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

An improved dynamic metabolic model for application to biota

Any major nuclear facility must ensure the conservation of biodiversity regarding radiation protection of biota. A special concern is for tritium (3H) and radiocarbon (14C) transfer in wild mammals, birds and reptiles. Hydrogen and carbon are the main components of biological tissues and enter the life cycle. The present study improves the scientific bases of a previous model, analyses the uncertainty of input parameters and tests the model for a larger range of mammals and birds. The biological and metabolic half-times for organically bound tritium (OBT) and 14C are linked with energy metabolism and recent results are revised in relation with metabolic scaling. A large data base regarding basal metabolic rate (BMR), field metabolic rate (FMR), and organ mass is used for input information of the present model, which considers brain as a separate compartment. Metabolic energy partition in organs of active animal is defined and the factors affecting the metabolic rate are analysed. Body and ambient temperature, diet and habitat, and phylogeny are important factors considered in animal adaptation to environment. The available experimental data for carbon turnover rates in animals are analysed and it is observed that the experimental conditions are not appropriate for wild animals. The link between 13,14C and 134,137Cs turnover rate is analysed and the present metabolic approach is successfully tested for mammals and reptiles. Considering animal adaptation and the large data base for 134,137Cs, the radiological impact of accidental releases of 3H and 14C on biota can be pursued in the future research.

Mitochondrial complex I inhibition triggers NAD+-independent glucose oxidation via successive NADPH formation, "futile" fatty acid cycling, and FADH2 oxidation

Inhibition of mitochondrial complex I (NADH dehydrogenase) is the primary mechanism of the antidiabetic drug metformin and various unrelated natural toxins. Complex I inhibition can also be induced by antidiabetic PPAR agonists, and it is elicited by methionine restriction, a nutritional intervention causing resistance to diabetes and obesity. Still, a comprehensible explanation to why complex I inhibition exerts antidiabetic properties and engenders metabolic inefficiency is missing. To evaluate this issue, we have systematically reanalyzed published transcriptomic datasets from MPP-treated neurons, metformin-treated hepatocytes, and methionine-restricted rats. We found that pathways leading to NADPH formation were widely induced, together with anabolic fatty acid biosynthesis, the latter appearing highly paradoxical in a state of mitochondrial impairment. However, concomitant induction of catabolic fatty acid oxidation indicated that complex I inhibition created a "futile" cycle of fatty acid synthesis and degradation, which was anatomically distributed between adipose tissue and liver in vivo. Cofactor balance analysis unveiled that such cycling would indeed be energetically futile (-3 ATP per acetyl-CoA), though it would not be redox-futile, as it would convert NADPH into respirable FADH2 without any net production of NADH. We conclude that inhibition of NADH dehydrogenase leads to a metabolic shift from glycolysis and the citric acid cycle (both generating NADH) towards the pentose phosphate pathway, whose product NADPH is translated 1:1 into FADH2 by fatty acid cycling. The diabetes-resistant phenotype following hepatic and intestinal complex I inhibition is attributed to FGF21- and GDF15-dependent fat hunger signaling, which remodels adipose tissue into a glucose-metabolizing organ.

Pharmacokinetics of Succinate in Rats after Intravenous Administration of Mexidol

The pharmacokinetics of succinate was studied in Wistar rats after a single intravenous administration of Mexidol in a dose 100 mg/kg body weight. The concentration of succinate in blood plasma, cytoplasmic and mitochondrial fractions of cells of the cerebral cortex, left-ventricular myocardium, and liver was measured by HPLC-MS/MS. After single intravenous administration of Mexidol, succinate was evenly distributed in organs and tissues and quickly eliminated from the body. The pharmacokinetics of succinate was described by a two-chamber model. An increase in the level of succinate in the cytoplasmic fraction of the liver, myocardium, and cerebral cortex cells and a minor increase in the mitochondrial fraction were observed. The maximum increase in the level of succinate in the cytoplasmic fraction was observed in the liver tissue, a less pronounced elevation was observed in the cerebral cortex and myocardium; no significant differences between the cerebral cortex and myocardium were observed by this parameter.

Effect of soybean grain (Glycine max L.) supplementation on the production and fatty acid profile in milk of grazing cows in the dry tropics of Mexico

Improving the lipid profile in milk of cows with the use of soybean grain (Glycine max L.) can be favored in the grazing systems in the dry tropics of Mexico. The objective was to evaluate the milk production, the chemical composition, and the fatty acids profile (FAs) of the milk of cows in continuous grazing and supplemented with and without ground roasted soybean in the dry tropics of Mexico. Ten cows randomly distributed in two equal groups were used. Daily during confinement for milking, the cows individually received the treatments on dry basis T0: supplement with 4.6 kg commercial concentrate® without soybean, T1: supplement with 3.7 kg commercial concentrate® with 380 g of soybean. During the 78 days of the experiment, milk production was measured in all cows, and samples were collected to determine the chemical composition and FAs profile. Milk production, protein, milk total fat, lactose, and non-fat solids did not vary with treatment (p >0.05). Linoleic acid content (C18: 2, cis, cis-∆9, ∆12) increased by 22% in milk fat of cows of the T1 (p ˂0.05). The sum of the mono- and polyunsaturated FAs 29.1%, the ratio of saturated-unsaturated FAs (1.65), and the atherogenicity index (1.71) also improved in the milk of cows supplemented with T1 (p ˂0.05). It was concluded that ground roasted soybean supplement in the diet of grazing dairy cows did not affect production and did improve the lipid profile in milk fat with favorable index to promote human health.

Mitochondrial Function, Fatty Acid Metabolism, and Body Composition in the Hyperbilirubinemic Gunn Rat

Background: Circulating bilirubin is associated with reduced adiposity in human and animal studies. A possible explanation is provided by in vitro data that demonstrates that bilirubin inhibits mitochondrial function and decreases efficient energy production. However, it remains unclear whether hyperbilirubinemic animals have similar perturbed mitochondrial function and whether this is important for regulation of energy homeostasis. Aim: To investigate the impact of unconjugated hyperbilirubinemia on body composition, and mitochondrial function in hepatic tissue and skeletal muscle. Materials and Methods: 1) Food intake and bodyweight gain of 14-week old hyperbilirubinemic Gunn (n = 19) and normobilirubinemic littermate (control; n = 19) rats were measured over a 17-day period. 2) Body composition was determined using dual-energy X-ray absorptiometry and by measuring organ and skeletal muscle masses. 3) Mitochondrial function was assessed using high-resolution respirometry of homogenized liver and intact permeabilized extensor digitorum longus and soleus fibers. 4) Liver tissue was flash frozen for later gene (qPCR), protein (Western Blot and citrate synthase activity) and lipid analysis. Results: Female hyperbilirubinemic rats had significantly reduced fat mass (Gunn: 9.94 ± 5.35 vs. Control: 16.6 ± 6.90 g, p < 0.05) and hepatic triglyceride concentration (Gunn: 2.39 ± 0.92 vs. Control: 4.65 ± 1.67 mg g^-1, p < 0.01) compared to normobilirubinemic controls. Furthermore, hyperbilirubinemic rats consumed fewer calories daily (p < 0.01) and were less energetically efficient (Gunn: 8.09 ± 5.75 vs. Control: 14.9 ± 5.10 g bodyweight kcal^-1, p < 0.05). Hepatic mitochondria of hyperbilirubinemic rats demonstrated increased flux control ratio (FCR) via complex I and II (CI+II) (Gunn: 0.78 ± 0.16 vs. Control: 0.62 ± 0.09, p < 0.05). Similarly, exogenous addition of 31.3 or 62.5 μM unconjugated bilirubin to control liver homogenates significantly increased CI+II FCR (p < 0.05). Hepatic PGC-1α gene expression was significantly increased in hyperbilirubinemic females while FGF21 and ACOX1 was significantly greater in male hyperbilirubinemic rats (p < 0.05). Finally, hepatic mitochondrial complex IV subunit 1 protein expression was significantly increased in female hyperbilirubinemic rats (p < 0.01). Conclusions: This is the first study to comprehensively assess body composition, fat metabolism, and mitochondrial function in hyperbilirubinemic rats. Our findings show that hyperbilirubinemia is associated with reduced fat mass, and increased hepatic mitochondrial biogenesis, specifically in female animals, suggesting a dual role of elevated bilirubin and reduced UGT1A1 function on adiposity and body composition.

Is the rate of metabolic ageing and survival determined by Basal metabolic rate in the zebra finch?

The relationship between energy metabolism and ageing is of great interest because aerobic metabolism is the primary source of reactive oxygen species which is believed to be of major importance in the ageing process. We conducted a longitudinal study on captive zebra finches where we tested the effect of age on basal metabolic rate (BMR), as well as the effect of BMR on the rate of metabolic ageing (decline in BMR with age) and survival. Basal metabolic rate declined with age in both sexes after controlling for the effect of body mass, indicating a loss of functionality with age. This loss of functionality could be due to accumulated oxidative damage, believed to increase with increasing metabolic rate, c.f. the free radical theory of ageing. If so, we would expect the rate of metabolic ageing to increase and survival to decrease with increasing BMR. However, we found no effect of BMR on the rate of metabolic ageing. Furthermore, survival was not affected by BMR in the males. In female zebra finches there was a tendency for survival to decrease with increasing BMR, but the effect did not reach significance (P<0.1). Thus, the effect of BMR on the rate of functional deterioration with age, if any, was not strong enough to influence neither the rate of metabolic ageing nor survival in the zebra finches.

Aging, life span, and energetics under adult dietary restriction in lepidoptera

Stressful conditions can affect resource allocation among different life-history traits. The effect of dietary restriction (DR) on longevity and reproduction has been studied in many species, but we know little about its effects on energetics, especially in flying animals that have high energy demand. We assessed the effects of DR on metabolic rate throughout the entire adult life span in two butterfly species, Colias eurytheme and Speyeria mormonia. We cut the food intake of adult females in half and measured resting metabolic rate (RMR) and flight metabolic rate (FMR) together with body mass repeatedly throughout life. In both species, DR reduced body mass, but mass-corrected FMR was not affected, indicating that flight capacity was retained. DR lowered RMR and reduced fecundity but had no effect on life span. FMR declined with age, but the rate of senescence was not affected by DR. In contrast, aging had a strong negative effect on RMR only in control females, whereas food-restricted females had more stable RMR throughout their lives. The results suggest that flight capacity is conserved during nutritional stress but that investment in flight and survival may negatively affect other important physiological processes when resources are limited.

Food intake and energy expenditure are increased in high-fat-sensitive but not in high-carbohydrate-sensitive obesity-prone rats

Obesity-prone (OP) rodents are used as models of human obesity predisposition. The goal of the present study was to identify preexisting defects in energy expenditure components in OP rats. Two studies were performed. In the first one, male Wistar rats ( n = 48) were fed a high-carbohydrate diet (HCD) for 3 wk and then a high-fat diet (HFD) for the next 3 wk. This study showed that adiposity gain under HCD was 2.9-fold larger in carbohydrate-sensitive (CS) than in carbohydrate-resistant (CR) rats, confirming the concept of “carbohydrate-sensitive” rats. Energy expenditure (EE), respiratory quotient (RQ), caloric intake (CI), and locomotor activity measured during HFD identified no differences in EE and RQ between fat-resistant (FR) and fat-sensitive (FS) rats, and indicated that obesity developed in FS rats only as the result of a larger CI not fully compensated by a parallel increase in EE. A specific pattern of spontaneous activity, characterized by reduced activity burst intensity, was identified in FS rats but not in CS ones. This mirrors a previous observation that under HCD, CS but not FS rats, exhibited bursts of activity of reduced intensity. In a second study, rats were fed a HFD for 3 wk, and the components of energy expenditure were examined by indirect calorimetry in 10 FR and 10 FS rats. This study confirmed that a low basal EE, reduced thermic effect of feeding, defective postprandial energy partitioning, or a defective substrate utilization by the working muscle are not involved in the FS phenotype.

Transgenerational effects of caloric restriction on appetite: a meta-analysis

Maternal undernutrition can result in significant alterations to the post-natal offspring phenotype, including body size and behaviour. For example, maternal food restriction has been implicated in offspring hyperphagia, potentially causing increased weight gain and fat accumulation. This could result in obesity and other adverse long-term health effects in offspring. We investigated the link between maternal caloric restriction during gestation and offspring appetite by conducting the first meta-analysis on this topic using experimental data from mammalian laboratory models (i.e. rats and mice). We collected 89 effect sizes from 35 studies, together with relevant moderators. Our analysis revealed weak and statistically non-significant overall effect on offspring's appetite. However, we found that lower protein content of restricted diets is associated with higher food intake in female offspring. Importantly, we show that a main source of variation among studies arises from whether, and how, food intake was adjusted for body mass. This probably explains many of the contradictory results in the field. Based on our results, we recommend using allometric scaling of food intake to body mass in future studies.

A 3-D mathematical model to identify organ-specific risks in rats during thermal stress

Early prediction of the adverse outcomes associated with heat stress is critical for effective management and mitigation of injury, which may sometimes lead to extreme undesirable clinical conditions, such as multiorgan dysfunction syndrome and death. Here, we developed a computational model to predict the spatiotemporal temperature distribution in a rat exposed to heat stress in an attempt to understand the correlation between heat load and differential organ dysfunction. The model includes a three-dimensional representation of the rat anatomy obtained from medical imaging and incorporates the key mechanisms of heat transfer during thermoregulation. We formulated a novel approach to estimate blood temperature by accounting for blood mixing from the different organs and to estimate the effects of the circadian rhythm in body temperature by considering day-night variations in metabolic heat generation and blood perfusion. We validated the model using in vivo core temperature measurements in control and heat-stressed rats and other published experimental data. The model predictions were within 1 SD of the measured data. The liver demonstrated the greatest susceptibility to heat stress, with the maximum temperature reaching 2°C higher than the measured core temperature and 95% of its volume exceeding the targeted experimental core temperature. Other organs also attained temperatures greater than the core temperature, illustrating the need to monitor multiple organs during heat stress. The model facilitates the identification of organ-specific risks during heat stress and has the potential to aid in the development of improved clinical strategies for thermal-injury prevention and management.

Integration of biological clocks and rhythms

Animals, plants, and microorganisms exhibit numerous biological rhythms that are generated by numerous biological clocks. This article summarizes experimental data pertinent to the often-ignored issue of integration of multiple rhythms. Five contexts of integration are discussed: (i) integration of circadian rhythms of multiple processes within an individual organism, (ii) integration of biological rhythms operating in different time scales (such as tidal, daily, and seasonal), (iii) integration of rhythms across multiple species, (iv) integration of rhythms of different members of a species, and (v) integration of rhythmicity and physiological homeostasis. Understanding of these multiple rhythmic interactions is an important first step in the eventual thorough understanding of how organisms arrange their vital functions temporally within and without their bodies.

The carbohydrate sensitive rat as a model of obesity

BACKGROUND

Sensitivity to obesity is highly variable in humans, and rats fed a high fat diet (HFD) are used as a model of this inhomogeneity. Energy expenditure components (basal metabolism, thermic effect of feeding, activity) and variations in substrate partitioning are possible factors underlying the variability. Unfortunately, in rats as in humans, results have often been inconclusive and measurements usually made after obesity onset, obscuring if metabolism was a cause or consequence. Additionally, the role of high carbohydrate diet (HCD) has seldom been studied.

METHODOLOGY/FINDINGS

Rats (n=24) were fed for 3 weeks on HCD and then 3 weeks on HFD. Body composition was tracked by MRI and compared to energy expenditure components measured prior to obesity.

RESULTS

1) under HFD, as expected, by adiposity rats were variable enough to be separable into relatively fat resistant (FR) and sensitive (FS) groups, 2) under HCD, and again by adiposity, rats were also variable enough to be separable into carbohydrate resistant (CR) and sensitive (CS) groups, the normal body weight of CS rats hiding viscerally-biased fat accumulation, 3) HCD adiposity sensitivity was not related to that under HFD, and both HCD and HFD adiposity sensitivities were not related to energy expenditure components (BMR, TEF, activity cost), and 4) only carbohydrate to fat partitioning in response to an HCD test meal was related to HCD-induced adiposity.

CONCLUSIONS/SIGNIFICANCE

The rat model of human obesity is based on substantial variance in adiposity gains under HFD (FR/FS model). Here, since we also found this phenomenon under HCD, where it was also linked to an identifiable metabolic difference, we should consider the existence of another model: the carbohydrate resistant (CR) or sensitive (CS) rat. This new model is potentially complementary to the FR/FS model due to relatively greater visceral fat accumulation on a low fat high carbohydrate diet.

Detection of thermogenesis in rodents in response to anti-obesity drugs and genetic modification

Many compounds and genetic manipulations are claimed to confer resistance to obesity in rodents by raising energy expenditure. Examples taken from recent and older literature, demonstrate that such claims are often based on measurements of energy expenditure after body composition has changed, and depend on comparisons of energy expenditure divided by body weight. This is misleading because white adipose tissue has less influence than lean tissue on energy expenditure. Application of this approach to human data would suggest that human obesity is usually due to a low metabolic rate, which is not an accepted view. Increased energy expenditure per animal is a surer way of demonstrating thermogenesis, but even then it is important to know whether this is due to altered body composition (repartitioning), or increased locomotor activity rather than thermogenesis per se. Regression analysis offers other approaches. The thermogenic response to some compounds has a rapid onset and so cannot be due to altered body composition. These compounds usually mimic or activate the sympathetic nervous system. Thermogenesis occurs in, but may not be confined to, brown adipose tissue. It should not be assumed that weight loss in response to these treatments is due to thermogenesis unless there is a sustained increase in 24-h energy expenditure. Thyroid hormones and fibroblast growth factor 21 also raise energy expenditure before they affect body composition. Some treatments and genetic modifications alter the diurnal rhythm of energy expenditure. It is important to establish whether this is due to altered locomotor activity or efficiency of locomotion. There are no good examples of compounds that do not affect short-term energy expenditure but have a delayed effect. How and under what conditions a genetic modification or compound increases energy expenditure influences the decision on whether to seek drugs for the target or take a candidate drug into clinical studies.

Robustness and aging--a systems-level perspective

The theory of robustness describes a system level property of evolutionary systems, which predicts tradeoffs of great interest for the systems biology of aging, such as accumulation of non-heritable damage, occurrence of fragilities and limitations in performance, optimized allocation of restricted resources and confined redundancies. According to the robustness paradigm cells and organisms evolved into a state of highly optimized tolerance (HOT), which provides robustness to common perturbations, but causes tradeoffs generally characterized as "robust yet fragile". This raises the question whether the ultimate cause of aging is more than a lack of adaptation, but an inherent fragility of complex evolutionary systems. Since robustness connects to evolutionary designs, consideration of this theory provides a deeper connection between evolutionary aspects of aging, mathematical models and experimental data. In this review several mechanisms influential for aging are re-evaluated in support of robustness tradeoffs. This includes asymmetric cell division improving performance and specialization with limited capacities to prevent and repair age-related damage, as well as feedback control mechanisms optimized to respond to acute stressors, but unable to halt nor revert aging. Improvement in robustness by increasing efficiencies through cellular redundancies in larger organisms alleviates some of the damaging effects of cellular specialization, which can be expressed in allometric relationships. The introduction of the robustness paradigm offers unique insights for aging research and provides novel opportunities for systems biology endeavors.

Basal metabolic rate is positively correlated with parental investment in laboratory mice

The assimilation capacity (AC) hypothesis for the evolution of endothermy predicts that the maternal basal metabolic rate (BMR) should be positively correlated with the capacity for parental investment. In this study, we provide a unique test of the AC model based on mice from a long-term selection experiment designed to produce divergent levels of BMR. By constructing experimental families with cross-fostered litters, we were able to control for the effect of the mother as well as the type of pup based on the selected lines. We found that mothers with genetically determined high levels of BMR were characterized by higher parental investment capacity, measured as the offspring growth rate. We also found higher food consumption and heavier visceral organs in the females with high BMR. These findings suggested that the high-BMR females have higher energy acquisition abilities. When the effect of the line type of a foster mother was controlled, the pup line type significantly affected the growth rate only in the first week of life, with young from the high-BMR line type growing more rapidly. Our results support the predictions of the AC model.

Context-dependent correlation between resting metabolic rate and daily energy expenditure in wild chipmunks

Several empirical studies have shown that variation in daily energy expenditure (DEE) and resting metabolic rate (RMR) is influenced by environmental and individual factors, but whether these shared influences are responsible for, or independent of, relationships between DEE and RMR remains unknown. The objectives of this study were to (i) simultaneously evaluate the effects of environmental and individual variables on DEE and RMR in free-ranging eastern chipmunks (Tamias striatus) and (ii) quantify the correlation between DEE and RMR before and after controlling for common sources of variation. We found that the influence of individual factors on DEE and RMR is most often shared, whereas the influence of environmental factors tends to be distinct. Both raw and mass-adjusted DEE and RMR were significantly correlated, but this correlation vanished after accounting for the shared effect of reproduction on both traits. However, within reproductive individuals, DEE and RMR remained positively correlated after accounting for all other significant covariates. The ratio of DEE to RMR was significantly higher during reproduction than at other times of the year and was negatively correlated with ambient temperature. DEE and RMR appear to be inherently correlated during reproduction, but this correlation does not persist during other, less energy-demanding periods of the annual cycle.

Small organ size contributes to the slow pace of life in tropical birds

Attributes of an animal's life history, such as reproductive rate or longevity, typically fall along a 'slow-fast' continuum. Animals at the fast end of this continuum, such as temperate birds, are thought to experience high rates of mortality and invest more resources in reproduction, whereas animals at the slow end, such as tropical birds, live longer, have fewer offspring and invest more resources in self-maintenance. We have previously shown that tropical birds, compared with temperate species, have a reduced basal (BMR) and peak metabolic rate (PMR), patterns consistent with a slow pace of life. Here, we elucidate a fundamental linkage between the smaller mass of central organs of tropical species and their reduced BMR, and between their smaller flight muscles and reduced PMR. Analyses of up to 408 species from the literature showed that the heart, flight muscles, liver, pancreas and kidneys were smaller in tropical species. Direct measurements on 49 species showed smaller heart, lungs, flight muscles, liver, kidneys, ovaries and testes in tropical species, as well as lower feather mass. In combination, our results indicate that the benign tropical environment imposes a relaxed selection pressure on high levels of sustained metabolic performance, permitting species to reduce the mass of organs that are energetically costly to maintain. Brain, gizzard and intestine were exceptions, even though energy turnover of brain and intestine are high. Feather mass was 37% lower in tropical species compared with similar-sized temperate birds, supporting the idea that temperate birds require more insulation for thermoregulation.

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.

Age dependency on some physiological and biochemical parameters of male Wistar rats in controlled environment

The aim of the study was to assess the age dependence on some physiological and serum chemistry parameters of male Wistar rats for the estimation of reference values in controlled environment. We are presenting values obtained from a large number of animals such as survival, average life span, body mass, food and water intake, serum chemistry parameters as total protein, albumin, transferrin and ferritin in serum. One part of this work compares the relationship between rat and human age. The maximal life span of our rats was determined to be about 4.4 years. The average life span was 3.75 years. The body weight quickly rose to the 85th week of life and then remained in the range of about 640-660 g up to the 163rd week when it began to decline. Food intake rose from the beginning to the maximum of about 39 g in the 33rd week and then decreased to about 20 g in the 163rd week. The water intake had a similar dynamics (about 43 mL in the 33rd week and 33 mL in the 163rd week). Levels of total protein in serum increased with age, in contrast, albumin levels decreased. Transferrin and ferritin decreased to approximately the 160th week of life and then increased.

Identification of behavioral and metabolic factors predicting adiposity sensitivity to both high fat and high carbohydrate diets in rats

Individuals exhibit a great variation in their body weight (BW) gain response to a high fat diet. Identification of predictive factors would enable better directed intervention toward susceptible individuals to treat obesity, and uncover potential mechanisms for treatment targeting. We set out to identify predictive behavioral and metabolic factors in an outbred rat model. 12 rats were analyzed in metabolic cages for a period of 5 days during both high carbohydrate diet (HCD), and transition to a high fat diet (HFD). After a recovery period, rats were given a HFD for 6 days to identify those resistant or sensitive to it according to BW gain. Rats were dissected at the end of the study to analyze body composition. This showed that small differences in final BW hid large variations in adiposity, allowing separation of rats into a second classification (final adiposity). Since these rats had been fed a HCD during most of their life, under which most of the adiposity presumably evolved, we considered this carbohydrate-sensitivity or -resistance. Meal size and meal number were found to be good predictors of sensitivity to a HFD, intensity of motor activity and ingestion speed good predictors of sensitivity to a HCD. Rats that were sensitive to the HCD could be resistant to the HFD and vice versa. This points to four types of individuals (carbohydrate/fat resistant/sensitive) though our sample size inhibited deeper investigation of this. This contributes to the idea that to be “obesity prone” does not necessarily need a HFD, it can also happen under a HCD, and be a hidden adiposity change with stable BW.

Metabolomics of aerobic metabolism in mice selected for increased maximal metabolic rate

Maximal aerobic metabolic rate (MMR) is an important physiological and ecological variable that sets an upper limit to sustained, vigorous activity. How the oxygen cascade from the external environment to the mitochondria may affect MMR has been the subject of much interest, but little is known about the metabolic profiles that underpin variation in MMR. We tested how seven generations of artificial selection for high mass-independent MMR affected metabolite profiles of two skeletal muscles (gastrocnemius and plantaris) and the liver. MMR was 12.3% higher in mass selected for high MMR than in controls. Basal metabolic rate was 3.5% higher in selected mice than in controls. Artificial selection did not lead to detectable changes in the metabolic profiles from plantaris muscle, but in the liver amino acids and tricarboxylic acid cycle (TCA cycle) metabolites were lower in high-MMR mice than in controls. In gastrocnemius, amino acids and TCA cycle metabolites were higher in high-MMR mice than in controls, indicating elevated amino acid and energy metabolism. Moreover, in gastrocnemius free fatty acids and triacylglycerol fatty acids were lower in high-MMR mice than in controls. Because selection for high MMR was associated with changes in the resting metabolic profile of both liver and gastrocnemius, the result suggests a possible mechanistic link between resting metabolism and MMR. In addition, it is well established that diet and exercise affect the composition of fatty acids in muscle. The differences that we found between control lines and lines selected for high MMR demonstrate that the composition of fatty acids in muscle is also affected by genetic factors.

Hypercarnivory and the brain: protein requirements of cats reconsidered

The domestic hypercarnivores cat and mink have a higher protein requirement than other domestic mammals. This has been attributed to adaptation to a hypercarnivorous diet and subsequent loss of the ability to downregulate amino acid catabolism. A quantitative analysis of brain glucose requirements reveals that in cats on their natural diet, a significant proportion of protein must be diverted into gluconeogenesis to supply the brain. According to the model presented here, the high protein requirement of the domestic cat is the result of routing of amino acids into gluconeogenesis to supply the needs of the brain and other glucose-requiring tissues, resulting in oxidation of amino acid in excess of the rate predicted for a non-hypercarnivorous mammal of the same size. Thus, cats and other small hypercarnivores do not have a high protein requirement per se, but a high endogenous glucose demand that is met by obligatory amino acid-based gluconeogenesis. It is predicted that for hypercarnivorous mammals with the same degree of encephalisation, endogenous nitrogen losses increase with decreasing metabolic mass as a result of the allometric relationships of brain mass and brain metabolic rate with body mass, possibly imposing a lower limit for body mass in hypercarnivorous mammals.

High levels of whole-body energy expenditure are associated with a lower coupling of skeletal muscle mitochondria in C57Bl/6 mice

Considerable variation in energy expenditure is observed in C57Bl/6 mice on a high-fat diet. Because muscle tissue is a major determinant of whole-body energy expenditure, we set out to determine the variation in energy expenditure and its possible association with skeletal muscle mitochondrial function upon high-fat diet intervention. Metabolic cages using indirect calorimetry were used to assess whole-body energy metabolism in C57Bl/6 male mice during the first 3 days of high-fat diet intervention. Mice were grouped in a negative or positive residual nocturnal energy expenditure group after correction of total nocturnal energy expenditure for body mass by residual analysis. The positive residual energy expenditure group was characterized by higher uncorrected total nocturnal energy expenditure and food intake. On day 7, mitochondria were isolated from the skeletal muscle of the hind limb. Mitochondrial density was determined by mitochondrial protein content and did not differ between the positive and negative residual energy expenditure groups. Using high-resolution respirometry, mitochondrial oxidative function was assessed using various substrates. Mitochondria from the positive residual energy expenditure group were characterized by a lower adenosine diphosphate-stimulated respiration and lower respiratory control rates using palmitoyl-coenzyme A as substrate. These results indicate that reduced mitochondrial coupling is associated with positive residual energy expenditure and high rates of total energy expenditure in vivo.

Pmch expression during early development is critical for normal energy homeostasis

Postnatal development and puberty are times of strong physical maturation and require large quantities of energy. The hypothalamic neuropeptide melanin-concentrating hormone (MCH) regulates nutrient intake and energy homeostasis, but the underlying mechanisms are not completely understood. Here we use a novel rat knockout model in which the MCH precursor Pmch has been inactivated to study the effects of loss of MCH on energy regulation in more detail. Pmch(-/-) rats are lean, hypophagic, osteoporotic, and although endocrine parameters were changed in pmch(-/-) rats, endocrine dynamics were normal, indicating an adaptation to new homeostatic levels rather than disturbed metabolic mechanisms. Detailed body weight growth and feeding behavior analysis revealed that Pmch expression is particularly important during early rat development and puberty, i.e., the first 8 postnatal weeks. Loss of Pmch resulted in a 20% lower set point for body weight that was determined solely during this period and remained unchanged during adulthood. Although the final body weight is diet dependent, the Pmch-deficiency effect was similar for all diets tested in this study. Loss of Pmch affected energy expenditure in both young and adult rats, although these effects seem secondary to the observed hypophagia. Our findings show an important role for Pmch in energy homeostasis determination during early development and indicate that the MCH receptor 1 system is a plausible target for childhood obesity treatment, currently a major health issue in first world countries.

Metabolic correlates of selection on aerobic capacity in laboratory mice: a test of the model for the evolution of endothermy

According to the aerobic capacity model of the evolution of endothermy, high levels of basal/resting metabolic rate (BMR/RMR) underlying endothermy have evolved as a correlated response to selection for high rates of aerobic metabolism (V(O(2)max)). To test the model we studied metabolic, behavioural and morphological correlates of replicated selection on maximum body mass-corrected metabolism elicited by swimming (V(O(2)swim)) in male laboratory mice. While 10 generations of selection did not change body mass, it resulted in a 12% difference in V(O(2)swim) between mice of selected and control line types and significant, correlated responses in maximum metabolic rates elicited by exposure to cold in a helium-oxygen atmosphere (V(O(2)He)), and during forced running on a motorized treadmill (V(O(2)run)). Selected and control lines also significantly differed with respect to duration of running (a measure of stamina, t(run)), and the distance run to exhaustion (d(e)). However, the selection protocol did not result in elevated BMR and voluntary activity. Higher V(O(2)max) in selected animals was positively correlated with higher masses of gastrocnemius muscles and heart but not of other visceral organs (intestine, stomach, liver and kidneys). These findings provide a mechanistic explanation for the lack of correlation between basal and maximal metabolic rates in selected mice. Overall, our study does not support the assumptions of the aerobic capacity model for the evolution of endothermy.

Metabolic ageing in individual zebra finches

Oxidative stress is suggested as a contributor to the ageing process. Knowledge of the relationship between age and energy expenditure may contribute to our understanding of ageing patterns, due to the link between oxygen consumption and free radical production. However, studies on basal metabolic rate (BMR) and age have generally been cross-sectional, which may confound estimates of the age effect due to disproportionate mortality (also known as 'selective disappearance'). We therefore performed a longitudinal study of BMR using captive zebra finches (Taeniopygia guttata) up to 5 years of age. BMR declined with age in individuals of both sexes when body mass was controlled for. Males gained mass with age while females did not. There was no evidence for disproportionate mortality with respect to BMR in either sex. To our knowledge, this is the first longitudinal study of avian BMR over such a long proportion of the lifespan of the study species.

The dynamic transfer of 3H and 14C in mammals: a proposed generic model

Associated with the present debate regarding the potential revival of nuclear energy there is an increased interest in assessing the radiological risk to the public and also the environment. Tritium and (14)C are key radionuclides of interest in many circumstances (e.g. heavy water reactors, waste storage and fusion reactors). Because the stable analogues of these two radionuclides are integral to most biological compounds, their modelling should follow general principles from life sciences. In this paper, a model of the dynamics of (14)C and (3)H in mammals is proposed on the basis of metabolic understanding and of, as far as possible, readily available data (e.g. for organ composition and metabolism). The model is described together with validation tests (without calibration) for a range of farm animals. Despite simplifications, the model tests are encouraging for a range of animal types and products (tissues and milk), and further improvements are suggested.

Is basal metabolic rate influenced by age in a long-lived seabird, the snow petrel?

Ageing is associated with a decline in basal metabolic rate (BMR) in many species, including humans. The evolutionary and physiological causes underlying the relationship between age and BMR are poorly understood. Studies of procellariiform seabirds may provide valuable insight because they have a longer maximum lifespan than expected from their body size and rates of energy metabolism. Such studies are rare, however, because there are few populations with a high proportion of individuals of known age. We performed a cross-sectional study of energy metabolism in relation to age in a long-lived seabird, the snow petrel Pagodroma nivea. In an Antarctic population that has been subject to a long-term research program, including annual banding of chicks since 1963, we measured BMR of individuals aged between 8 and 39 years. We show that the BMR of the snow petrel does not decrease with increasing age. BMR seems to be sustained at a fixed level throughout the investigated age-span. We review this result in light of the disposable soma theory of ageing, and we discuss whether species-specific relationships between age and basal metabolic rate can be related to differences in maximum lifespan.

Tissue iron distribution and urinary mineral excretion vary depending on the form of iron (FeSO4 or NaFeEDTA) and the route of administration (oral or subcutaneous) in rats given high doses of iron

Sodium iron ethylenediaminetetraacetate (NaFeEDTA) has considerable promise as an iron fortificant in food. However, effects of administering high levels of NaFeEDTA on tissue iron distribution and mineral excretion are not well understood. The objectives of this study were to assess nonheme iron distribution in the body and urinary excretion of Ca, Mg, Cu, Fe, and Zn after daily administration of high levels of iron to rats over 21 days. Iron was either given orally with food or injected subcutaneously, as either FeSO 4 or NaFeEDTA. Selected tissues were collected for nonheme iron analysis. Estimated total body nonheme iron levels were similar in rats fed NaFeEDTA or FeSO 4, but the tissue distribution was different: it was 53% lower in the liver and 86% higher in the kidneys among rats fed NaFeEDTA than among those fed FeSO 4. In contrast, body nonheme iron was 3.2-fold higher in rats injected with FeSO 4 than in rats injected with NaFeEDTA. Administering NaFeEDTA orally elevated urinary Cu, Fe, and Zn excretion compared with FeSO 4 (1.41-, 11.9-, and 13.9-fold higher, respectively). We conclude that iron is dissociated from the EDTA complex prior to or during intestinal absorption. A portion of intact FeEDTA may be absorbed via a paracellular route at high levels of intake but is mostly excreted in the urine. Metal-free EDTA may be absorbed and cause elevated urinary excretion of Fe, Cu, and Zn.

Physiological genetics of dietary restriction: uncoupling the body temperature and body weight responses

Numerous physiological and molecular changes accompany dietary restriction (DR), which has been a major impediment to elucidating the causal basis underlying DR's many health benefits. Two major metabolic responses to DR that potentially underlie many of these changes are the body temperature ( Tb) and body weight (BW) responses. These responses also represent an especially difficult challenge to uncouple during DR. We demonstrate in this study, using two recombinant inbred (RI) panels of mice (the LXS and LSXSS) that naturally occurring genetic variation serves as a powerful tool for modulating Tb and BW independently during DR. The correlation coefficient between the two responses was essentially zero, with R = −0.04 in the LXS and −0.03 in the LSXSS, the latter averaged across replicate cohorts. This study is also the first to report that there is highly significant ( P = 10−10) strain variation in the Tb response to DR in the LXS (51 strains tested), with strain means ranging from 2 to 4°C below normal. The results suggest that the strain variation in the Tb response to DR is largely due to differences in the rate of heat loss rather than heat production (i.e., metabolic rate). This variation can thus be used to assess the long-term effects of lower Tb independent of BW or metabolic rate, as well as independent of food intake and motor activity as previously shown. These results also suggest that murine genetic variation may be useful for uncoupling many more responses to DR.

The Influence of Folic Acid, Vitamins B2and B6Supplementation on Feed Intake, Body and Organs Weight, and Liver Fatty Acids Composition of Rats Subjected to 3 months Moderate Protein Deprivation

This study was conducted to determine the effect of a 3-month dietary protein restriction - protein provided 9% of energy (20% in control group). In this dietary restriction folic acid, vitamins B(2) and B(6) were delivered in amount three times above the standard level. It was observed that animals fed a protein restricted (PR) diet weighed about 5% less than animals consuming adequate diet, but the difference was not statistically significant. Enrichment of PR diet with vitamin B or folic acid caused tendency to further suppression of weight gain, and in case of vitamin B(6) these differences were statistically significant. However, such body weight (BW) suppression was not observed when all studied vitamins were used together. Significant reductions in relative liver weight (vitamin B(2) addition), the heart (folic acid) and the lungs (vitamin B(6)) were observed. The PR diet, when all vitamins were added together, caused a decrease in weights of the lungs, heart and liver scaled to BW of rats, simultaneously with a significant increase in testis weight. Feed intake and feed conversion ratio were higher in animals given PR diet without a significant influence of vitamin supplementation (except vitamin B(6) causing further increase in feed conversion ratio). Hepatic fatty acids composition of rats was not affected by protein restriction, as well as by single vitamin supplementation. However, dietary supplementation of all examined vitamins together caused a decrease in monounsaturated fatty acids followed by an increase in polyunsaturated fatty acids participation in total fatty acids pool. It seems that enrichment of PR diet with a mixture of folic acid, vitamins B(2) and B(6) resulted in a partial reverse of growth suppression and reduction in testis size in rats.

Gender and obesity influence sodium intake and fluid regulation in Zucker rats following repeated sodium depletions

The Zucker obese rat is an important model for the metabolic syndrome, which includes renal disease and salt-sensitive hypertension, suggesting abnormalities of body fluid regulation. Here, in Zucker rats, lean and obese, and of both sexes, we compared 48 h of sodium intake and fluid regulation responses with repeated depletions with furosemide to repeated control saline injections. Increased urine volume excretion was observed after each furosemide administration for the 4 groups and obese rats excreted more than the leans on the control days. Male obese rats did not excrete sodium nor increase intake of 2% NaCl following the first furosemide administration, whereas the other 3 groups did. Subsequent depletions increased 2% NaCl consumption and urinary sodium excretion in all groups. Males excreted more sodium in their urine than the females on the control days. Females showed an increase in 2% NaCl intake on control days. Water intake increased in the female leans after each depletion, increased in the males after the 2nd and 3rd depletion and increased in the obese females only after the 2nd depletion. These findings show clearly that there are gender- and weight-related differences in the response of Zucker rats to furosemide-induced depletion. However, the main differences occurred with the first depletion. With repeated depletions the rats adjusted sodium and fluid intake and excretion so that differences due to gender and body weight tended to disappear. Our findings caution against drawing conclusions about differences due to gender and body weight based on single treatments.

Muscle type-specific fatty acid metabolism in insulin resistance: an integrated in vivo study in Zucker diabetic fatty rats

Intramyocellular lipid content (IMCL) serves as a good biomarker of skeletal muscle insulin resistance (IR). However, intracellular fatty acid metabolites [malonyl-CoA, long-chain acyl-CoA (LCACoA)] rather than IMCL are considered to be responsible for IR. This study aimed to investigate dynamics of IMCL and fatty acid metabolites during fed-to-starved-to-refed transition in lean and obese (IR) Zucker diabetic fatty rats in the following different muscle types: soleus (oxidative), extensor digitorum longus (EDL, intermediary), and white tibialis anterior (wTA, glycolytic). In the fed state, IMCL was significantly elevated in obese compared with lean rats in all three muscle types (soleus: 304%, EDL: 333%, wTA: 394%) in the presence of elevated serum triglycerides but similar levels of free fatty acids (FFA), malonyl-CoA, and total LCACoAs. During starvation, IMCL in soleus remained relatively constant, whereas in both rat groups IMCL increased significantly in wTA and EDL after comparable dynamics of starvation-induced FFA availability. The decreases of malonyl-CoA in wTA and EDL during starvation were more pronounced in lean than in obese rats, although there were no changes in soleus muscles for both groups. The concomitant increase in IMCL with the fall of malonyl-CoA support the concept that, as a reaction to starvation-induced FFA availability, muscle will activate lipid oxidation more the lower its oxidative capacity and then store the rest as IMCL.

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.

Gene or size: metabolic rate and body temperature in obese growth hormone-deficient dwarf mice

OBJECTIVE

SMA1 mice carry a missense mutation in the growth hormone gene that leads to semidominant dwarfism and obesity. In this study, the basic thermal and metabolic properties of SMA1 mice were examined to detect metabolic alterations that can support the accretion of excess fat.

RESEARCH METHODS AND PROCEDURES

Basal and resting metabolic rates (RMRs) in wild-type and SMA1 (sma1/+ and sma1/sma1) mice were determined by indirect calorimetry. Body temperature (T(b)) was recorded using intraperitoneally implanted temperature-sensitive transmitters, and body composition was determined by DXA.

RESULTS

SMA1 mice have proportionally lower basal and resting metabolic rates, higher body mass (BM)-specific RMRs, and a higher lower critical temperature, and display a decrease in T(b) by 0.4 degrees C in sma1/+ and 0.9 degrees C in sma1/sma1.

DISCUSSION

The analysis of gene effects on BM and energy expenditure in mouse mutants must consider the appropriate allometric relationship between BM and metabolic rate. With the exception of T(b), all metabolic alterations observed in SMA1 reflect reduced size.

Effect of somatic growth, strain, and sex on double-chamber plethysmographic respiratory function values in healthy mice

Double-chamber plethysmography has been recognized since 1979 as a reference technique to measure pulmonary function values in guinea pigs, but it has not gained attention for use in mice. Theoretically, however, this technique combines the advantages of single-chamber plethysmography with a quantitative assessment of flow and/or volume and a calculated resistance, the interpretation of which in terms of bronchoconstriction is not disputed. Here we show that, when appropriately preconditioned, mice are able to gradually grow accustomed to the apparatus and display extremely stable nasal and thoracoabdominal flow tracings. Overall, strain, sex, and somatic growth had a significant effect on pulmonary function values. The changes in specific airway resistance (sRaw) and enhanced pause (Penh) values were never in the same direction, indicating that they measure different things. The respiratory frequency was far higher in C57BL/6 compared with BALB/c mice. Peak flows, minute volume, specific tidal and minute volumes, and sRaw were also higher, but Penh was smaller. Males breathed at a higher frequency than females, leading to a higher minute volume. Nevertheless, the specific volumes were considerably higher among females. Penh was lower in males, whereas sRaw was identical in both sexes. Changes associated with somatic growth were rapid and important between 5 and 9 wk, then slowed down between 9 and 12-13 wk and became almost imperceptible after.

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.

A preexercise alpha-lactalbumin-enriched whey protein meal preserves lipid oxidation and decreases adiposity in rats

The composition of the preexercise food intake is known to affect substrate utilization during exercise and thus can affect long-term changes in body weight and composition. These parameters were measured in male rats exercised 2 h daily over 5 wk, either in the fasting state or 1 h after they ingested a meal enriched with glucose (Glc), whole milk protein (WMP), or alpha-lactalbumin-enriched whey protein (CPalphaL). Compared with fasting, the Glc meal increased glucose oxidation and decreased lipid oxidation during and after exercise. In contrast, the WMP and CPalphaL meals preserved lipid oxidation and increased protein oxidation, the CPalphaL meal increasing protein oxidation more than the WMP meal. At the end of the study, body weight was larger in the WMP-, Glc-, and CPalphaL-fed rats than in the fasted ones. This resulted from an increased fat mass in the WMP and Glc rats and to an increased lean body mass, particularly muscles, in the CPalphaL rats. We conclude that the potential of the CPalphaL meal to preserve lipid oxidation and to rapidly deliver amino acids for use during exercise improved the efficiency of exercise training to decrease adiposity.

High-resolution magnetic resonance imaging tracks changes in organ and tissue mass in obese and aging rats

Magnetic resonance imaging (MRI) has the ability to discriminate between various soft tissues in vivo. Whole body, specific organ, total adipose tissue (TAT), intra-abdominal adipose tissue (IAAT), and skeletal muscle (SM) weights determined by MRI were compared with weights determined by dissection and chemical analysis in two studies with male Sprague-Dawley rats. A 4.2-T MRI machine acquired high-resolution, in vivo, longitudinal whole body images of rats as they developed obesity or aged. Weights of the whole body and specific tissues were determined using computer image analysis software, including semiautomatic segmentation algorithms for volume calculations. High correlations were found for body weight (r = 0.98), TAT (r = 0.99), and IAAT (r = 0.98) between MRI and dissection and chemical analyses. MRI estimated the weight of the brain, kidneys, and spleen with high accuracy (r > 0.9), but overestimated IAAT, SM, and liver volumes. No differences were detected in organ weights using MRI and dissection measurements. Longitudinal MRI measurements made during the development of obesity and aging accurately represented changes in organ and tissue mass.