Effect Of Cold Acclimation Research Articles

Regulation of GDP binding and uncoupling-protein concentration in brown-adipose-tissue mitochondria. The effects of cold-acclimation, warm-reacclimation and noradrenaline.

We have used a specific immunoassay for uncoupling protein and [3H]GDP binding to study the acute and chronic responses of brown-adipose-tissue (BAT) mitochondria of warm-acclimated rats to housing at 4 degrees C and cold-acclimated rats to housing at 27 degrees C. These studies have shown the following. (1) In the cold-exposed rat the increase in mitochondrial uncoupling-protein concentration parallels the increase in GDP binding from 1 day to 5 days, but that acutely (initial 4 h) the increase in GDP binding is not associated with any change in uncoupling-protein concentration. 2. In the cold-acclimated rat rehoused at 27 degrees C, GDP binding fell by over 50% in the first 2 days, without any change in uncoupling-protein concentrations. 3. Noradrenaline acutely (30 min) increased BAT mitochondrial GDP binding of lean and obese Zucker rats, without any change in uncoupling-protein concentrations. 4. The increases in GDP binding in cold-exposed rats were associated with increases in the rate of swelling of mitochondria in the presence of valinomycin and potassium acetate. The evidence supports the hypothesis that the acute response of the rat to changes in environmental temperature are associated with unmasking or remasking of uncoupling protein, whereas chronically changes in uncoupling-protein concentration predominate.

Effect of Cold Acclimation on Bulk Tissue Electrical Impedance

Stem and electrode electric impedance at 14 frequencies were monitored during cold acclimation of alfalfa (Medicago sativa L.) and birdsfoot trefoil (Lotus corniculatus L.). Cold acclimation significantly increased high frequency (e.g. 1.11 megahertz) resistance and reactance but not low frequency (49 hertz) resistance and reactance of both species. High frequency resistance of living stems was equivalent to the average resistance at all frequencies of dead stems and the resistance of dead stems (y) was related to stem water content (x):y = 9.28 - 4.11x + 0.47x(2), R = 0.92. The low-high frequency (49 hertz/1.11 megahertz) resistance ratio decreased during cold acclimation. A time constant believed to be a function of membrane resistance and capacitance was not affected by cold acclimation.

Effect of Cold Acclimation on Bulk Tissue Electrical Impedance

The resistive and reactive components of electrical impedance were measured for birdsfoot trefoil (Lotus corniculatus L.) stems at freezing temperatures to -8 degrees C. As temperature decreased the specific resistance at frequencies between 49 hertz and 1.11 megahertz of stems from cold acclimated plants increased more rapidly than from nonacclimated plants. This temperature dependence of specific resistance could be characterized by an Arrhenius activation energy; cold acclimated stems had a larger Arrhenius activation energy than nonacclimated stems. The low frequency resistance is believed to characterize the extracellular region of the stems and the high frequency resistance is believed to characterize the intracellular region of the stems. Cold acclimation increased the intracellular but not the extracellular resistance at nonfreezing temperatures. Cold acclimated stems were not injured by freezing to -8 degrees C and thawing, but nonacclimated stems were injured by freezing to temperatures between -2.2 and -5.6 degrees C and thawing. Injury to nonacclimated stems at freezing temperatures below -2.2 degrees C was indicated by a decrease in the ratio of resistance at 49 Hz to that at 1.11 megahertz.

Effect of environmental temperature on dietary obesity in Osborne-Mendel rats.

The effects of cold acclimation on cellularity, lipoprotein lipase (LPL) activity and lipolysis were studied in white adipose tissue of rats fed a high fat diet. Male Osborne-Mendel rats (7 weeks old) were exposed at either 28 or 5 degrees C for 10 weeks. The rats were fed a semipurified diet (normal fat (NL): 5% lard, high fat (HL): 54% lard) for the last 9 weeks. Caloric intake with NL and HL diets were comparable and cold exposure led to the same increase with both diets. At 28 degrees C, HL diet initiated both hypertrophy and hyperplasia; however, at 5 degrees C only hyperplasia was observed. Total LPL activity showed high stimulation both in 28 and 5 degrees C HL rats. In vitro lipolytic stimulation by norepinephrine was lowered at 5 degrees C and abolished at 28 degrees C in HL-fed rats. HL diet resulted in enhanced lipid deposition without an increase in caloric intake. Even in cold-adapted Osborne-Mendel rats a relative obesity could be produced by a HL diet.

Gangliosides and energy substrates in brown adipose tissue of cold-acclimated rat.

Effect of cold acclimation on gangliosides as well as triglyceride and glycogen in brown adipose tissue was studied in rats. Ganglioside GM3 level per unit fresh weight and per unit fat-free-dry-matter was significantly higher in cold-acclimated rats (CA) than in warm controls, while the tissue triglyceride and glycogen levels were lower in CA. GM3 may be involved in cold-induced proliferation and differentiation of brown adipose tissue.

Thermogenin amount and activity in hamster brown fat mitochondria: effect of cold acclimation.

To investigate the acclimation process in a hibernator, four different parameters of thermogenin amount and activity were investigated in brown adipose tissue mitochondria from cold-exposed and cold-acclimated Syrian hamsters. Hamsters, which are hibernators, have been considered to be "primed" for thermogenesis and thus not to show cold-acclimation effects, but here a significant increase in [3H]GDP-binding capacity was observed (from 0.5 nmol in control to 0.9 nmol GDP/mg in cold-acclimated hamsters), and this increase was paralleled by an increase in thermogenin antigen amount, as measured in an enzyme-linked immunosorbent assay. The transient nature of the effect of cold exposure on [3H]GDP binding, characteristically observed with rat mitochondria, was not observed with hamster mitochondria, and the increase in [3H]GDP binding occurred without a change in the dissociation constant (0.7 microM). The increase in thermogenin amount was paralleled by an increase both in GDP-sensitive Cl- permeability of the mitochondria and in GDP-sensitive respiration. It was established that it is the maximal activity of thermogenin that is rate limiting for thermogenesis in isolated mitochondria, provided that an optimal substrate is used (such as palmitoyl carnitine). Cold acclimation also increased the total amount of mitochondria in the tissue, leading totally to a sixfold increase in thermogenin content of the hamster. It is concluded that (contrary to the general view) hamsters show the expected physiological, pharmacological, and biochemical signs of cold acclimation (i.e., an increased capacity for nonshivering thermogenesis).

Muscle and brown adipose tissue fatty acid profiles in cold-exposed rats.

Effects of cold acclimation and cold exposure for 25 generations on triglyceride (TG)-, total phospholipid (PL)-, and cardiolipin (CL)-fatty acid (FA) compositions were studied in the different types of skeletal muscles (red and white muscles from quadriceps, and soleus) as well as brown adipose tissue (BAT) in rats. TG: in cold-acclimated rats (CA) and rats reared in cold for 25 generations (25G) white muscle showed the decreased saturated FA (SA) and increased polyunsaturated FA (PU). In soleus of 25G, monounsaturated FA (MU) and PU increased, and SA decreased. In BAT, SA increased and MU decreased in CA, and SA and PU decreased, and MU increased in 25G. PL: in red muscle of CA, SA increased and PU decreased. In red muscle of 25G the similar but more marked changes were found accompanied by lowered arachidonic acid and unsaturation index (UI). In BAT, SA, PU, arachidonic acid, and UI increased in CA, and arachidonic acid increased in 25G. CL: in red and white muscles of 25G, oleic acid and MU increased. In BAT, arachidonic acid increased in CA and 25G, and UI increased in 25G. These results suggest that FA unsaturation of CL in the muscles as well as BAT is involved in an enhanced thermogenesis in cold-exposed rats.

The effects of cold acclimation on electrocardiogram parameters in five species of turtles

1. 1. The effects of thermal acclimation at 25 or 5°C on electrical activity in the heart were investigated in Pseudemys scripta, Terrapene Carolina, Chrysemys picta marginata, Chrysemys picta dor salis, Chelydra serpentina, and Stemotherus odoratus. 2. 2. The durations of the QRS complex and P-R, R-T and R-R intervals were found to increase with decreasing body temperature in all animals tested. 3. 3. The amplitudes of the P and T waves and QRS complex were dependent upon both acclimation temperature and test temperature. 4. 4. Differences between acclimation groups in the change in QRS amplitudes between 20 and 0°C were statistically significant for all species.

The effect of cold acclimation and exercise training on cold tolerance in aged C57BL/6J mice.

We investigated whether intermittent cold acclimation and low intensity exercise training, two interventions known to improve thermoregulatory function in young rodents, enhanced cold tolerance in aged C57BL/6J mice. Mice, aged 18 to 20 months, were randomly assigned to four treatment conditions: (a) intermittent cold acclimation (CA) (50 min per day, 5 times per week for 3 weeks at 5 degrees C), (b) submaximal treadmill exercise (EX) (15 m min-1 for 30 min, 5 times per week for 8 weeks, (c) sequential treatment of CA + EX, and (d) control group. Mice were exposed to a 3-hr cold stress test (15 degrees C) prior to and following treatment. CA aged mice maintained normothermia and demonstrated significant increases in oxygen consumption and brown adipose tissue protein concentration compared with controls; enhanced cold tolerance was probably due to increased utilization of nonshivering thermogenesis. EX aged mice had elevated O2 consumption and increased skeletal muscle enzyme activity compared with controls; however, cold tolerance was not enhanced compared with CA mice. The data suggest that intermittent CA effectively reduces hypothermia during cold challenge in aged mice.

Effects of cold acclimation in dystrophic hamsters: reduction of heart necrosis.

The effects of cold acclimation on brown adipose tissue, heart, and skeletal muscles were evaluated to assess if the increase in metabolic activity associated with chronic exposure to 4 degrees C had any influence on the progression of the syndrome in dystrophic hamsters. Body weight gain was much slower in dystrophic animals kept at 22 degrees C and was unaffected by cold acclimation. Rates of O2 consumption and CO2 production were similar in normal and dystrophic hamsters kept at 22 degrees C, and both were increased in cold-acclimated normal and dystrophic animals. The amount of interscapular brown adipose tissue was about one-half of normal in dystrophic hamsters kept at 22 degrees C. In response to cold acclimation, as in normal hamsters, brown adipose tissue of dystrophic hamsters grew and increased its thermogenin content by more than fourfold. However, the concentration of thermogenin in isolated mitochondria remained unchanged. Heart ventricular hypertrophy was also observed in both normal and dystrophic hamsters after cold acclimation. The number and extent of cardiac necrotic lesions were significantly reduced in cold-acclimated dystrophic animals when compared with age-matched dystrophic hamsters kept at 22 degrees C. Heart calcium content and plasma creatine kinase levels were also reduced in dystrophic hamsters after cold acclimation. However, in soleus muscles the prevalence of centronucleated fibers, an indirect cumulative index of necrosis, as well as the extent of tissue necrosis were not significantly reduced in cold-acclimated dystrophic animals. Thus cold acclimation of dystrophic hamsters appeared to reduce necrosis predominantly in the heart.

Effect of cold acclimation on glucagon receptors of rat white adipocytes.

In order to determine the role of glucagon in cold acclimation, the changes in glucagon receptor were investigated in white adipocytes from cold-acclimated rats by establishing a glucagon radioreceptor assay method for isolated white adipocytes. The following conditions were found to be appropriate for specific glucagon receptor binding assay; cell concentration of about 1 X 10(5) cells/ml, 15 min preincubation with glucagon and 30 min-reaction at 25 degrees C in the presence of bacitracin (1 mg/ml). Cold acclimation decreased the size and increased the number of epididymal white adipocytes. Cold acclimation increased the number of glucagon receptors of white adipocytes, resulting in 140% in terms of unit cell, and 260% increase per unit surface area and 210% increase per whole tissue. However, the affinity of the binding site for glucagon was not affected. The results suggested that an enhanced metabolic response of cold-acclimated rats to glucagon could be partly explained by the increased number of glucagon receptor in white adipocytes.

Effects of cold acclimation on the activity of lipoprotein lipase in adipose tissues of genetically obese Zucker rats

1.1. The activity of lipoprotein lipase (LPL) was studied in interscapilar brown adipose tissue (BAT), epididymal white adipose tissue (WAT) and in the heart of lean and obese adult Zucker rats maintained at 22°C or adapted to cold (10°C).2.2. In WAT the specific activity per gram of tissue was lower in obese than in lean rats but the total activity within the tissue was three-fold higher. Cold acclimation did not modify total activity in either lean or obese rats. In BAT, but not in the heart, both specific and total activities were lower in obese than in lean animals. They were enhanced in both tissues following cold acclimation.3.3. Six-hour fasting led to a decrease in specific activity in WAT of lean rats but had no effect in obese animals; an increase was observed in BAT and heart of both genotypes.4.4. Insulin administration has no effect on activities in WAT in either 22 or 10°C adapted obese rats. Norepinephrine administration stimulates LPL activity in BAT and heart of all groups.5.5. It is concluded that the lack of development of obesity previously observed in obese rats following cold acclimation is not due to a decreased capacity of lipid uptake by WAT. It might in part be due to an increased lipid oxidation in BAT.

The expansion potential of isolated protoplasts: Effect of cold acclimation and osmotic contraction

The expansion potential of isolated protoplasts: Effect of cold acclimation and osmotic contraction

Effect of cold acclimation on the phospholipid composition of the plasma membrane of rye leaves

Effect of cold acclimation on the phospholipid composition of the plasma membrane of rye leaves

Increased α1-adrenergic receptor density in brown adipose tissue of cold-acclimated rats and hamsters

Binding sites for [ 3H]prazosin were characterized in crude membrane fractions from rat brown adipose tissue. Based on agonist (norepinephrine ≅ phenylephrine ⪢ isoprenaline) and antagonist (prazosin ⪢ yohimbine > propranolol) potencies to compete with [ 3H]prazosin, the binding sites were identified as α 1-receptors, not previously described in rat brown adipose tissue. As the [ 3H]prazosin binding sites could be observed in isolated brown fat cell preparations, they were probably postsynaptic. The effect of cold acclimation was studied in crude membrane fractions from control and cold-acclimated (4°C) rats and hamsters. Cold acclimation did not change the affinity of the receptor for agonists and antagonists, but there was a significant increase in the number of α 1-receptors (per mg protein), both in rat (100% increase) and hamster (40% increase) brown fat. Based on these results and on earlier results on β-receptors from this and other laboratories, it is suggested that activation of brown adipose tissue is associated with an increase in the relative density of α 1-receptors (i.e. in the α 1/ β ratio) and an increased significance of α 1-adrenergic pathways for the function of the tissue.

Cold acclimation in Pinus sylvestris: Phospholipids in purified plasma membranes from needles of pine

Effects of cold acclimation on needles of Scots pine (Pinus sylvestris L., Provenance Södra Ydre) were studied at the membrane level. Before and after a period of cold acclimation the plasma membranes were isolated from the needles by a aqueous polymer two‐phase partition technique. Fatty acid composition of total lipids or of individual phospholipids from the plasma membrane showed that the plasma membrane fraction was different from the other microsomal fractions analyzed, especially the 18:2 levels of the individual phospholipids. Furthermore, the cold acclimation period did not result in a decreased saturation level in the plasma membranes. Different steps in cold acclimation reactions at the membrane level are discussed.

Effect of cold acclimation on Na+/K+ transport in hamster liver cells

The effects of prolonged cold exposure of Syrian hamsters on liver membrane (Na+/K+-ATPase activity and on liver intracellular K+ levels was examined. Membrane preparations from cold-acclimated hamsters (6°C for 3 weeks) exhibited significantly higherVmax values for (Na+/K+)-ATPase and significantly greater ouabain binding. These data support the view that in the liver of these cold-exposed hamsters, there is an increase in the number of operational pumps. The fact that the intact liver cells (isolated via liver perfusion) from the cold-acclimated hamsters: (a) did not have higher concentrations of intracellular K+ (despite the presence of more operational pumps); and (b) exhibited greater rates of K+ loss when the pumps were inhibited by maximal ouabain suggests that the K+ leak across the liver cell plasma membrane is increased in the cold-acclimated hamsters. Although the physiological significance of these results needs further evaluation, these membrane changes may be of adaptive value for hibernation.

Effect of Cold Acclimation on Intracellular Ice Formation in Isolated Protoplasts

When cooled at rapid rates to temperatures between -10 and -30 degrees C, the incidence of intracellular ice formation was less in protoplasts enzymically isolated from cold acclimated leaves of rye (Secale cereale L. cv Puma) than that observed in protoplasts isolated from nonacclimated leaves. The extent of supercooling of the intracellular solution at any given temperature increased in both nonacclimated and acclimated protoplasts as the rate of cooling increased. There was no unique relationship between the extent of supercooling and the incidence of intracellular ice formation in either nonacclimated or acclimated protoplasts. In both nonacclimated and acclimated protoplasts, the extent of intracellular supercooling was similar under conditions that resulted in the greatest difference in the incidence of intracellular ice formation-cooling to -15 or -20 degrees C at rates of 10 or 16 degrees C/minute. Further, the hydraulic conductivity determined during freeze-induced dehydration at -5 degrees C was similar for both nonacclimated and acclimated protoplasts. A major distinction between nonacclimated and acclimated protoplasts was the temperature at which nucleation occurred. In nonacclimated protoplasts, nucleation occurred over a relatively narrow temperature range with a median nucleation temperature of -15 degrees C, whereas in acclimated protoplasts, nucleation occurred over a broader temperature range with a median nucleation temperature of -42 degrees C. We conclude that the decreased incidence of intracellular ice formation in acclimated protoplasts is attributable to an increase in the stability of the plasma membrane which precludes nucleation of the supercooled intracellular solution and is not attributable to an increase in hydraulic conductivity of the plasma membrane which purportedly precludes supercooling of the intracellular solution.

Effects of cold acclimation on the feeding pattern and energetic metabolism of genetically obese Zucker rats

1. 1. The feeding pattern, growth rate and energetic metabolism were studied in obese Zucker rats of 5–12 weeks of age kept at ambient temperatures of 22 or 10°C. 2. 2. During this period, the increment in obesity of the 22°C-exposed animal was found to be due to diurnal hyperphagia and not to a lowered resting metabolism. 3. 3. In the 10°C-exposed rat the development of non-shivering thermogenesis associated with a lack of enhancement of food intake leads to prevent the obesity.

Effects of cold acclimation on cold hardiness in the flea beetle, phyllotreta cruciferae

Effects of cold acclimation on cold hardiness in the flea beetle, phyllotreta cruciferae