentioned above were recorded on Day 1 and at the end of HA (Day 16). On these two days, subjects rested for 10 min, then cycled at 60% of VO2max for 60 min and rested again for 20 min (recovery) in an improvised heat chamber. Rectal temperature (Tre), mean skin temperature (Tsk) heart rate (HR), ratings of perceived exertion (RPE), thermal sensation (TS), local sweat rate and percent dehydration were recorded during the test. Sweat concentration was analysed for sodium [Na+]sweat and potassium. Blood samples were analysed for biochemical changes, electrolytes and hematologic indices. Urine samples were collected before and after each test and analysed for electrolytes.After the period of acclimation the percent dehydration during exercise significantly increased from 1.77+/-0.09% (Day 1) to 2.14+/-0.07% (Day 16). Resting levels of hemoglobin, hematocrit and red blood cells decreased significantly while [Na+]sweat increased significantly. For Tre and Tsk there were no differences at rest. Tre, HR, RPE, TS, plasma lactate concentration, hemoglobin and hematocrit at the 40th min of exercise were significantly lower after the period of acclimation but mean corpuscular hemoglobin and serum osmolality were significantly higher while no difference was seen in [Na+]sweat and Tsk. It can be concluded that tropic-dwelling subjects, although exposed to prolonged passive heat exposure, were not fully heat acclimatized. To achieve further HA, they should gradually expose themselves to exercise-heat stress in a hot environment.

Acclimatization↗
PubMed2005

Evolutionary and acclimation-induced variation in the thermal limits of heart function in congeneric marine snails (genus Tegula): implications for vertical zonation.

We analyzed the thermal limits of heart function for congeneric species of the marine snail Tegula that have different patterns of vertical zonation. T. funebralis is found in the low to mid-intertidal zone, and T. brunnea and T. montereyi live in the low-intertidal or subtidally. As indices of thermal limits of heart function, we used the temperature at which heart rate initially decreased rapidly during heating (the Arrhenius break temperature, or ABT) and the temperature at which heart ceased to beat with either heating or cooling (the flatline temperature, or FLT(hot) or FLT(cold), respectively). These three indices provide an estimate of the thermal range within which Tegula heart function is maintained. For field-acclimatized specimens, the thermal range of the high-intertidal T. funebralis was greater than those of its two lower-occurring congeners (higher ABT, higher FLT(hot), lower FLT(cold)). We also demonstrated the effects of constant thermal acclimation on the heart rate response to heat stress. Acclimation to 14 degrees C and 22 degrees C resulted in increases in ABT and FLT(hot), with the largest changes in T. brunnea and T. montereyi. Although T. funebralis is more heat tolerant and eurythermal than its two lower-occurring congeners, it can encounter field body temperatures that exceed ABT, indicating that T. funebralis faces a larger threat from heat stress, in situ. These findings are consistent with recent studies on other taxa of marine invertebrates that have shown, somewhat paradoxically, that warm-adapted, eurythermal intertidal species may be more impacted by global warming than congeneric subtidal species that are less heat tolerant.

Acclimatization↗