Adaptive changes in energy expenditure during mild and severe feed restriction in the rat

Energy expenses on prey processing are comparable, but paid at a higher metabolic scope and for a longer time in ambush vs active predators: a multispecies study on snakes

Snakes are characterized by distinct foraging strategies, from ambush to active hunting, which can be predicted to substantially affect the energy budget as a result of differential activity rates and feeding frequencies. Intense foraging activity and continuously upregulated viscera as a result of frequent feeding leads to a higher standard metabolic rate (SMR) in active than in ambush predators. Conversely, the costs of digestion (Specific Dynamic Action—SDA) are expected to be higher in ambush predators following the substantial remodelling of the gut upon ingestion of a meal after a long fasting period. This prediction was tested on an interspecific scale using a large multispecies dataset (> 40 species) obtained from published sources. I found that the metabolic scope and duration of SDA tended to reach higher values in ambush than in active predators, which probably reflects the greater magnitude of postprandial physiological upregulation in the former. In contrast, the SDA energy expenditure appeared to be unrelated to the foraging mode. The costs of visceral activation conceivably are not negligible, but represent a minor part of the total costs of digestion, possibly not large enough to elicit a foraging-mode driven variation in SDA energy expenditure. Non-mutually exclusive is that the higher costs of structural upregulation in ambush predators are balanced by the improved, thus potentially less expensive, functional performance of the more efficient intestines. I finally suggest that ambush predators may be less susceptible than active predators to the metabolic ‘meltdown effect’ driven by climate change.

Low 24-hour core body temperature as a thrifty metabolic trait driving catch-up fat during weight regain after caloric restriction

The recovery of body weight after substantial weight loss or growth retardation is often characterized by a disproportionately higher rate of fat mass vs. lean mass recovery, with this phenomenon of "preferential catch-up fat" being contributed by energy conservation (thrifty) metabolism. To test the hypothesis that a low core body temperature (T_c) constitutes a thrifty metabolic trait underlying the high metabolic efficiency driving catch-up fat, the Anipill system, with telemetry capsules implanted in the peritoneal cavity, was used for continuous monitoring of T_c for several weeks in a validated rat model of semistarvation-refeeding in which catch-up fat is driven solely by suppressed thermogenesis. In animals housed at 22°C, 24-h T_c was reduced in response to semistarvation (-0.77°C, P < 0.001) and remained significantly lower than in control animals during the catch-up fat phase of refeeding (-0.27°C on average, P < 0.001), the lower T_c during refeeding being more pronounced during the light phase than during the dark phase of the 24-h cycle (-0.30°C vs. -0.23°C, P < 0.01) and with no between-group differences in locomotor activity. A lower 24-h T_c in animals showing catch-up fat was also observed when the housing temperature was raised to 29°C (i.e., at thermoneutrality). The reduced energy cost of homeothermy in response to caloric restriction persists during weight recovery and constitutes a thrifty metabolic trait that contributes to the high metabolic efficiency that underlies the rapid restoration of the body's fat stores during weight regain, with implications for obesity relapse after therapeutic slimming and the pathophysiology of catch-up growth.

Feeding restriction alleviates high carbohydrate diet-induced oxidative stress and inflammation of Megalobrama amblycephala by activating the AMPK-SIRT1 pathway

This study investigated the effects of restricted feeding on the growth performance, oxidative stress and inflammation of Megalobrama amblycephala fed high-carbohydrate (HC) diets. Fish (46.94 ± 0.04 g) were randomly assigned to four groups containing the satiation of a control diet (30% carbohydrate) and three satiate levels (100% (HC1), 80% (HC2) and 60% (HC3)) of the HC diets (43% carbohydrate) for 8 weeks. Results showed that HC1 diet remarkably decreased final weight (FW), weight gain rate (WGR), specific growth rate (SGR), feed conversion ratio (FCR), hepatic activities of total anti-oxidation capacity (T-AOC), superoxide dismutase (SOD) and catalase (CAT), the AMP/ATP ratio, the p-AMPKα/t-AMPKα ratio, sirtuin-1 (SIRT1) protein expression and hepatic transcriptions of AMPKα2, SIRT1, nuclear factor erythroid 2-related factor 2 (Nrf2), catalase (CAT), manganese superoxide dismutase (Mn-SOD), glutathione peroxidase 1 (GPx1) and interleukin10 (IL 10) compared to the control group, whereas the opposite was true for protein efficiency ratio (PER), nitrogen retention efficiency (NRE), energy retention efficiency (ERE), plasma glucose levels, alanine transaminase (AST) and aspartate aminotransferase (ALT) activities, hepatic contents of malondialdehyde (MDA), tumour necrosis factor α (TNF α) and interleukin 1β (IL 1β), ATP and AMP contents and hepatic transcriptions of kelch-like ECH associating protein 1 (Keap1), IkB kinase α (IKK α), nuclear factor kappa B (NF-κB), TNF α, IL 1β, interleukin 6 (IL 6) and transforming growth factor β (TGF β). As for the HC groups, fish fed the HC2 diet obtained relatively high values of SGR, PER, NRE, ERE, hepatic activities of T-AOC, SOD and CAT, the AMP/ATP ratio, the p-AMPKα/t-AMPKα ratio, SIRT1 protein expression and hepatic transcriptions of AMPKα2, Nrf2, CAT, copper/zinc superoxide dismutase (Cu/Zn-SOD), Mn-SOD, GPx1, glutathione S-transferase (GST) and interleukin10 (IL 10), while the opposite was true for hepatic content of IL 6 and transcription of IKK α. Overall, an 80% satiation improved the growth performance and alleviated the oxidative stress and inflammation of blunt snout bream fed HC diets via the activation of the AMPK-SIRT1 pathway and the up-regulation of the activities and transcriptions of Nrf2-modulated antioxidant enzymes coupled with the depression of the levels and transcriptions of the NF-κB-mediated pro-inflammatory cytokines.

Calorie Restriction Modulates Reproductive Development and Energy Balance in Pre-Pubertal Male Rats

The objective was to determine effects of feed restriction and refeeding on reproductive development and energy balance in pre-pubertal male rats. Sprague Dawley rats (n = 32, 24 days old, ~65 g), were randomly allocated into four treatments (n = 8/treatment): (1) Control (CON, ad libitum feed; (2) Mild Restriction (MR, rats fed 75% of CON consumption); (3) Profound Restriction (PR, 50% of CON consumption); or (4) Refeeding (RF, 50% restriction for 14 days, and then ad libitum for 7 days). Feed restriction delayed reproductive development and decreased energy balance and tissue accretion, with degree of reproductive and metabolic dysfunctions related to restriction severity. In RF rats, refeeding largely restored testis weight, sperm production (per gram and total), plasma IGF-1, leptin and insulin concentrations and energy expenditure, although body composition did not completely recover. On Day 50, more CON and RF rats than PR rats were pubertal (5/6, 4/5 and 1/6, respectively; plasma testosterone >1 ng/mL) with the MR group (4/6) not different. Our hypothesis was supported: nutrient restriction of pre-pubertal rats delayed reproductive development, induced negative energy balance and decreased metabolic hormone concentrations (commensurate with restriction), whereas short-term refeeding after profound restriction largely restored reproductive end points and plasma hormone concentrations, but not body composition.

The Role of Leptin in Maintaining Plasma Glucose During Starvation

For 20 years it has been known that concentrations of leptin, a hormone produced by the white adipose tissue (WAT) largely in proportion to body fat, drops precipitously with starvation, particularly in lean humans and animals. The role of leptin to suppress the thyroid and reproductive axes during a prolonged fast has been well defined; however, the impact of leptin on metabolic regulation has been incompletely understood. However emerging evidence suggests that, in starvation, hypoleptinemia increases activity of the hypothalamic-pituitary-adrenal axis, promoting WAT lipolysis, increasing hepatic acetyl-CoA concentrations, and maintaining euglycemia. In addition, leptin may be largely responsible for mediating a shift from a reliance upon glucose metabolism (absorption and glycogenolysis) to fat metabolism (lipolysis increasing gluconeogenesis) which preserves substrates for the brain, heart, and other critical organs. In this way a leptin-mediated glucose-fatty acid cycle appears to maintain glycemia and permit survival in starvation.

Physical activity level among children recovering from severe acute malnutrition

OBJECTIVE

To assess the level and predictors of physical activity at discharge among children recovering from severe acute malnutrition (SAM).

METHODS

We conducted a prospective study among 69 children 6-59 months of age admitted with SAM for nutritional rehabilitation at Mulago National Referral Hospital, Uganda. Using hip-mounted triaxial accelerometers, we measured physical activity expressed as counts per minute (cpm) during the last three days of hospital treatment. As potential predictors, we assessed clinical and background characteristics, duration to transition phase and duration of hospitalisation, serum C-reactive protein and whole-blood docosahexaenoic acid (DHA). Multiple linear regression analyses were used to identify predictors of physical activity.

RESULTS

The median (IQR) age was 15.5 (12.6; 20.5) months. At discharge, the mean (SD) movement was 285 (126) cpm. Physical activity was 43 (19; 67) cpm higher for each unit increase in weight-for-height z-score (WHZ) and 72 (36; 108) cpm higher for each centimetre increase in MUAC. Whole-blood DHA on admission was also a positive predictor of physical activity, whereas duration to transition phase and duration of hospitalisation were both negative predictors.

CONCLUSION

The level of physical activity at discharge among children treated for SAM was low. WHZ, MUAC and DHA on admission were positive predictors of physical activity, whereas duration of stabilisation and hospitalisation was negative predictors of physical activity. These results suggest that assessment of physical activity may be used as a marker of recovery.

Limits to sustained energy intake. XV. Effects of wheel running on the energy budget during lactation

The capacity of animals to dissipate heat may constrain sustained energy intake during lactation. We examined these constraints at peak lactation in MF1 mice that had ad libitum access to food, or that had to run a pre-set target on running wheels to obtain ad libitum access to food. The voluntary distance run decreased sharply during pregnancy and peak lactation. When lactating females were provided with 80% of their estimated food requirements, and had to run pre-set distances of 2, 4 or 6 km before given access to additional ad libitum food, most of them did not complete the running target during late lactation and the mice with the highest targets failed to reach their targets earlier in lactation. There were consequently significant group differences in asymptotic food intake (2 km, 16.97±0.40 g day−1; 4 km, 14.29±0.72 g day−1; and 6 km, 12.65±0.45 g day−1) and weaned litter masses (2 km, 71.11±2.39 g; 4 km, 54.63±4.28 g and 6 km, 47.18±2.46 g). When the females did run sufficiently to gain ad libitum food access, their intake did not differ between the different distance groups or from controls that were not required to run. Thus, despite being physically capable of running the distances, mice could not exercise sufficiently in lactation to gain regular ad libitum access to food, probably because of the risks of hyperthermia when combining heat production from exercise with thermogenesis from lactation.

Contribution of Different Mechanisms to Compensation for Energy Restriction in the Mouse

OBJECTIVE

Restriction of energy intake produces weight loss, but the rate of loss is seldom sustained. This is presumed to be a consequence of compensatory reductions in energy expenditure, although the exact contributions of different components to the energy budget remain uncertain. We examined the compensatory responses of mice to a 20% dietary restriction.

RESEARCH METHODS AND PROCEDURES

We measured body mass, body fatness, body temperature, and the components of daily energy expenditure for 50 MF1 mice. Forty mice were then placed on a restricted diet at 80% of their ad libitum intake for 50 days. The remaining 10 mice continued to feed ad libitum. Ten days before the end of the restriction period, the same measurements were taken.

RESULTS

There were no significant differences between the control and restricted groups in any parameters before restriction. During the restriction period, body mass increased in both the control and restricted groups, but at a slower rate in the restricted mice. The control group increased in both fat and fat free mass; however, although the restricted group increased fat to the same extent as the controls, fat free mass increased to a lesser extent. The contributions of the different components of the expended energy to compensate for the reduced energy intake were energy deposition, 2.2%; resting metabolic rate, 22.3%; and activity, 75.5%.

DISCUSSION

Mice were able to compensate almost completely for the restricted energy intake that was achieved by altering the amount of energy required for each component of the energy budget except digestive efficiency.

Indirect calorimetry in laboratory mice and rats: principles, practical considerations, interpretation and perspectives

In this article, we review some fundamentals of indirect calorimetry in mice and rats, and open the discussion on several debated aspects of the configuration and tuning of indirect calorimeters. On the particularly contested issue of adjustment of energy expenditure values for body size and body composition, we discuss several of the most used methods and their results when tested on a previously published set of data. We conclude that neither body weight (BW), exponents of BW, nor lean body mass (LBM) are sufficient. The best method involves fitting both LBM and fat mass (FM) as independent variables; for low sample sizes, the model LBM + 0.2 FM can be very effective. We also question the common calorimetry design that consists of measuring respiratory exchanges under free-feeding conditions in several cages simultaneously. This imposes large intervals between measures, and generally limits data analysis to mean 24 h or day-night values of energy expenditure. These are then generally compared with energy intake. However, we consider that, among other limitations, the measurements of Vo(2), Vco(2), and food intake are not precise enough to allow calculation of energy balance in the small 2-5% range that can induce significant long-term alterations of energy balance. In contrast, we suggest that it is necessary to work under conditions in which temperature is set at thermoneutrality, food intake totally controlled, activity precisely measured, and data acquisition performed at very high frequency to give access to the part of the respiratory exchanges that are due to activity. In these conditions, it is possible to quantify basal energy expenditure, energy expenditure associated with muscular work, and response to feeding or to any other metabolic challenge. This reveals defects in the control of energy metabolism that cannot be observed from measurements of total energy expenditure in free feeding individuals.

Estimation of activity related energy expenditure and resting metabolic rate in freely moving mice from indirect calorimetry data

Physical activity (PA) is a main determinant of total energy expenditure (TEE) and has been suggested to play a key role in body weight regulation. However, thus far it has been challenging to determine what part of the expended energy is due to activity in freely moving subjects. We developed a computational method to estimate activity related energy expenditure (AEE) and resting metabolic rate (RMR) in mice from activity and indirect calorimetry data. The method is based on penalised spline regression and takes the time dependency of the RMR into account. In addition, estimates of AEE and RMR are corrected for the regression dilution bias that results from inaccurate PA measurements. We evaluated the performance of our method based on 500 simulated metabolic chamber datasets and compared it to that of conventional methods. It was found that for a sample time of 10 minutes the penalised spline model estimated the time-dependent RMR with 1.7 times higher accuracy than the Kalman filter and with 2.7 times higher accuracy than linear regression. We assessed the applicability of our method on experimental data in a case study involving high fat diet fed male and female C57Bl/6J mice. We found that TEE in male mice was higher due to a difference in RMR while AEE levels were similar in both groups, even though female mice were more active. Interestingly, the higher activity did not result in a difference in AEE because female mice had a lower caloric cost of activity, which was likely due to their lower body weight. In conclusion, TEE decomposition by means of penalised spline regression provides robust estimates of the time-dependent AEE and RMR and can be applied to data generated with generic metabolic chamber and indirect calorimetry set-ups.

Central angiotensin II has catabolic action at white and brown adipose tissue

Considerable evidence implicates the renin-angiotensin system (RAS) in the regulation of energy balance. To evaluate the role of the RAS in the central nervous system regulation of energy balance, we used osmotic minipumps to chronically administer angiotensin II (Ang II; icv; 0.7 ng/min for 24 days) to adult male Long-Evans rats, resulting in reduced food intake, body weight gain, and adiposity. The decrease in body weight and adiposity occurred relative to both ad libitum- and pair-fed controls, implying that reduced food intake in and of itself does not underlie all of these effects. Consistent with this, rats administered Ang II had increased whole body heat production and oxygen consumption. Additionally, chronic icv Ang II increased uncoupling protein-1 and β(3)-adrenergic receptor expression in brown adipose tissue and β3-adrenergic receptor expression in white adipose tissue, which is suggestive of enhanced sympathetic activation and thermogenesis. Chronic icv Ang II also increased hypothalamic agouti-related peptide and decreased hypothalamic proopiomelanocortin expression, consistent with a state of energy deficit. Moreover, chronic icv Ang II increased the anorectic corticotrophin- and thyroid-releasing hormones within the hypothalamus. These results suggest that Ang II acts in the brain to promote negative energy balance and that contributing mechanisms include an alteration in the hypothalamic circuits regulating energy balance, a decrease in food intake, an increase in energy expenditure, and an increase in sympathetic activation of brown and white adipose tissue.

A general model for ontogenetic growth under food restriction

Food restriction (FR) retards animals' growth. Understanding the underlying mechanisms of this phenomenon is important to conceptual problems in life-history theory, as well as to applied problems in animal husbandry and biomedicine. Despite a considerable amount of empirical data published since the 1930s, there is no relevant general theoretical framework that predicts how animals vary their energy budgets and life-history traits under FR. In this paper, we develop such a general quantitative model based on fundamental principles of metabolic energy allocation during ontogeny. This model predicts growth curves under varying conditions of FR, such as the compensatory growth, different age at which FR begins, its degree and its duration. Our model gives a quantitative explanation for the counterintuitive phenomenon that under FR, lower body temperature and lower metabolism lead to faster growth and larger adult size. This model also predicts that the animals experiencing FR reach the same fraction of their adult mass at the same age as their ad libitum counterparts. All predictions are well supported by empirical data from mammals and birds of varying body size, under different conditions of FR.

Effects of chronic weight perturbation on energy homeostasis and brain structure in mice

Maintenance of reduced body weight in lean and obese human subjects results in the persistent decrease in energy expenditure below what can be accounted for by changes in body mass and composition. Genetic and developmental factors may determine a central nervous system (CNS)-mediated minimum threshold of somatic energy stores below which behavioral and metabolic compensations for weight loss are invoked. A critical question is whether this threshold can be altered by environmental influences and by what mechanisms such alterations might be achieved. We examined the bioenergetic, behavioral, and CNS structural responses to weight reduction of diet-induced obese (DIO) and never-obese (CON) C57BL/6J male mice. We found that weight-reduced (WR) DIO-WR and CON-WR animals showed reductions in energy expenditure, adjusted for body mass and composition, comparable (-10-15%) to those seen in human subjects. The proportion of excitatory synapses on arcuate nucleus proopiomelanocortin neurons was decreased by ∼50% in both DIO-WR and CON-WR mice. These data suggest that prolonged maintenance of an elevated body weight (fat) alters energy homeostatic systems to defend a higher level of body fat. The synaptic changes could provide a neural substrate for the disproportionate decline in energy expenditure in weight-reduced individuals. This response to chronic weight elevation may also occur in humans. The mouse model described here could help to identify the molecular/cellular mechanisms underlying both the defense mechanisms against sustained weight loss and the upward resetting of those mechanisms following sustained weight gain.

Oscillators entrained by food and the emergence of anticipatory timing behaviors

Circadian rhythms are adjusted to the external environment by the light-dark cycle via the suprachiasmatic nucleus, and to the internal environment of the body by multiple cues that derive from feeding/fasting. These cues determine the timing of sleep/wake cycles and all the activities associated with these states. We suggest that numerous sources of temporal information, including hormonal cues such as corticoids, insulin, and ghrelin, as well as conditioned learned responses determined by the temporal relationships between photic and feeding/fasting signals, can determine the timing of regularly recurring circadian responses. We further propose that these temporal signals can act additively to modulate the pattern of daily activity. Based on such reasoning, we describe the rationale and methodology for separating the influences of these diverse sources of temporal information. The evidence indicates that there are individual differences in sensitivity to internal and external signals that vary over circadian time, time since the previous meal, time until the next meal, or with duration of food deprivation. All of these cues are integrated in sites and circuits modulating physiology and behavior. Individuals detect changes in internal and external signals, interpret those changes as "hunger," and adjust their physiological responses and activity levels accordingly.

Effect of acute and chronic caloric restriction and metabolic glucoprivation on spontaneous physical activity in obesity-prone and obesity-resistant rats

Caloric restriction (CR) and metabolic glucoprivation affect spontaneous physical activity (SPA), but it's unknown whether these treatments similarly affect SPA in selectively bred obesity-prone (OP) and -resistant (OR) rats. OR rats have greater basal SPA and are more responsive to treatments that modulate SPA, such as orexin A administration. We hypothesized that OR rats would be more sensitive to other treatments modulating SPA. To test this, continuous 24-h SPA was measured before and during acute (24 h) and chronic (8 wk) CR in OR, OP, and Sprague-Dawley rats. Pharmacological glucoprivation was produced by injection of 2-deoxyglucose (2-DG), and SPA was measured 5 h postinjection. Acute CR increased SPA in all groups; however, the effect was dependent on the index of SPA and time interval during the 24-h time period. In contrast to OR rats, chronic CR increased distance traveled, ambulatory episodes, and time spent in ambulation and stereotypy during the time interval preceding anticipation of food in OP and Sprague-Dawley rats. Although the effects of 2-DG treatment on SPA were minimal, OR rats had significantly greater SPA than OP and Sprague-Dawley rats independent of treatment. That chronic CR failed to result in significant changes in SPA in OR rats suggests that these rats may be especially unresponsive to treatments modulating feeding. This insensitivity coupled with elevated basal SPA levels may in part mediate phenotypic traits of lean rats.

Amylin-mediated restoration of leptin responsiveness in diet-induced obesity: magnitude and mechanisms

Previously, we reported that combination treatment with rat amylin (100 microg/kg.d) and murine leptin (500 microg/kg.d) elicited greater inhibition of food intake and greater body weight loss in diet-induced obese rats than predicted by the sum of the monotherapy conditions, a finding consistent with amylin-induced restoration of leptin responsiveness. In the present study, a 3 x 4 factorial design was used to formally test for a synergistic interaction, using lower dose ranges of amylin (0, 10, and 50 microg/kg.d) and leptin (0, 5, 25, and 125 microg/kg.d), on food intake and body weight after 4 wk continuous infusion. Response surface methodology analysis revealed significant synergistic anorexigenic (P < 0.05) and body weight-lowering (P < 0.05) effects of amylin/leptin combination treatment, with up to 15% weight loss at doses considerably lower than previously reported. Pair-feeding (PF) experiments demonstrated that reduction of food intake was the predominant mechanism for amylin/leptin-mediated weight loss. However, fat loss was 2-fold greater in amylin/leptin-treated rats than PF controls. Furthermore, amylin/leptin-mediated weight loss was not accompanied by the counterregulatory decrease in energy expenditure and chronic shift toward carbohydrate (rather than fat) utilization observed with PF. Hepatic gene expression analyses revealed that 28 d treatment with amylin/leptin (but not PF) was associated with reduced expression of genes involved in hepatic lipogenesis (Scd1 and Fasn mRNA) and increased expression of genes involved in lipid utilization (Pck1 mRNA). We conclude that amylin/leptin interact synergistically to reduce body weight and adiposity in diet-induced obese rodents through a number of anorexigenic and metabolic effects.

The contribution of animal models to the study of obesity

Obesity results from prolonged imbalance of energy intake and energy expenditure. Animal models have provided a fundamental contribution to the historical development of understanding the basic parameters that regulate the components of our energy balance. Five different types of animal model have been employed in the study of the physiological and genetic basis of obesity. The first models reflect single gene mutations that have arisen spontaneously in rodent colonies and have subsequently been characterized. The second approach is to speed up the random mutation rate artificially by treating rodents with mutagens or exposing them to radiation. The third type of models are mice and rats where a specific gene has been disrupted or over-expressed as a deliberate act. Such genetically-engineered disruptions may be generated through the entire body for the entire life (global transgenic manipulations) or restricted in both time and to certain tissue or cell types. In all these genetically-engineered scenarios, there are two types of situation that lead to insights: where a specific gene hypothesized to play a role in the regulation of energy balance is targeted, and where a gene is disrupted for a different purpose, but the consequence is an unexpected obese or lean phenotype. A fourth group of animal models concern experiments where selective breeding has been utilized to derive strains of rodents that differ in their degree of fatness. Finally, studies have been made of other species including non-human primates and dogs. In addition to studies of the physiological and genetic basis of obesity, studies of animal models have also informed us about the environmental aspects of the condition. Studies in this context include exploring the responses of animals to high fat or high fat/high sugar (Cafeteria) diets, investigations of the effects of dietary restriction on body mass and fat loss, and studies of the impact of candidate pharmaceuticals on components of energy balance. Despite all this work, there are many gaps in our understanding of how body composition and energy storage are regulated, and a continuing need for the development of pharmaceuticals to treat obesity. Accordingly, reductions in the use of animal models, while ethically desirable, will not be feasible in the short to medium term, and indeed an expansion in activity using animal models is anticipated as the epidemic continues and spreads geographically.

Calorie-restricted mice that gorge show less ability to compensate for reduced energy intake

Caloric restriction in mice can trigger gorging behaviour, which is characterized by periods of excessive food ingestion in a short time. Animals that gorge are thought to have a reduced metabolism compared to those that nibble their food over a longer period and might therefore be more able to compensate for reduced energy intake. We examined whether mice that gorged showed less weigh loss during restriction. We placed female mice (n=60) on a restriction of 75% of their ad libitum food intake (FI) for 22 days. FI and body mass (BM) were measured at 1, 2 and 24 h after food provision. Ten controls remained feeding ad lib and we selected the 10 strongest gorgers and 10 strongest non-gorgers for comparison. Mice had BM, FI, resting metabolic rate (RMR), body composition, body temperature, daily energy expenditure (DEE) and circulating levels of the regulatory hormones leptin and ghrelin measured. Gorgers had a significantly lower BM at the end of restriction than non-gorgers or controls, indicating that they were less able to compensate for the reduced energy. Both groups of restricted mice had reduced RMR, however reduced activity was only used as an energy saving mechanism in non-gorgers. Gorging mice had a significantly lower level of circulating leptin than controls and non-gorgers but no differences in ghrelin levels. Gorging mice were, in fact, less able to compensate for reduced energy intake, as they reduced RMR by a similar extent as non-gorgers, but did not reduce activity compared to non-gorgers on the same restriction level. The reduced leptin levels may drive the gorging behaviour.

Rat models of caloric intake and activity: relationships to animal physiology and human health

Every rodent experiment is based on important parameters concerning the levels of caloric intake and physical activity. In many cases, these decisions are not made consciously, but are based on traditional models. For experimental models directed at the study of caloric intake and activity, the selection of parameters is usually aimed at modeling human conditions, the ultimate goal of which is to gain insight into the pathophysiology of the disease process in man. In each model, it is important to understand the influence of diet, exercise, and genetic background on physiology and the development of disease states. Along the continuum of energy intake from caloric restriction to high-fat feeding, and of energy output from total inactivity to forced exercise, a number of models are used to study different disease states. In this paper, we will evaluate the influence of the quantity and composition of diet and exercise in several animal models, and will discuss how each model can be applied to various human conditions. This review will be limited to traditional models using the rat as the experimental animal, and although it is not an exhaustive list, the models presented are those most commonly represented in the literature. We will also review the mechanisms by which each affects rat physiology, and will compare these to the analogous mechanisms in the modeled human disease state. We hope that the information presented here will help researchers make choices among the available models and will encourage discussion on the interpretation and extrapolation of results obtained from traditional and novel rodent experiments on diet, exercise, and chronic disease.

Behavioral, physiological, and molecular differences in response to dietary restriction in three inbred mouse strains

Food restriction paradigms are widely used in animal studies to investigate systems involved in energy regulation. We have observed behavioral, physiological, and molecular differences in response to food restriction in three inbred mouse strains, C57BL/6J, A/J, and DBA/2J. These are the progenitors of chromosome substitution and recombinant inbred mouse strains used for mapping complex traits. DBA/2J and A/J mice increased their locomotor activity during food restriction, and both displayed a decrease in body temperature, but the decrease was significantly larger in DBA/2J compared with A/J mice. C57BL/6J mice did not increase their locomotor activity and displayed a large decrease in their body temperature. The large decline in body temperature during food restriction in DBA/2J and C57BL/6J strains was associated with a robust reduction in plasma leptin levels. DBA/2J mice showed a marked decrease in white and brown adipose tissue masses and an upregulation of the antithermogenic hypothalamic neuropeptide Y Y(1) receptor. In contrast, A/J mice showed a reduction in body temperature to a lesser extent that may be explained by downregulation of the thermogenic melanocortin 3 receptor and by behavioral thermoregulation as a consequence of their increased locomotor activity. These data indicate that genetic background is an important parameter in controlling an animal's adaptation strategy in response to food restriction. Therefore, mouse genetic mapping populations based on these progenitor lines are highly valuable for investigating mechanisms underlying strain-dependent differences in behavioral physiology that are seen during reduced food availability.

Src homology 3-domain growth factor receptor-bound 2-like (endophilin) interacting protein 1, a novel neuronal protein that regulates energy balance

To identify genes involved in the central regulation of energy balance, we compared hypothalamic mRNA from lean and obese Psammomys obesus, a polygenic model of obesity, using differential display PCR. One mRNA transcript was observed to be elevated in obese, and obese diabetic, P. obesus compared with lean animals and was subsequently found to be increased 4-fold in the hypothalamus of lethal yellow agouti (A(y)/a) mice, a murine model of obesity and diabetes. Intracerebroventricular infusion of antisense oligonucleotide targeted to this transcript selectively suppressed its hypothalamic mRNA levels and resulted in loss of body weight in both P. obesus and Sprague Dawley rats. Reductions in body weight were mediated by profoundly reduced food intake without a concomitant reduction in metabolic rate. Yeast two-hybrid screening, and confirmation in mammalian cells by bioluminescence resonance energy transfer analysis, demonstrated that the protein it encodes interacts with endophilins, mediators of synaptic vesicle recycling and receptor endocytosis in the brain. We therefore named this transcript Src homology 3-domain growth factor receptor-bound 2-like (endophilin) interacting protein 1 (SGIP1). SGIP1 encodes a large proline-rich protein that is expressed predominantly in the brain and is highly conserved between species. Together these data suggest that SGIP1 is an important and novel member of the group of neuronal molecules required for the regulation of energy homeostasis.

Neuropeptide Y prepares rats for scheduled feeding

When neuropeptide Y (NPY) is administered centrally, meal-anticipatory responses are elicited. If an increase of endogenous NPY is a signal that heralds an imminent large caloric load, timed daily NPY injections may be expected to condition meal-anticipatory responses that facilitate ingestion. Rats received 4-h access to food beginning in the morning and then timed (1600 h), daily third-ventricular injections of NPY or saline for 7 days. On test day ( day 8), animals received the conditioning drug (NPY or saline) or the opposite drug. Food was available immediately after injection on test day, and intake was measured. Rats conditioned with NPY and then given saline ate significantly more than rats conditioned with saline and then given saline; they ate the same amount as rats given NPY. Although they ate more, rats trained with NPY did not have changed plasma glucose, insulin, or ghrelin. These data suggest that NPY plays a role in mediating conditionable food-anticipatory responses that help to cope with the effects of large caloric loads.

Long-Evans and Sprague-Dawley rats exhibit divergent responses to refeeding after caloric restriction

Mature male Sprague-Dawley (SD) and Long-Evans (LE) rats were instrumented with telemetry transmitters for measurement of heart rate (HR) and housed in room calorimeters for assessment of food intake and oxygen consumption (Vo(2)) at standard laboratory temperatures (23 degrees C) to examine physiological responses to caloric restriction (CR; 60% of baseline ad libitum calories for 2 wk) and refeeding. Ad libitum controls had stable food intake (84-88 kcal/day) and gained weight at rates of 3-4 g/day. Groups from both strains assigned to CR exhibited similar patterns of weight loss and reductions in Vo(2) and HR. Upon refeeding, SD rats exhibited a mild, transient hyperphagic response (1 day) accompanied by sustained suppression of Vo(2) and HR that remained evident 8 days after refeeding. In contrast, LE rats exhibited sustained daily hyperphagia that persisted 8 days after refeeding and was accompanied by a complete restoration of HR and Vo(2). The lower HR and Vo(2) observed during refeeding in SD rats were not due to reduced locomotor activity. The results reveal a strain-dependent divergent response to recovery from CR. We conclude that during recovery from CR, homeostatic stimulation of appetite or suppression of energy expenditure may occur selectively to restore body weight.

Non-exercise activity thermogenesis (NEAT)

Non-exercise activity thermogenesis (NEAT) is the energy expended for everything we do that is not sleeping, eating or sports-like exercise. NEAT can be measured by one of two approaches. The first approach is to measure or estimate total NEAT. Here, total daily energy expenditure is measured and from it, the basal metabolic rate-plus-thermic effect of food is subtracted. The second approach is the factoral approach whereby the components of NEAT are quantified and total NEAT calculated by summing these components. The amount of NEAT that humans perform represents the product of the amount and types of physical activities and the thermogenic cost of each activity. The factors that impact a human's NEAT are readily divisible in biological factors such as weight, gender and body composition and environmental factors such occupation or dwelling within a "concrete jungle." The impact of these factors combined explains the substantial variance in human NEAT. The variability in NEAT might be viewed as random and unprogrammed but human data contradict this thesis. It appears that changes in NEAT accompany experimentally induced changes in energy balance and may be important in the physiology of weight change. NEAT and a sedentary lifestyle may thus be of profound importance in obesity.

Nonexercise activity thermogenesis (NEAT): environment and biology

Nonexercise activity thermogenesis (NEAT) is the energy expended for everything that is not sleeping, eating, or sports-like exercise. It includes the energy expended walking to work, typing, performing yard work, undertaking agricultural tasks, and fidgeting. NEAT can be measured by one of two approaches. The first is to measure or estimate total NEAT. Here, total daily energy expenditure is measured, and from it "basal metabolic rate-plus-thermic effect of food" is subtracted. The second is the factoral approach, whereby the components of NEAT are quantified, and total NEAT is calculated by summing these components. The amount of NEAT that humans perform represents the product of the amount and types of physical activities and the thermogenic cost of each activity. The factors that impact a human's NEAT are readily divisible into environmental factors, such as occupation or dwelling within a "concrete jungle," and biological factors such as weight, gender, and body composition. The combined impact of these factors explains the substantial variance in human NEAT. The variability in NEAT might be viewed as random, but human and animal data contradict this. It appears that changes in NEAT subtly accompany experimentally induced changes in energy balance and are important in the physiology of weight change. Inadequate modulation of NEAT plus a sedentary lifestyle may thus be important in obesity. It then becomes intriguing to dissect mechanistic studies that delineate how NEAT is regulated into neural, peripheral, and humoral factors. A scheme is described in this review in which NEAT corresponds to a carefully regulated "tank" of physical activity that is crucial for weight control.

Non-exercise activity thermogenesis

Non-exercise activity thermogenesis (NEAT) is the energy expended that is not from sleeping, eating or sports-like exercise. It ranges from the energy expended walking to work, typing, performing yard work, undertaking agricultural tasks and fidgeting. NEAT can be measured by one of two approaches. The first approach is to measure or estimate total NEAT. Here, total daily energy expenditure is measured and from it is subtracted BMR + thermic effect of food. The second is the factoral approach whereby the components of NEAT are quantified and total NEAT calculated by summing these components. The amount of NEAT that human subjects perform represents the product of the amount and types of physical activities and the thermogenic cost of each activity. The factors that affect the NEAT of a human subject are readily divisible into biological factors, such as weight, gender and body composition, and environmental factors, such as occupation or dwelling within a 'concrete jungle'. The combined impact of these factors explains the substantial variance in human NEAT. The variability in NEAT might be viewed as random but human data contradict this perception. It appears that changes in NEAT subtly accompany experimentally-induced changes in energy balance and are important in the physiology of weight change. NEAT and sedentariness may thus be important in obesity. It then becomes intriguing to dissect mechanistic studies that delineate how NEAT is regulated by neural, peripheral and humoral factors. NEAT may be a carefully-regulated 'tank' of physical activity that is crucial for weight control.

Energy restriction with protein restriction increases basal metabolism and meal-induced thermogenesis in rats

We previously observed an increased sympathetic nervous system (SNS) activity that was partly responsible for a defect in the insulin secretion response to glucose after postweaning protein-energy restriction (PER) in female rats. These results, together with other data on low-protein feeding, suggested that a low protein-to-energy ratio (P/E) in the diet could stimulate energy expenditure (EE), but direct measurements of EE have never been reported under conditions of PER. The goal of the present study was thus to quantify the changes induced by PER to body composition, the various parameters of EE, and plasma triiodothyronine levels. PER induced severe growth retardation, but the subcutaneous white and interscapular brown adipose tissue masses were preserved. Basal metabolism, meal-induced thermogenesis, and triiodothyronine levels were increased, but substrate utilization by the working muscles was unaffected. Meal-induced thermogenesis was increased by spontaneous activity in PER rats only. These results suggest that rats adapt to a low P/E in the diet by burning part of their excess nonprotein energy and storing the remaining excess in subcutaneous adipose tissue.

Energy expenditure of rhesus monkeys subjected to 11 years of dietary restriction

Dietary restriction (DR) is currently the only paradigm that has consistently extended maximal life span and reduced the onset of age-related chronic diseases in all of the nonprimate species tested. Although it is controversial, some investigators have suggested that the underlying mechanisms may be mediated by adaptations in energy expenditure. We evaluated the extent to which DR alters energy metabolism in a unique cohort of rhesus monkeys submitted to DR for 11 yr. Total energy expenditure (doubly labeled water), resting energy expenditure (REE; indirect calorimetry), and nonbasal energy expenditure (calculated by difference) were measured in DR (n = 12) and control (n = 11) animals. Body composition was determined by dual energy x-ray absorptiometry. Both fat mass and fat-free mass were lower in the restricted animals (56 and 12%, respectively). DR induced a 17% lower total energy expenditure that was attributable to a 20% decrease in REE without changes in the nonbasal energy expenditure. Adjusted for fat-free mass, REE was 13% lower with DR (-250 kJ/d). Taken together with a reanalysis of previous DR experiments published in humans, rodents, and monkeys, these results suggest that DR may lower REE independent of the DR-induced changes in body composition. Whether this reduction in REE contributes to the life-extending properties of DR warrants further analysis, but it suggests that the long-standing debate regarding DR effects on metabolic rates may derive from the lack of consensus on how to adjust for body size and composition.

Non-exercise activity thermogenesis (NEAT)

Non-exercise activity thermogenesis (NEAT) is the energy expended for everything we do that is not sleeping, eating or sports-like exercise. It ranges from the energy expended walking to work, typing, performing yard work, undertaking agricultural tasks and fidgeting. Even trivial physical activities increase metabolic rate substantially and it is the cumulative impact of a multitude of exothermic actions that culminate in an individual's daily NEAT. It is, therefore, not surprising that NEAT explains a vast majority of an individual's non-resting energy needs. Epidemiological studies highlight the importance of culture in promoting and quashing NEAT. Agricultural and manual workers have high NEAT, whereas wealth and industrialization appear to decrease NEAT. Physiological studies demonstrate, intriguingly, that NEAT is modulated with changes in energy balance; NEAT increases with overfeeding and decreases with underfeeding. Thus, NEAT could be a critical component in how we maintain our body weight and/or develop obesity or lose weight. The mechanism that regulates NEAT is unknown. However, hypothalamic factors have been identified that specifically and directly increase NEAT in animals. By understanding how NEAT is regulated we may come to appreciate that spontaneous physical activity is not spontaneous at all but carefully programmed.

Energy metabolism and expression of uncoupling proteins 1, 2, and 3 after 21 days of recovery from intracerebroventricular mouse leptin in rats

Animals tend to maintain a lower body weight for an extended period after leptin administration has ended. This may be due to an enhancement of metabolic rate that persists after treatment withdrawal. Our objectives were to determine the period of leptin influence, when injected intracerebroventricularly (icv), on food intake, body weight, and energy expenditure. Additionally, the relationship between expressions of UCP1, UCP2, and UCP3 in different adipose tissues and heat production (HP) was assessed. Twenty-four adult male Sprague-Dawley rats were injected intracerebroventricularly with either 10 g mouse leptin or 10 l vehicle once per day for 4 days. At 24 h after the last injection, one group was killed while the other was placed in calorimetry chambers and monitored for 21 days of recovery. Leptin-injected rats exhibited an overshoot of food intake and respiratory quotient (RQ) during recovery, but body weight remained significantly lower up to 6 days. HP decreased in both groups over time but remained higher in the leptin group through recovery. However, retained energy (RE) was significantly greater than control for about 8 days. Overall, UCP expression was reduced at the end of recovery in parallel with the decline in HP. Brown adipose tissue (BAT) was the most responsive to leptin administration by dramatically changing UCP1 and UCP3 mRNA levels. Our data show that leptin has extended effects on energy expenditure but relieves control on food intake and RQ after treatment withdrawal. This translated into a reduced positive energy balance that slowed body weight recovery.

Invited Review: pulmonary alveoli: formation, the "call for oxygen," and other regulators

The lung's only known essential function is to provide sufficient alveolar surface to meet the organism's need for oxygen and elimination of CO(2). The importance of the magnitude of alveolar surface area (Sa) to O(2) uptake (VO(2)) is supported by the presence among mammals of a direct linear relationship between Sa and VO(2). This match has been achieved, despite the higher body mass-specific VO(2) of small organisms compared with large, by a greater subdivision of alveolar surface, not by a larger relative lung volume in small organisms. This highly conserved relationship between alveolar architecture and VO(2) suggests the presence of similarly conserved mechanisms that control the onset, rate, and cessation of alveolus formation and alveolar size, which are also influenced by retinoids and thyroid and corticosteroid hormones. Furthermore, the "call for oxygen" is met at a breathing rate and tidal volume at which the work of breathing is lowest. Thus there is a complex, fascinating, but poorly understood, signaling relationship among VO(2), the neural regulation of breathing, and lung architecture, composition, and mechanics.

Angiotensin II regulates oxygen consumption

Previous studies demonstrated that angiotensin II (ANG II) decreases body weight. This study examined whether ANG II regulates body weight through energy expenditure. Acute ANG II administration decreased oxygen consumption. To determine whether this effect was maintained, rats were infused with ANG II or saline for 14 days. Oxygen consumption was transiently decreased on day 1 of ANG II infusion; however, body weight and food intake were reduced for 14 days. In pair-feeding studies, reductions in food intake accounted for 63% of the effect of ANG II on body weight but did not influence systolic pressure, water intake, or oxygen consumption. With 28 days of ANG II infusion, differences in body weight between ANG II and control rats were of greater magnitude. An initial decrease in oxygen consumption was followed by a rebound increase. Coadministration of losartan prevented the effect of ANG II on body weight, food intake, blood pressure, and water intake. However, losartan only partially prevented ANG II reductions in oxygen consumption. These results demonstrate that ANG II transiently decreases oxygen consumption through mechanisms unrelated to food intake. With chronic ANG II exposure, energy expenditure may contribute to sustained reductions in body weight.

Prediction of basal metabolism from organ size in the rat: relationship to strain, feeding, age, and obesity

Use of the weight of various organs and tissues together with their specific metabolic activity for prediction of basal metabolism (BM) seems to be promising. In this study we compared the use of this method with those based on simple or multiple regression analyses. We observed that 97.4% of differences in BM in a group of nine adult male Wistar rats weighing 273–517 g could be accounted for by changes in tissue and organ weights. BM measured in lean Zucker and Sprague-Dawley rats did not diverge from the prediction of the model by >1.6%. According to the organ-based model as well as multiple regression analyses, but not simple regression analyses, BM was increased 18–21% in young rats, decreased 6–7% in food restricted/refed rats, and decreased 19–21% in aged rats. Only with obese rats did the predictions of the two methods diverge. The main reason for this discrepancy seems to be the way adipose tissue size and metabolism are taken into account.

A paradoxical increase in resting energy expenditure in malnourished patients near death: the king penguin syndrome

BACKGROUND

The metabolic expression of extreme starvation on the verge of death is unknown in humans.

OBJECTIVE

The objective was to compare the resting energy expenditure (REE) of 5 extremely malnourished dying patients [body mass index (in kg/m(2)): 9.77 +/- 0.1] with that of 16 less-malnourished anorexia nervosa (AN) patients.

DESIGN

REE was measured by indirect calorimetry and body composition was measured by anthropometry and dual-frequency bioelectrical impedance analysis. Fasting serum insulin, thyroid hormone, and catecholamine concentrations were also determined.

RESULTS

At the start of refeeding, REE was high in each of the 5 extremely malnourished dying patients, whereas it was low in the 16 AN patients (mean +/- SD: 5174 +/- 391 kJ/d compared with 3844 +/- 619 kJ/d; P < 0.05). The high REE value in the 5 extremely malnourished dying patients was associated with almost no fat mass (FM), high urinary nitrogen loss (16.4 +/- 2.9 g/d), low serum fatty acid concentrations (0.36 +/- 0.23 mmol/L), and low or normal serum insulin, thyroid hormone, and catecholamine concentrations. During the first 2-4 wk of refeeding, REE and nitrogen loss decreased, whereas fatty acid concentrations increased in each of the 4 surviving patients; REE and urinary nitrogen output increased in the 16 AN patients.

CONCLUSION

In malnourished persons near death, there is an increase in REE and in protein catabolism. The reason for this increase is unknown but could relate to consumption of the last mobilizable muscle mass and to diseased cellular membranes.

Concurrent reductions in blood pressure and metabolic rate during fasting in the unrestrained SHR

Fasting produces multiple cardiovascular, metabolic, and behavioral responses. To examine the interrelationship between these responses, male spontaneously hypertensive rats (SHR; n = 8) implanted with cardiovascular telemetry devices were housed in metabolic chambers at 23 degrees C for 22-h daily measurements of physiological variables. The experimental apparatus was designed so that ingestive behavior was detected by photobeams and locomotion was detected by a load sensor. Cardiovascular and metabolic status were determined as both a function of the circadian cycle (12-h dark and 10-h light), as well as during periods of inactivity (no ingestion and minimal locomotion) within the dark and light phases. Data were obtained during baseline, 48-h of caloric deprivation, and 6 days of refeeding. Fasting produced significant reductions in mean arterial pressure (dark: -9.2+/-1.3 from 143.7+/-3.7 mm Hg; light: -8.6+/-1.8 from 140.1+/-3.7 mm Hg), heart rate (dark: -43.4+/-5.2 from 330.0+/-5.2 beats/min; light: -27.4+/-5.2 from 294.0+/-5.2 beats/min), and oxygen consumption (dark: -5.0+/-0.6 from 20.6+/-0.3 ml x min(-1) x kg (0.75); light: -2.7+/-0.2 from 14.9 +/-0.2 ml x min(-1) x kg(0.75)). Analysis of inactive periods during both light and dark phases revealed that these reductions were not dependent on behavioral effects. We conclude that fasting produces concurrent and interrelated reductions in cardiovascular and metabolic function in the SHR. The merging of cardiovascular telemetry, indirect calorimetry, and behavioral monitoring provides a powerful approach for investigation of the integrative physiological responses to energetic challenges.

Feeding interruptions, diurnal mass changes and daily routines of behaviour in the zebra finch

We investigated daily changes in body mass, fat reserves and crop contents, and diurnal organization of behaviour, in the zebra finch, Taeniopygia guttata, in relation to experimental manipulations of food availability. Diurnal mass change and the organization of foraging behaviour during the day were in general agreement with recent theoretical predictions. Foraging intensity, and hence rate of mass gain, was most rapid immediately after dawn and before dusk. The experimental birds did not alter either mean body mass or their diurnal mass trajectory after a period of 2 weeks when food was made unavailable for 2 h a day at unpredictable times. Instead, they changed their allocation of time to different activities during the day, decreasing the mean amount of time spent locomoting and increasing the mean amount of time spent inactive over the day. Thus, contrary to a number of recent studies on different species, zebra finches appear to respond to unpredictable interruptions in food supply by reducing energetically expensive activities rather than adjusting their levels of energy reserves. Copyright 1998 The Association for the Study of Animal Behaviour Copyright 1998 The Association for the Study of Animal Behaviour.

Changes in respiratory quotient elicited in rats by a conditioned stimulus predicting food

The present study examined whether changes in energy expenditure and energy substrate utilization occur in rats exposed to a conditioned stimulus that signals food. In a differential conditioning procedure, rats were given conditioning sessions where one of two cues (either a flashing light or buzzer) predicted a carbohydrate-rich meal (CS+) while the other cue predicted no food (CS-). In two subsequent test sessions, indirect calorimetry was used to measure respiratory quotient, energy expenditure, and locomotor activity before, during, and after a 15-min CS+ or CS- presentation. The CS+ was found to significantly increase respiratory quotient, indicating a shift in the energy substrate being utilized toward carbohydrate. The CS+ also increased energy expenditure and locomotor activity, but these effects were more variable across rats. It is concluded that respiratory quotient may rise in anticipation of a carbohydrate-rich meal. Possible mechanisms underlying this effect are discussed.

Metabolic action of neuropeptide Y in relation to its effect on feeding

Because energy homeostasis depends on a continuous balance between food intake, energy expenditure, and energy storage, it was expected that neuropeptide Y (NPY) could act not only on food intake but also on metabolic parameters. Using an original calorimetric device that allows the computation of the background metabolism (energy expenditure free from the cost of locomotor activity), we assessed the effect of a microinjection of NPY upon the quantitative (background metabolism, thermic effect of food) and qualitative (respiratory quotient) components of energy metabolism. NPY was injected into the juxtafornical hypothalamus at a dose that promotes feeding behavior (1 microg/0.5 microL) and enhances locomotor activity. Although total metabolism was increased proportionally to locomotion, no effect of NPY on background metabolism was observed when no food was available. Only following a calibrated meal given 30 min after the microinjection did NPY induce a delayed decrease in respiratory quotient whereas the postprandial background metabolism remained unaffected. In conclusion, only the new-generation calorimeters can show that the NPY-induced rise in overall metabolic rate is entirely accounted for by the unavoidable enhancement in locomotor activity and that the only metabolic effect of NPY is the delayed postprandial respiratory quotient decrease, suggesting a postabsorptive orientation toward more lipid utilization.

Human diversity, environmental adaptation and neural crest

The relationship between anatomical/physiological traits, environmental adaptability and neural crest is described, and possible mechanisms leading to human diversity are suggested. It is concluded that environmental adaptation seems to be limited to those structures of neural crest origin.

Components of energy expenditure in the mdx mouse model of Duchenne muscular dystrophy

Previous observations showing that basal heat production rates and glucose metabolism were reduced in mdx mouse skeletal muscles incubated in vitro led us to study the components of total energy expenditure by open-circuit indirect calorimetry in the intact, free-moving mdx mouse. Our purpose was to verify if the mdx mouse exhibited whole-body alterations in energy metabolism. The results revealed that total and basal energy expenditure, as well as spontaneous activity, energetic cost of activity, and, therefore, energy expended in relation to activity were not significantly different in C57B1/10 (control) and in dystrophic (mdx) mice. In contrast, the thermic effect of food was 32% larger in mdx than in control mice and was accompanied by significant differences in post-prandial glucose and lipid oxidation. The present in vivo study could not show a direct demonstration that impaired glucose metabolism by skeletal muscles participated in this phenomenon. However, since post-prandial glucose metabolism by skeletal muscles contributes a significant part of the thermic effect of food, the present data are in line with previous studies in vitro that show that mdx mouse skeletal muscles probably suffer an impaired control of their energy metabolism.