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PubMed1989

Metabolic cold acclimation after repetitive intermittent cold exposure in rat.

Repetitive intermittent cold exposure (5 degrees C, 6 h/day, 4 weeks) (ICE) resulted in the same cold adaptability as assessed by an enhanced cold tolerance (less drop of colonic temperature at -5 degrees C) and nonshivering thermogenesis (NST) (greater noradrenaline-induced heat production) as that elicited by continuous cold exposure (5 degrees C, 4 weeks) (CA) in rats. Although shorter intermittent (5 degrees C, 2 h/day, 4 weeks) (ICE-2 hr) as well as shorter continuous (5 degrees C, 1 week) (CA-1 wk) cold exposure effected an improved cold adaptability, the magnitude of cold tolerance and NST was smaller as compared with that in CA and ICE. The cold deacclimation process as reflected on the decreased NST did not differ between CA and ICE. Food intake was less in ICE than CA, while increase in body weight during the acclimation period was greater in the former. Increase in adrenal weight was greater in CA than ICE, but plasma corticosterone level did not differ among warm controls (WC), CA, and ICE in resting state (after 18-20 h at warm control temperature of 25 degrees C). Weights of interscapular and dorsocervical brown adipose tissue (BAT) increased to the same degree in CA and ICE. Plasma glucagon level in resting state did not differ among groups, while BAT glucagon levels significantly increased in CA and ICE, but they were higher in dorsocervical site than interscapular site in all acclimated states. Acute cold exposure (-5 degrees C, 15 min) caused increases in plasma corticosterone, glucagon levels, and in BAT glucagon levels in all acclimated groups. The extent of increase was significantly less for plasma glucagon in CA, while plasma corticosterone increased similarly in all groups. These results indicate that repetitive short-term cold exposure could elicit the same cold adaptability as that induced by continuous exposure, but requiring only one-fourth of the time of continuous cold exposure. Moreover, it is suggested that glucagon is involved in both CA and ICE, but the same extent of cold adaptability can be obtained in the less energy-requiring and less stressful state in ICE.

Acclimatization↗

PubMed1992

Effects of cold acclimation on cold-induced changes in lipid metabolism of rat brown adipose tissue.

Effects of acute cold exposure (0 degree C, 12 h) on lipid metabolism of the interscapular brown adipose tissue (BAT) were studied in warm controls (25 degrees C) (WC) and cold-acclimated rats (5 degrees C, 4 weeks) (CA). 1) We confirmed that cold acclimation brought about decreased BAT triglyceride (TG) level and increased BAT phospholipid (PL) level. The indexes of unsaturation, such as unsaturation index and polyunsaturated fatty acids/saturated fatty acids ratio, of bulky fatty acids (FA) (palmitic, stearic, oleic, and linoleic acids) decreased in TG, while those increased in PL. Rare FA (eicosadienoic acid, homo-gamma-linoleinic acid, lignoceric acid) level, which were about five times higher in PL than TG in WC, decreased in both TG and PL in CA. 2) Effect of acute cold exposure in WC: The level as well as the amount of TG in BAT was greatly reduced and the indexes of unsaturation in TG-FA increased. The most part of reduced TG (85%) was explained by the bulky FA. Rare FA explained only 1.1% of reduced TG. PL level in BAT did not change, but its amount decreased. The indexes of unsaturation increased in PL-FA. 3) Effect of acute cold exposure in CA: CA was placed in warm temperature of 25 degrees C before cold exposure. In contrast with the cold-reduced TG in WC, either the level or the total amount of TG in BAT did not change, but the indexes of unsaturation in TG-FA decreased. The level as well as the total amount of PL in BAT increased. The arachidonic index and arachidonate in PL-FA decreased, but the indexes of unsaturation did not change. These results indicate as a whole that acute cold exposure as well as cold acclimation influences BAT lipid metabolism in FA compositions as well as amount of TG and PL, suggesting that such changes are related to thermogenic activity of this tissue.

Acclimatization↗

PubMed1993

Alterations of insulin content and insulin binding to plasma membranes in rat brown adipose tissue during cold exposure and cold acclimation.

We examined the insulin content, insulin binding to plasma membranes, and in vitro oxygen consumption of brown adipose tissue (BAT) from warm-acclimated (25 degrees C), acute cold-exposed (5 degrees C, 24 h: CE), and cold-acclimated (5 degrees C, 4 weeks: CA) rats. Plasma insulin level was significantly lower in CE rats, but it did not differ between CA rats and warm controls. Insulin content per mg BAT weight from CE and CA rats were about three-times higher than those from controls. 125I-insulin binding to plasma membranes of BAT from CE rats was higher and that from CA rats was lower than that from respective warm controls. Scatchard plots analysis showed that the number of insulin binding sites per mg protein of BAT plasma membranes from CE rats increased by 100%, while that from CA rats decreased by 35% without any changes of affinity constant. Basal oxygen consumption of BAT from CE rats was higher than warm controls, and suppressed by insulin. Insulin did not affect basal oxygen consumption of BAT from CA and warm control rats. Noradrenaline-induced oxygen consumption of BAT from warm controls and CE rats was suppressed by insulin. These findings suggested that insulin was involved in the regulation of BAT thermogenesis by changing insulin status in BAT (content and binding to plasma membranes) during cold exposure and cold acclimation.

Acclimatization↗

PubMed1987

Fiber composition and capillarity in growing guinea pigs acclimated to cold and cold plus hypoxia.

The central portion of the medial head of the gastrocnemius of control (normoxic and normothermic), hypoxia-, cold-, and cold plus hypoxia-acclimated guinea pigs was analyzed for capillary supply and fiber composition to elucidate changes in capillarity induced by environmental stresses. The muscle was cut at midbelly, frozen, sectioned, and stained for myosin ATPase. Fiber cross-sectional areas; percentages of slow-twitch oxidative (SO), fast-twitch oxidative-glycolytic (FOG), and fast-twitch glycolytic (FG) fibers; and numbers of capillaries around each fiber type were measured. Growth rates of all four guinea pig groups were similar. Capillarity was not affected by acclimation to hypoxia. Cold and cold plus hypoxia acclimation led to increased numbers of capillaries around the fiber in all three fiber types. In addition, significant increases in the percentage of FOG fibers and concomitant decreases in the percentage of FG fibers compared to controls were found in cold and in cold plus hypoxia indicating that a transformation of fiber type from FG to FOG had occurred. The increase in FOGs at the expense of the FGs did not occur in the guinea pigs grown in a hypoxic environment. The increased total capillarity in those muscles studied was the result of more capillaries around all fiber types and was not due to simple transformation of fibers.

Acclimatization↗

PubMed1997

[The adaptive changes in vascular endothelial cell and resistance to frostbite in cold acclimated rats].

Several functions of vascular endothelial cells (VEC) were investigated in rats acclimated to cold (CA) and with frostbitten feet. The results indicated that in CA rats, the number of endothelial cells in circulatory blood and the contents of 6-keto -PGF1 alpha and TXB2 in plasma were markedly higher, the activity of serum angiotensin I converting enzyme (ACE) was lower, compared with those in rats non-acclimated to cold (NCA), whereas T/P ratio of the two groups was close to each other. After the rats were frostbitten, those parameters in NCA group increased sharply except for a decrease in ACE activity. But in CA group, those parameters decreased temporarily or did not change obviously and the tissue survival area (TSA) significantly increased. The above findings suggest that the adaptive changes in increase of metabolic turnover rate and function of VEC after cold acclimation may be beneficial to the body to enhance the resistance to frostbite and repairing ability.

6-Ketoprostaglandin F1 alpha↗

PubMed2001

Multigeneration zinc acclimation and tolerance in Daphnia magna: implications for water-quality guidelines and ecological risk assessment.

Development of zinc tolerance is described for the cladoceran Daphnia magna Straus. Zinc tolerance (i.e., toxicity and deficiency) was monitored during successive generations of D. magna acclimated to different zinc concentrations. Survival, reproduction, carapax length measurements, and cellular energy allocation assessments were used as test endpoints. Special attention was paid to the consequences of zinc deficiency. The zinc acclimation concentration clearly influenced the overall fitness of the organism. After several generations of acclimation, an optimal concentration curve was observed, with an optimum zinc concentration between 300 and 450 microg/L. Zinc deficiency resulted in a lower zinc tolerance, a higher coefficient of variation for brood size, and an increased pH sensitivity. These results clearly indicate that (background) zinc concentrations present in test and culture media have to be considered in the evaluation of toxicity test results, especially when the toxicity data are used for water-quality guideline derivation and/or ecological risk assessment. Culture and test media containing very little or no zinc do not provide a basis for useful ecotoxicological data.

Adaptation, Physiological↗

PubMed2002

Resting energy expenditure of rats acclimated to hypergravity.

BACKGROUND: The use of centrifugation at 1 G has been advocated as a control condition during spaceflight and as a countermeasure to compensate for the adverse effects of spaceflight. Rodents are the primary animal model for the study of the effects of spaceflight and will be used in the evaluation of centrifugation as a countermeasure and means of control at 1 G during flight. HYPOTHESIS: The present study was designed to assess whether resting energy expenditure (EER) of male rats was increased in relation to the magnitude of the level of gravity to which the animals were exposed. The influence of body mass and age on resting energy expenditure (EER) of male rats (n = 42, age 40-400 d) was determined following 2 wk of acclimation to 1, 2.3, or 4.1 G. Hypergravity environments were created by centrifugation. Measurements were made at the gravity level to which the animal was acclimated and during the lights-on period. RESULTS: In rats matched for body mass (approximately 400 g), mean O2 consumption and CO2 production were higher (18% and 27%, respectively) in the 2.3- and 4.1 -G groups than controls. Mean respiratory exchange ratio (RER) increased from 0.80 to 0.87. EER was increased from 47 +/- 0.1 kcal x d(-1) at 1 G, to 57 +/- 1.5 and 58 +/- 2.2 kcal x d(-1) at 2.3 and 4.1 G, respectively. There was no difference in EER between the hypergravity groups. When age differences were considered, EER (kcal x kg(-1) x d(-1)) with increased gravity was 40% higher than at 1 G. The increase in EER was not proportional over gravity levels. CONCLUSION: Acclimation of rats to hypergravity increases their EER, dependent on body mass and age, and may alter substrate metabolism. The increase in EER was not related to the level of gravity increase.

Adaptation, Physiological↗

PubMed1975

[Role of thyroid hormone in cold adaptation. 1. Requirement of thyroxine during the course of cold acclimation as estimated by noradrenaline sensitivity (author's transl)].

The amount of thyroxine required for the development and maintenance of cold acclimation was investigated in the rat. Warm-adapted thyroidectomized rats could not survive at 5 degrees C. When thyroxine was replaced, these rats could survive and responded to noradrenaline with increased oxygen consumption in proportion to the dose of replaced thyroxine. Judged from the amount of thyroxine in thyroidectomized rats necessary to restore noradrenaline sensitivity to the same level as seen in intact controls, 30 degrees C-adapted rats were found to require 3.3 mug thyroxine/100 g b.w./day, while 5 degrees C-adapted rats required only 1.2 mug. It is concluded that the amount of thyroxine necessary to produce cold acclimation is much larger than that for the maintenance of cold acclimation.

Acclimatization↗

PubMed2003

Effect of cold acclimation on hemorheological behavior in rats with frostbite.

The hemorheological behavior pre- and post-freezing and tissue survival area (TSA) of frostbitten hind feet in cold-acclimated rats (group CA) and the control (group C) were observed in order to go further into the mechanism of cold acclimation. The results indicated that blood viscosity and RBC aggregation tendency were lowered and RBC deformability improved obviously in CA rats as compared with those in group C (p<0.01). After the rats' hind feet were frozen, the hemorheological behavior in both group CA and C rats was changed abnormally and the changes were less serious in CA rats than those in C rats. The TSA of CA rats was much larger than that of C rats (p<0.01). The aforesaid results revealed that after rats were acclimated to cold, their resistance to freezing increased and their adaptive changes in hemorheological behavior occurred. The extent of abnormal changes in hemorheological behavior caused by freezing was reduced in CA rats, therefore the disorder microcirculation could be improved. These changes were beneficial to the frostbitten tissue to recovering and healing. So it is considered that in CA rats, the adaptive change in hemorheological behavior is one of the cause enhancing resistance to frostbite.

Acclimatization↗

PubMed1991

Are adrenal catecholamines involved in the enhancement of aldosterone production in cold acclimated rats?

In order to determine the possible role of adrenal catecholamines in the enhancement of aldosterone production in cold acclimated rats, dopamine (DA), noradrenaline (NA) and adrenaline (A) contents of adrenals were investigated in cold acclimated (or not), hypophysectomized (or not) rats. The DA content, DA being an inhibitor of aldosterone synthesis, increased in hypophysectomized rats and remained unchanged in sham-operated ones following cold exposure. The NA and A contents, these being, in vitro, stimulators of aldosterone production did not increase, in either group of cold acclimated rats. It is concluded that adrenal catecholamines do not seem to be implicated in the enhancement of aldosterone production.

Acclimatization↗

PubMed1991

The role of interscapular brown adipose tissue in cold acclimation in the rat.

The role of the interscapular brown adipose tissue (IBAT) in the defense against cold exposure and subsequent acclimation to it was studied in the rat, a homeotherm. When placed at 4 degrees C, the rat was able to maintain a constant core temperature even though skin and even more so tail temperature dropped drastically. Metabolic rate became significantly higher than control animals kept at 23 degrees C after 24 hrs and continued to rise throughout the 6 weeks exposure period. Starting at week 1, there was hypertrophy of the IBAT with concomitant proliferation of mitochondria. Bilateral surgical removal of IBAT led to significant reduction in metabolic rate only in the fully cold-acclimated rat. However, the survival rate was not affected. It is thus concluded that IBAT played an important but not absolutely essential role in cold acclimation.

Acclimatization↗

PubMed1988

Thermogenic mechanisms in cold-acclimated animals.

1. This paper reviews the mechanisms of thermogenesis after cold-acclimation. 2. Upon exposure to cold, the oxygen consumption of animals increases by means of shivering and non-shivering thermogenesis. As cold exposure progresses, shivering decreases while non-shivering thermogenesis increases, so that the cold-acclimated animal produces heat mostly by non-shivering thermogenesis. 3. Brown adipose tissue in several species, including man, is an essentially thermogenic organ that produces heat by uncoupling mechanisms in mitochondria. 4. The activity of brown adipose tissue can be assessed by physiological and biochemical methods. 5. After cold acclimation, the activity and mass of brown adipose tissue are higher than in control animals. Brown adipose tissue is considered the main factor responsible for non-shivering thermogenesis.

Acclimatization↗

PubMed1985

Effects of cold acclimation on adipose tissue lipolysis and cellularity in the hypophysectomized rat.

The study investigated the effects of hypophysectomy and cold acclimation on cellularity and lipolytic capacity of adipose tissue. Hypophysectomized rats (H) were compared to age matched or weight matched controls. Rats were exposed to either 28 degrees C or 15 degrees C ambient temperature for five weeks. In H, despite the inhibition of body growth, it was observed that the growth of epididymal adipose tissue is not entirely inhibited. In comparison with weight matched controls, increase in tissue weight is found to be due to an adipocyte hypertrophy without changes in cell number. No effect of cold acclimation on adipose tissue weight, cellularity and insulinemia were observed in the H group. The in vitro lipolysis effect of norepinephrine was suppressed in 28 degrees C H; a partial recovery of this effect was observed after cold acclimation. This fact is not dependent on adipocyte size, but possibly on structural or metabolic modifications.

Acclimatization↗

PubMed1977

Changes in fine structure of rat skeletal muscle related to cold acclimation.

Mitochondria became larger and some numerous in the internal red fibers of M. quadriceps femoris and neck muscle in cold-acclimated rats than in warm-acclimated ones, while they became less in number in spite of remarkable increase of size in the external white fibers of the former muscle. Mitochondrial cristae and sarcoplasmic reticuli developed better in the muscles of cold-acclimated rats.

Acclimatization↗

PubMed1977

[Morpholigic and physiologic repercussions of partial removal of brown adipose tissue in rats acclimated to different temperatures].

Rats were chronically acclimated to 28 degrees C or 5 degrees C or submitted to daily variations of ambiant temperature. Ten or thirty days after removal of about 40% of the total brown adipose tissue (whole interscapular and 25% of abdominal tissues), the weight of the different pads of brown adipose tissue, thyroid and adrenals were determined. In all the groups, there was a large decrease of brown adipose tissue weight for the first ten days due to the shock following the operation. Then, the brown adipose tissue weight was restaured and, only in constant cold accliclimated rats, compensative hypertrophies of axillary and thoracic brown adipose tissue were found. Adrenals weight was significantly increased after the operation; in the two groups of cold acclimated rats, that increase was still significant one month later. However, the corticosterone production rate was not increased. These results are discussed in relation to the physiolocical role of brown adipose tissue in cold acclimated animals.

Acclimatization↗

PubMed1978

Acclimation of young calves to high temperatures: physiologic responses.

Four 2- to 3-month-old male Bos taurus calves kept in an ambient environment of 18.3 C and 50% relative humidity for a week were then exposed to 40.5 C and 50% relative humidity atmosphere in a climatic chamber for short-term (2 weeks) acclimation. The exposure time was 12 hours each day. Their respiratory rate, skin temperature, and rectal temperature rose sharply on the 1st day of exposure and then gradually declined with continued exposure. The heart rate, on the ohter hand, declined with successive days of exposure. A gradual increase in sweating rates of calves was observed after the 2nd day of exposure. Most of the acclimation in these physiologic measurements was completed in the first 9 to 10 days of exposure and it was concluded that young calves have a well-developed power of acclimation to high temperature

Acclimatization↗

PubMed1995

Body weight loss during acute hypoxia: effects of increased convective oxygen transport or previous acclimation.

Body weight loss and growth retardation occur in rats exposed to simulated high altitude, which may be related to the hypoxemia-induced reduction in the convective oxygen transport (COT). The present study was thus performed to determine whether transfusion polycythemia, increased affinity of hemoglobin for oxygen, or previous acclimation to hypobaria (factors that increase COT) are able to counteract its effect on body weight during the early period of exposure, which appears to be a suitable parameter to test the effectiveness of acclimatization. Polycythemia was induced in weanling rats by two ip injections of 2.5 ml/100 g b.wt of packed homologous red cells. The rise in hemoglobin O2 affinity was brought about in adult rats by giving them 0.5 g/dl sodium cyanate in the drinking water for 3 weeks. A lower body weight loss during the early period of exposure to hypobaria was seen in treated rats than in controls. However, body weight loss was still important, which would indicate that compensation was probably not complete. When growing rats were acclimated to simulated altitude, a sudden increase in body weight was observed when they were brought back to ground levels. When animals were taken to altitude again, they lost weight at a rate not significantly different to that found in non-acclimated ones. The results obtained indicate that treatments do not prevent the studied effect of hypoxia and suggest that hypophagia and the resultant initial body weight loss and secondary depression of body growth could be considered as protective mechanisms against the environmental challenge, although further investigation will be necessary to confirm the hypothesis.

Acclimatization↗

PubMed1996

Human acclimation to work in warm and humid environments.

The aim of this study was to analyse the acclimation of male Europeans during a forty-one day stay in the hot and humid climate of Thailand. We also tried to examine the phases of acclimation which would eventually be used by trainers in the elaboration of the schedule of athletes' preparation to participate in competitions in a tropical climate. Twelve Polish male subjects ageing 21-38 years participated in these examinations. In Poland and Thailand the cycloergometric exercise test with the load of 53% of VO2max was performed until a 1.2 degrees C (delta Tre) increase in rectal temperature was reached. The exercise test was executed in the same environmental conditions (i.e. 30 +/- 1 degrees C and 70 +/- 3% of relative humidity). The duration of this exercise test (DE) was used as a criterion for the efficiency of thermoregulatory functions. During acclimation, three peaks of greater exercise thermoregulatory efficiency have been found, i.e. on the 4th-5th, 11th-12th and 29th-30th days of stay. These findings are particularly important for professional athletes who wish to prepare themselves for competitions held in hot and humid climates.

Acclimatization↗