Fasting in the American marten (<Emphasis Type="Italic">Martes americana</Emphasis>): a physiological model of the adaptations of a lean-bodied animal

The American marten (Martes americana) is a boreal forest marten with low body adiposity throughout the year. The aim of this study was to investigate the adaptations of this lean-bodied species to fasting for an ecologically relevant duration (48 h) by exposing eight farm-bred animals to total food deprivation with seven control animals. Selected morphological and hematological parameters, plasma and serum biochemistry, endocrinological variables and liver and white adipose tissue (WAT) enzyme activities were determined. After 48 h without food, the marten were within phase II of fasting with depleted liver and muscle glycogen stores, but with active lipid mobilization indicated by the high lipase activities in several WAT depots. The plasma ghrelin concentrations were higher due to food deprivation, possibly increasing appetite and enhancing foraging behavior. The lower plasma insulin and higher cortisol concentrations could mediate augmented lipolysis and the lower triiodothyronine levels could suppress the metabolic rate. Fasting did not affect the plasma levels of stress-associated catecholamines or variables indicating tissue damage. In general, the adaptations to short-term fasting exhibited some differences compared to the related farm-bred American mink (Mustela vison), an example of which was the better ability of the marten to hydrolyze lipids despite its significantly lower initial fat mass.     

Adaptations to fasting in the American mink (Mustela vison): carbohydrate and lipid metabolism

The aim of this study was to investigate whether the actively wintering American mink Mustela vison is strictly dependent on continuous food availability or if it has evolved physiological adaptations to tolerate nutritional scarcity. Fifty farm-bred male minks were divided into a fed control group and four experimental groups fasted for 2, 3, 5 or 7 days. The rate of weight loss was several-fold higher (1.5-3.2% day(-1)) in the mink than recorded previously in larger carnivores utilizing passive wintering strategies. The minks remained normoglycaemic, although their liver glycogen stores and glucose-6-phosphatase activities decreased during fasting. Adipose tissue constituted approximately 36% of their body mass after 7 days of food deprivation. Intra-abdominal fat, especially retroperitoneal but also mesenteric adipose tissue, were the most important fat depots to be hydrolyzed, but the ability of the mink to utilize its body lipids during fasting may be limited. The increased liver size, hepatic triacylglycerol accumulation and increases in the activities of plasma aminotransferases indicated liver dysfunction. Food deprivation also affected the red blood cell indices, and the blood monocyte and lymphocyte counts decreased suggesting immunosuppression during fasting. The results of the present study suggest that the mink has not evolved sophisticated adaptations to wintertime fasting.     

Food deprivation in the common vole (<Emphasis Type="Italic">Microtus arvalis</Emphasis>) and the tundra vole (<Emphasis Type="Italic">Microtus oeconomus</Emphasis>)

Arvicolinae voles are small herbivores relying on constant food availability with weak adaptations to tolerate prolonged food deprivation. The present study performed a comparative analysis on the responses to 4–18 h of food deprivation in the common vole (Microtus arvalis) and the tundra vole (Microtus oeconomus). Both species exhibited rapid decreases in the plasma and liver carbohydrate concentrations during phase I of fasting and the decline in the liver glycogen level was more pronounced in the tundra vole. The plasma thyroxine concentrations of the common vole decreased after 4 h. Lipid mobilization (phase II of fasting) was indicated by the increased plasma free fatty acid levels after 8–18 (the common vole) or 4–18 h (the tundra vole) and by the elevated lipase activities. In the tundra vole, the plasma ghrelin concentrations increased after 12 h possibly to stimulate appetite. Both species showed increased liver lipid concentrations after 4 h and plasma aminotransferase and creatine kinase activities after 12–18 h of food deprivation implying liver dysfunction and skeletal muscle damage. No signs of stimulated protein catabolism characteristic to phase III of fasting were present during 18 h without food.     

Short-term fasting induces intra-hepatic lipid accumulation and decreases intestinal mass without reduced brush-border enzyme activity in mink (<Emphasis Type="Italic">Mustela vison</Emphasis>) small intestine

For many mammalian species short-term fasting is associated with intestinal atrophy and decreased digestive capacity. Under natural conditions, strictly carnivorous animals often experience prey scarcity during winter, and they may therefore be particularly well adapted to short-term food deprivation. To examine how the carnivorous gastrointestinal tract is affected by fasting, small-intestinal structure, brush-border enzyme activities and hepatic structure and function were examined in fed mink (controls) and mink that had been fasted for 1–10 days. During the first 1–2 days of fasting, intestinal mass decreased more rapidly than total body mass and villus heights were reduced 25–40%. In contrast, tissue-specific activity of the brush-border enzymes sucrase, maltase, lactase, aminopeptidase A and dipeptidylpeptidase IV increased 0.5- to1.5-fold at this time, but returned to prefasting levels after 6 days of fasting. After 6–10 days of fasting there was a marked increase in the activity of hepatic enzymes and accumulation of intra-hepatic lipid vacuoles. Thus, mink may be a useful model for studying fasting-induced intestinal atrophy and adaptation as well as mechanisms involved in accumulation of intra-hepatic lipids following food deprivation in strictly carnivorous domestic mammals, such as cats and ferrets.Communicated by I.D. Hume     

Effects of season,food deprivation and re-feeding on leptin,ghrelin and growth hormone in arctic foxes (<Emphasis Type="Italic">Alopex lagopus</Emphasis>) on Svalbard,Norway

The arctic fox (Alopex lagopus) is a medium-sized predator of the high Arctic experiencing extreme seasonal fluctuations in food availability, photoperiod and temperature. In this study, the plasma leptin, ghrelin and growth hormone (GH) concentrations of male arctic foxes were determined during a food deprivation period of 13 days and the subsequent recovery in November and May. Leptin, ghrelin and GH were present in arctic fox plasma in amounts comparable to other carnivores. The plasma leptin concentrations did not react to food deprivation unlike in humans and rodents. However, the leptin levels increased during re-feeding as an indicator of increasing energy reserves. The relatively high ghrelin–leptin ratio, decrease in the plasma ghrelin concentration, an increase in the circulating GH concentrations and the observed negative correlation between plasma ghrelin and free fatty acid levels during fasting suggest that these hormones take part in the weight-regulation and energy metabolism of this species by increasing fat utilisation during food deprivation. The results strengthen the hypothesis that the actions of these weight-regulatory hormones are species–specific and depend on seasonality and the life history of the animals.Abbreviations FFA free fatty acid - GH growth hormone - RMR resting metabolic rate Communicated by G. Heldmaier     

Comparative fuel metabolism in Gentoo and King Penguins: adaptation to brief versus prolonged fasting

To compare fuel utilization in large birds adapted to brief or prolonged fasting, protein and lipid utilization were quantified in the Gentoo Penguin (Pygoscelis papua) and the King Penguin (Aptenodytes patagonica). The inshore feeder Gentoo Penguin fasts for only a few days in its colony, while King Penguin chicks starve for several months in the subantarctic winter and male King Penguins starve for 5–6 weeks at the beginning of their breeding cycle. After an initial decrease in both daily body mass loss and nitrogen excretion during the first days of food deprivation, these two parameters thereafter stabilized at low values. At that time, protein utilization accounted for 15% of total energy expenditure in Gentoo Penguins and only 6% in King Penguin chicks during winter, the remainder (85% and 94%, respectively) being provided by fat oxidation. Similar percentages in fuel metabolism as seen in chicks during winter were reached in fasting adult King Penguins and spring chicks. However, a seasonal adaptation occurs in fasting chicks because energy expenditure is lower during winter. As previously described in starved mammals, the effectiveness in protein sparing could be related to the initial adiposity of the birds: the larger the fat stores (about 9% and 30% in Gentoo Penguins and winter chicks of King Penguins, respectively), the longer the fast duration and the better the level of protein conservation.     

Metabolic responses induced by fasting in the common vampire bat<Emphasis Type="Italic"> Desmodus rotundus</Emphasis>

This study explored the effects of fasting on body fuel mobilization in the common vampire bat (Desmodus rotundus) fed a high-protein diet (bovine blood). An uncommon fragility during food deprivation has been reported for this species to the point of untimely deaths after only 2–3 nights of fasting. The immediate biochemical responses to fasting, however, have not been established. Thus, blood glucose, plasma FFA, glycogen, protein, and fat concentrations in the liver and muscles were determined in fed and 24-, 48- and 72 h-fasted individuals. The results indicate that D. rotundus is unable to maintain adequate levels of blood glucose during fasting, probably due to low tissue stores of energy fuels or difficulty in mobilizing them. Other factors may play an important role in this species abundance, such as the previously reported behavior of reciprocal blood regurgitation.Abbreviations FFA free fatty acids - F24 24 hours-fasted bats - F48 48 hours-fasted bats - F72 72 hours-fasted batsCommunicated by: L.C.-H. Wang     

Physiological adaptations of the raccoon dog (<Emphasis Type="Italic">Nyctereutes procyonoides</Emphasis>) to seasonal fasting-fat and nitrogen metabolism and influence of continuous melatonin treatment

The raccoon dog (Nyctereutes procyonoides) is a middle-sized canid with profound autumnal fattening followed by winter sleep. This study investigated the effects of prolonged fasting-induced winter sleep on the fat and nitrogen metabolism of the species. Half of the animals were treated with continuous-release melatonin implants to induce artificial short photoperiod. Autumnal accumulation of fat was characterized by low plasma free fatty acid (FFA), diacylglycerol (DG), and triacylglycerol (TG) levels. After transition to winter catabolism, the circulating lipid levels increased due to enhanced lipolysis. Two months of fasting resulted in a steady 3.1 kg weight loss (28% of body mass, 0.47% day^–1). Storage fat was mobilized during the winter sleep reflected by the elevated FFA and DG concentrations. The lowered insulin levels could be a stimulator for TG hydrolysis. The plasma total amino acid concentrations, urea levels, and urea-creatinine ratios decreased due to fasting, whereas ammonia and total protein concentrations remained stable. The effects of melatonin on energy metabolism were modest. The results indicate that the raccoon dog is well adapted to long-term wintertime fasting utilizing fat as the principal metabolic fuel. The species can maintain its protein catabolism constant for at least 60 days. Decreased cortisol and thyroid hormone concentrations may contribute to protein sparing.Electronic Supplementary Material Supplementary material is available in the online version of this article at Abbreviations AA amino acids - -AB -aminobutyrate - Ala alanine - ANOVA analysis of variance - Arg arginine - BM body mass - BMI body mass index - Chol cholesterol - Cit citrulline - DG diacylglycerols - FFA free fatty acids - GH growth hormone - Gln glutamine - Gly glycine - 3-MH 3-methylhistidine - MR metabolic rate - NH ₃ ammonia - Orn ornithine - PC phosphatidylcholine - Phe phenylalanine - PL phospholipids - Pro proline - Ser serine - SM sphingomyelin - T ₃ triiodothyronine - T ₄ thyroxine - T _a ambient temperature - TAA total amino acids - T _b body temperature - TG triacylglycerols - TL total lipids - TP total protein - U/C urea–creatinine - WAT white adipose tissue Communicated by G. Heldmaier     

Relationships between lipid availability and protein utilization during prolonged fasting

Summary Mammals and birds adapt to prolonged fasting by mobilizing fat stores and minimizing protein loss. This strategy ends with an increase in protein utilization associated with behavioural changes promoting food foraging. Using the Zucker rat as a model, we have investigated the effect of severe obesity on this pattern of protein loss during long-term fasting. Two interactions between the initial adiposity and protein utilization were found. First, protein conservation was more effective in obese than in lean rats: fatty rats had a three times lower daily nitrogen excretion and proportion of energy expenditure deriving from proteins, and a lower daily protein loss in various muscles. This phase of protein sparing is moreover nine times longer in the fatty rats. Second, obese animals did not show the late increase in nitrogen excretion that occurred in their lean littermates. Total body protein loss during starvation was larger in fatty rats (57% versus 29%) and, accordingly, total protein loss was greater in their muscles. At the end of the experiment, lean and obese rats had lost 98% and 82%, respectively, of their initial lipid reserves, and fatty rats still had an obese body composition. These results support the hypothesis that in severely obese humans and animals a lethal cumulative protein loss is reached long before the exhaustion of fat stores, while the phase of protein conservation is still continuing. In contrast, in lean rats, survival of fasting seems to depend on the availability of lipid fuels. The data also suggest that accumulation of too much fat in wild animals is detrimental for survival, because it eliminates the late phase of increase in nitrogen excretion that is linked to a food foraging behaviour anticipating a lethal depletion of body reserves.Abbreviations dm/dt daily loss in body mass - EDL extensor digitorum longus muscle - FFA free fatty acids - -OHB -hydroxybutyrate     

Nutrient reserve dynamics and energetics during long-term fasting in the king penguin (Aptenodytes patagonicus)

Males of king penguins (Aptenodytes patagonicus) naturally fast during one month at the beginning of their breeding cycle in the sub-Antarctic islands. Previous qualitative data have shown that this species adapts to prolonged fasting by mobilizing fat stores and minimizing protein loss and that this strategy ends with a progressive increase in protein utilization. In the present study, the quantification of nutrient utilization from body composition of captive birds indicates that, during the phase of protein conservation, 93% of the energy produced derives from the oxidation of fat stores, body protein accounting for the remainder (7%). Tissue composition analysis shows that integument (feathers, skin and subdermal fat) is the main lipid source (65% of the fat loss) during this period, and that pectoral muscles provide the majority of body protein (57% of the total loss). If the fast is prolonged until a body mass below 10 kg is reached, there is a progressive four-fold increase (from 1 68 to 6.50 gN/24h) in nitrogen excretion, together with a progressive exhaustion of fat stores. This shift in fuel metabolism is not a direct consequence of total lipid depletion, because 22% of the initial fat content still remains when proteins are no longer spared. During this later metabolic phase, protein is not only provided by pectoral muscles (71% of the loss), but also by hindlimb muscles (13%), and there remains only 2% of the initial amount of lipid in the integument at the end of the fast. Total energy expenditure is close to the fasting basal metabolic rate during the phase of protein conservation (2.52 W/kg), but it increases by 33% (3.36 W/kg) during the phase of protein wasting. This difference is probably due to a rise in locomotor activity, that is interpreted as reflecting a stimulation of food foraging behaviour before the lethal depletion of nutrient reserves.     

A proteomic approach to identify differentially expressed plasma proteins between the fed and prolonged fasted states

Prolonged fasting is characterized by consecutive phases, a short period of adaptation (phase 1), phase 2 (P2) characterized by fat oxidation, and phase 3 (P3) during which energy requirements are mostly derived from increased protein utilization. At this latter stage, food seeking behavior is induced. Very few circulating biomolecules have been identified that are involved in the response to prolonged fasting. To this end, rat plasma samples were compared by a proteomic approach, using 2‐DE. The results revealed a selective variation of the levels of apolipoprotein A‐IV, A‐I, and E, haptoglobin, transthyretin, plasma retinol binding‐protein, and vitamin D binding‐protein in P2 and P3. The variations in protein levels were confirmed by ELISA. Changes in mRNA levels encoding these proteins did not systematically correlate well with protein concentrations, and tissue‐specific regulation of mRNA expression was observed, underlining the complex metabolic regulation in response to food deprivation. In late fasting, the marked reduction of apolipoprotein A‐IV levels could contribute to the alarm signal that triggers refeeding. The variations of the other differentially expressed proteins are more likely related to lipid metabolism and insulin signaling alterations.     

Bone marrow fat mobilization in relation to lipid and protein catabolism during prolonged fasting in barn owls

 To assess the role of bone marrow fat in survival during a period of negative energy balance, we investigated the relationship between the time-course of marrow fat mobilization and the metabolic states associated with body fuel utilization during a prolonged fast. In order to mimic the winter fast of the barn owl (Tyto alba), captive birds were subjected to fasts of various durations at 5 °C ambient temperature. Body mass and plasma metabolites were used to determine the metabolic state at the end of fasting. Skeleton composition remained unchanged throughout phase II of fasting, during which the birds essentially rely on lipid fuels. During the following phase III, characterized by an increase in net body protein breakdown, the lipid mass in skeleton marrow decreased sharply by 78%, concomitant with an increase of the bone water content. This marrow fat mobilization occurred in all parts of the skeleton. This observation supports the hypothesis that bone marrow fat is not only involved in local nutrition, but can also be used as a lipid reserve for total energy requirements. However, in contrast to other fat deposits, marrow fat is mobilized only during phase III of the fast, when the last shift from lipid to protein fuel metabolism occurs. Thus, metabolic and/or hormonal changes associated with this transition could be involved in bone marrow fat mobilization. Lastly, our results suggest that the measurement of bone marrow fat can be used as an accurate index of the nutritional status (i.e. phase II or phase III) in barn owls. Accepted: 4 July 1996     

THE PHYSIOLOGICAL TRANSITION FROM FASTING TO FEEDING IN WEANED ELEPHANT SEAL PUPS

We studied energetics and food utilization in young elephant seals as they were first introduced to solid food following their long post-weaning fast. Using radioactive tracer techniques, we monitored changes in body composition, protein metabolism, and metabolic rate during fasting and initial feeding. In fasting animals, fat stores supplied nearly all energetic requirements. In feeding animals, 49% of protein ingested was retained as body tissue, allowing protein mass to increase. Body fat was lost at rates comparable to rates in fasting animals and continued to fuel the bulk of metabolism. Weight loss was arrested when animals consumed 786 g/d, or 40 kcal/kg^0.75/d, which was far less than their metabolic rates (63–206 kcal/kg 0.75 /d). Surprisingly, the young seals were able to maintain weight and store protein while energy intake was below metabolic needs. This was possible because animals gained weight as water; they retained wellhydrated proteinaceous tissue while losing poorly-hydrated adipose tissue.     

Exceptional long-term starvation ability and sites of lipid storage of the Arctic pteropod <Emphasis Type="Italic">Clione limacina</Emphasis>

The Arctic pteropod Clione limacina was collected in Kongsfjorden, Svalbard, in mid June 2004, to study the lipid metabolism within the sites of lipid storage structures during long-term starvation. Animals survived in an aquarium without any food for nearly 1 year (356 days). Size, number of lipid droplets, dry and lipid mass, lipid class and fatty acid compositions of C. limacina were determined and separately analysed for the digestive gland and the remaining integument. During the starvation period, animals shrunk from 22.4 to 12 mm in length on average, and the number of lipid droplets decreased from 1,600 to 1,000 per animal. Dry mass (DM) and total lipid mass both dropped by about 80% from day 200 to the end. The lipid content as percentage DM of the total organism did not decrease significantly ranging from 43.8 to 32.3%DM. The lipid content of the trunk was moderate with about 20%DM. The digestive gland was very rich in lipids with more than 70%DM throughout the experiment and is the major site of lipid metabolism and storage. Triacylglycerols (TAG) decreased, in the total organism, from high initial levels of 62.6 to 43% of total lipid at the end. In contrast, the proportions of 1-O-alkyldiacylglycerols [diacylglycerol ethers (DAGE)] remained almost constant, varying between 20.4 and 28.4%. In the digestive gland, TAG ranged from 60.3 to 64.8% and DAGE from 23.6 to 32.2% from day 200 to the end of the experiment. TAG and DAGE of the trunk were most likely located in the lipid droplets and were almost depleted at the end of starvation. Besides their function as lipid deposit DAGE may also act as protecting substance against bacterial and fungal infections. During the first 200 days of starvation, the fatty acid compositions showed only small variations. Thereafter, fatty acids typical for storage lipids decreased in all body compartments. In adaptation to long periods of food scarcity, C. limacina has evolved various strategies as body shrinkage, utilisation of body constituents not essential for survival, a very low metabolism and slow lipid consumption.     

Early changes in plasma hormones and metabolites during fasting in king penguin chicks

Summary Chicks of the king penguin (Aptenodytes patagonica) can tolerate a fast of 4–6 months during the subantarctic winter. The aim of this work was to study their initial response to food deprivation. Nine chicks were starved for 18 days. Two phases of starvation were defined according to changes in the specific daily loss in body mass: it decreased by 92% in phase I (6.6±0.3 days) and remained steady and low in phase II. Phase I was marked by a large decline in protein utilization, indicated by decreases in plasma levels of alanine (58%), uric acid (89%) and urea (76%) together with a decrease in circulating corticosterone (60%) and thyroxine (75%). In phase I, plasma insulin concentration decreased (61%) in some birds, but did not change in others; plasma pancreatic glucagon was stable whereas gut-glucagon decreased by 75%. Free fatty acids and -hydroxybutyrate concentrations gradually rode during the fast to 5 to 6 times pre-fast levels. Glycemia remained unchanged. Phase II was characterized by no change in plasma concentrations of protein-derived metabolites and by no or little change in circulating hormone levels. From comparison with previous data, we conclude that there are similar early adjustments to food deprivation in king penguin chick, rat and man: (1) a decrease in resting metabolic rate, (2) a decrease in protein utilization, and (3) mobilization of fat stores. The key, adaptations to long-term fasting in these species are therefore effectiveness in protein sparing and ability to prolong this situation.Abbreviations GLI glucagon-like immunoreactivity - PG pancreatic glucagon - -OHB -hydroxybutyrate - FFA free fatty acids - T ₃ triiodothyronine - T ₄ thyroxine     

Metabolic responses to food deprivation and refeeding in juveniles of Rutilus rutilus (Teleostei: Cyprinidae)

Synopsis Effect of food deprivation and refeeding on metabolic parameters were studied in juvenile Rutilus rutilus, weighing 280–460 mg. Tissue hydration increased with the length of the starvation period, reaching a new steady state after 4–5 weeks. Total protein concentration remained constant at about 60% of dry body mass. The concentration of glycogen decreased during food deprivation, a new steady state being reached at about 30% of control values after 4 weeks. Refeeding caused a dramatic increase of glycogen concentration which exceeded the value in fed controls by 6- to 9-fold. This is seen as a tactic for rapid storage of food energy, to be used later for the synthesis of body materials. With respect to their responses to food deprivation the 12 enzymes investigated formed four groups: (1) activity unaffected by food deprivation or refeeding (COX, THIOL, CK, GOT); (2) activity drops to about 60% of control value during the initial phase of food deprivation but remains constant thereafter (PK, LDH, Pase); (3) slow but continuous decrease in activity during the whole period of starvation, i.e. up to 7 weeks (PFK, OGDH, CS, FBPase); (4) activity increases during food deprivation, decreases again upon refeeding (GPT). A model is discussed which distinguishes between four phases in the general response of young fish to food deprivation and refeeding: stress, transition, adaptation, and recovery.     

Food Choice in Masked Titi Monkeys (Callicebus personatus melanochir): Selectivity or Opportunism?

I investigated whether the food choice in masked titi monkeys (Callicebus personatus melanochir) is selective with respect to energy or phytochemical characteristics of the food resources or opportunistic in relation to food abundance. I collected data on food choice and availability of food resources for 1 year in a forest fragment of the Atlantic rain forest in Eastern Brazil and analyzed main food items of the masked titi monkeys—fleshy fruit parts, seeds, and young leaves—for protein, lipid, carbohydrates, acid detergent fiber, tannin, and total energy content. A rich season of high food availability is distinct from a lean season with low food availability. Effects of food chemicals on food selection are not apparent. The main factor in food choice in both seasons is the abundance of the food items. Thus, for Callicebus personatus melanochir, opportunistic foraging seems to be the optimal strategy.     

Protein utilization during starvation in fat and lean Svalbard ptarmigan (Lagopus mutus hyperboreus)

Summary Body protein sparing during starvation has been examined in fat and lean Svalbard ptarmigan. Protein utilization was determined from daily N excretion and from the rate of decrease in body mass. Changes in plasma concentrations of -hydroxybutyrate, free fatty acids, glucose, and uric acid were also recorded. When fat birds were starved for 15 days protein catabolism initially fell (phase I) and was thereafter kept low (phase II). This was evident from the temporal pattern in both N excretion and body mass loss. In two birds, N excretion eventually increased, revealing enhanced protein catabolism and thus a third phase of starvation. Changes in protein utilization were paralleled by changes in plasma uric acid. Approximately 9% of the energy demand was covered by breakdown of body protein during phase II. The importance of fat catabolism in providing energy was indicated by markedly elevated plasma levels of -hydroxybutyrate and free fatty acids. When lean birds were starved for 5 days there appeared to be no phase II. The temporal pattern of body mass loss indicated phase I and III but that of N excretion only phase III. The relative contribution of body protein to energy demand increased from 22% at day 2 to 41% at the end of starvation and was paralleled by increased plasma uric acid. When data from lean and fat birds were pooled, the changes in uric acid and N excretion were highly correlated (r=0.92, P<0.001), indicating that plasma uric acid is a reliable index of protein breakdown in starving Svalbard ptarmigan. In conclusion, starving fat Svalbard ptarmigan have a much greater capacity to spare body protein than lean birds. Fat birds effectively reduce protein catabolism and maintain this at a low level whereas starving lean birds increase protein catabolism.Abbreviations -OHB -hydroxybutyrate - BM body mass - BMR basal metabolic rate; dne daily nitrogen excretion - FFA free fatty acids - MR metabolic rate     

Adaptive mechanisms during food restriction in <Emphasis Type="Italic">Acomys russatus</Emphasis>: the use of torpor for desert survival

The golden spiny mouse (Acomys russatus) is an omnivorous desert rodent that does not store food, but can store large amounts of body fat. Thus, it provides a good animal model to study physiological and behavioural adaptations to changes in food availability. The aim of this study was to investigate the time course of metabolic and behavioural responses to prolonged food restriction. Spiny mice were kept at an ambient temperature of 27°C and for 3 weeks their food was reduced individually to 30% of their previous ad libitum food intake. When fed ad libitum, their average metabolic rate was 82.77±3.72 ml O₂ h^–1 during the photophase and 111.19±4.30 ml O₂ h^–1 during the scotophase. During food restriction they displayed episodes of daily torpor when the minimal metabolic rate gradually decreased to 16.07±1.07 ml O₂ h^–1, i.e. a metabolic rate depression of approximately 83%. During the hypometabolic bouts the minimum average body temperature T_b, decreased gradually from 32.6±0.1°C to 29.0±0.4°C, with increasing duration of consecutive bouts. In parallel, the animals increased their activity during the remaining daytime. Torpor as well as hyperactivity was suppressed immediately by refeeding. Thus golden spiny mice used two simultaneous strategies to adapt to shortened food supply, namely energysaving torpor during their resting period and an increase in locomotor activity pattern during their activity period.     

Mobilization and recovery of energy stores in traíra, Hoplias malabaricus Bloch (Teleostei, Erythrinidae) during long-term starvation and after re-feeding

In some neotropical environments, fishes often experience periods of poor food supply, especially due to extreme fluctuations in rainfall regime. The fish species that experience periods of drought such as the traíra Hoplias malabaricus (Bloch 1794), may stand up to long-term food deprivation. In this study, experiments were performed in order to determine the dynamic of utilization of endogenous reserves in this species during starvation. Adult traíra were both fasted for 30–240 days and re-fed for 30 days following 90 and 240 days of fasting. Glycogen and perivisceral fat were primary energy substrates consumed. During the first 30 days, fish consumed hepatic and muscular glycogen, without exhausting these reserves, and used lipids from perivisceral fat. Hepatic lipids were an important energy source during the first 60 days of starvation and perivisceral fat were consumed gradually, being exhausted after 180 days. Protein mobilization was noticeable after 60 days of fasting, and became the major energy source as the lipid reserves were decreased (between 90 and 180 days). Following the longest periods of food deprivation, fish had utilized hepatic glycogen again. Fish re-fed for 30 days after 90 and 240 days of fasting were able to recover hepatic glycogen stores, but not the other energy reserves.