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PubMed1995

Immunohistochemical, ultrastructural and morphometric evidence for brown adipose tissue recruitment due to cold acclimation in old rats.

OBJECTIVE: The aim of this work was to study the reactivity to chronic cold stress of interscapular brown adipose tissue (IBAT) in old rats by stereological, immunohistochemical and ultrastructural methods. DESIGN: Five 2-year-old rats were cold-acclimated at 4 degrees C for 4 weeks and six rats were used as controls (20-23 degrees C). MEASUREMENTS: The following were measured: IBAT volume and weight; unilocular and multilocular brown adipocyte content; preadipocyte number; multilocular cell mitochondrial area; cristae length and density per mitochondrion, and immunoreactivity for the brown adipose tissue specific uncoupling protein (UCP). RESULTS: Following cold acclimation, IBAT increased significantly in weight, volume, relative mass and number of multilocular adipocytes (170%). The number of unilocular adipocytes did not vary significantly. Multilocular adipocytes of both cold-acclimated rats and controls expressed the uncoupling protein, but in the experimental group cristae length and density per mitochondrion were significantly higher. Multilocular adipocyte precursors were observed in only one cold-acclimated rat but not in controls. CONCLUSION: The response of brown adipose tissue of old rats to chronic cold stimulus is similar to that observed in young and adult rats. Cold acclimation induces brown adipocyte recruitment: their number increases significantly, they test UCP-positive and their mitochondria are significantly more active than in controls. On the other hand, the number of unilocular adipocytes is not significantly affected, which may serve to improve the utilization of the heat produced by thermogenesis.

Acclimatization↗

PubMed1997

Cognitive performance during short acclimation to severe hypoxia.

BACKGROUND: Exposure to high altitudes requires acclimation or acclimatization, to prevent the negative effects of severe hypoxia. Among several methods, short acclimation with intermittent exposure to severe hypoxia in a hypobaric chamber triggers efficient physiological pre-adaptation mechanisms (11-13). However, we have little knowledge about the cognitive repercussions of such an acclimation protocol. METHODS: Four mountaineers were tested daily in the course of a short acclimation protocol (5 d). After their SaO2 (arterial oxyhemoglogin saturation) were recorded, they carried out a choice reaction time task (Manikin test) twice every day; first at ground level (250 m, control sessions), second at the highest altitude of the day (D1 = 5000 m, D2 = 5500 m, D3 = 6000 m, D4 = 6500 m, D5 = 7000 m). RESULTS: High altitude SaO2 level decreased during the first 3 d, then stabilized around 72-73%. Despite a slight and transient increase at the highest altitude relative to the ground level in D4, the error rate remained low throughout the protocol. Further, response time to the Manikin task did not show significant changes among the days during the acute stage of hypoxia relative to ground level up to 7000 m. CONCLUSIONS: On the whole, it seems that a short acclimation protocol based on intermittent exposure to simulated high altitudes triggered adaptive processes without major impairment in a choice reaction time task during the acute stages of severe hypoxia.

Acclimatization↗

PubMed1975

The influence of thyroxine and acclimation temperature on glycogen reserves of the frog Rana pipiens.

Leopard frogs were given daily injections of Na-l-thyroxine (2.0 mug/10 g body weight) for seven days, and control animals were given daily injections of the vehicle. During the period of treatment, half of the frogs were acclimated, in darkness and without food, at a constant temperature of 15 degrees C, whereas the remainder of the animals were acclimated at 25 degrees C. At the end of the seventh day, the frogs were killed by decapitation, and the glycogen concentration in samples of liver tissue and skeletal muscle was determined spectrophotometrically. Total hepatic glycogen of each frog subsequently was calculated from data on glycogen concentration and liver weight. Treatment of leopard frogs with thyroxine had no apparent effect on hepatic glycogen reserves of animals acclimated at 15 degrees C, but there was a striking reduction in glycogen content of livers from hyperthyroid frogs held at 25 degrees C. Mobilization of hepatic glycogen in thyroxine-treated animals held at 25 degrees C presumably was secondary to a general stimulation of oxidative metabolism. Treatment with thyroxine had no effect on the concentration of glycogen in skeletal muscle of leopard frogs held at either of the acclimation temperatures used in this study.

Acclimatization↗

PubMed1981

Metabolic responses of striped bass (Morone saxatilis) to temperature acclimation. I. Alterations in carbon sources for hepatic energy metabolism.

The relative contribution of carbohydrate and lipid energy metabolism in liver tissue of temperature-acclimated striped bass was examined in vitro. Respirometry experiments were conducted to assess the role of various endogenous foodstuffs in providing reduced two-carbon fragments for aerobic metabolism. Liver composition was measured as a reflection of foodstuff flux and storage. Catabolism of 14C-labeled substrates to 14CO2 was monitored to estimate the tissue capacity for utilization of various classes of compounds. When measured at the temperature of acclimation, oxygen uptake (VO2) by liver slices shows near perfect compensation between 15 and 25 degrees C, whereas a 2.75-fold increase is found between 5 and 15 degrees C. Respiratory quotients (R.Q.) near unity are found at 5 degrees C and decrease to 0.85 and 0.82 at 15 and 25 degrees C, respectively. Inhibition of VO2 by iodoacetic acid, a glycolytic inhibitor, is near 60% at 5 degrees C and decreases to 30-40% at 15 and 25 degrees C. Evolution of 14CO2 from 14C-labeled glucoses and palmitate confirms a conservation of liver tissue capacity for carbohydrate utilization between acclimation temperatures of 5 and 15 degrees C, and an increasing capacity for utilization of fatty acids as temperature increases. Ratios of 14CO2 from 14C-6-and 14C-1-labeled glucoses indicate a relative increase in the participation of the pentose shunt in carbohydrate metabolism with cold acclimation. The results are consistent with an increasing reliance on carbohydrates for energy metabolism in the cold, whereas lipid substrates are utilized more at warm temperatures. These changes may be adaptive in partitioning energy reserves for seasonal activities of migration and reproduction.

Adaptation, Physiological↗

PubMed1988

Effect of hyperoxia acclimation on catalase and glutathione peroxidase activities and in vivo peroxidation products in various tissues of the frog Rana ridibunda perezi.

Among vertebrates, adult amphibians are known to be especially tolerant to exposure to high environmental oxygen tensions. To clarify the basis for this high O2 tolerance, adult Rana ridibunda perezi frogs were acclimated for 15 days to water-air phases with either 149 mm Hg O2 (normoxia) or 710 mm Hg O2 (hyperoxia). At the end of the acclimation, various morphometric and biochemical parameters related to oxidative stress were measured in seven organs and tissues. Hyperoxia acclimation did not change either the total weight of the animals or the total and relative wet weights of the organs studied, except for the brain, which showed weight increases in the hyperoxic group. In vivo tissue peroxidation increased in the kidney; decreased in the skeletal muscle and skin; and did not change in the liver, lung, brain, and heart after hyperoxic exposures. Whereas liver, lung, and skin showed glutathione peroxidase (GSH-Px) activities with both cumene hydroperoxide (cumene-OOH) and H2O2 as substrates, skeletal muscle only showed H2O2 GSH-Px activity. Hyperoxia acclimation did not change either catalase (CAT) or GSH-Px activities in any organ, except for the liver in which CAT activity was induced by hyperoxia. Thus hyperoxia tolerance in this species does not need the induction of H2O2-detoxifying enzymes in the majority of the organs. It is suggested that the high O2 tolerance of this amphibian species is related to its comparatively high constitutive GSH-Px activities.

Adaptation, Physiological↗

PubMed2005

K+-Phosphatase activity of gill (Na+, K+)-ATPase from the blue crab, Callinectes danae: low-salinity acclimation and expression of the alpha-subunit.

The kinetic properties of a microsomal gill (Na(+), K(+)) ATPase from the blue crab, Callinectes danae, acclimated to 15 per thousand salinity for 10 days, were analyzed using the substrate p-nitrophenylphosphate. The (Na(+), K(+))-ATPase hydrolyzed the substrate obeying Michaelian kinetics at a rate of V=102.9+/-4.3 U.mg(-1) with K(0.5)=1.7+/-0.1 mmol.L(-1), while stimulation by magnesium (V=93.7+/-2.3 U.mg(-1); K(0.5)=1.40+/-0.03 mmol.L(-1)) and potassium ions (V=94.9+/-3.5 U.mg(-1); K(0.5)=2.9+/-0.1 mmol.L(-1)) was cooperative. K(+)-phosphatase activity was also stimulated by ammonium ions to a rate of V=106.2+/-2.2 U. mg(-1) with K(0.5)=9.8+/-0.2 mmol.L(-1), following cooperative kinetics (n(H)=2.9). However, K(+)-phosphatase activity was not stimulated further by K(+) plus NH(4) (+) ions. Sodium ions (K(I)=22.7+/-1.7 mmol.L(-1)), and orthovanadate (K(I)=28.1+/-1.4 nmol.L(-1)) completely inhibited PNPPase activity while ouabain inhibition reached almost 75% (K(I)=142.0+/-7.1 micromol.L(-1)). Western blotting analysis revealed increased expression of the (Na(+), K(+))-ATPase alpha-subunit in crabs acclimated to 15 per thousand salinity compared to those acclimated to 33 per thousand salinity. The increase in (Na(+), K(+))-ATPase activity in C. danae gill tissue in response to low-salinity acclimation apparently derives from the increased expression of the (Na(+), K( (+) ))-ATPase alpha-subunit; phosphate-hydrolyzing enzymes other than (Na(+), K(+))-ATPase are also expressed. These findings allow a better understanding of the kinetic behavior of the enzymes that underlie the osmoregulatory mechanisms of euryhaline crustaceans.

Animals↗

PubMed1982

Routine oxygen consumption and characteristics of the myotomal muscle in tench: effects of long-term acclimation to hypoxia.

Tench (Tinca tinca) were acclimated to either aerated (P02 17.6 KPa) or hypoxic water (P02 1.5 KPa) at 15 degrees C. Fish acclimated to P02 17.6 KPa had a routine oxygen consumption (mls O2/Kg bodyweight/h) of 32.7 in aerated water. Upon acute exposure to Po2 1.5 KPa oxygen consumption decreased to 10.8 and 15.6 in fish acclimated to aerated and hypoxic water, respectively. On the basis of staining for glycogen and for the activities of myofibrillar ATPase and succinic dehydrogenase, three main fibre types can be differentiated in the myotomal muscle. Fibres have been classified as slow, fast aerobic and fast glycolytic. Fast aerobic fibres can be distinguished histochemically by their alkaline-stable Ca2+-activated myofibrillar ATPase activity and their intermediate levels of staining for glycogen and succinic dehydrogenase activity. The patterns of innervation of the fibre types have been investigated by staining neuromuscular endplates and peripheral axons for acetylcholinesterase activity. Motor axons to slow fibres branch extensively giving rise to a number of diffuse endplate formations on the same and adjacent fibres. Fast glycolytic fibres also have a complex pattern of innervation with 8-20 endplates per fibre. A large proportion of the endplates belonged to separate axons. Cross-sectional areas and perimeters of fibres, the number of capillaries/fibre and the lengths of contacts between capillaries and fibres were determined from low-magnification electron micrographs. Acclimation to hypoxia resulted in a decrease in the number of capillaries per fibre for both slow (1.8 to 1.0) and fast (0.8 to 0.2) muscles. The capillary perimeter supplying 1 micrometer 2 of fibre cross-sectional area decreased by 43% and 76% for slow and fast fibres, respectively.

Adaptation, Physiological↗

PubMed1996

Differences in protein patterns of gill epithelial cells of the fish Gillichthys mirabilis after osmotic and thermal acclimation.

Different protein patterns in gill epithelium of a euryhaline and eurythermal teleost fish (Gillichthys mirabilis, Family Gobiidae) in response to long-term (2 months) osmotic and thermal acclimation were found for the first time. Gill epithelial cells were isolated to remove extracellular proteins and quantify specialized cell types. Chloride cells were identified on the basis of size (> 10 microns) and bright appearance after [2-(p-dimethylaminostyryl)-1-methyl-pyridinium-iodine] staining. Small mitochondria-rich cells were < 5 microns in diameter and showed intermediate fluorescence. Abundance of chloride cells and small mitochondria-rich cells was significantly influenced by osmotic but not thermal acclimation (dilute seawater/25 degrees C: 1.4 +/- 0.2% chloride cells, 11.9 +/- 4.6% small mitochondria-rich cells; seawater/25 degrees C: 2.4 +/- 0.6% chloride cells, 2.2 +/- 1.3% small mitochondria-rich cells; seawater/10 degrees C: 2.9 +/- 0.3% chloride cells, 1.2 +/- 0.7% small mitochondria-rich cells). Pavement cells, identified by low fluorescence and intermediate size (5-10 microns), largely predominated under all conditions (> 85% of cells). Thus, they represented the major protein source in gill epithelium. Differences in protein patterns were detectable using two-dimensional but not one-dimensional electrophoresis. Of 602 proteins identified by charge and molecular weight properties, only two were induced by high temperature (25 degrees C) and three in response to cold acclimation (10 degrees C). Nine proteins were induced in diluted seawater-acclimated fish, whereas no seawater-induced proteins were found. We hypothesize that proteins induced under dilute seawater conditions are important for the function of pavement cells in gills of hyper-osmoregulating G. mirabilis.

Acclimatization↗

PubMed1989

Effect of photoperiod and acclimation temperature on nonshivering thermogenesis and GDP-binding of brown fat mitochondria in the Djungarian hamster Phodopus s. sungorus.

Acclimation to short photoperiod at 23 degrees C constant Ta caused P. sungorus to improve their NST capacity from 752 to 1,082 mW. Chronic cold exposure in short photoperiod further enhanced the NST capacity, reaching a maximum level of 1,573 mW at -5 degrees C acclimation temperature. Improvements in NST capacity were always accompanied by an increase in brown fat mitochondrial mass and GDP-binding of brown fat mitochondria, in proportion with the cold load applied during temperature acclimation (23 degrees, 15 degrees, 5 degrees, -5 degrees C). Brown fat mitochondrial protein increased from 7.41 mg (23 degrees C Ta, long photoperiod) through 21.6 mg (23 degrees C Ta, short photoperiod) and 81.6 mg (-5 degrees C Ta, short photoperiod). This approximately 10-fold increase was accompanied by a approximately 35-fold increase in GDP-binding (2.0, 7.3 and 71.6 nmol GDP bound, respectively), demonstrating that the increase in capacity for uncoupled respiration in brown fat is of primary significance for thermogenic acclimation to cold as well as to short photoperiod.

Acclimatization↗

PubMed1986

Effect of nafenopin, a peroxisome proliferator, on energy metabolism in the rat as a function of acclimation temperature.

The effects of the peroxisome proliferator, nafenopin, on body temperature, apparent gross food efficiency and activity of interscapular brown adipose tissue (IBAT) peroxisomes and mitochondria of rats acclimated at 23 degrees C or at 32 degrees C have been studied. In 23 degrees C-acclimated rats, nafenopin treatment induced an atrophy of IBAT characterized by a decrease of tissue wet weight, of amounts of mitochondrial and peroxisomal proteins and of mitochondrial total succinate dehydrogenase activity to 67%, 67%, 65% and 57%, respectively of control values. It also resulted in a 1.9-fold stimulation of peroxisome total acyl CoA oxidase activity and had no effect on apparent gross food efficiency or colonic temperature. Acclimation at 32 degrees C per se induced an atrophy of IBAT and a decrease of total catalase and acyl CoA oxidase activities to 23% and 35%, respectively of values obtained in rats acclimated at 23 degrees C. Nafenopin treatment had no effect on IBAT wet weight, on the amounts of mitochondrial and peroxisomal proteins or on total succinate dehydrogenase activity; it resulted in a 2.9- and a 3.7-fold stimulation of the catalase and acyl CoA oxidase activities, respectively with no change in IBAT oxygen consumption. Apparent gross food efficiency was decreased to 54% of control value and colonic temperature increased by 0.91 degrees C. These results may be interpreted in the following way: nafenopin may, at 23 degrees C ambient temperature, induce an extra-heat production in other tissues than IBAT. This extra-heat production is fully compensated via the thermoregulatory feedback control. This compensation cannot occur at thermoneutrality.

Acclimatization↗

PubMed1985

The effect of temperature- and oxygen-acclimation on phospholipids of goldfish (Carassius auratus L.) brain mitochondria.

Goldfish (Carassius auratus L.) were temperature- and oxygen-acclimated and the composition of the phospholipids and their acyl groups in brain mitochondria was determined. The proportion of ethanolamine to choline phospholipid was greater while the plasmenyl ethanolamine value (P-GPE/D- + P-GPE) was lower at the low acclimation temperature. For the ethanolamine glycerophospholipids, a rise in the ratio n-6/n-3 fatty acyl groups occurred with cold acclimation. No significant change in the ratio was exhibited by phosphatidyl choline. When the oxygen level was increased, at either acclimation temperature, a rise in the GPE/GPC ratio and the plasmenyl ethanolamine value resulted. The n-6/n-3 ratio was generally increased for the ethanolamine classes when the oxygen concentration was raised. The possible significance of these changes is discussed.

Acclimatization↗

PubMed1977

Differential biosynthesis of molecular species of 1,2-diacyl-sn-glycerols and phosphatidylcholines in cold and warm acclimated goldfish (Carassius auratus L.).

The initial incorporation of glycerol-3H into the molecular species of liver 1,2-diacyl-sn-glycerols and phosphatidylcholines was studied in vivo using goldfish acclimated to 10 C and 30 C. A 1.5- and 2.2-fold higher proportion of the total radioactivity in the diacylglycerols from cold acclimated fish was found to be associated with the trienoic and pentaenoic species, respectively, when compared to warm acclimated fish. In the phosphatidylcholines, 1.9- and 1.3-fold greater percentages of the newly-incorporated radioactivity were found in tetraenoic and pentaenoic molecules, respectively, from cold relative to warm acclimated fish which suggests a preferential synthesis of these molecules relative to other molecular species in response to a lowering of environmental temperature. The present results indicate, therefore, that environmental temperature influences the complement of molecular species of diacylglycerols an phosphatidylcholines which fish produce by way of de novo biosynthesis in vivo.

Acclimatization↗

PubMed2002

The mechanisms and costs of physiological and toxicological acclimation to waterborne silver in juvenile rainbow trout (Oncorhynchus mykiss).

Juvenile rainbow trout were exposed to 0, 0.1, 1, 3, and 5 micro g/l silver (Ag, as AgNO3) for 23 days. Specific growth rate, cumulative food consumption, food-conversion efficiency, and critical swimming speed (U(crit)) were significantly reduced during 5 micro g/l Ag exposure, demonstrating a physiological cost of silver acclimation. Only the 5 microg/l Ag treatment had significant cumulative mortality (5.2%). Fish were most susceptible to silver on days 5 and 15. Exposure to 5 microg/l Ag significantly lowered plasma Na+ and Cl- on days 5 and 10, but plasma ion concentration recovered thereafter. Unidirectional Na+ uptake and gill Na/K-ATPase activity were significantly inhibited by 3 and 5 microg/l Ag exposure. Na+ uptake was inhibited by 3 micro g/l Ag at day 5 alone, whereas the effects at the highest Ag exposure persisted until day 15. Gill Na/K-ATPase was inhibited on day 5 in both the 3 and 5 microg/l Ag treatments but increased to approx. 1.5 times of control levels by day 23. Only the 3 and 5 microg/l Ag treatments produced toxicological acclimation (at least twofold elevations in 168-h LC50 values in fish subsampled on days 15 and 23). We conclude that physiological acclimation results from compensatory changes in Na+ transport at the gills, and that these changes may eventually lead to toxicological acclimation.

Acclimatization↗

PubMed2006

Food deprivation alters osmoregulatory and metabolic responses to salinity acclimation in gilthead sea bream Sparus auratus.

The influence of acclimation to different environmental salinities (low salinity water, LSW; seawater, SW; and hyper saline water, HSW) and feeding conditions (fed and food deprived) for 14 days was assessed on osmoregulation and energy metabolism of several tissues of gilthead sea bream Sparus auratus. Fish were randomly assigned to one of six treatments: fed fish in LSW, SW, and HSW, and food-deprived fish in LSW, SW, and HSW. After 14 days, plasma, liver, gills, kidney and brain were taken for the assessment of plasma osmolality, plasma cortisol, metabolites and the activity of several enzymes involved in energy metabolism. Food deprivation abolished or attenuated the increase in gill Na+,K+-ATPase activity observed in LSW- and HSW-acclimated fish, respectively. In addition, a linear relationship between renal Na+,K+-ATPase activity and environmental salinity was observed after food deprivation, but values decreased with respect to fed fish. Food-deprived fish acclimated to extreme salinities increased production of glucose through hepatic gluconeogenesis, and the glucose produced was apparently exported to other tissues and served to sustain plasma glucose levels. Salinity acclimation to extreme salinities enhanced activity of osmoregulatory organs, which is probably sustained by higher glucose use in fed fish but by increased use of other fuels, such as lactate and amino acids in food-deprived fish.

Acclimatization↗

PubMed2006

Is BMR repeatable in deer mice? Organ mass correlates and the effects of cold acclimation and natal altitude.

Basal metabolic rate (BMR) is probably the most studied aspect of energy metabolism in vertebrate endotherms. Numerous papers have explored its mass allometry, phylogenetic and ecological relationships, and ontogeny. Implicit in many of these studies (and explicit in some) is the view that BMR responds to selection, which requires repeatability and heritability. However, BMR is highly plastic in response to numerous behavioral and environmental factors and there are surprisingly few data on its repeatability. Moreover, the mechanistic underpinnings of variation in BMR are unclear, despite considerable research. We studied BMR repeatability in deer mice (Peromyscus maniculatus) across intervals of 30-60 days, and also examined the influence of birth altitude (3,800 m versus 340 m) and temperature acclimation (to approximately 5 or approximately 20 degrees C) on BMR, and the relationship between BMR and organ size. Neither acclimation temperature nor natal altitude alone influenced BMR, but the combination of birth at high altitude and cold acclimation significantly increased BMR. Few visceral organ masses were correlated to BMR and most were inconsistent across natal altitudes and acclimation temperatures, indicating that no single organ 'controls' variation in BMR. In several treatment groups, the mass of the 'running motor' (combined musculoskeletal mass) was negatively correlated to BMR and the summed mass of visceral organs was positively correlated to BMR. We found no repeatability of BMR in any treatment group. That finding-in sharp contrast to high repeatability of BMR in several other small endotherms-suggests little potential for direct selection to drive BMR evolution in deer mice.

Acclimatization↗

PubMed2000

Digestive plasticity and the cost of acclimation to dietary chemistry in the omnivorous leaf-eared mouse Phyllotis darwini.

We examined the costs associated with acclimation in an omnivorous mouse (Phyllotis darwini) fed two contrasting diets (carbohydrate-rich and protein-rich). We studied the response of gut morphology and digestive performance in animals shifted to a novel diet at different developmental stages. When acclimated adult animals were shifted to the alternative diet, energy digestibility decreased. We also found long-term consequences to diet acclimation. Animals reacclimated for 15 days to an alternative diet did not increase digestive performance. Although no effects of diet on gut morphology were noted, a significant positive correlation between energy digestibility and small intestinal length was found, explaining most of the variability observed in energy digestibility. These results suggest that caution should be used when defining adaptive changes if the possible cost of acclimation is neglected.

Acclimatization↗

PubMed2001

Differential effect of cold acclimation on blood composition in rats and hamsters.

Male rats and hamsters were exposed to a progressively lower air temperature and shorter photoperiod to simulate the onset of winter. Normothermic hamsters had a higher haematological oxygen carrying capacity (OCC) and coagulability (shorter prothrombin time and activated partial thromboplastin time) than rats. Cold acclimation significantly increased the OCC of rats, which parallels an increased metabolic rate, while no differences were observed in hamsters. Red cell transit time through filters was faster in the acclimated rats but not in hamsters, reflecting the lower mean cell volume due to a decreased rate of clearance from the circulation. Platelet counts were significantly lower in both cold-acclimated rats and hamsters, and there was a significant leucopenia in rats, which would reduce the degree of microvascular blockade. Whole blood viscosity, plasma viscosity, and serum osmolarity showed little change in either species. However, whole blood viscosity was significantly lower in cold-acclimated hamsters than control hamsters at the lowest shear rate tested (0.95 s(-1)). Interestingly, plasma viscosity and serum osmolarity were significantly lower in hamsters exposed to low temperatures for a shorter period (4 weeks), and may reflect the development of a reduced coagulability. These data suggest that blood composition in hamsters contributes to an innate tolerance of low temperatures, maintaining tissue perfusion under hypothermic conditions and aiding arousal from hibernation.

Acclimatization↗

PubMed2000

Modulation of leptin sensitivity by short photoperiod acclimation in the Djungarian hamster, Phodopus sungorus.

During seasonal acclimation, Djungarian hamsters spontaneously exhibit a reduction in food intake, body mass and body fat stores, which is externally cued by shortening of day length in autumn and controlled by a sliding set-point. We investigated the function of the leptin adipostatic feedback system in the photoperiodic control of seasonal acclimation. In response to mouse recombinant leptin injections for 10 days, long day photoperiod (LD) and short day photoperiod (SD)-acclimated hamsters decreased food intake and body mass. The reduction of body mass was due to the depletion of body fat, as revealed by carcass composition analysis. In SD hamsters, leptin caused a larger reduction of body fat mass than observed under LD conditions, whereas the anorectic effect was similar in both photoperiods. The serum leptin concentration was 9.3 +/- 1.2 ng/ml in LD-acclimated hamsters and decreased significantly to 4.2 +/- 0.8 ng/ml and 2.1 +/- 0.6 ng/ml in hamsters exposed to SD for 66 days and 116 days, respectively (P < 0.001). A strong positive correlation between total body fat mass and serum leptin concentration was found (rS = 0.935, P < 0.0001, n = 70). Despite the anorectic action of exogenous leptin, higher endogenous leptin levels in LD hamsters were paralleled by higher food intake in LD hamsters as compared to SD hamsters. This paradoxical finding further supports the increased leptin sensitivity in SD hamsters as judged from leptin treatment experiments. We tested the functional significance of leptin for the controlled down-regulation of food intake and body mass induced by short photoperiod. Food restriction for 10 days during the transition phase decreased body mass below the desired sliding set-point, which was recovered in control hamsters following ad libitum refeeding. Treatment with mouse recombinant leptin during ad libitum refeeding inhibited the recovery of body mass and blunted the increase of food intake observed in controls, indicating that the sliding set-point utilizes leptin as a signal for the adjustment of the appropriate body mass level.

Acclimatization↗