Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “acclimation”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

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

At least 1,315 records · Page 73Linked to original sources
PubMed1997

OXYGEN DEFICIENCY AND ROOT METABOLISM: Injury and Acclimation Under Hypoxia and Anoxia.

Oxygen deficiency in the rooting zone occurs with poor drainage after rain or irrigation, causing depressed growth and yield of dryland species, in contrast with native wetland vegetation that tolerates such conditions. This review examines how roots are injured by O2 deficiency and how metabolism changes during acclimation to low concentrations of O2. In the root apical meristem, cell survival is important for the future development; metabolic changes under anoxia help maintain cell survival by generating ATP anaerobically and minimizing the cytoplasmic acidosis associated with cell death. Behind the apex, where cells are fully expanded, ethylene-dependent death and lysis occurs under hypoxia to form continuous, gas-filled channels (aerenchyma) conveying O2 from the leaves. This selective sacrifice of cells may resemble programmed cell death and is distinct from cell death caused by anoxia. Evidence concerning alternative possible mechanisms of anoxia tolerance and avoidance is presented.

Journal Article↗
PubMed1982

Cold acclimation in insulin secretion of isolated perfused pancreas of the rat.

The secretory function of the endocrine and exocrine pancreas in the process of cold acclimation has been studied in rats fed at an ambient temperature of 2 degrees C. In anesthetized rats, plasma glucose decreased immediately after cold exposure and increased again toward the basal level after 20 days of continuous cold exposure. Plasma insulin level in these rats also decreased immediately after cold exposure, and the low level was maintained throughout the whole period of cold exposure. In the isolated perfused rat pancreas, the basal insulin output estimated before the stimulation with glucose decreased immediately after the cold exposure and increased gradually during the continuous cold exposure. In these preparations, the initial and the second phases of insulin output were induced by sustaining stimulation with 16.7 mM glucose. Changes in the glucose-induced initial and second phases showed a diphasic pattern during the course of cold exposure. Thus, there was temporary decrease within a week of cold exposure followed by a gradual increase after 3 wk of this condition. The diphasic insulin output in the preparation isolated from rats fed during cold exposure for 6 wk was twice as much as that in the preparation isolated from the rats fed during exposure to 23 degrees C for 5 wk. In the isolated perfused rat pancreas, a monophasic insulin output was induced by sustaining stimulation with 0.1 microM ACh. The monophasic insulin output showed an increasing tendency during cold exposure, but the increase was insignificant because of a larger individual variation.

Acetylcholine↗
PubMed2003

Modulation of mitochondrial nitric oxide synthase and energy expenditure in rats during cold acclimation.

To preserve thermoneutrality, cold exposure is followed by changes in energy expenditure and basal metabolic rate (BMR). Because nitric oxide (NO) modulates mitochondrial O(2) uptake and energy levels, we analyzed cold effects (30 days at 4 degrees C) on rat liver and skeletal muscle mitochondrial NO synthases (mtNOS) and their putative impact on BMR. Cold exposure delimited two periods: A (days 1-10), with high systemic O(2) uptake and weight loss, and B (days 10-30), with lower O(2) uptake and fat deposition. mtNOS activity and expression decreased in period A and then increased in period B by 60-100% in liver and skeletal muscle (P < 0.05). Conversely, mitochondrial O(2) uptake remained initially high in the presence of l-arginine and later fell by 30-50% (P < 0.05). On this basis, the estimated fractional contribution of liver plus muscle to total BMR varied from 40% in period A to 25% in period B. The transitional modulation of mtNOS in rat cold acclimation could participate in adaptive responses that favor calorigenesis or conservative energy-saving mechanisms.

Acclimatization↗
PubMed1980

Acclimation, temperature selection, and heat exchange in the turtle, Chrysemys scripta.

Turtles acclimated to temperatures between 3 and 19 degrees C were placed in a thermal gradient. The animals usually selected temperatures above 28 degrees C within 1 h after placement in the gradient, attaining a final thermal preferendum between 31 and 33 degrees C. Turtles placed in the gradient for extended periods of time were more active during the day; the temperature selected was not related to activity or time of day. Turtles were transferred from a constant temperature bath at 10 or 30 degrees C to a calorimeter at 30 or 10 degrees C. Mean body temperature (Tb) and temperatures of the heart (The), brain (Tbr), and cloaca (Tcl) as well as heart rate were continuously monitored. In a 0.76-kg turtle, temperatures increased to two-thirds of the final difference between the initial temperature and the final temperature in the following times (min): Tb, 5.5; The, 6.0; Tcl, 9.0. The increase in Tbr varied depending on whether the head was extended or retracted. Rapid changes in ambient water temperature had relatively little effect on the heart rate of a submerged turtle. Heart rates were closely related to The and were practically independent of brain temperature.

Acclimatization↗
PubMed1981

Coronary circulation in hearts from hibernating, normothermic, and cold-acclimated hamsters.

We have investigated the influence of temperature, acute global ischemia, adenosine administration, and alterations in perfusion pressure on the coronary circulation of isolated, perfused spontaneously beating hearts from hibernating, normothermic, and cold-acclimated (nonhibernating) hamsters. No differences in heart rates were observed among groups at either 9 or 38 degrees C. Hearts from hibernating hamsters showed some differences in autoregulatory capacity at both the low and normal temperatures. All hearts exhibited similar responses to 30 s of global ischemia at both temperatures, with a marked reduction in the response at 9 degrees C. Similarly, the magnitude of the vasculature response to adenosine (250 micrograms) at 38 and 9 degrees C was equal in both normothermic and hibernating hearts perfused at 38 degrees C. Responses were abolished in all groups at 9 degrees C. We conclude that the altered ability of hibernating hearts to autoregulate is possibly due to intrinsic differences initiated by hibernation, while the responses to adenosine, and global ischemia are largely temperature-dependent effects.

Acclimatization↗
PubMed1985

Potentiated muscular thermogenesis in cold-acclimated muscovy duckling.

The capacity for nonshivering thermogenesis (NST) was examined in 26- to 27-day cold-acclimated (CA) muscovy ducklings reared for 21 days at 4 degrees C. Metabolic rate and integrated electromyographic (EMG) muscle activity were measured at ambient temperature ranging from -10 to 28 degrees C. Compared with controls reared at 30 degrees C, CA ducklings were more resistant to cold and had higher peak metabolic rate in extreme cold. Shivering threshold temperature of CA ducklings was 14.2 degrees C lower than lower critical temperature, whereas for controls the two temperatures were similar. Thus CA ducklings exhibited an NST in moderate cold. In addition, at temperatures that produced shivering, EMG activity in CA duckling muscle was lesser than that of controls, even at a higher metabolic rate. Because these ducklings are devoid of brown adipose tissue, these results indicated an increased thermogenic efficiency of muscular activity in CA ducklings.

Acclimatization↗
PubMed1993

Skeletal muscle as the major site of nonshivering thermogenesis in cold-acclimated ducklings.

Despite their lack of brown adipose tissue, 6-wk-old cold-acclimated muscovy ducklings (4 degrees C; CA) exhibit nonshivering thermogenesis (NST) in the cold. To determine the site of this NST, the regional distribution of blood flow was measured by the microsphere method in the thermoneutral zone (25 degrees C) and during acute exposure to cold (8 degrees C). Ducklings reared at thermal neutrality (TN), which use shivering to produce extra heat in the cold, were compared with CA ducklings, which substitute NST for shivering. Further, the contribution of skeletal muscle thermogenesis to the increased heat production in the cold was estimated by measuring leg muscle blood flow and arteriovenous difference in oxygen content [(a-v)O2] across the leg, enabling an estimation of muscle O2 consumption. During cold exposure, a similar increase in total leg muscle blood flow occurred in TN and CA ducklings (+127 and +130% respectively), while hepatic arterial blood flow increased less (+56 to +37%, respectively). This rise in blood flow was accounted for by an increase in cardiac output, which was smaller in CA than in TN ducklings, and in both groups by a redistribution of blood flow to the most thermogenic organs (skeletal muscles and liver). The (a-v)O2 across the leg was not changed by cold exposure, indicating that the increase in leg muscle O2 consumption resulted mainly from the increase in blood flow.(ABSTRACT TRUNCATED AT 250 WORDS)

Acclimatization↗
PubMed1993

Increased role of skeletal muscle in the calorigenic response to glucagon of cold-acclimated ducklings.

The site of the calorigenesis observed in birds after glucagon was sought in control and cold-acclimated (CA) ducklings. Twenty-four 6-wk-old muscovy ducklings were reared either at thermoneutrality (TN) (25 degrees C) or in the cold (4 degrees C) from the age of 1 wk. Glucagon-induced calorigenesis (GIC) was estimated at 25 degrees C after a peritoneal glucagon injection (103 nmol/kg). Glucagon induced a higher increase in animal heat production (indirect calorimetry) and body temperature in CA (+45% and +1.1 degrees C) than in control ducklings (+30% and +0.4 degree C). In CA ducklings, the perfusion rate (thermal clearance method) and temperature of gastrocnemius increased (+130% and +1.0 degree C) shortly after glucagon, whereas tissue oxygenation (polarography) decreased (-34%). There was no significant effect of glucagon in TN controls. These changes, which peaked 45-60 min after glucagon injection, indicated a prolonged increase of muscle O2 consumption in CA ducklings. Leg muscle blood flow (radioactive microspheres) measured 45 min after glucagon was slightly increased in controls (+20%; P < 0.05), while in CA ducklings, the increase was larger (+76%; P < 0.05). The arteriovenous difference in O2 content was not markedly affected by glucagon in both groups. These parameters indicated an increase in leg muscle O2 uptake in response to glucagon of +29% in controls and +76% in CA ducklings. In controls, 28% of the GIC measured in vivo could be attributed to whole body skeletal muscles, compared with 53% in CA ducklings. The remaining part might be accounted for mostly by the liver.(ABSTRACT TRUNCATED AT 250 WORDS)

Acclimatization↗
PubMed1994

The uncoupling protein thermogenin during acclimation: indications for pretranslational control.

To analyze the regulation of the content of the uncoupling protein thermogenin in brown adipose tissue, we have selected a physiological transition phase during which to investigate the relationship between the level of mRNA and the level of the ensuing protein product. Mice preacclimated to 28 degrees C were transferred to 4 degrees C. Cold acclimation led to the expected increases in brown fat total protein and RNA content. Two recruited proteins were analyzed: the cytosolic glycerol-3-phosphate dehydrogenase and the mitochondrial uncoupling protein thermogenin. The activity of the dehydrogenase acutely followed the level of the corresponding mRNA, indicating pretranslational control. However, for thermogenin there was a marked time delay between the establishment of the fully recruited level of thermogenin mRNA (after only approximately 4 h of cold exposure) and that of thermogenin itself (after > 3 wk). By reiterative computer simulation, it was investigated whether a model only involving pretranslational regulation could be invoked for either system. For glycerol-phosphate dehydrogenase, a plausible model could be constructed, provided the protein half-life was shorter than approximately 24 h. Despite the long time delay between full thermogenin mRNA recruitment and full thermogenin protein recruitment, a plausible pretranslational control model could also be constructed, provided that the protein half-life was approximately 5 days. This computed value was in good agreement with the half-life obtained from independent thermogenin half-life studies. It is implied that pretranslational control may suffice to explain the regulation of thermogenin content in brown adipose tissue during a warm-to-cold transition period.

Acclimatization↗
PubMed1998

Slow inactivation of cardiac L-type Ca2+ channel induced by cold acclimation of guinea pig.

Whole cell L-type Ca2+ current was recorded in ventricular myocytes dissociated from guinea pigs that were bred at ambient temperatures ranging between daily averages of 4 and 29 degrees C. The dynamic voltage range of inactivation, as measured using 400-ms conditioning pulses and a holding potential of -40 mV, extended from -50 to -20 mV in myocytes prepared in summer. In winter, the inactivation curve was shifted to more negative potentials than in summer. Double-pulse experiments revealed that the negative shift was due to slow-inactivation kinetics. The negative shift of inactivation could be induced in myocytes prepared from animals that had been kept at 5 degrees C for > 3 wk in the summer. The negative shift in Ca2+ current inactivation could be abolished by adding guanosine 5'-O-(2-thiodiphosphate) (5 mM) to the pipette solution, but not by adding staurosporine (2 microM) or 1-(5-isoquinolinylsulfonyl)-2-methylpiperazine (100 microM) to the bath. The cold acclimation may introduce the slow inactivation of the cardiac L-type Ca2+ channel through an unknown pertussis toxin-insensitive G protein.

Acclimatization↗
PubMed1998

Ca2+ uptake and Cd2+ accumulation in larval tilapia (Oreochromis mossambicus) acclimated to waterborne Cd2+.

The present study compares the rates of Ca2+ uptake and Cd2+ accumulation in tilapia (Oreochromis mossambicus) between larvae preexposed to Cd2+ and naive larvae. Preexposure to Cd2+ induces some form of adaptation that attenuates the effects of Cd2+ later on. Exposure to Cd2+ decreased the uptake of Ca2+ but did not suppress the accumulation rate of Cd2+. A 12-fold increase in 96-h half-maximal lethal concentration was found in tilapia larvae preexposed to 0.45 microM Cd2+ from hatching for 3 days in comparison with naive 3-day-old larvae. The effects of Cd2+ on Ca2+ influx kinetics in larvae preexposed to 0.18 microM Cd2+ for 3 days were examined. The Michaelis constant for Ca2+ in the 0.18 microM Cd2+ preexposed larvae did not change significantly in the presence of Cd2+, whereas maximal velocity increased by approximately 23%. An enhanced Ca2+ uptake efficiency ( approximately 18%) was found in these Cd2+-acclimated larvae. The criterion that determines the survival of tilapia larvae encountering Cd2+ challenge is the degree of interference with Ca2+ homeostasis instead of the absolute amount of Cd2+ accumulated.

Acclimatization↗
PubMed1998

Increased in vitro fatty acid supply and cellular transport capacities in cold-acclimated ducklings (Cairina moschata).

In cold-acclimated (CA) birds, lipids play a crucial role in regulatory thermogenesis by acting both as substrates for and activators of thermogenic processes. The capacity to supply lipids to thermogenic tissues, which could limit cold thermogenesis, was assessed in CA ducklings (5 wk old, 4 degrees C) and compared with thermoneutral controls (TN, 25 degrees C). In CA ducklings, basal lipolytic activity of adipose tissue fragments was higher (202 +/- 9 vs. 130 +/- 14 nmol glycerol released . 100 mg tissue-1 . h-1, +55%) than in TN controls, while glucagon had a much higher stimulatory effect (+140 to +500% depending on dose). This was consistent with increased plasma levels of nonesterified fatty acids (FA, +57%) and glycerol (+31%) in vivo. In vitro endothelial lipase activity per organ was higher in CA than in TN ducklings in red gastrocnemius muscle (6.3 +/- 0.6 vs. 3.5 +/- 0.3 microeq nonesterified FA released per hour, +80%) and liver (+55%). The intracellular FA-binding capacity of (12-18 kDa) proteins was higher in gastrocnemius muscle (+43%) and liver (+74%) from CA ducklings. In gastrocnemius, it was linked to a higher content (21 +/- 2 vs. 15 +/- 2 microg/mg protein, +37%) of an intracellular 15.4-kDa FA-binding protein. These in vitro results indicate that coordinated increases in FA supply from adipose tissue, cellular uptake of lipoprotein-derived FA, and intracellular FA transport capacity occur in CA ducklings endowed with higher thermogenic capacity and cold endurance.

Acclimatization↗
PubMed2001

Energy intake and fur in summer- and winter-acclimated Siberian hamsters (Phodopus sungorus).

Few studies have directly addressed the impact of fur on seasonal changes in energy intake. The daily food intake of Siberian hamsters (Phodopus sungorus) was measured under simulated summer and winter conditions in intact animals and those with varying amounts of pelage removed. Energy intake increased up to 44% above baseline control values for approximately 2-3 wk after complete shaving. Increases in food intake varied with condition and were greater in hamsters housed in short than long day lengths and at low (5 degrees C) than moderate (23 degrees C) ambient temperatures. Removal of 8 cm(2) of dorsal fur, equivalent to 30% of the total dorsal fur surface, increased food intake, but removal of 4 cm(2) had no effect. An 8-cm(2) fur extirpation from the ventral surface did not increase food consumption. Food intake was not influenced differentially by fur removal from above brown adipose tissue hot spots. Fur plays a greater role in energy balance in winter- than summer-acclimated hamsters and conserves energy under a wide range of environmental conditions.

Acclimatization↗
PubMed1985

Arginine vasotocin and glomerular filtration rate in saltwater-acclimated ducks.

We examined the relationship between whole kidney glomerular filtration rate (GRF) and the plasma concentration of immunoreactive arginine vasotocin (AVT), the avian antidiuretic hormone, in saltwater-acclimated ducks. During steady-state diuresis, driven by infusion of sodium chloride solutions, transient reductions of [14C]inulin clearance (3 ml X min-1 X kg-1) occurred when plasma AVT concentrations were roughly doubled by systemic injection of synthetic AVT or after stimulation of endogenous AVT release by perfusion of the third ventricle with hypertonic artificial cerebrospinal fluid (CSF). Transient increases in GFR occurred when plasma AVT was reduced during inhibition of its endogenous release by hypotonic ventricle perfusion. GFR also increased after injection of AVT antiserum but returned to control values within 30 min, while plasma AVT concentration remained very low for at least 1 day. During antidiuresis evoked by infusion of strongly hypertonic saline, GFR values estimated from plasma disappearance curves of [125I]iothalamate were not different from the GFR values estimated subsequently with the same method in the same ducks made diuretic by hypotonic saline infusions, although AVT concentrations were depressed during the latter as compared with the former infusion. Factors other than AVT must be important for the control of GFR during sustained osmotic stress.

Adaptation, Physiological↗
PubMed1977

Ouabain-sensitive liver and diaphragm respiration in cold-acclimated hamster.

The in vitro respiratory rates of liver and diaphragm from hamsters were compared before and after prolonged cold exposure (5 degrees C, 3-4 wk). In the presence or absence of glucose, respiratory rates were elevated in both tissues from the cold-acclimated hamsters, and these cold-induced increases were significantly reduced by ouabain. This ouabain inhibition is consistent with the hypothesis that cold exposure of these rodents stimulates the energy demands of the Na+/K+ transport system in liver and diaphragm, with these demands providing a driving force, at least in part, for respiration and accompanying cellular thermogenesis.

Acclimatization↗
PubMed1980

Lung morphometry in guinea pigs acclimated to cold during growth.

Weanling male guinea pigs, Cavia porcellus [initial weight (W) = 200-250 g], were chronically acclimated to 5 degrees C for 2-18 wk before they were killed. Controls were raised at 22 degrees C. Food and water were given ad lib., and growth was the same in both groups. Under pentobarbital anesthesia (30 mg/kg), lungs were fixed by tracheal instillation of glutaraldehyde and processed for electron microscopy. Lung volume (VL, ml) was measured by displacement; alveolar and capillary surface areas (SA and Sc, m2) were determined morphometrically. Regressions of lung variables vs. W at 22 degrees C (range of W = 89-1,274 g) were as follows: VL = 0.175 W0.676, SA = 0.0097 W0.759, and Sc = 0.0055 W0.825; for 5 degrees C animals (range of W = 239-1,074 g): VL = 0.384 W0.584, SA = 0.0334 W0.594, and Sc = 0.032 W0.562. The total arithmetic mean thickness of lung tissue did not vary with W, and averaged 1.39 microns at 22 degrees C and 1.41 microns at 5 degrees C. VL, SA, and Sc are significantly greater in 5 degrees C guinea pigs than in 22 degrees C animals when W = 300-600 g, but are indistinguishable between groups when W > 700 g. Chronic increases in oxygen consumption, which occur with prolonged exposure to cold, result in accelerated lung development in immature guinea pigs toward normal adult dimensions.

Acclimatization↗
PubMed1982

Body fluid and hematologic adjustments during resting cold acclimation in rhesus monkey.

The purpose of this study was to examine body fluid adjustments during prolonged cold exposure in primates. Six male rhesus monkeys were acclimated for 35 days and 6 degrees C and 80% rh. Red cell mass, extracellular fluid volume, and total body water (TBW) were determined with 51Cr, 35SO4, and 3H2O, respectively, prior to and at various intervals during the cold stress. TBW was increased throughout the exposure, whereas changes in extravascular compartments had occurred within the 1st wk of cold exposure, after which they returned to control values. An increased concentration of blood constituents on day 1 was not accompanied by a decrease in cardiovascular volume. Blood volume and plasma volume in relation to TBW were significantly increased on day 3 and remained increased during the remainder of the exposure. These cardiovascular volume changes were accompanied by a significant hemodilution on day 3 and a gradual return to control values. An increased plasma osmolality and expansion of the erythrocytes (decrease in mean corpuscular hemoglobin concentration) were observed throughout the cold stress. These data suggest that the rhesus monkey may be an adequate primate model for studies of body fluid adjustments, especially during prolonged cold exposure, in primates in general, including the human.

Acclimatization↗
PubMed1984

Renal clearance of urea, inulin, and p-aminohippurate in heat-acclimated rats.

Clearance values of urea, inulin, and p-aminohippurate (PAH) were measured in heat-acclimated (HA) rats exposed for 3 wk to 35 degrees C, in control rats (C) exposed to 23 degrees C, and in HA rats deacclimated (DA) for 3 wk. In HA rats, urea clearance was lower by 73%, inulin clearance by 61%, and PAH clearance by 56%, compared with C rats. The clearance values of these substances returned to the control values in DA rats. The data suggest that the low clearance values reflect both reduced renal blood flow and possible changes in the capacity of the glomeruli for filtration and the tubules for either reabsorption or secretion.

Acclimatization↗