SEARCH · PubMed Health

Results for “acclimation”

Explore indexed PubMed citations for clinical trials, systematic reviews and public health research. Read source abstracts and follow each citation to its original PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 127 records · Page 7Linked to original sources

PubMed2004

Prior heat acclimation confers protection against noise-induced hearing loss.

Exposure to intense noise stress can cause a permanent noise-induced hearing loss which is thought to be due to elevation of reactive oxygen species in excess of the inherent antioxidant mechanisms of the cell. However, preconditioning to low levels of stress of one type can activate cellular mechanisms leading to the elevation of antioxidant levels so that the cell is then better able to tolerate subsequent severe stress of a different type. This has been called cross-tolerance. Here, we tested this hypothesis by acclimating rats to a moderate heat stress (30 days at 34 degrees C). The rats were exposed to 113 dB SPL noise for 3 days (12 h/day) in three different groups: heat acclimated then noise exposed; noise exposed and then heat acclimated; heat acclimated, then noise exposed and then heat acclimated again. Permanent changes in auditory function--auditory nerve brainstem evoked responses (ABR) and distortion product otoacoustic emissions (DPOAEs)--were evaluated in each of these animals and compared with those in rats exposed to noise only and in control groups of rats. Statistical evaluation of the results showed that when assessed with ABR, each of the heat-acclimated, noise-exposed groups was protected from the noise, even the group that was heat-acclimated after the noise exposure. When assessed with DPOAE, protection was statistically apparent only in the group that was heat acclimated, then exposed to noise, and not in the other groups. Thus, heat acclimation provides protection against permanent noise-induced hearing loss.

Acclimatization↗

PubMed1994

MECHANISM OF THE NET UPTAKE OF WATER IN MOULTING BLUE CRABS (CALLINECTES SAPIDUS) ACCLIMATED TO HIGH AND LOW SALINITIES

Blue crabs (Callinectes sapidus Rathbun) acclimated to a salinity of 2 approximately doubled in wet mass (excluding carapace) during the period from 10 h before moult to 2 h after moult. Both in blue crabs acclimated to 2 salinity and in crabs acclimated to 28 salinity, the drinking rate increased from approximately 0.4 ml 100 g-1 h-1 at 1 day prior to moult to approximately 8 ml 100 g-1 h-1 during the first hour after moult. The drinking rate had decreased 1 day after moult in both salinities, but was significantly higher in crabs acclimated to high salinity (1.84±0.16 ml 100 g-1 h-1) than in crabs acclimated to low salinity (0.26±0.04 ml 100 g-1 h-1). Drinking accounted for two-thirds of the weight gain during the first hour after moult at both acclimation salinities, indicating that water enters the body at moult primarily through the gut rather than through the gills. [14C]polyethylene glycol, added as a tracer in the bath water, was concentrated in the midgut gland rather than in the stomach, implicating the midgut gland as the primary site of water absorption. The rate of water efflux was significantly greater in crabs acclimated to 30 salinity (66.4±9.0 ml 100 g-1 h-1) than in crabs acclimated to 2 salinity (34.0±4.7 ml 100 g-1 h-1). The osmotic uptake of water is equal at both salinities as a result of the decreased water permeability at low salinity. The rate of urine formation was estimated to be between 0.5 and 1 ml 100 g-1 h-1 during the first hour after moult in crabs acclimated to both low and high salinities, suggesting that the antennal gland plays a relatively small role in water regulation during this period.

Journal Article↗

PubMed1995

Plasticity of muscle contractile properties following temperature acclimation in the marine fish Myoxocephalus scorpius

Live fibre bundles were isolated from the fast myotomal muscle of short-horned sculpin (Myoxocephalus scorpius L.) and isometric contractile properties and the forcevelocity (PV) relationship determined at 5, 10 and 15 °C. Experiments were carried out on winter- and summer-caught sculpins and on individuals acclimated for 68 weeks to either 5 or 15 °C (12 h:12 h light:dark). Maximum tetanic tension (P0) in fibres from 15 °C-acclimated fish increased from 125 kN m-2 at 5 °C to 282 kN m-2 at 15 °C (R10=2.3). For 5 °C-acclimated fish, P0 was 139 kN m-2 at 5 °C, but fell to 78 kN m-2 at 15 °C, consistent with a partial failure of excitationcontraction coupling at high temperatures. Peak force at 15 °C was increased 2.2 times following depolarisation with a high-K+ solution, but was unaffected by the addition of caffeine and/or eserine to the Ringer's solution. The results from winter- and summer-caught fish were similar to those from 5 °C- and 15 °C-acclimated sculpins respectively. In 15 °C-acclimated fish, the power output of muscle fibres calculated from the PV relationship was 55 W kg-1 at 5 °C and 206 W kg-1 at 15 °C. The PV relationship at 5 °C was significantly less curved in muscle fibres from 5 °C- than from 15 °C-acclimated fish. After normalizing the curves for P0 and Vmax, it was found that the change in curvature was sufficient to produce a 40 % increase in relative power output at 5 °C in cold-acclimated fish. The maximum contraction speed of muscle fibres at 15 °C was 2.4 times higher in 15 °C- than in 5 °C-acclimated fish. It was concluded that acclimation modifies the contractile properties of fast muscle fibres at both low and high temperatures.

Journal Article↗

PubMed1995

Swimming kinematics of fast starts are altered by temperature acclimation in the marine fish Myoxocephalus scorpius

The swimming kinematics of prey capture was studied in short-horned sculpin (Myoxocephalus scorpius L.) acclimated for 68 weeks to either 5 °C or 15 °C (12 h:12 h light:dark) using 15 °C-acclimated shrimps as prey. Fish acclimated to 5 °C remained interested in feeding following an acute rise in temperature to 15 °C over 12 h. Prey capture was a stereotyped behaviour consisting of stalking and stationary phases, followed by an S-shaped fast-start (stage 1), a propulsive stroke (stage 2) and a glide of variable duration during which the mouth was expanded and protruded to suck in the prey (stage 3). The duration of the preparatory stroke (half tail-beat, stage 1) was significantly shorter at 15 °C (48.8 ms) than at 5 °C (108.3 ms) in the 5 °C-acclimated sculpin (Q10=2.2). For 5 °C-acclimated fish, at 5 °C, the maximum values for acceleration and velocity along the path travelled by the fish were 16.2 m s-2 and 0.8 m s-1 respectively. Both variables were relatively independent of acute temperature change (Q10=1.11.2; P>0.1). At 15 °C, the maximum velocity was 33 % higher and the tail-beat duration of the propulsive stroke was 37 % shorter in 15 °C-acclimated than in 5 °C-acclimated fish. Both stride length and tail-beat amplitude were significantly higher (28 and 23 % respectively) in 15 °C- compared with 5 °C-acclimated sculpin at 15 °C. The results demonstrate plasticity in the major kinematic variables of fast-starts following warm acclimation sufficient to increase the percentage of successful attacks during prey capture from 23.2 to 73.4 %.

Journal Article↗

PubMed1995

The thermal acclimation of burst escape performance in fish: an integrated study of molecular and cellular physiology and organismal performance

Goldfish (Family Cyprinidae, Carassius auratus) and killifish (Family Cyprinodontidae, Fundulus heteroclitus) were acclimated to 10, 20 and 35 °C for 4 weeks. The thermal acclimation of C-start (escape swimming) performance and the physiological properties of fast twitch muscle fibres that underlie it were investigated in these species at the molecular (myosin isoform expression), biochemical (myofibrillar ATPase activity), cellular (contractile kinetics) and organismal levels of organisation. Peptide maps were obtained for fast muscle myosin heavy chains, isolated from 10 °C- and 35 °C-acclimated fish. Different myosin heavy chain isoforms were expressed in response to a change in acclimation temperature in goldfish, but myosin heavy chain isoform expression was unaffected by acclimation temperature in killifish. Compared with fish acclimated to 35 °C, acclimation to 10 °C increased the activity of fast muscle myofibrillar ATPase assayed at 10 °C fivefold in goldfish and only 50 % in killifish. Muscle twitch contraction time at 10 °C decreased significantly in response to acclimation to 10 °C in both species; however, the magnitude of this response was much greater in goldfish (100 %) than in killifish (30 % or less). In goldfish, these changes in the physiological properties of fast twitch fibres during 10 °C acclimation resulted in a six- to eightfold increase in the speed and turning velocity of fish performing C-starts at 10 °C. By comparison, the somewhat smaller acclimatory response of killifish fast muscle properties was accompanied by only a minor (50 % or less) adjustment in locomotor performance. Thermal acclimatory responses of fast muscle at the molecular, biochemical and cellular levels of organisation are clearly reflected in alterations in organismal escape performance.

Journal Article↗

PubMed1997

cDNA cloning of myosin heavy chain isoforms from carp fast skeletal muscle and their gene expression associated with temperature acclimation.

We have isolated cDNA clones encoding fast skeletal muscle myosin heavy chains of carp acclimated to 10, 20 and 30 degrees C for over 5 weeks. All clones covered at least the full length of L-meromyosin, the C-terminal part of the myosin molecule. Nucleotide sequence analysis on cDNA clones showed three types of 3' untranslated sequences, demonstrating that carp expresses at least three myosin heavy chain isoforms in fast skeletal muscle in an acclimation-temperature-dependent manner. cDNAs were identified which were the predominant types expressed in 10 degrees C- and 30 degrees C-acclimated fish, as well as an intermediate type present at all acclimation temperatures. Northern blot analysis using probes of three kinds of DNA fragments from the 3' untranslated region of carp acclimated to 10, 20 and 30 degrees C further confirmed the presence of acclimation-temperature-specific isoforms. In addition, it was found that mRNA levels of three isoforms were altered in an acclimation-temperature-dependent manner. When the deduced amino acid sequences of three types of carp L-meromyosin were compared with those of homoiotherms, the 30 degrees C-acclimated type was more similar to those of homoiotherms than was the 10 degrees C-acclimated type.

Acclimatization↗

PubMed1998

L-type Ca2+ current in fish cardiac myocytes: effects of thermal acclimation and beta-adrenergic stimulation.

A patch-clamp analysis of L-type Ca2+ current in ventricular myocytes of cold- and warm-acclimated rainbow trout (Oncorhynchus mykiss) and crucian carp (Carassius carassius) hearts was performed. Trout were acclimated at 4 and 17 degrees C and carp at 4 and 24 degrees C for a minimum of 4 weeks. Ventricular myocytes were isolated by enzymatic dissociation using collagenase and trypsin. Marked species-specific differences were noted in Ca2+ current density and its ss-adrenergic regulation. The density of basal Ca2+ current in crucian carp (6.9-7.4 pA pF-1) was almost double that of trout (4.2-4.5 pA pF-1) ventricular myocytes. Maximal beta-adrenergic stimulation increased Ca2+ current by approximately 2.3-fold in trout but by only 1.4-fold in crucian carp, so that Ca2+ current densities in the presence of 10 micromol l-1 isoprenaline were almost equal in trout (8.6-10.5 pA pF-1) and carp (9.6-10.4 pA pF-1) cardiac cells. Direct activation of adenylate cyclase by forskolin (10 micromol l-1) was also associated with similar interspecies differences in the stimulation of Ca2+ current. Thermal acclimation did not change either the density or the kinetics of L-type Ca2+ current in crucian carp ventricular myocytes. In trout cardiac cells, thermal acclimation had no effects on the density of Ca2+ current, but the rate of current inactivation was accelerated after acclimation to cold temperature. As a consequence of faster current decay, the contribution of sarcolemmal Ca2+ current to total cellular [Ca2+] was smaller in cold-acclimated than in warm-acclimated trout. The responses of Ca2+ current to maximal beta-adrenergic stimulation by isoprenaline or to direct activation of adenylate cyclase by forskolin were not changed by thermal acclimation in either species. It is concluded (1) that the density of sarcolemmal Ca2+ current is not increased after acclimation to cold, (2) that sarcolemmal Ca2+ influx through L-type Ca2+ channels can make a significant contribution to contractile [Ca2+] in both teleost species studied and (3) that ss-adrenergic stimulation of Ca2+ current is more important in modulating cardiac contractility in trout than in carp.

Acclimatization↗

PubMed1987

Body temperature of acclimated broilers during exposure to high temperature.

Short-term acclimation to high temperatures increased resistance of broilers to heat exposure. Two trials were conducted to determined the effect of acclimation on body temperature (Tb) during heat exposure. Broilers, 46-days old, were maintained at control or acclimating temperatures for 4 days. The control temperature was a constant 21 C with a 10 C dewpoint, and the acclimating temperature was a diurnal cycle of 24-35-24 C with a constant 21 C dewpoint. During the 4th day, broilers of both groups were exposed to temperatures of 41 C and 23 C dewpoint for 210 min. Body temperature was determined at the beginning of the heat exposure and at 30-min intervals until the end of the exposure. The Tb of both groups increased throughout heat exposure, but acclimated broilers had significantly lower Tb than control broilers from 90 through 210 min. Acclimated broilers had significantly lower heat stress mortality. The data show that acclimated broiler's Tb rises upon exposure to heat but that acclimation gives the capacity to stabilize Tb above normal Tb. The data also suggest Tb is preferable to mortality as a measure of acclimation in broilers.

Acclimatization↗

PubMed2005

Sodium or potassium ions activate different kinetics of gill Na, K-ATPase in three seawater- and freshwater-acclimated euryhaline teleosts.

The effects of [Na(+)] or [K(+)] on Na, K-ATPase activity of FW-acclimated and SW-acclimated tilapia, puffer and milkfish were examined in gill homogenates. [Na(+)] or [K(+)] stimulated Na, K-ATPase hydrolyzing ATP in all experimental groups. ATP hydrolysis stimulated by [Na(+)] or [K(+)] followed Michaelian-Menten kinetics. Km values for [K(+)] (i.e., Km(K)), were lower in SW- than FW-acclimated tilapia and puffer fishes (tilapia: 8.69+/-0.22 vs. 11.93+/-1.17 mM; puffer: 13.51+/-1.39 vs. 30.52+/-2.66 mM). Km values for [Na(+)] (i.e., Km(Na)), were lower in FW- than SW-acclimated milkfish (3.76+/-0.54 vs. 7.55+/-1.08 mM). These data suggest that [K(+)] stimulates ATP hydrolysis to rates higher in SW- than FW-acclimated tilapia and puffer fishes, while [Na(+)] stimulated ATP hydrolysis at rates higher in FW- than SW-acclimated milkfish. This is the first demonstration that Na, K-ATPase activity of euryhaline tilapia, puffer, and milkfish modulated by [Na(+)] or [K(+)] have different effects between FW- and SW-acclimated groups. Such responses as changes in properties of branchial Na, K-ATPase may contribute to improve the osmoregulatory capacity of tilapia, puffer and milkfish to acclimate in seawater and fresh water.

Acclimatization↗

PubMed1993

Mechanisms of hyperosmotic acclimation in Xenopus laevis (salt, urea or mannitol).

The acclimation of the clawed toad Xenopus laevis to hyperosmotic solutions of NaCl (balanced solution of sea salt), urea or mannitol was studied. The animals could not be acclimated to salt solutions more concentrated than 400 mosm.1-1. Urea was tolerated till 500 mmol.1-1. Plasma osmolality was always hyperosmotic to the environmental solution, but with diminished osmotic gradient at the highest tolerated solutions. Plasma urea concentration approached 90 mmol.1-1, similar in the three solutions of acclimation. Urine volume was very small under all conditions. Serum aldosterone and corticosterone did not differ significantly, although there was a slight tendency towards lower aldosterone in the NaCl solution. In vivo water uptake in tap water acclimated animals was very small, and was higher in the other groups. Only the salt- and urea-acclimated, but not the tap water and mannitol-acclimated groups responded with a clear increase following injection of oxytocin or theophylline. In vitro urea fluxes were similar and invariable in both directions under all conditions. No significant effect of theophylline was observed. Sodium transport measured by the short-circuit technique in vitro was lower in salt- and mannitol-acclimation conditions, and was stimulated significantly under all conditions in response to serosal oxytocin or theophylline. It is concluded that Xenopus laevis can osmoregulate at a limited range of external solutions. It is limited in the increase of its plasma urea concentration; the transport properties of the skin do not change very much upon acclimation, except for the hydroosmotic response to oxytocin.

Adaptation, Physiological↗

PubMed1995

Renal function at steady state in a toad (Bufo viridis) acclimated in hyperosmotic NaCl and urea solutions.

Kidney function of the euryhaline toad Bufo viridis was studied in animals acclimated to tap water and solutions of NaCl (230 and 500 mosmol.kg-1 H2O) and urea (500 mmol.l-1) in steady-state conditions. An ureter was catheterized for continuous urine collection and blood was sampled from an iliac artery. A single injection of 3H-inulin served for estimation of glomerular filtration rate: this was in the range of 15-27 ml.kg-1.h-1 and did not differ significantly in any of the acclimation conditions. Urine flow, on the other hand, varied considerably and was highest in tap water (18.2 +/- 3.2 ml.kg-1.h-1; urine/plasma inulin ratio = 0.88), lower in 230 mosmol.kg-1 H2O NaCl solution (13.5 +/- 3.9 ml.kg-1.h-1; u/p inulin ratio = 1.73) and lowest in 500 mosmol.kg-1 H2O NaCl or urea acclimation solutions (5-7 ml.kg-1.h-1; u/p inulin = 3.7-4.2). Clearance of free water was high in the tap water group, lower in 230 mosmol.kg-1 H2O NaCl solution, and much lower in the hyperosmotic acclimation conditions. Clearances of both Na+ and Cl- were similar under our experimental conditions, but changed independently in accordance to the composition of the acclimation solution. Potassium clearance was similar in all acclimation conditions, and a constant plasma K+ concentration was maintained. Urea clearance was high in tap water and 500 mmol.l-1 urea acclimation groups and low in the NaCl acclimations.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1990

Finger and forearm vasodilatatory changes after local cold acclimation.

To determine the vascular changes induced by local cold acclimation, post-ischaemia and exercise vasodilatation were studied in the finger and the forearm of five subjects cold-acclimated locally and five non-acclimated subjects. Peak blood flow was measured by venous occlusion plethysmography after 5 min of arterial occlusion (PBFisc), after 5 min of sustained handgrip at 10% maximal voluntary contraction (PBFexe), and after 5 min of both treatments simultaneously (PBFisc + exe). Each test was performed at room temperature (25 degrees C, SE 1 C) (non-cooled condition) and after 5 min of 5 degrees C cold water immersion (cooled condition). After the cold acclimation period, the decrease in skin temperature was more limited in the cold-acclimated compared to the non-acclimated (P less than 0.01). The PBFisc was significantly reduced in the cooled condition only in the cold-acclimated subjects (finger: 8.4 ml.100 ml-1.min-1, SE 1.1, P less than 0.01; forearm: 5.8 ml.100 ml-1.min-1, SE 1.5, P less than 0.01) compared to the non-cooled condition. Forearm PBFexe was significantly decreased in the cooled condition only in the cold-acclimated subjects (non-cooled: 7.4 ml.100 ml-1.min-1, SE 1.2; cooled: 3.9 ml.100 ml-1.min-1, SE 2.6, P less than 0.05) indicating that muscle blood flow was also reduced.(ABSTRACT TRUNCATED AT 250 WORDS)

Acclimatization↗

PubMed1985

Partial purification and kinetic characterization of the microsomal phospholipase A2 from thermally acclimated rainbow trout (Salmo gairdneri).

Phospholipase A2 (PLA2) was extracted from liver microsomal membranes of both 5 and 20 degrees C-acclimated rainbow trout (Salmo gairdneri), using the non-ionic detergent, Triton X-100. Further purification was achieved by precipitation with 35-65% ammonium sulfate followed by gel filtration chromatography in the presence of 0.1% Triton X-100 on Sephadex G-200. These procedures resulted in a 30-fold purification and the removal of all traces of phospholipid from the enzyme of both warm- and cold-acclimated trout. Column elution profiles were similar for both acclimation groups, yielding a molecular weight estimate for the trout liver enzyme of 73,000. Comparisons of activity levels and kinetic parameters of PLA2 from warm- and cold-acclimated fish indicated that compensation for temperature at non-saturating substrate concentrations was an attribute of both the particulate (microsomal) enzyme and the lipid-free protein. Cold acclimation resulted in higher activity below Vmax due primarily to decreased apparent Km values. These adaptations to temperature could not be attributed to the interaction of the enzyme with the membrane lipids, but were due to qualitative changes in the enzyme that resulted from acclimation. Other adaptive qualities of PLA2, such as reduced Km in response to acute decreases in temperature in warm-acclimated fish, were only apparent in particulate preparations, and thus were a function of the protein-lipid complex. These data suggest that an acclimation-induced increase in the activity of PLA2 may result in the activation of a deacylation-reacylation cycle at cold temperatures.

Acclimatization↗

PubMed1995

Effects of 6 versus 12 days of heat acclimation on heat tolerance in lightly exercising men wearing protective clothing.

This study investigated the influence of 6 versus 12 days of heat acclimation on the tolerance of low-intensity exercise in the heat while wearing protective clothing. Sixteen young men were acclimated by treadmill walking (50% of each subject's maximal aerobic power for 60 min.day-1) in a climatic chamber [40 degrees C dry bulb (db), 30% relative humidity] for either 6 consecutive days or two 6-day periods, separated by a 1-day rest. Before and after heat acclimation, the subjects performed a heat-exercise test (1.34 m.s-1, 0% grade; 40 degrees C db, 30% relative humidity), either under control conditions [wearing normal light combat clothing (continuous exercise; n = 5)] or when wearing protective clothing resistant against nuclear, biological, and chemical (NBC) agents (repeated bouts of 15-min walk + 15-min rest; n = 8). Criteria for halting the test exercise were a rectal temperature (Tre) of 39.3 degrees C, a heart rate (fc) > or = 95% of the subject's observed maximum, unwillingness of the subject to continue, or the elapse of 150 min. Heat acclimation decreased overall test values of Tre, fc, and mean skin temperature for both control and protective clothing conditions. When wearing normal combat clothing, acclimation responses were about twice as large after 12 than after 6 days, but the response was not increased by longer acclimation when wearing NBC protective clothing. Both 6 and 12 days of acclimation increased tolerance times in NBC protective clothing by about 15 min [from 97 (4) to 112 (6) min and from 108 (10) to 120 (10) min for 6 and 12 days, respectively]. We conclude that the physiological strain and limitation of heat-exercise tolerance imposed by wearing NBC protective clothing are not reduced if heat acclimation is prolonged from 6 to 12 days.

Acclimatization↗

PubMed2003

Effects of temperature acclimation on maximum heat production, thermal tolerance, and torpor in a marsupial.

Marsupials, unlike placental mammals, are believed to be unable to increase heat production and thermal performance after cold-acclimation. It has been suggested that this may be because marsupials lack functional brown fat, a thermogenic tissue, which proliferates during cold-acclimation in many placentals. However, arid zone marsupials have to cope with unpredictable, short-term and occasionally extreme changes in environmental conditions, and thus they would benefit from an appropriate physiological response. We therefore investigated whether a sequential two to four week acclimation in Sminthopsis macroura (body mass approx. 25 g) to both cold (16 degrees C) and warm (26 degrees C) ambient temperatures affects the thermal physiology of the species. Cold-acclimated S. macroura were able to significantly increase maximum heat production (by 27%) and could maintain a constant body temperature at significantly lower effective ambient temperatures (about 9 degrees C lower) than when warm-acclimated. Moreover, metabolic rates during torpor were increased following cold-acclimation in comparison to warm-acclimation. Our study shows that, despite the lack of functional brown fat, short-term acclimation can have significant effects on thermoenergetics of marsupials. It is likely that the rapid response in S. macroura reflects an adaptation to the unpredictability of the climate in their habitat.

Acclimatization↗

PubMed2000

Adaptive modification of membrane phospholipid fatty acid composition and metabolic thermosuppression of brown adipose tissue in heat-acclimated rats.

Thermogenesis, especially facultative thermogenesis by brown adipose tissue (BAT), is less important in high ambient temperature and the heat-acclimated animals show a lower metabolic rate. Adaptive changes in the metabolic activity of BAT are generally found to be associated with a modification of membrane phospholipid fatty acid composition. However, the effect of heat acclimation on membrane phospholipid fatty acid composition is as yet unknown. In this study, we examined the thermogenic activity and phospholipid fatty acid composition of interscapular BAT from heat-acclimated rats (control: 25+/-1 degrees C, 50% relative humidity and heat acclimation: 32+/-0.5 degrees C, 50% relative humidity). Basal thermogenesis and the total thermogenic capacity after noradrenaline stimulation, as estimated by in vitro oxygen consumption of BAT (measured polarographically using about 1-mm(3) tissue blocks), were smaller in the heat-acclimated group than in the control group. There was no difference in the tissue content of phospholipids between the groups when expressed per microgram of DNA. The phospholipid fatty acid composition was analyzed by a capillary gas chromatograph. The state of phospholipid unsaturation, as estimated by the number of double bonds per fatty acid molecule, was similar between the groups. The saturated fatty acid level was higher in the heat-acclimated group. Among the unsaturated fatty acids, heat acclimation decreased docosahexaenoic acid and oleic acid levels, and increased the arachidonic acid level. The tissue level of docosahexaenoic acid correlated with the basal oxygen consumption of BAT (r=0.6, P<0.01) and noradrenalinestimulated maximum values of oxygen consumption (r=0.5, P<0.05). Our results show that heat acclimation modifies the BAT phospholipid fatty acids, especially the n-3 polyunsaturated fatty acid docosahexaenoic acid, which is possibly involved in the metabolic thermosuppression.

Adaptation, Physiological↗

PubMed1977

Adaptation of biological membranes to temperature. The effect of temperature acclimation of goldfish upon the viscosity of synaptosomal membranes.

The fluidity of synaptosomal membrane preparations isolated from goldfish acclimated to 5, 15 and 25 degrees C and from rat has been estimated using the fluorescence polarisation technique with 1,6-diphenyl-1,3,5-hexatriene as probe. Membranes of cold-acclimated goldfish were more fluid than those of warm-acclimated goldfish when measured at an intermediate temperature, indicating a temperature-dependent regulation of this parameter. Similarly, membranes of warm-acclimated goldfish were more fluid than those prepared from rat brain. Liposomes prepared from the purified phospholipids of goldfish and rat synaptosomal preparations showed differences similar to those of the native membranes. Increased membrane fluidity of cold-acclimated goldfish was correlated with a decrease in the proportion of saturated fatty acids of the major phospholipid classes and an increased unsaturation index in choline phosphoglycerides. Rat membranes showed a substantial reduction in unsaturation index and an increase in the proportion of saturated fatty acids compared to the membranes of 25 degrees C-acclimated goldfish. The cholesterol content of synaptosomal membranes of goldfish was unaffected by acclimation treatment. The role of homeoviscous adaptation in the compensation of the rates of membrane processes during thermal acclimation, and upon the resistance adaptation of poikilotherms to extreme temperatures is discussed.

Acclimatization↗

PubMed1981

Temperature adaptation of biological membranes. The effects of acclimation temperature on the unsaturation of the main neutral and charged phospholipids in mitochondrial membranes of the carp (Cyprinus carpio L.).

The phospholipid composition, fatty acid pattern and cholesterol content are studied in mitochondria of red lateral muscle of carp acclimated to high and low environmental temperatures. The results of the experiments are: mitochondria from cold-acclimated carp contain higher proportions of ethanolamine phosphatides than mitochondria from warm-acclimated fish, the opposite is true for the choline phosphatides. Thus, at constant pH, the membrane phospholipids are slightly more negatively charged at low acclimation temperature. The total plasmalogen content is reduced in the cold; this reduction is caused by a decrease in the proportion of the choline plasmalogens. The ethanolamine phosphoglycerides contain approx. 20% of the alk-1-enyl acyl type, irrespective of the acclimation temperature. There is no temperature-dependent difference in the low proportion of cholesterol. The fatty acids of total mitochondrial phospholipids are characterized by large amounts of the n-3 and n-6 families. The ratio of unsaturated to saturated fatty acids and the unsaturation index are remarkably higher than those reported for comparable mammalian phospholipids. Cold acclimation of carp does not significantly increase the unsaturation of total phospholipids. A fatty acid analysis of the main isolated phospholipids, however, shows that cold acclimation considerably increases unsaturation of the neutral phosphatidylcholine, whereas it dramatically decreases unsaturation of the negatively charged cardiolipin. It is suggested that the observed fatty acid substitution in phosphatidylcholine indicates a temperature-induced fluidity adaptation within the mitochondrial lipid bilayer, whereas the inverse acclimation pattern of cardiolipin provides a suitable lipid to accommodate the temperature-dependent modifications in the dynamic surface shape of integral membrane proteins.

Acclimatization↗