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PubMed1987

Evaluation of a temperate environment test to predict heat tolerance.

A temperate environment heat tolerance test (HTT) was formerly reported (Shvartz et al. 1977b) to distinguish heat acclimatized humans from former heat stroke patients. The purpose of this investigation was to evaluate the ability of HTT to measure acute individual changes in the HR and Tre responses of normal subjects, induced by classical heat acclimation procedures, thereby assessing the utility and sensitivity of HTT as a heat tolerance screening procedure. On day 1, 14 healthy males performed HTT (23.2 +/- 0.5 degrees C db, 14.9 +/- 0.5 degrees C wb) by bench stepping (30 cm high, 27 steps x min-1) for 15 min at 67 +/- 3% VO2max. On days 2-9, all subjects underwent heat acclimation (41.2 +/- 0.3 degrees C db, 28.4 +/- 0.3 degrees C wb) via treadmill exercise. Heat acclimation trials (identical on days 2 and 9) resulted in significant decreases in HR (170 +/- 3 vs 144 +/- 5 beats x min-1), Tre (39.21 +/- 0.09 vs 38.56 +/- 0.17 degrees C), and ratings of perceived exertion; plasma volume expanded 5.2 +/- 1.7%. On day 10, subjects repeated HTT; day 1 vs day 10 HR were statistically similar (143 +/- 6 vs 137 +/- 6 beats x min-1, p greater than 0.05) but Tre decreased significantly (37.7 +/- 0.1 vs 37.5 +/- 0.1 degrees C, p less than 0.05). Group mean HTT composite score (day 1 vs day 10) was unchanged (63 +/- 5 vs 72 +/- 6, p greater than 0.05), and individual composite scores indicated that HTT did not accurately measure HR and Tre trends at 41.2 +/- degrees C in 6 out of 14 subjects.(ABSTRACT TRUNCATED AT 250 WORDS)

Acclimatization↗
PubMed1984

After effects of chronic hypoxia on cardiac output and muscle blood flow at rest and exercise.

Cardiac output (Q, by N2-CO2 rebreathing) and limb muscle blood flow (qm, from 133Xe clearance) were determined in eight male subjects at rest and during cycloergometric loads immediately before and 12 days after return from the 1981 Swiss Lhotse Shar (8,398 m) Expedition. Compared to control conditions, after exposure to hypoxia: 1) Q was unchanged at rest and at 75 watts (W) but was 18% less (P less than 0.01) at 150 W with constant heart rate (approximately 140 beats X min-1); 2) qm in the vastus lateralis was identical at rest but 26% and 39% less (P less than 0.05 and P less than 0.001, respectively) at two submaximal leg work loads (75 and 125 W); 3) qm in the biceps at 50 W was 34% less (P less than 0.01); 4) hemoglobin flow (QHb and qmHb), similarly to blood flow (Q and qm), was significantly reduced; 5) the qm adjustment rate, measured from the time required to attain a new steady state upon a square wave change of work load starting from rest, was slower, particularly at the lower work loads. From the above results as well as from corresponding morphometric findings showing in the same subjects: 1) a decrease of the ratio between fiber section and number of capillaries and 2) a rise of the mitochondrial to fiber volume ratio, it is concluded that during altitude acclimatization peripheral O2 delivery becomes more efficient.

Acclimatization↗
PubMed1977

Physiological responses of dogs on exposure to hot, arid conditions. Acid-base status.

Acid-base parameters were determined in chronically cannulated dogs exposed to ambient temperatures increasing from 25-47 degrees C (with relative humidity below 30%). pH increased from 7.409 +/- 0.004 (S.E.M.) to 7.538 +/- 0.017, PaCO2 decreased from 33.0 +/- 0.5 to 20.9 +/- 1.2 torr, and [HCO3-] decreased from 20.9 +/- 0.3 to 17.2 +/- 0.4 mEq/l. Minimal base excess change, together with a rapid return to normal parameters upon recooling to 25 degrees C, suggests that the stress is almost exclusively respiratory, with little metabolic involvement. Analysis of serial exposures shows no acclimatization effect in acid-base status. This suggests the possible existence of natural acclimation to heat in dogs maintained in a warm climate, permitting excellent tolerance of hot, arid conditions with limited acid-base disturbance.

Acclimatization↗
PubMed1985

Seasonal adaptation of brown adipose tissue in the Djungarian Hamster.

The composition and oxidative capacity of brown adipose tissue (BAT) were investigated in Djungarian hamsters kept under natural photoperiod, either indoors at neutral Ta (23 degrees C) or under outdoor conditions. BAT comprises up to 5% of the body weight in summer/indoor hamsters, with lipid representing 86% of the total tissue mass. Tissue mass and thermogenic capacity are inversely related during seasonal adaptation: 30% decrease of total DNA, accompanied by extensive lipid depletion, reduces the amount of BAT by almost 60% during acclimatization from summer/indoor to winter/outdoor conditions. Mitochondrial protein in BAT is increased by a factor of 2.6 concomitantly, and by a factor of 4 when related to body weight (body weight reduction 36%). Cytochrome oxidase activity in different brown fat deposits varies by up to 150% in summer/indoor hamsters; depending on the fat pad, the enzyme activity is increased 200%-700% during adaptation to winter/outdoor conditions. Natural photoperiod is decisive in determining the seasonal adaptation of DNA content in BAT and of body weight. Short photoperiod alone may lead to depletion of lipid content of BAT and thus decrease the tissue mass practically to the lowest seasonal level, even though both parameters may be also influenced by Ta. One third of the maximum adaptive increase of tissue mitochondria may be attributed to seasonal changes in photoperiod and up to two thirds to Ta. Photoperiod establishes a fixed fundament of slow-reacting functional adaptation of BAT, whereas the effect of decreased Ta depends on the rate and duration of cold influence.

Acclimatization↗
PubMed1995

Free and total thyroid hormones in humans at extreme altitude.

Alterations in circulatory levels of total T4 (TT4), total T3 (TT3), free T4 (FT4), free T3 (FT3), thyrotropin (TSH) and T3 uptake (T3U) were studied in male and female sea-level residents (SLR) at sea level, in Armed forces personnel staying at high altitude (3750 m) for prolonged duration (acclimatized low-landers, ALL) and in high-altitude natives (HAN). Identical studies were also performed on male ALL who trekked to an extreme altitude of 5080 m and stayed at an altitude of more than 6300 m for about 6 months. The total as well as free thyroid hormones were found to be significantly higher in ALL and HAN as compared to SLR values. Both male as well as female HAN had higher levels of thyroid hormones. The rise in hormone levels in different ALL ethnic groups drawn from amongst the southern and northern parts of the country was more or less identical. In both HAN and ALL a decline in FT3 and FT4 occurred when these subjects trekked at subzero temperatures to extreme altitude of 5080 m but the levels were found to be higher in ALL who stayed at 6300 m for a prolonged duration. Plasma TSH did not show any appreciable change at lower altitudes but was found to be decreased at extreme altitude. The increase in thyroid hormones at high altitude was not due to an increase in hormone binding proteins, since T3U was found to be higher at high altitudes.(ABSTRACT TRUNCATED AT 250 WORDS)

Acclimatization↗
PubMed1993

Seasonal acclimation of prairie deer mice.

Prairie deer mice responded to long nights by reducing their metabolic rates, core temperatures, thermal conductances and incremental metabolic responses to cold stimulus, while increasing their capacities for nonshivering thermogenesis. Some winter animals spontaneously entered daily torpor in the mornings and thereby further reduced their metabolic rates and core temperatures. Provision of exogenous melatonin (by subdermal implants) mimiced short photoperiod effects on metabolic rates and core temperatures of wild-caught, laboratory maintained animals. Provision of supplemental dietary tryptophan to laboratory animals conditioned to natural light cycles mimiced metabolic effects of long nights in summer animals, and further reduced metabolic rates of winter mice, but did not affect their core temperature levels. Newly caught, laboratory maintained deer mice responded to natural seasonal clues of short-photoperiod and increased dietary tryptophan by reducing their resting energy requirements through both lower metabolic and lower core temperature levels. Short photoperiod and seasonal change also promoted gonadal involution, and resulted in more socially tolerant huddling by mice with reduced core temperature. Reduced 24-hour LH excretion rates were also observed in winter animals which were exposed to seasonal light cycles at warm (25 degrees C) room temperatures. We propose that seasonal acclimatization involves pineal effects on sex hormone-influenced social behaviors and on resting metabolism. These effects serve to conserve resting energy expenditure and promote hypothermic insulation by wild prairie deer mice.

Acclimatization↗
PubMed1977

Corticotropin and nonshivering thermogenesis.

Chronic treatment with corticotropin led to reduced calorigenic effect of norepinephrine in cold acclimatized rats, but potentiated its effect in controls. This inhibitory effect was not due to the observed decrease in corticosterone plasma level, as it was shown by metopirone administration. It is concluded that corticotropin could have a competitive action on receptor sites mediating the calorigenic effect of norepinephrine in nonshivering thermogenesis.

Acclimatization↗
PubMed1983

Equine anhidrosis: a review of pathophysiologic mechanisms.

Anhidrosis is loss of the ability to sweat. The problem is seen in horses kept in a hot humid climate, and it may cause severe impairment of thermoregulation in the equine athlete. British Thoroughbreds imported to her tropical colonies are the earliest recorded cases, and since then the syndrome has come to be described as one of Thoroughbreds, usually performance athletes, undergoing acclimatization to heat and humidity. A recent epidemiologic study of cases in Florida has shown, however, that many different breeds, and long time inhabitants of a hot climate, may be affected. Equine sweat glands are of the apocrine type, and sweating is stimulated by direct local release of epinephrine from adrenergic nerve endings and by circulating epinephrine. Lack of sweating could be due to a number of possible flaws in a sequence from central nervous stimulation through sweat stimulation and secretion to delivery of sweat to the skin surface. The most likely possibilities are inadequate sweat gland response due to habituation of receptors to a high circulating level of epinephrine and occlusion of the sweat ducts by keratin plugs. Hormonal or metabolic imbalance may play a role both in the onset and secondary signs associated with anhidrosis.

Acclimatization↗
PubMedDate not supplied

Stability of heartbeat interval distributions in chronic high altitude hypoxia.

Recent studies of nonlinear dynamics of the long-term variability of heart rate have identified nontrivial long-range correlations and scale-invariant power-law characteristics (l/f noise) that were remarkably consistent between individuals and were unrelated to external or environmental stimuli (Meyer et al., 1998a). The present analysis of complex nonstationary heartbeat patterns is based on the sequential application of the wavelet transform for elimination of local polynomial nonstationary behavior and an analytic signal approach by use of the Hilbert transform (Cumulative Variation Amplitude Analysis). The effects of chronic high altitude hypoxia on the distributions and scaling functions of cardiac intervals over 24 hr epochs and 4 hr day/nighttime subepochs were determined from serial heartbeat interval time series of digitized 24 hr ambulatory ECGs recorded in 9 healthy subjects (mean age 34 yrs) at sea level and during a sojourn at high altitude (5,050 m) for 34 days (Ev-K2-CNR Pyramid Laboratory, Sagarmatha National Park, Nepal). The results suggest that there exists a hidden, potentially universal, common structure in the heterogeneous time series. A common scaling function with a stable Gamma distribution defines the probability density of the amplitudes of the fluctuations in the heartbeat interval time series of individual subjects. The appropriately rescaled distributions of normal subjects at sea level demonstrated stable Gamma scaling consistent with a single scaled plot (data collapse). Longitudinal assessment of the rescaled distributions of the 24 hr recordings of individual subjects showed that the stability of the distributions was unaffected by the subject's exposure to a hypobaric (hypoxic) environment. The rescaled distributions of 4 hr subepochs showed similar scaling behavior with a stable Gamma distribution indicating that the common structure was unequivocally applicable to both day and night phases and, furthermore, did not undergo systematic changes in response to high altitude. In contrast, a single function stable over a wide range of time scales was not observed in patients with congestive heart failure or patients after cardiac transplantation. The functional form of the scaling in normal subjects would seem to be attributable to the underlying nonlinear dynamics of cardiac control. The results suggest that the observed Gamma scaling of the distributions in healthy subjects constitutes an intrinsic dynamical property of normal heart function that would not undergo early readjustment or late acclimatization to extrinsic environmental physiological stress, e.g., chronic hypoxia.

Acclimatization↗
PubMed1985

Transcutaneous PO2 monitoring during a Himalayan ascent.

Transcutaneous PO2 (PtcO2) measurements were taken daily on seven subjects during two nine day ascents of the Himalayas to an altitude of 4,579 meters. Five of the subjects lived in areas under 450 meters (Group I), while two subjects lived at an altitude of 3,100 meters (Group II). The PtcO2 values decreased with increasing altitude. The Group II subjects had PtcO2 values greater than the Group I subjects and the difference became greater with increasing altitude. The linear regression lines of PtcO2/pbO2 to Group I during ascent and decent were lower than the regression line for Group II (PbO2 is the barometric oxygen partial pressure). The regression line for Group I data during the second half of the trek approached the data for Group II. We conclude that acclimatization to high altitude is possibly associated with increasing peripheral tissue oxygenation as assessed by PtcO2 values.

Acclimatization↗
PubMed2002

Production of herbicide-resistant transgenic Panax ginseng through the introduction of the phosphinothricin acetyl transferase gene and successful soil transfer.

Herbicide-resistant transgenic Panax ginseng plants were produced by introducing the phosphinothricin acetyl transferase (PAT) gene that confers resistance to the herbicide Basta (bialaphos) through Agrobacterium tumefaciens co-cultivation. Embryogenic callus gathered from cotyledon explants of P. ginseng were pre-treated with 0.5 M sucrose or 0.05 M MgSO(4 )before Agrobacterium infection. This pre-treatment process markedly enhanced the transient expression of the beta-glucuronidase (GUS) gene. Embryogenic callus was initially cultured on MS medium supplemented with 400 mg/l cefotaxime for 3 weeks and subsequently subcultured five times to a medium containing 25 mg/l kanamycin and 300 mg/l cefotaxime. Somatic embryos formed on the surfaces of kanamycin-resistant callus. Upon development into the cotyledonary stage, these somatic embryos were transferred to a medium containing 50 mg/l kanamycin and 5 mg/l gibberellic acid to induce germination and strong selection. Integration of the transgene into the plants was confirmed by polymerase chain reaction and Southern analyses. Transfer of the transgenic ginseng plantlets to soil was successfully accomplished via acclimatization in autoclaved perlite. Not all of the plantlets survived in soil that had not been autoclaved because of fungal infection, particularly in the region between the roots and leaves. Transgenic plants growing in soil were observed to be strongly resistant to Basta application.

Acclimatization↗
PubMed2003

Developing a scale-up system for the micropropagation of cucumber (Cucumis sativus L.): the effect of growth retardants, liquid culture and vessel size.

We investigated the effect of the growth retardant flurprimidol, the phase of the culture medium (solid versus liquid) and the size of the liquid culture vessel (250-ml flask versus 2.5-l airlift bioreactor) on the micropropagation of cucumber (Cucumis sativus L.) from nodal explants. Flurprimidol at concentrations of 0.1-2 mg l(-1) caused considerable growth retardation but increased, albeit slightly, the number of branches and buds and stimulated (solid medium) or reduced (liquid medium) the accumulation of NO(3)-and PO(4)(3-). Flurprimidol had varying effects on the accumulation of soluble sugars and antioxidant compounds. Bioreactor-derived plants showed an increased fresh weight and size but a decreased content of macronutrients, solid sugars, ascorbic acid and free antioxidant phenolics. The majority (95%) of the plants were successfully acclimatized after being graft on squash. The perspective for an efficient, commercial-level use of bioreactors in combination with growth retardants of this commercially important vegetable species is discussed.

Acclimatization↗
PubMed2004

Control of development and valepotriate production by auxins in micropropagated Valeriana glechomifolia.

Valeriana glechomifolia is a plant species endemic to southern Brazil that accumulates valepotriates, which are terpene derivatives, in all of its organs. Valepotriates are the presumed sedative generic components of the pharmaceutically used species of Valeriana. The influence of various concentrations of the auxins indole-3-acetic acid, indole-3-butyric acid and alpha-naphthaleneacetic acid on the growth of micropropagated V. glechomifolia was investigated under conditions of transient and continuous exposure. Changes in the development of roots and shoots as well as the production of the valepotriates acevaltrate, valtrate and didrovaltrate (analyzed by high-performance liquid chromatography) were evaluated. The best performance in valepotriate production, growth and survival under ex vitro conditions following plant acclimatization was achieved in the continuous presence of 5.71 microM IAA. When cultured in medium containing IAA plants produced stable levels of valepotriates throughout the entire cultivation period.

Acclimatization↗
PubMed2002

Geographic variation of freeze-tolerance in the earthworm Dendrobaena octaedra.

Freeze-tolerance and some of the underlying biochemical defence mechanisms in the earthworm Dendrobaena octaedra was investigated. Survival after slow cooling to -2 degrees C, -4 degrees C, or -6 degrees C was analysed in D. octaedra from three geographic regions representing large differences in winter temperature (Denmark, Finland and Greenland). A large variation in freeze-tolerance between the three populations of D. octaedra was found. Earthworms from the northern populations (Finland and Greenland) tolerated lower temperatures (-6 degrees C) than earthworms from the Danish population (poor survival at -4 degrees C and -2 degrees C). In the Finnish population, freezing led to the production of high concentrations of glucose, which reached values much higher than controls (94 mg g(-1) vs. 2 mg g(-1) dry weight). Other potential cryoprotectants were not elevated after freezing. The Danish and Greenlandic populations had substantially lower mean glucose levels after freezing than the Finnish population (about 15 mg g(-1)). Danish earthworms rapidly frozen did not accumulate glucose, and did not survive freezing at -2 degrees C. Danish earthworms exposed to osmotic stress in Ringer's solutions, containing different concentrations of glycerol, showed significantly elevated glucose levels, but did not survive rapid freezing. It was determined if freezing had an influence on the reproduction of the earthworms. After warming to summer temperatures (15 degrees C), survivors of freezing produced viable cocoons. In a field experiment it was tested if natural acclimatization during autumn and winter months had an effect on freeze-tolerance in the Danish population. There was a significant increase of post-freeze survival during this period. The results of the freezing experiments are discussed in relation to the general ecology of D. octaedra.

Acclimatization↗
PubMed2005

Seasonal thermoregulatory responses in mammals.

This study examined the proportional seasonal winter adjustments of total and mass-specific basal power (watts and watts g-1, respectively), thermal conductance (watts g-1 degrees C-1), non-shivering thermogenesis capacity (ratio of NST/basal power), body temperature ( degrees C), and body mass (g) of mammals. The responses are best summarized for three different body size classes; small mammals (<100 g), intermediate-sized mammals (0.1-10 kg), and large mammals (>10 kg). The principal adjustments of the small mammals center on energy conservation, especially the Dehnel Effect, the winter reduction in body size of as much as 50%, accompanied by reductions in mass-specific basal power. On average, these reductions reduce the total basal power approximately in direct proportion to the mass reductions. Reductions in mass-specific basal power are matched by concomitant reductions in conductance to maintain the setpoint body temperature during winter. The overall thermoregulatory adjustments in small mammals serve to (a) lower overall winter power consumption, (b) maintain the setpoint body temperature, and (c) lower the lower critical limit of thermoneutrality and hence thermoregulatory costs. In intermediate-size mammals, the seasonal response is centered more on increasing thermogenic capacity by increasing basal power and NST capacity, accompanied by predictable and large reductions in conductance. The Dehnel effect is negligible. Very large mammals undergo the largest reductions in total and mass-specific basal power and conductance. However, there are too few data to resolve whether the reductions in total basal power can be attributed to the Dehnel effect, because the moderate decreases in body mass may also be caused by nutritional stress. Apart from the seasonal changes in basal power, these observations are consistent with the predictions of Heldmaier's seasonal acclimatization model.

Acclimatization↗
PubMed1999

Effects of temperature and photoperiod on thermogenesis in plateau pikas (Ochotona curzoniae) and root voles (Microtus oeconomus).

We examined the effects of temperature and photoperiod on metabolic thermogenesis and the thermogenic characteristics of brown adipose tissue in plateau pikas (Ochotona curzoniae) and root voles (Microtus oeconomus), the dominant species of small mammals in the alpine meadow ecosystems on the Qinghai-Tibetan Plateau. Pikas and voles were acclimated in the following groups: (1) Long day-warm temperature (16L:8D, 23 degrees C) (2) Long day-cold temperature (16L:8D, 5 degrees C), (3) short day-warm temperature (8L:16D, 23 degrees C), and (4) short day-cold temperature (8L:16D, 5 degrees C). Both temperature and photoperiod were important environmental cues for changes in thermogenesis for both species. Low temperature and short photoperiod induced increases in metabolic rate, nonshivering thermogenesis (NST), mitochondrial protein contents of brown adipose tissue, and cytochrome C oxidase activity of brown adipose tissue mitochondria in both species. Plateau pikas were more sensitive to cold (79% of the total NST response) than to short photoperiod (21%), while root voles were more sensitive to short photoperiod (60% of the total NST response) than to cold (40%), although cold clearly enhanced thermogenesis. Their thermogenic characteristics correlated with their preferred habitats: plateau pikas are found mainly in more exposed microhabitats in open sunny meadow, while root voles live in more sheltered microhabitats in relatively closed shrub. Our results also showed that temperature and photoperiod combined induce thermogenic adjustments in both species in seasonal acclimatization in their alpine meadow macrohabitat.

Acclimatization↗
PubMed2000

Effects of breathing control on cardiocirculatory modulation in Caucasian lowlanders and Himalayan Sherpas.

This study was performed to investigate the influence of breathing control on the autonomic cardiac regulation at high altitude in adapted and non-adapted awake subjects. We recorded electrocardiogram and pulse oximetry in 14 short-term acclimatized lowlanders and 14 Himalayan Sherpas during resting conditions at an altitude of 5,050 m. Spectrum analysis was performed on synchronized 15 min periods of R-R intervals and the oxygen saturation of arterial blood (SaO2). Despite mean SaO2 being similar in lowlanders and Himalayan Sherpas [78.5 (SD 7.0)% compared to 79.4 (SD5.8)%, respectively], fluctuations in SaO2 were significantly increased in lowlanders compared to Sherpas, thus indicating an unstable regulation of respiration control in lowlanders. Regression analysis demonstrated a significant relationship between spectrum power of SaO2 and the relative power of R-R intervals in the frequency band between 0.01 and 0.08 Hz in lowlanders, but not in Sherpas. Our results demonstrate differences in respiratory and autonomic cardiac control between non-adapted lowlanders and Himalayan high-altitude residents and indicate that unstable breathing control during chronic hypobaric hypoxia is significantly correlated with the autonomic cardiocirculatory regulation.

Acclimatization↗
PubMedDate not supplied

Extracellular pH defense against lactic acid in normoxia and hypoxia before and after a Himalayan expedition.

The extracellular pH defense against the lactic acidosis resulting from exercise can be estimated from the ratios -delta[La].delta pH-1 (where delta[La] is change in lactic acid concentration and delta pH is change in pH) and delta[HCO3-].delta pH-1 (where delta[HCO3-] is change in bicarbonate concentration) in blood plasma. The difference between -delta[La].delta pH-1 and delta[HCO3-].delta pH-1 yields the capacity of available non-bicarbonate buffers (mainly hemoglobin). In turn, delta[HCO3-].delta pH-1 can be separated into a pure bicarbonate buffering (as calculated at constant carbon dioxide tension) and a hyperventilation effect. These quantities were measured in 12 mountaineers during incremental exercise tests before, and 7-8 days (group 1) or 11-12 days (group 2) after their return from a Himalayan expedition (2800-7600 m altitude) under conditions of normoxia and acute hypoxia. In normoxia -delta[La].delta pH-1 amounted to [mean (SEM)] 92 (6) mmol.l-1 before altitude, of which 19 (4), 48 (1) and 25 (3) mmol.l-1 were due to hyperventilation, bicarbonate and non-bicarbonate buffering, respectively. After altitude -delta[La].delta pH-1 was increased to 128 (12) mmol.l-1 (P < 0.01) in group 1 and decreased to 72 (5) mmol.l-1 in group 2 (P < 0.05), resulting mainly from apparent large changes of non-bicarbonate buffer capacity, which amounted to 49 (14) mmol.l-1 in group 1 and to 10 (2) mmol.l-1 in group 2. In acute hypoxia the apparent increase in non-bicarbonate buffers of group 1 was even larger [140 (18) mmol.l-1]. Since the hemoglobin mass was only modestly elevated after descent, other factors must play a role. It is proposed here that the transport of La- and H+ across cell membranes is differently influenced by high-altitude acclimatization.

Acclimatization↗