The predictive validity of clinical ratings for an extreme environment.
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Adolescent↗
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The psychological effects of service in British Antarctica: a study using the General Health Questionnaire.
This study follows the psychological profile of a group of Antarctic explorers on a remote base in British Antarctica. Each month for 1 year the 60-item General Health Questionnaire (GHQ) was administered to the 12-man complement and the results compared to those of a control group. Three men resigned and left, 4 months later, at the end of winter. Their scoring showed marked differences from the others, including the highest scores in the severe depression factor scale. The GHQ was accepted by the men despite the intrusive threat it offered in such a small community; there was also a seasonal variation in scoring, with higher scores in the winter, and no evidence of long-term psychological sequelae in those who stayed.
Adult↗
Changes in serum triiodothyronine (T3) kinetics after prolonged Antarctic residence: the polar T3 syndrome.
Humans who live in Antarctica for greater than 5 continuous months demonstrate alterations in the hypothalamic-pituitary-thyroid axis. These changes are characterized by 1) increased pituitary release of TSH in response to iv TRH, 2) increased serum clearance of orally administered T3, and 3) normal serum total, free T4, and unstimulated TSH levels. To clarify the mechanism responsible for these findings, serum kinetic studies of 125I-labeled T4 and T3 were carried out in a group of normal men, first in California, then after 20 and 42 weeks of continuous Antarctic residence. The kinetic parameters were calculated by noncompartmental analysis. The mean T4 residence time (MRT) was not different before and after 42 weeks (5.54 +/- 0.50 and 5.08 +/- 0.43 days). The total T4 volume of distribution (TVd) tended to fall over the same period (4.30 +/- 0.12, 3.56 +/- 0.27 L/m2), but was not significantly different (P = 0.075). In contrast to T4, there was an increase from control values for the T3 MRT from 0.83 +/- 0.03 to 1.10 +/- 0.03 days (P less than 0.002) and a more than doubling of the T3 TVd from 15.55 +/- 0.52 to 47.24 +/- 5.09 L/m2 (P less than 0.002) after 42 wk of Antarctic residence. Energy intake increased approximately 40% throughout the study without a change in body weight. The changes in T3 kinetic parameters may be accounted for by increased extravascular tissue binding. The marked increase in T3 TVd and the small increase in MRT are associated with increased T3 production and clearance and only minor changes in T4 kinetics. This is the first description of a mechanism for the change in thyroid hormone economy occurring with extended residence in Antarctica.
Adult↗
Impairment in cognitive and exercise performance during prolonged antarctic residence: effect of thyroxine supplementation in the polar triiodothyronine syndrome.
Humans who work in Antarctica display deficits in cognition, disturbances in mood, increased energy requirements, a decline of thyroid hormone products, and an increase of serum TSH. We compared measurements in 12 subjects, before deployment (baseline), with 11 monthly studies during Antarctic residence (AR). After 4 months of AR (period 1), half of the subjects (T(4) group) received L-thyroxine [64 nmol.day(-)(1) (0.05 mg.day(-)(1))]; and the other half, a placebo (placebo group) for the next 7 months of AR (period 2). During period 1, there was a 12.3 +/- 5.1% (P < 0.03) decline on the matching-to-sample (M-t-S) cognitive task and an increase in depressive symptoms, compared with baseline. During the intervention in period 2, M-t-S scores for the T(4)-treated group returned to baseline values; whereas the placebo group, in contrast, showed a reduced M-t-S score (11.2 +/- 1.3%; P < 0.0003) and serum free T(4) (5.9 +/- 2.4%; P < 0.02), compared with baseline. The change in M-t-S score was correlated with the change in free T(4) (P < 0.0003) during both periods, and increases in serum TSH preceded worsening scores in depression, tension, anger, lack of vigor, and total mood disturbance (P < 0.001) during period 2. Additionally, the submaximal work rate for a fixed O(2) use decreased 22.5 +/- 4.9% in period 1 and remained below baseline in period 2 (25.2 +/- 2.3%; P < 0.005) for both groups. After 4 months of AR, the L-thyroxine supplement was associated with improved cognition, which seems related to circulating T(4). Submaximal exercise performance decrements, observed during AR, were not changed with this L-thyroxine dose.
Adult↗
Metabolic plasticity and critical temperatures for aerobic scope in a eurythermal marine invertebrate (Littorina saxatilis, Gastropoda: Littorinidae) from different latitudes.
Effects of latitudinal cold adaptation and cold acclimation on metabolic rates and aerobic scope were studied in the eurythermal marine gastropod Littorina saxatilis from temperate North Sea and sub-arctic White Sea areas. Animals were acclimated for 6-8 weeks at control temperature (13 degrees C) or at 4 degrees C, and their respiration rates were measured during acute temperature change (1-1.5 degrees C h(-1)) in a range between 0 degrees C and 32 degrees C. In parallel, the accumulation of anaerobic end products and changes in energy status were monitored. Starting from 0 degrees C, aerobic metabolic rates of L. saxatilis rose quickly with increasing temperatures up to a point at or slightly above the respective acclimation temperature. Beyond this value, thermal sensitivity of oxygen consumption rate V((O(2))) greatly decreased in a wide, 15 degrees C range of experimental temperatures. This change in metabolic regulation was also reflected in the activation energy of aerobic metabolism (E(a)), which was approximately seven times lower at temperatures above Arrhenius breakpoint temperatures (ABTs) than at temperatures below ABTs. Warming progressively led to a discrepancy between energy demand and energy production, as demonstrated by a decrease in the levels of high-energy phosphates [phosho-L-arginine (PLA) and ATP], and resulted in the onset of anaerobiosis at critically high temperatures, indicating a limitation of aerobic scope. The comparison of aerobic and anaerobic metabolic rates in L. saxatilis in air and water suggests that the heat-induced onset of anaerobiosis is due to the insufficient oxygen supply to tissues at high temperatures. Cold acclimation led to an increase in aerobic metabolic rates and a considerable downward shift of the upper critical temperature in North Sea L. saxatilis but not in White Sea L. saxatilis. Limited metabolic plasticity in response to cold acclimation in sub-arctic White Sea snails as compared with their temperate North Sea counterparts suggests that metabolic depression occurs during overwintering under the more extreme winter conditions at the White Sea.
Acclimatization↗
Endothermic heat production in honeybee winter clusters.
In order to survive cold northern winters, honeybees crowd tightly together in a winter cluster. Present models of winter cluster thermoregulation consider the insulation by the tightly packed mantle bees as the decisive factor for survival at low temperatures, mostly ignoring the possibility of endothermic heat production. We provide here direct evidence of endothermic heat production by 'shivering' thermogenesis. The abundance of endothermic bees is highest in the core and decreases towards the surface. This shows that core bees play an active role in thermal control of winter clusters. We conclude that regulation of both the insulation by the mantle bees and endothermic heat production by the inner bees is necessary to achieve thermal stability in a winter cluster.
Acclimatization↗
Characterisation of intestinal peptide transporter of the Antarctic haemoglobinless teleost Chionodraco hamatus.
H(+)/peptide cotransport was studied in brush-border membrane vesicles (BBMV) from the intestine of the haemoglobinless Antarctic teleost Chionodraco hamatus by monitoring peptide-dependent intravesicular acidification with the pH-sensitive dye Acridine Orange. Diethylpyrocarbonate-inhibited intravesicular acidification was specifically achieved in the presence of extravesicular glycyl-L-proline (Gly-L-Pro) as well as of glycyl-L-alanine (Gly-L-Ala) and D-phenylalanyl-L-alanine (D-Phe-L-Ala). H(+)/Gly-L-Pro cotransport displayed saturable kinetics, involving a single carrier system with an apparent substrate affinity (K(m,app)) of 0.806+/-0.161 mmol l(-1). Using degenerated primers from eel and human (PepT1) transporter sequence, a reverse transcription-polymerase chain reaction (RT-PCR) signal was detected in C. hamatus intestine. RT-PCR paralleled kinetic analysis, confirming the hypothesis of the existence of a PepT1-type transport system in the brush-border membranes of icefish intestine. Functional expression of H(+)/peptide cotransport was successfully performed in Xenopus laevis oocytes after injection of poly(A)(+) RNA (mRNA) isolated from icefish intestinal mucosa. Injection of mRNA stimulated D-Phe-L-Ala uptake in a dose-dependent manner and an excess of glycyl-L-glutamine inhibited this transport. H(+)/peptide cotransport in the Antarctic teleost BBMV exhibited a marked difference in temperature optimum with respect to the temperate teleost Anguilla anguilla, the maximal activity rate occurring at approximately 0 degrees C for the former and 25 degrees C for the latter. Temperature dependence of icefish and eel intestinal mRNA-stimulated uptake in the heterologous system (oocytes) was comparable.
Amino Acid Sequence↗
Myogenic cell cycle duration in Harpagifer species with sub-Antarctic and Antarctic distributions: evidence for cold compensation.
In teleosts, the proliferation of myogenic progenitor cells is required for muscle growth and nuclear turnover. We measured the cell cycle and S-phase duration of myogenic cells in the fast myotomal muscle of two closely related Harpagifer species by cumulative S-phase labelling with 5-bromo-2'-deoxyuridine (BrdU). Harpagifer antarcticus is a stenothermal species from the Antarctic peninsula (experiencing temperatures of -2 degrees C to +1 degrees C) and Harpagifer bispinis is a eurythermal species from the Beagle Channel, Tierra del Fuego (living at +4 degrees C in winter and up to 11 degrees C in summer). Specific growth rates in the adult stages studied were not significantly different from zero. Myogenic progenitor cells were identified using an antibody against c-met. Seventy-five percent of the c-met(+ve) cells were in a proliferative state in both species. Cell cycle time was 150 h at 5 degrees C and 81.3 h at 10 degrees C in H. bispinis (Q(10)=3.4). Cell cycle duration was 35% shorter in H. antarcticus at 0 degrees C (111 h) than in H. bispinis at 5 degrees C. The predicted cell cycle time for H. bispinis at 0 degrees C (based on the Q(10) relationship) was 277 h, which was more than double that measured for the Antarctic species at this temperature. The results obtained are compatible with an evolutionary adjustment of cell cycle time for function at low temperature in the Antarctic species.
Acclimatization↗
Seasonal acquisition of chill tolerance and restructuring of membrane glycerophospholipids in an overwintering insect: triggering by low temperature, desiccation and diapause progression.
Adults of the insect Pyrrhocoris apterus acquire chill tolerance through the process of autumnal acclimatization. Field and laboratory experiments were conducted to separate the triggering effects of low temperatures, desiccation and diapause progression on the physiological characteristics related to chill tolerance with emphasis on the restructuring of glycerophospholipid (GPL) composition. Changes in relative proportions of major molecular species of glycerophosphoethanolamines (GPEtns) and glycerophosphocholines (GPChols) in thoracic muscle and fat body tissues were followed using HPLC coupled to electrospray ionisation mass spectrometry. The increase in relative proportion of 1-palmitoyl-2-linoleyl-sn-GPEtn at the expense of 1,2-dilinoleyl-sn-GPChol was the most prominent feature of the complex change observed in both tissues during autumnal acclimatization in the field. The relative proportion of total GPEtns increased, while the proportion of total GPChols decreased. The relative proportion of unsaturated fatty acyls slightly decreased. A similar restructuring response was seen during acclimatization in the field and cold acclimation in the laboratory. By contrast, the GPL changes related to desiccation and diapause progression were relatively small, differed qualitatively from the cold-acclimation response, and were accompanied with no increase of chill tolerance. Other features of autumnal acclimatization, i.e. depression of supercooling capacity and accumulation of polyhydric alcohols, were also triggered solely by low temperatures.
Acclimatization↗
Heat-shock protein expression is absent in the antarctic fish Trematomus bernacchii (family Nototheniidae).
The heat-shock response, the enhanced expression of one or more classes of molecular chaperones termed heat-shock proteins (hsps) in response to stress induced by high temperatures, is commonly viewed as a 'universal' characteristic of organisms. We examined the occurrence of the heat-shock response in a highly cold-adapted, stenothermal Antarctic teleost fish, Trematomus bernacchii, to determine whether this response has persisted in a lineage that has encountered very low and stable temperatures for at least the past 14-25 million years. The patterns of protein synthesis observed in in vivo metabolic labelling experiments that involved injection of (35)S-labelled methionine and cysteine into whole fish previously subjected to a heat stress of 10 degrees C yielded no evidence for synthesis of any size class of heat-shock protein. Parallel in vivo labelling experiments with isolated hepatocytes similarly showed significant amounts of protein synthesis, but no indication of enhanced expression of any class of hsp. The heavy metal cadmium, which is known to induce synthesis of hsps, also failed to alter the pattern of proteins synthesized in hepatocytes. Although stress-induced chaperones could not be detected under any of the experimental condition used, solid-phase antibody (western) analysis revealed that a constitutively expressed 70 kDa chaperone was present in this species, as predicted on the basis of requirements for chaperoning during protein synthesis. Amounts of the constitutively expressed 70 kDa chaperone increased in brain, but not in gill, during 22 days of acclimation to 5 degrees C. The apparent absence of a heat-shock response in this highly stenothermal species is interpreted as an indication that a physiological capacity observed in almost all other organisms has been lost as a result of the absence of positive selection during evolution at stable sub-zero temperatures. Whether the loss of the heat-shock response is due to dysfunctional genes for inducible hsps (loss of open reading frames or functional regulatory regions), unstable messenger RNAs, the absence of a functional heat-shock factor or some other lesion remains to be determined.
Acclimatization↗
Mitochondrial oxyconformity and cold adaptation in the polychaete Nereis pelagica and the bivalve Arctica islandica from the Baltic and White Seas.
The rates of oxygen uptake of the marine polychaete Nereis pelagica and the bivalve Arctica islandica depend on the availability of ambient oxygen. This is manifest both at the tissue level and in isolated mitochondria studied between oxygen tensions (P(O2)) of 6.3 and 47.6 kPa (47-357 mmHg). Oxyconformity was found in both Baltic Sea (Kiel Bight) and cold-adapted White Sea populations of the two species. However, mitochondria isolated from White Sea specimens of N. pelagica and A. islandica showed a two- to threefold higher aerobic capacity than mitochondria prepared from Baltic Sea specimens. We tested whether mitochondrial oxyconformity can be explained by an additional electron pathway that is directly controlled by P(O2). Mitochondrial respiration of both invertebrate species was inhibited by cyanide (KCN) and by salicylhydroxamic acid (SHAM). The overall rate of mitochondrial oxygen consumption increased at high P(O2). Phosphorylation efficiency (ADP/O ratio) decreased at elevated P(O2) (27.5-47.6 kPa, 206-357 mmHg), regardless of whether malate or succinate was used as a substrate. In contrast to the invertebrate mitochondria studied, mitochondria isolated from bovine heart, as an oxyregulating control species, did not show an elevated rate of oxygen uptake at high P(O2) in any respiratory state, with the exception of state 2 malate respiration. In addition, rates of ATP formation, respiratory control ratios (RCR) and ADP/O ratios remained virtually unchanged or even tended to decreased. In conclusion, the comparison between mitochondria from oxyregulating and oxyconforming organisms supports the existence of an alternative oxidase in addition to the classical cytochrome c oxidase. In accordance with models discussed previously, oxidative phosphorylation does not explain the rate of mitochondrial oxygen consumption during progressive activation of the alternative electron transport system. We discuss the alternative system, thought to be adaptive in confined, usually hypoxic environments, where excess oxygen can be eliminated and oxygen levels can be kept low by an increase in the rate of oxygen consumption, thereby minimizing the risk of oxidative stress.
Acclimatization↗
Physiological basis of temperature-dependent biogeography: trade-offs in muscle design and performance in polar ectotherms.
Polar, especially Antarctic, oceans host ectothermic fish and invertebrates characterized by low-to-moderate levels of motor activity; maximum performance is reduced compared with that in warmer habitats. The present review attempts to identify the trade-offs involved in adaptation to cold in the light of progress in the physiology of thermal tolerance. Recent evidence suggests that oxygen limitations and a decrease in aerobic scope are the first indications of tolerance limits at both low and high temperature extremes. The cold-induced reduction in aerobic capacity is compensated for at the cellular level by elevated mitochondrial densities, accompanied by molecular and membrane adjustments for the maintenance of muscle function. Particularly in the muscle of pelagic Antarctic fish, among notothenioids, the mitochondrial volume densities are among the highest known for vertebrates and are associated with cold compensation of aerobic metabolic pathways, a reduction in anaerobic scope, rapid recovery from exhaustive exercise and enhanced lipid stores as well as a preference for lipid catabolism characterized by high energy efficiency at high levels of ambient oxygen supply. Significant anaerobic capacity is still found at the very low end of the activity spectrum, e.g. among benthic eelpout (Zoarcideae). In contrast to the cold-adapted eurytherms of the Arctic, polar (especially Antarctic) stenotherms minimize standard metabolic rate and, as a precondition, the aerobic capacity per milligram of mitochondrial protein, thereby minimizing oxygen demand. Cost reductions are supported by the downregulation of the cost and flexibility of acid-base regulation. At maintained factorial scopes, the reduction in standard metabolic rate will cause net aerobic scope to be lower than in temperate species. Loss of contractile myofilaments and, thereby, force results from space constraints due to excessive mitochondrial proliferation. On a continuum between low and moderately high levels of muscular activity, polar fish have developed characteristics of aerobic metabolism equivalent to those of high-performance swimmers in warmer waters. However, they only reach low performance levels despite taking aerobic design to an extreme.
Acclimatization↗
A survey of snowmobile injuries and hazards.
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Accident Prevention↗
Comparison of metabolic, temperature, heart rate and ventilatory responses to exercise at extreme ambient temperatures (0 degrees and 35 degrees C.).
Eight male subjects exercised on a bicycle ergometer for one half to one hour at loads demanding 52 to 59% of Vo2max on two separate occasions, once with ambient temperature held at 0 degrees C and once in a 35 degrees C environment. Throughout exercise and during recovery in a 25 degrees C environment, measurements were made of oxygen consumption, ventilation, heart rate, muscle-rectal-skin temperatures, and blood lactic acid. In the hot condition significant increases in heart rate, blood lactates, sweat loss, muscle, rectal and skin temperature responses were observed. At 0 degrees C Vo2 was significantly elevated during exercise over that in the 35 degrees C condition. Despite the elevated Vo2 response in the cold, higher body temperatures measured in the heat were associated with a significantly higher (P less than .025) recovery Vo2 (x = 866 ml), which was of the magnitude predicted by the van't Hoff-Arrhenius relationship.
Adult↗
Fat utilization enhanced by exercise in a cold environment.
To study substrate utilization during cold temperature exercise, seven men dressed in shorts, T-shirts, and light gloves performed 60 min of continuous cycle ergometer exercise at -10 degrees C and 22 degrees C. The workload at both temperatures represented 66% of the cycle-measured maximal heart rate. Oxygen consumption and respiratory exchange ratio (RER) were measured at rest and during 60 min of exercise. Rates of total and fat energy utilization (kJ X min-1) during exercise were calculated from VO2 and RER. A two-factor repeated measures analysis of variance indicated that at rest oxygen consumption averaged 56% higher and RER 5% lower at -10 degrees C. During exercise, oxygen consumption averaged 10% higher (P less than 0.05), and RER averaged 2% lower (P less than 0.05) at -10 degrees C. The rates of total energy use (mean +/- SD = 39.3 +/- 1.2 vs 35.7 +/- 1.3 kJ X min-1; P less than 0.05) were significantly higher at -10 degrees C than at 22 degrees C. In addition, the rate of fat use increased significantly in both groups after 30 min of exercise. The cumulative total energy expenditure for 60 min of exercise was 13% higher (2379 +/- 308 vs 2110 +/- 415 kJ; P less than 0.05 and the cumulative fat expenditure was 35% higher (979 +/- 209 vs 724 +/- 184 kJ: P less than 0.05) in the cold environment. These results indicate that a cold environment can significantly enhance fat utilization during endurance exercise.
Adipose Tissue↗
Plasma lipids concentrations in obese children living in a cold area.
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Adolescent↗
The potential impacts of climate variability and change on temperature-related morbidity and mortality in the United States.
Heat and heat waves are projected to increase in severity and frequency with increasing global mean temperatures. Studies in urban areas show an association between increases in mortality and increases in heat, measured by maximum or minimum temperature, heat index, and sometimes, other weather conditions. Health effects associated with exposure to extreme and prolonged heat appear to be related to environmental temperatures above those to which the population is accustomed. Models of weather-mortality relationships indicate that populations in northeastern and midwestern U.S. cities are likely to experience the greatest number of illnesses and deaths in response to changes in summer temperature. Physiologic and behavioral adaptations may reduce morbidity and mortality. Within heat-sensitive regions, urban populations are the most vulnerable to adverse heat-related health outcomes. The elderly, young children, the poor, and people who are bedridden or are on certain medications are at particular risk. Heat-related illnesses and deaths are largely preventable through behavioral adaptations, including the use of air conditioning and increased fluid intake. Overall death rates are higher in winter than in summer, and it is possible that milder winters could reduce deaths in winter months. However, the relationship between winter weather and mortality is difficult to interpret. Other adaptation measures include heat emergency plans, warning systems, and illness management plans. Research is needed to identify critical weather parameters, the associations between heat and nonfatal illnesses, the evaluation of implemented heat response plans, and the effectiveness of urban design in reducing heat retention.
Climate↗