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PubMed1970

The environmental control of cold acclimation in apple.

The role of photoperiod and temperature in the cold acclimation of living Haralson apple (Pyrus malus L.) bark was studied in the autumn under field conditions in Minnesota. Whole trees, or different parts of the same tree, were exposed to either natural conditions, artifically lengthened days, or artificially warmed nights, or they were subjected to manual leaf removal. The results indicate that acclimation occurs in two stages which are induced by short days and frost (or low temperature), respectively. Leaves were stimulated by short days to produce translocatable substance(s) which promoted cold acclimation of the living bark. Leaves of plants grown under long days were the source of a translocatable substance(s) which inhibited acclimation. The second stage of hardiness, induced by frost (or low temperature), did not involve translocatable factors.Inductive short days could overcome the effect of high temperatures, and low temperatures could overcome the effect of noninductive long days in promoting the first stage of acclimation to -30 C. Frost was necessary for maximum hardiness to -55 C. Plants grown in a greenhouse, in the autumn, under long days and high temperatures acclimated slightly in spite of the noninductive conditions. Short days and frost (or low temperatures) appeared to regulate different and independent endogenous acclimation processes.

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PubMed1976

Alterations in Chloroplast Thylakoids during Cold Acclimation.

Freeze-fracture electron microscopy reveals a decreased particle concentration on the inner fracture face of acclimated thylakoids, suggestive of some alteration(s) in the hydrophobic region. Sonic oscillation causes a reversal of the altered particle concentration in acclimated thylakoids and suggests that increases in unsaturation of fatty acids can, at most, account for only part of the altered particle concentration. The particles on the inner fracture face of acclimated thylakoids are of one size group (+/- 140 A) as compared to two size groups (+/- 100 A and +/- 165 A) for nonacclimated thylakoids. The paracrystalline array might be associated with the acclimated state of thylakoids. Nonacclimated thylakoids require 50 mm sucrose for maximum protection of light-dependent proton uptake, while acclimated thylakoids require 25 mm sucrose, and the protection afforded acclimated thylakoids during a freeze-thaw cycle is greater. Sucrose is required for alterations in acclimated thylakoids to be manifested. Apparently increased hardiness is not only associated with changes in cellular environment but also alterations in membranes.

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PubMed1980

Characteristics of Cold Acclimation and Deacclimation in Tuber-bearing Solanum Species.

The effect of temperatures on cold acclimation and deacclimation in foliage tissues was studied in Solanum commersonii (Oka 4583), a tuber-bearing potato. The threshold temperature for cold acclimation was about 12 C. In a temperature range of 2 to 12 C, the increase in hardiness was dependent on the acclimating temperature; the lower the acclimating temperature, the more hardiness achieved. A day/night temperature of 2 C, regardless of photoperiod, appeared to the optimum acclimating temperature for the Solanum species studied. A subfreezing temperature hardened plants less effectively. The maximum level of hardiness could be reached after 15 days of cold acclimation. However, it took only 1 day to deacclimate the hardened plants to a preacclimation level when plants were subjected to a warm regime from cold. The degree of deacclimation was dependent on the temperature of the warm regime.Based on cold tolerance and the capacity to acclimate to cold, tuber-bearing Solanum species could be grouped into five categories. Chilling injury was also observed in some of the tuber-bearing Solanum species.

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PubMed1987

Plasma Membrane Lipid Alterations Associated with Cold Acclimation of Winter Rye Seedlings (Secale cereale L. cv Puma).

Highly enriched plasma membrane fractions were isolated from leaves of nonacclimated (NA) and acclimated (ACC) rye (Secale cereale L. cv Puma) seedlings. Collectively, free sterols, steryl glucosides, and acylated steryl glucosides constituted >50 mole% of the total lipid in both NA and ACC plasma membrane fractions. Glucocerebrosides containing hydroxy fatty acids constituted the major glycolipid class of the plasma membrane, accounting for 16 mole% of the total lipid. Phospholipids, primarily phosphatidylcholine and phosphatidylethanolamine with lesser amounts of phosphatidylglycerol, phosphatidic acid, phosphatidylserine, and phosphatidylinositol, comprised only 32 mole% of the total lipid in NA samples. Following cold acclimation, free sterols increased from 33 to 44 mole%, while steryl glucosides and acylated steryl glucosides decreased from 15 to 6 mole% and 4 to 1 mole%, respectively. Sterol analyses of these lipid classes demonstrated that free beta-sitosterol increased from 21 to 32 mole% (accounting for the increase in free sterols as a class) at the expense of sterol derivatives containing beta-sitosterol. Glucocerebrosides decreased from 16 to 7 mole% of the total lipid following cold acclimation. In addition, the relative proportions of associated hydroxy fatty acids, including 22:0 (h), 24:0 (h), 22:1 (h), and 24:1 (h), were altered. The phospholipid content of the plasma membrane fraction increased to 42 mole% of the total lipid following cold acclimation. Although the relative proportions of the individual phospholipids did not change appreciably after cold acclimation, there were substantial differences in the molecular species. Di-unsaturated molecular species (18:2/18:2, 18:2/18:3, 18:3/18:3) of phosphatidylcholine and phosphatidylethanolamine increased following acclimation. These results demonstrate that cold acclimation results in substantial changes in the lipid composition of the plasma membrane.

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PubMed1992

Solute Accumulation and Compartmentation during the Cold Acclimation of Puma Rye.

During cold acclimation of Puma rye (Secale cereale L. cv Puma), the intracellular osmotic potential nearly doubles. During this period, the accumulation of glycinebetaine, proline, and soluble sugars was monitored. The amount of glycinebetaine increased from 290 to 1300 micrograms per gram fresh weight during the 4-week acclimation period. Proline content did not change during the first 3 weeks of acclimation but then increased from 27 to 580 micrograms per gram fresh weight during the next 3 weeks. The total soluble sugar content more than doubled by the second week of cold acclimation, increasing from 11 to 26 milligrams per gram fresh weight. Most of this increase can be attributed to the accumulation of sucrose and raffinose, whose levels increased from 2.4 and 0 to 11 and 5 milligrams per gram fresh weight, respectively. The content of monosaccharides, predominantly glucose, remained at a constant 10 milligrams per gram fresh weight throughout the acclimation period. A comparison of the sugar content of protoplasts versus vacuoles isolated from cold-acclimated leaves revealed that the extravacuolar volume contained monosaccharides, sucrose, and raffinose. Thus, the increased amounts of sucrose and raffinose that occur during cold acclimation are present in compartments external to the vacuole and may contribute to cryoprotection.

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PubMed2007

Impact of temperature on the relationship between respiration and nitrogen concentration in roots: an analysis of scaling relationships, Q10 values and thermal acclimation ratios.

* The impact of nitrogen (N) supply on the temperature response of root respiratory O(2) uptake (R) was assessed in several herbaceous species grown in solution culture. Warm-grown (25 : 20 degrees C, day:night) plants differing in root N concentration were shifted to 13 : 8 degrees C for 7 d to cold-acclimate. * Log-log plots of root R vs root N concentration both showed that R increased with increasing tissue N concentration, irrespective of the growth temperature. Although the regression slopes of the log-log plots did not differ between the warm-grown and cold-acclimated plants, cold-acclimated plants did exhibit a higher y-axis intercept than their warm-grown counterparts. This suggests that cold acclimation of root R is not entirely dependent on cold-induced increases in tissue N concentration and that scaling relationships (i.e. regression equations fitted to the log-log plots) between root R and N concentration are not fixed. * No systematic differences were found in the short-term Q(10) (proportional change in R per 10 degrees C change in temperature), or degree of cold acclimation (as measured by the proportional difference between warm- and cold-acclimated roots) among roots differing in root N concentration. The temperature response of root R is therefore insensitive to tissue N concentration. * The insensitivity of Q(10) values and acclimation to tissue N concentration raises the possibility that root R and its temperature sensitivity can be predicted for a range of N supply scenarios.

Acclimatization↗

PubMed2004

Sustained and generalized extracellular fluid expansion following heat acclimation.

We measured intra- and extravascular body-fluid compartments in 12 resting males before (day 1; control), during (day 8) and after (day 22) a 3-week, exercise-heat acclimation protocol to investigate plasma volume (PV) changes. Our specific focus was upon the selective nature of the acclimation-induced PV expansion, and the possibility that this expansion could be sustained during prolonged acclimation. Acclimation was induced by cycling in the heat, and involved 16 treatment days (controlled hyperthermia (90 min); core temperature = 38.5 degrees C) and three experimental exposures (40 min rest, 96.9 min (s.d. 9.5 min) cycling), each preceded by a rest day. The environmental conditions were a temperature of 39.8 degrees C (s.d. 0.5 degrees C) and relative humidity of 59.2% (s.d. 0.8%). On days 8 and 22, PV was expanded and maintained relative to control values (day 1: 44.0 +/- 1.8; day 8: 48.8 +/- 1.7; day 22: 48.8 +/- 2.0 ml kg(-1); P < 0.05). The extracellular fluid compartment (ECF) was equivalently expanded from control values on days 8 (279.6 +/- 14.2 versus 318.6 +/- 14.3 ml kg(-1); n= 8; P < 0.05) and 22 (287.5 +/- 10.6 versus 308.4 +/- 14.8 ml kg(-1); n= 12; P < 0.05). Plasma electrolyte, total protein and albumin concentrations were unaltered following heat acclimation (P > 0.05), although the total plasma content of these constituents was elevated (P < 0.05). The PV and interstitial fluid (ISF) compartments exhibited similar relative expansions on days 8 (15.0 +/- 2.2%versus 14.7 +/- 4.1%; P > 0.05) and 22 (14.4 +/- 3.6% versus 6.4 +/- 2.2%; P= 0.10). It is concluded that the acclimation-induced PV expansion can be maintained following prolonged heat acclimation. In addition, this PV expansion was not selective, but represented a ubiquitous expansion of the extracellular compartment.

Acclimatization↗

PubMed1980

Parallel regression of cold-induced changes in ultrastructure, composition, and properties of brown adipose tissue mitochondria during recovery of rats from acclimation to cold.

When cold-acclimated rats are returned to a thermoneutral environment (28 degrees C) after 5 weeks at 4 degrees C, the size of the enlarged interscapular brown adipose tissue decreases during the 1st week. The altered composition of the mitochondria, however, reverts to normal during deacclimation more rapidly than the size of the tissue: a marked decrease in binding of purine nucleotides occurs by 3 days and a decrease in the proportion of polypeptides of molecular weight 25 000-35 000 occurs by 1 day. The very rapid decrease in the polypeptides, compared with the slower decrease in binding of purine nucleotides, known to be to a 32 000 polypeptide, suggests an initial conversion of masked binding sites to another form. Mitochondria isolated from cold-acclimated rats are larger than those of warm-acclimated rats, a difference which appears slowly during acclimation to cold, requiring 7-14 days for full development; during deacclimation the increase in size disappears by 7 days. The ultrastructure of mitochondria isolated from cold-acclimated rats shows inmerices arranged in numerous, narrow, interconnecting parallel sheets in contrast to the sparser broad tubes and bands in mitochondria isolated from warm-acclimated rats. This difference in ultrastructure develops in a biphasic manner during acclimation to cold: an initial appearance (1-12 h) of the parallel arrangement, associated with a transient increase in size, is no longer apparent at 1-3 days and reappears only after 7-14 days. During deacclimation the reversal to the tubular form requires approximately 7 days. During deacclimation the changes in brown adipose tissue mitochondrial composition, structure, size, and properties and in tissue size appear to occur independently.

Acclimatization↗

PubMed1991

Oxygen uptake of isolated toad skin epithelium: micromeasurement and effect of ionic acclimation.

Oxidative metabolism of isolated toad skin epithelium (Bufo viridis) was investigated in vitro under open-circuit conditions using the spectrophotometric oxyhemoglobin micromethod. This highly sensitive technique has been adapted for studying several epithelia in parallel and for detecting possible regional variations of oxygen uptake in individual epithelium. Changes in the proportion of mitochondria-rich cells (MRC) by ionic acclimation affected oxidative metabolism under nontransporting condition. After acclimation of animals to either NaNO3 or NaCl solutions (100 mmol/l, for greater than 2 wk), the number of MRC per square millimeter in epithelia from nonacclimated and NaNO3- and NaCl-acclimated animals was 350 +/- 113, 460 +/- 196, and 107 +/- 52, respectively. O2 uptake of nonacclimated and NaNO3-acclimated epithelia was significantly higher than that of NaCl-acclimated epithelia (i.e., 0.89 and 0.90 vs. 0.57 nmol O2.h-1.mm-2, respectively). The correlation established between O2 uptake and number of MRC allowed evaluation of the respiration rate of one single MRC, i.e., approximately 1 pmol O2/h. The lowest mitochondrial oxidative activity was found in the epithelia from NaCl-acclimated toads where the uncoupler 2,4-dinitrophenol (50 mumols/l) had the highest relative stimulatory effect (+114%). Acetazolamide (50 mumols/l), a potent inhibitor of carbonic anhydrase mainly present in the MRC, reduced selectively by 31% O2 uptake of the MRC-rich epithelia (NaNO3 acclimated). O2 uptake increased significantly by approximately 80% when basolateral pH increased from 5.8 to 7.8, but did not depend on apical pH. These findings indicate that under nontransporting (open-circuit) conditions, aerobic metabolism of the isolated toad skin epithelium is related to the density and/or characteristics of the MRC.(ABSTRACT TRUNCATED AT 250 WORDS)

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PubMed1986

Adaptive changes in insulin and glucagon secretion during cold acclimation in the rat.

Arginine-stimulated insulin and glucagon outputs from isolated perfused pancreata of warm-acclimated and 2-, 4-, and 6-wk cold-acclimated rats (4 degrees C) were determined to assess whether observed changes in these parameters were a result of cold exposure per se or a part of the adaptive process of cold acclimation. Progressive and sequential changes were seen in both insulin and glucagon outputs. At 2 wk cold acclimation, glucagon rose and insulin output tended to fall, at 4 wk, glucagon output remained elevated and insulin output was further reduced, and at 6 wk, glucagon output had returned to control levels, whereas insulin output was substantially further reduced. These changes resulted in reduction of the insulin-to-glucagon molar ratio of the total arginine-induced output from 7.27 +/- 1.76 (SE) in the warm acclimate to 2.31 +/- 0.79 (SE) at 2 wk, 1.42 +/- 0.29 (SE) at 4 wk, and 1.26 +/- 0.21 (SE) at 6 wk cold acclimation. The data do not provide in vitro support for the hypothesis that changes in pancreatic hormone secretion in vivo are a consequence of cold exposure and not cold acclimation.

Acclimatization↗

PubMed2003

Acclimation of S aurata to various salinities alters energy metabolism of osmoregulatory and nonosmoregulatory organs.

The impact of different environmental salinities on the energy metabolism of gills, kidney, liver, and brain was assessed in gilthead sea bream (Sparus aurata) acclimated to brackish water [BW, 12 parts/thousand (ppt)], seawater (SW, 38 ppt) and hyper saline water (HSW, 55 ppt) for 14 days. Plasma osmolality and levels of sodium and chloride presented a clear direct relationship with environmental salinities. A general activation of energy metabolism was observed under different osmotic conditions. In liver, an enhancement of glycogenolytic and glycolytic potential was observed in fish acclimated to BW and HSW compared with those in SW. In plasma, an increased availability of glucose, lactate, and protein was observed in parallel with the increase in salinity. In gills, an increased Na+-K+-ATPase activity, a clear decrease in the capacity for use of exogenous glucose and the pentose phosphate pathway, as well as an increased glycolytic potential were observed in parallel with the increased salinity. In kidney, Na+-K+-ATPase activity and lactate levels increased in HSW, whereas the capacity for the use of exogenous glucose decreased in BW- and HSW- acclimated fish compared with SW-acclimated fish. In brain, fish acclimated to BW or HSW displayed an enhancement in their potential for glycogenolysis, use of exogenous glucose, and glycolysis compared with SW-acclimated fish. Also in brain, lactate and ATP levels decreased in parallel with the increase in salinity. The data are discussed in the context of energy expenditure associated with osmotic acclimation to different environmental salinities in fish euryhaline species.

Acclimatization↗

PubMed1981

Effects of temperature acclimation on crayfish hemocyanin oxygen binding.

Crayfish, Pacifastacus leniusculus, were acclimated to 10, 20, and 25 degrees C for 1 mo. Hemocyanin from animals at these three acclimation temperatures showed distinctly different oxygen binding patterns. At any particular set of test temperature and pH, hemocyanin from 10 degrees C-acclimated animals had the lowest oxygen affinity and the greatest cooperativity, whereas hemocyanin from 25 degrees C-acclimated animals had the highest oxygen affinity and the lowest cooperativity. When tested at their own acclimation temperature, and at normal hemolymph pH for that temperature, all three hemocyanins showed oxygen pressure for half-saturation of hemoglobin of 6-7 Torr. Thus acclimation keeps oxygen affinity centered around a narrow range of values. The acclimation response probably eliminates hemocyanin oxygen affinity as a major factor in the decline of oxygen uptake ability in the crayfish above 20 degrees C. The structural basis for the observed functional changes in the hemocyanin is not yet clear.

Acclimatization↗

PubMed1995

Cold acclimation-recruited nonshivering thermogenesis: the Syrian hamster is not an exception.

Biochemical evidence from in vitro studies of brown adipose tissue in Syrian hamsters indicates a significant degree of recruitment of the tissue as an effect of cold acclimation. However, earlier in vivo studies indicate a lack of recruitment of nonshivering thermogenesis in the intact animal as a result of cold acclimation. Because of this apparent discrepancy, the occurrence of cold acclimation-recruited nonshivering thermogenesis in hamsters was investigated. Hamsters were cold acclimated to 6 degrees C or remained at 24 degrees C (controls), and their thermogenic response was investigated in an open-circuit system at 24 degrees C. Cold acclimation resulted in a small increase in resting metabolic rate and a major increase in the thermogenic response to norepinephrine (61% increase over resting metabolic rate in controls and 156% increase in cold-acclimated animals). The absolute beta 3-specific adrenergic agonist CGP-12177 also induced a high rate of nonshivering thermogenesis, which was similarly recruited. It was concluded that, concerning the relative effect of recruitment on the capacity for nonshivering thermogenesis, the intact hamsters responded as would be predicted from in vitro experiments. Thus the hamster does not seem to constitute an exception to the general patterns described for other rodents concerning recruitment of nonshivering thermogenesis due to cold acclimation.

Acclimatization↗

PubMed1998

Thermogenesis is beta3- but not beta1-adrenergically mediated in rat brown fat cells, even after cold acclimation.

To examine if acclimation of rats to cold led to alterations in the coupling between different beta-receptor subtypes and thermogenesis in brown fat cells, we investigated the adrenergic response patterns in brown fat cells isolated from warm-acclimated (28 degreesC) and cold-acclimated (4 degreesC) rats. In the cells from warm-acclimated rats, the relative affinities (EC50) for different agonists (isoprenaline, BRL-37344, norepinephrine, CGP-12177, dobutamine, and salbutamol) were those expected from their interaction with a beta3-receptor. The response to norepinephrine was competitively inhibited by propranolol with a pA2 of approximately 6, implying interaction at the beta3-receptor. No evidence for a beta1-receptor-mediated response to the beta1-selective agonist dobutamine could be obtained; the low-affinity response observed was most likely through the beta3-receptor. The beta1-antagonist ICI-89406 could not inhibit a specific fraction of the thermogenic response to norepinephrine. Thus beta3-receptors were the only beta-receptors involved in the control of thermogenesis in brown fat cells from warm-acclimated rats. A modified method of preparation was developed to isolate functional cells from cold-acclimated animals. Also in these cells, the beta-receptor coupled to thermogenesis was the beta3-receptor, although the response was desensitized with an approximately sevenfold shift in EC50 values. The pA2 for propranolol inhibition of norepinephrine-induced thermogenesis was also 6 here, and that for ICI-89406 was 5.5, also implying interaction at the beta3-receptor. Thus acclimation to cold did not alter the beta-adrenergic receptor subtype (beta3) involved in the control of thermogenesis.

Acclimatization↗

PubMed1999

Heat acclimation increases the basal HSP72 level and alters its production dynamics during heat stress.

It has been previously shown that heat acclimation leads to an elevated basal level of 72-kDa heat shock protein (HSP72). Augmented expression of HSP72 is considered as a cytoprotective response. This led us to hypothesize that alterations in the heat shock protein (HSP) defense pathway are an integral part of the heat acclimation repertoire. To investigate this, we studied the temporal profile of basal HSP expression upon acclimation and the dynamics of their accumulation subsequent to acute heat stress (HS). In parallel, HSP72 mRNA level before and after HS was measured. For comparison, HSC mRNA [the constitutive member of 70-kDa HSP (HSP70) family] was measured in similar conditions. Heat acclimation was attained by continuous exposure of rats to 34 degrees C for 0, 1, 2, and 30 days. HS was attained by exposure to 41 or 43 degrees C for 2 h. Thermoregulatory capacity of the rats was defined by rectal temperature, heating rate, and the cumulative heat strain invoked during HS. HSP72 and HSP70 gene transcripts were measured in the left ventricle of the heart by means of Western immunoblotting and semiquantitative RT-PCR, respectively. The resultant acclimatory change comprised a higher resting level of the encoded 72-kDa protein (Delta175%, P < 0.0001). After HS, peak HSP72 mRNA level was attained, 40 and 20 min post-HS at 41 and 43 degrees C, respectively, vs. 60 and 40 min in the nonacclimated group. The subsequent HSP synthesis, however, was dependent on the severity of the cumulative heat strain. At the initial phase of heat acclimation, augmented HSP72 transcription unaccompanied by HSP synthesis was observed. It is concluded that upon heat acclimation, the HSP defense pathway is predisposed to a faster response. At the initial phases of heat acclimation, inability to elevate the HSP cytosolic level rules out their direct cytoprotective role.

Acclimatization↗

PubMed2000

The biomechanics and evolutionary significance of thermal acclimation in the common carp Cyprinus carpio.

The effects of thermal acclimation were investigated in the common carp Cyprinus carpio L. Acclimation and acute temperature effects were tested during ontogeny from larval [9.5 mm total length (L)] to juvenile (69.0 mm L) stages and between 8 and 21 degrees C. The myosin heavy chain (MHC) composition, myofibrillar Mg(2+)-Ca(2+)-ATPase activity, and muscle strains showed significant thermal acclimation effects. MHCs were only expressed in an acclimation temperature-dependent fashion in fish longer than 37 mm. During fast starts, the temperature had a significant effect on the white muscle strain (33% increase and 50% decrease with increasing acclimation and acute temperature, respectively) and contraction duration (25% decrease with increasing acute temperature). Increases in hydrodynamic efficiency (0.19 to 0.38) and hydrodynamic power requirements (Q(10) = 3.2) occurred with increasing acute temperature (10 to 20 degrees C). Competing hypotheses about the evolutionary significance of the temperature acclimation response were tested. Acclimation extended the temperature range for fast-start behavior, but no improvements in performance at the whole animal level were found between 8 and 21 degrees C.

Acclimatization↗

PubMed2001

Heat acclimation and heat stress have different effects on cholinergic-induced calcium mobilization.

There is evidence that the signal transduction array responsible for the secretion of water in evaporative cooling by the submaxillary gland of the rat is subject to heat acclimatory responses. The objectives of the present study were 1) to examine whether heat acclimation affects intracellular Ca(2+) mobilization and, in turn, submaxillary glandular responsiveness; 2) to assess whether the acclimatory responses differ from those evoked on heat stress (HS). Experiments were conducted on submaxillary glands of rats acclimated at 34 degrees C for 0, 2 [short-term heat acclimation (STHA)], and 30 [long-term heat acclimation (LTHA)] days. The resting cytosolic calcium concentration ([Ca(2+)](c)) and the carbamylcholine-evoked calcium signal ([Ca(2+)](s)) of dispersed glandular cells were measured using the fluorescent dye fura 2 AM. Inositol-1,4,5-trisphosphate (IP(3))-sensitive endoplasmic reticulum Ca(2+) stores were determined in permeabilized cells using fura 2 potassium salt. STHA resulted in a drop in both [Ca(2+)](s) and IP(3)-sensitive Ca(2+) stores. On LTHA, the [Ca(2+)](s) amplitude reverted to the preacclimation value, whereas the IP(3)-sensitive Ca(2+) stores remained low. The drop in [Ca(2+)](s) on STHA is in accord with the decreased glandular output (measured by (86)Rb efflux) observed during this acclimation phase. However, after LTHA the enhanced glandular output despite reduced [Ca(2+)](s) levels suggests an increased efficiency of cellular secretory mechanisms in that group. Collectively, the alterations in [Ca(2+)](s) support our biphasic acclimation model (Horowitz M, Kaspler P, Marmari Y, and Oron Y. J Appl Physiol 80: 77--85, 1996.). In nonacclimated glands, HS caused an elevation in [Ca(2+)](s) coincidentally with a decrease in the IP(3) Ca(2+) stores. In contrast, [Ca(2+)](s) in both STHA and LTHA glands was not affected by HS, despite a marked increase in the IP(3)-sensitive Ca(2+) stores in the LTHA glands. The opposing responses to HS and heat acclimation in calcium signaling and stores confirm the specificity of each process.

Acclimatization↗

PubMed1977

Skin blood flow and sweating changes following exercise training and heat acclimation.

Eight subjects underwent an exercise training program (10 days at 75% VO2max for 1 h/day at 25 degrees C db/13 degrees C wb) and a heat-acclimation program (10 days at 50% VO2max for 1 h/day at 35 degrees C db/32 degrees C wb). The relations of chest sweat rate and of forearm blood flow to internal temperature were determined for each subject at a 25 degrees C ambient temperature before training, between training and acclimation, and following acclimation. Training shifted the vasodilation and sweating thresholds toward lower internal temperatures, and acclimation further lowered these thresholds. All threshold shifts were statistically significant (P less than 0.05). Training and acclimation both appeared to increase the slope of the sweating relation, but these effects were not statistically significant. Changes in the slope of the blood flow relation were small and inconsistent. Since arm blood flow is higher at any given internal temperature after acclimation, the lower blood flow which is reported to accompany heat acclimation must result from the lower body temperatures.

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