Mean Metabolic Rates Research Articles

Measurement of glucose metabolism in the occipital lobe and frontal cortex after oral administration of [1-13C]glucose at 9.4 T

For the first time, labeling effects after oral intake of [1-13C]glucose are observed in the human brain with pure 1H detection at 9.4 T. Spectral time series were acquired using a short-TE 1H MRS MC-semiLASER (Metabolite Cycling semi Localization by Adiabatic SElective Refocusing) sequence in two voxels of 5.4 mL in the frontal cortex and the occipital lobe. High-quality time-courses of [4-13C]glutamate, [4-13C]glutamine, [3-13C]glutamate + glutamine, [2-13C] glutamate+glutamine and [3-13C]aspartate for individual volunteers and additionally, group-averaged time-courses of labeled and non-labeled brain glucose could be obtained. Using a one-compartment model, mean metabolic rates were calculated for each voxel position: The mean rate of the TCA-cycle (Vtca) value was determined to be 1.36 and 0.93 μmol min−1 g−1, the mean rate of glutamine synthesis (Vgln) was calculated to be 0.23 and 0.45 μmol min−1 g−1, the mean exchange rate between cytosolic amino acids and mitochondrial Krebs cycle intermediates (Vx) rate was found to be 0.57 and 1.21 μmol min−1 g−1 for the occipital lobe and the frontal cortex, respectively. These values were in agreement with previously reported data. Altogether, it can be shown that this most simple technique combining oral administration of [1-13C]Glc with pure 1H MRS acquisition is suitable to measure metabolic rates.

Hydrologic Setting Dictates the Sensitivity of Ecosystem Metabolism to Climate Variability in Lakes

Global change is influencing production and respiration in ecosystems across the globe. Lakes in particular are changing in response to climatic variability and cultural eutrophication, resulting in changes in ecosystem metabolism. Although the primary drivers of production and respiration such as the availability of nutrients, light, and carbon are well known, heterogeneity in hydrologic setting (for example, hydrological connectivity, morphometry, and residence) across and within regions may lead to highly variable responses to the same drivers of change, complicating our efforts to predict these responses. We explored how differences in hydrologic setting among lakes influenced spatial and inter annual variability in ecosystem metabolism, using high-frequency oxygen sensor data from 11 lakes over 8 years. Trends in mean metabolic rates of lakes generally followed gradients of nutrient and carbon concentrations, which were lowest in seepage lakes, followed by drainage lakes, and higher in bog lakes. We found that while ecosystem respiration (ER) was consistently higher in wet years in all hydrologic settings, gross primary production (GPP) only increased in tandem in drainage lakes. However, interannual rates of ER and GPP were relatively stable in drainage lakes, in contrast to seepage and bog lakes which had coefficients of variation in metabolism between 22–32%. We explored how the geospatial context of lakes, including hydrologic residence time, watershed area to lake area, and landscape position influenced the sensitivity of individual lake responses to climatic variation. We propose a conceptual framework to help steer future investigations of how hydrologic setting mediates the response of metabolism to climatic variability.

Indirect calorimetry of metabolic rate in college-age Japanese subjects during various office activities

Indoor climate regulations are based on an empirical thermal comfort model developed in the 1960s. The standard values for one of its fundamental parameters, which is the metabolic rate, is based on the data pertaining to European and North American men measured at that time and may overestimate the metabolic rate of modern Japanese, especially women. Therefore, applying standard values to modern Japanese may lead to inaccurate thermal comfort evaluation. The purpose of this research is to investigate the metabolic rates of Japanese individuals performing different office activities using accurate body surface area data in order to determine whether there exist differences between the measured and standard values. Three-dimensional measurements of the body surface area and indirect calorimetry were applied to determine their metabolic rates accurately. This study measured the mean metabolic rates of 45 college-age Japanese subjects while they were sitting quietly, sitting and typing, standing quietly, and standing and typing at 0.9 and 0.8 met, respectively, and 2.6 met each while they were walking at a speed of 4.0 km/h. These values are significantly lower than the standard values specified in the current international standards for all activity levels. Moreover, females exhibited lower metabolic rates than males, and significant differences between both biological sexes were found for all activity levels excluding walking. It was found that applying the metabolic rate values specified in the existing thermal comfort standards to college-age Japanese, particularly females, can lead to inaccurate thermal comfort evaluation and CO2 generation rate estimation for building occupants.

Submerged macrophytes affect the temporal variability of aquatic ecosystems

Abstract Submerged macrophytes are important foundation species that can strongly influence the structure and functioning of aquatic ecosystems, but only little is known about the temporal variation and the timescales of these effects (i.e. from hourly, daily, to monthly). Here, we conducted an outdoor experiment in replicated mesocosms (1,000 L) where we manipulated the presence and absence of macrophytes to investigate the temporal variability of their ecosystem effects. We measured several parameters (chlorophyll‐a, phycocyanin, dissolved organic matter [DOM], and oxygen) with high‐resolution sensors (15‐min intervals) over several months (94 days from spring to autumn), and modelled metabolic rates of each replicate ecosystem in a Bayesian framework. We also implemented a simple model to explore competitive interactions between phytoplankton and macrophytes as a driver of variability in chlorophyll‐a. Over the entire experiment, macrophytes had a positive effect on mean DOM concentration, a negative effect on phytoplankton biomass, and either a weak or no effect on mean metabolic rates, DOM composition, and conductivity. We also found that macrophytes increased the variance of dissolved organic carbon composition and metabolic rates, and, occasionally in the observed period, increased the variance of phytoplankton biomass and conductivity. The observation that macrophytes decreased the mean but increased the variance of phytoplankton biomass was consistent with the model that we implemented. Our high‐resolution time series embedded within a manipulative experiment reveal how a foundation species can affect ecosystem properties and processes that have characteristically different timescales of response to environmental variation. Specifically, our results show how macrophytes can affect short‐term dynamics of algal biomass, while also affecting the seasonal build‐up of DOM and the variance of ecosystem metabolism.

Can a Terrestrial Ectoparasite Disperse with Its Marine Host?

One of the most extreme examples of parasite adaptation comes from terrestrial ectoparasites exploiting marine hosts. Despite the ubiquity of such ectoparasitism and its ecological and evolutionary importance, investigations of the responses of ectoparasites to conditions encountered on their hosts are rare. In the case of penguins and their ticks, current understanding suggests that ticks freely parasitize their hosts on land but are incapable of surviving extended oceanic journeys. We examined this conjecture by assessing the physiological capacity of little penguin ticks to endure at-sea foraging and dispersal events of their hosts. Survival in penguins ticks was not significantly compromised by exposure to depths commonly associated with host dives (40 and 60 m), repeated seawater exposure relevant to the most common (30 s) and longest (120 s) recorded host dives, or extended (48 h) exposure to seawater. Mean (±SD) closed-phase durations in adult and nymphal ticks exhibiting discontinuous gas exchange ( and s, respectively) exceeded that of the maximum recorded host dive duration (120 s). Normoxic-anoxic-normoxic respirometry also confirmed spiracle closure. Mean metabolic rates ( and μL/h at 25°C for unfed and fed adult females, respectively) were significantly influenced by temperature; optimal and LT50 temperatures for adult ticks and fed nymphal ticks were typically higher than swimming penguin body temperatures. These findings suggest that marine host dispersal is unlikely to present an insurmountable barrier to long-distance tick dispersal. Such dispersal has important implications for evolutionary theory, conservation, and epidemiology.

The magnitude of the naturally occurring isotopic enrichment of 13C in exhaled CO2 is directly proportional to exercise intensity in humans

Due to various biochemical fractionation processes during lipid synthesis, the lipid molecules in the body contain substantially lower concentrations of 13C than the nonlipid molecules. Because of the isotopic differences between these two endogenous nutrient pools, any shift toward nonlipid fuel oxidation would be expected to increase in the δ13C of the exhaled breath. Interestingly, the possibility of whether or not an exercise-induced change actually occurs has been debated in literature for over two decades and researchers have still not reached a consensus. We measured ventilatory and metabolic variables before, during, and after exercise in forty-eight adults (n=25 females, n=23 males; 20.1±1.9years) assigned to either a resting treatment or one of three exercising treatments where they maintained a heart rate of 130, 150, or 170bpm for 56min. We found that the mean metabolic rates of the exercising groups increased 4.4-fold, 6.1-fold, and 7.7-fold above resting values, respectively. Exercise caused small increases in respiratory exchange ratios (e.g., from 0.83±0.08 to 0.86±0.10) indicative of increased carbohydrate oxidation, but these changes were too variable to be reliably correlated with exercise intensity. In contrast, the δ13C of the exhaled breath increased by 0.62±0.19‰, 1.14±0.29‰, and 1.79±0.50‰, respectively, for the three groups and was significantly correlated with the intensity of exercise. We also show that the isotopic difference of the lipid and nonlipids of the body is similar (~2.7‰) even when consuming bulk diets that are isotopically distinct (>8‰). If not corrected for, these exercise-induced changes in δ13C of the breath would be sufficiently large to skew the results of studies investigating the oxidative fates of exogenous nutritional supplements.

Characterising an artiodactyl family inhabiting arid habitats by its metabolism: Low metabolism and maintenance requirements in camelids

To test whether camelids, as an artiodactyl family, are characterised by comparatively low energy expenditure, we collated literature data from experiments where at least one camelid and one ruminant species received the same diet, and literature data on camelid metabolism and energy requirements. Additionally, we measured the maintenance and resting metabolism in five alpacas, six llamas and five Bactrian camels by chamber respirometry. Irrespective of whether dry matter intake was expressed as g kg−0.75 day−1, g kg−0.9 day−1, or g kg−1.0 day−1, camelids ingested significantly less food than domestic ruminants (data available for sheep and goats). Although metabolic rates and energy requirements reported for camelids vary over a large range, they are generally below the ‘average’ basal mammal metabolism, and below published energy requirements for ruminants. The mean metabolic rates measured in this study were 215 ± 68, 261 ± 33 and 248 ± 51 kJ kg−0.75 day−1 for alpacas, llamas and Bactrian camels, respectively. The corresponding resting metabolic rates averaged at 144 ± 64, 164 ± 38 and 192 ± 48 kJ kg−0.75 day−1. These findings confirm that camelids in general are characterised by relatively low metabolism and food intake, which might explain why this previously diverse group is currently limited to arid environments with low food resources where a reduced metabolism represents an advantage.

Short-term captivity influences maximal cold-induced metabolic rates and their repeatability in summer-acclimatized American goldfinches Spinus tristis

Abstract Studies of metabolic variation in birds have involved both wild and captive individuals, but few studies have investigated whether captivity directly influences metabolic rates, despite such variation potentially confounding conclusions regarding how metabolic rates respond to the conditions under study. In addition, whether short-term captivity influences metabolic rate repeatability in birds is currently uninvestigated. In this study, we measured Msum (maximal cold-induced metabolic rates) in summer acclimatized American goldfinches Spinus tristis directly after capture from wild populations, after approximately 2 weeks of indoor captivity (Captive 1), and again after an additional 1–2 weeks of captivity (Captive 2). Msum increased significantly (16.9%) following the initial captive period, but remained stable thereafter. Body mass (Mb) also increased significantly (9.2%) during the initial captive period but remained stable thereafter, suggesting that muscle growth and/or remodeling of body composition produced the observed metabolic variation. Mb and Msum were not significantly repeatable between wild and Captive 1 birds, but were significantly repeatable between Captive 1 and Captive 2 groups. These data suggest that caution must be exercised when extrapolating metabolic rates from short-term captive to wild populations. In addition, Msum was a repeatable trait for birds under conditions where mean metabolic rates remained stable, but Msum repeatability disappeared during acclimation to conditions promoting phenotypically flexible metabolic responses. This suggests that the capacity for phenotypic flexibility varies among individuals, and such variation could have fitness consequences.

Terrestrial locomotion imposes high metabolic requirements on bats

The evolution of powered flight involved major morphological changes in Chiroptera. Nevertheless, all bats are also capable of crawling on the ground and some are even skilled sprinters. We asked if a highly derived morphology adapted for flapping flight imposes high metabolic requirements on bats when moving on the ground. We measured the metabolic rate during terrestrial locomotion in mastiff bats, Molossus currentium, a species that is both a fast-flying aerial-hawking bat and an agile crawler on the ground. Metabolic rates of bats averaged 8.0±4.0 ml CO(2) min(-1) during a 1-min period of sprinting at 1.3±0.6 km h(-1). With rising average speed, mean metabolic rates increased, reaching peak values that were similar to those of flying conspecifics. Metabolic rates of M. currentium were higher than those of similar-sized rodents that sprinted at similar velocities under steady-state conditions. When M. currentium sprinted at peak velocities, its aerobic metabolic rate was 3-5 times higher than those of rodent species running continuously in steady-state conditions. Costs of transport (J kg(-1) m(-1)) were more than 10 times higher for running than for flying bats. We conclude that at the same speed bats experience higher metabolic rates during short sprints than quadruped mammals during steady-state terrestrial locomotion, yet running bats achieve higher maximal mass-specific aerobic metabolic rates than non-volant mammals such as rodents.

Mean mass-specific metabolic rates are strikingly similar across life's major domains: Evidence for life's metabolic optimum.

A fundamental but unanswered biological question asks how much energy, on average, Earth's different life forms spend per unit mass per unit time to remain alive. Here, using the largest database to date, for 3,006 species that includes most of the range of biological diversity on the planet-from bacteria to elephants, and algae to sapling trees-we show that metabolism displays a striking degree of homeostasis across all of life. We demonstrate that, despite the enormous biochemical, physiological, and ecological differences between the surveyed species that vary over 10(20)-fold in body mass, mean metabolic rates of major taxonomic groups displayed at physiological rest converge on a narrow range from 0.3 to 9 W kg(-1). This 30-fold variation among life's disparate forms represents a remarkably small range compared with the 4,000- to 65,000-fold difference between the mean metabolic rates of the smallest and largest organisms that would be observed if life as a whole conformed to universal quarter-power or third-power allometric scaling laws. The observed broad convergence on a narrow range of basal metabolic rates suggests that organismal designs that fit in this physiological window have been favored by natural selection across all of life's major kingdoms, and that this range might therefore be considered as optimal for living matter as a whole.

Elevated oxygen uptake and high rates of nitrogen excretion in early life stages of the cobia Rachycentron canadum (L.), a fast‐growing subtropical fish

Physiological energetics of cobia Rachycentron canadum were quantified for 18 to 82 days post‐hatch (dph) hatchery‐reared juveniles to better understand energy transformation and its implications in growth and survival. Mean oxygen consumption rates (; mg O2 h−1) of fish fed ad libitum and fish that were starved significantly increased with increasing wet mass (M; g), = 1·4291M0·8119 and = 1·1784M0·7833, respectively, with a significant reduction in mean metabolic rates of starved fish (19 to 27% specific dynamic action; SDA). Total ammonia nitrogen excretion rates (AMM, μmol h−1) also scaled with M and significantly decreased after starvation. Mean mass‐specific AMM and urea excretion rates are the highest reported in the literature, with urea accounting for approximately half the total nitrogen excretion measured in both fed and starved fish. Relatively high energetic rates may allow cobia to develop rapidly into pre‐juveniles and be less susceptible to predation and starvation at a comparatively early age.

Metabolism and thermoregulation in three species of rodent from Northeastern China

Metabolic rate, body temperature, and thermal conductance were determined in the gray red-backed vole ( Clethrionomys rufocanus), large Japanese field mouse ( Apodemus speciosus) and striped field mouse ( Apodemus agrarius) at a temperature range of 5–32.5°C. Oxygen consumption was measured by using a closed circuit respirometer. The thermal neutral zone of gray red-backed vole, large Japanese field mouse and striped field mouse were 22.5–27.5°C, 25–30°C and 25–27.5°C, respectively. The mean metabolic rates within thermal zone of these species were 3.62±0.18, 2.69±0.08, and 3.29±0.11 ml O 2 g −1 h −1, respectively, which are relatively higher than the predicted values based on their body mass. Non-shivering thermogenesis of these animals were 6.76±0.12, 5.56±0.39 and 6.13±0.28 ml O 2 g −1 h −1, respectively. Mean body temperature of the three species were 37.1±0.13°C, 36.9±0.2°C, and 37.5±0.2°C, respectively. Mean thermal conductance of the three species were 0.25±0.04, 0.23±0.00 and 0.25±0.00 ml O 2 g −1 h −1°C −1, respectively. The ecophysiological properties of these species were: (1) the gray red-backed vole and large Japanese field mouse had high body temperatures and metabolic rates, median non-shivering thermogenesis, relatively wide thermal neutral zones and low lower critical temperatures, and relatively high thermal conductance. All these characteristics might constrain their distribution and extension to extreme desert, low latitudes and hot regions in China. (2) the striped field mouse had high metabolic rate, body temperature and thermal conductance, median non-shivering thermogenesis, a relatively narrow thermal neutral zone and low lower critical temperature.

Contribution of denitrification to nitrogen, carbon, and oxygen cycling in tidal creek sediments of a New England salt marsh

The contribution of denitrification to sediment metabolism was studied at 2 sites (muddy and sandy) in unvegetated tidal creek sediments from a small Cape Cod, USA, salt marsh receiving nitrate-enriched groundwater flows (32 mmol m -2 d -1 ). Simultaneous measurements of sediment N2, CO2, O2, and dissolved inorganic N fluxes were made over annual cycles. A total of 46% of the ammonium remineralized within the sediments was transformed to N2 by coupled nitrification- denitrification (Dn). Denitrifying and nitrifying bacteria contributed 15 and 18% to total sediment C and O cycling, respectively. C, N, and O2 cycling rates were limited by both temperature and the availability of labile organic matter. Muddy sediment C content was twice that of sandy sediments, but was half as labile, resulting in similar mean metabolic rates between sediment types (mean muddy and sandy O2 consumption rates were 62 and 58 mmol m -2 d -1 , respectively; CO2 production was 58 and 46 mmol m -2 d -1 ; and Dn was 5.4 and 4.9 mmol N m -2 d -1 ). Sediment δ 13 C (-18.5 and -20.8‰) and the molar CO2:N flux ratio (6.1) at both sites are consistent with a sediment metabolism based on algal rather than macrophytic biomass, and groundwater nitrate was the dominant source of N supporting algal growth. Annually, Dn accounted for 72% of total denitrification, with the remainder accounted for by water column-supported denitrification. Since all the denitrified N orig- inated from groundwater nitrate, algal uptake must have initially out-competed denitrification for water column nitrate, but nearly half of this algal N was subsequently remineralized and denitrified.

Metabolism of pelagic cephalopods as a function of habitat depth: a reanalysis using phylogenetically independent contrasts.

Metabolic rates of deep-living animals have been intensely studied (1). Within pelagic fishes, crustaceans, and cephalopods, a strong decline in rates of mass-specific metabolism with depth has been observed. Childress and Mickel (2) put forward the visual interactions hypothesis to explain this general pattern. Their hypothesis states that reduced metabolic rates among many deep-sea pelagic taxonomic groups result from relaxed selection for strong locomotory abilities for visual predator-prey interactions in the light-limited deep sea. This pattern has, however, been tested using mean metabolic rates for species as individual data points. Felsenstein (3) warned that, because species are descended in a hierarchical fashion from common ancestors, they generally cannot be considered as independent data points in statistical analyses. Statistical methods have recently been developed that incorporate phylogenetic information into comparative studies to create phylogenetically independent values that can then be used in statistical analyses. Reliable independent phylogenetic information has only recently become available for some deep-sea organisms. The present contribution reanalyzed the metabolic rates (4, 5) of pelagic cephalopods as a function of, for consistency with previous studies, MDO (minimum depth of occurrence) using phylogenetic independent contrasts derived from a recent molecular phylogeny (6). This analysis confirms the existence of a significant negative relationship between metabolism and minimum habitat depth in pelagic cephalopods but suggests that phylogenetic history also has

Comparison between estimated worn clothing insulation and required calculated clothing insulation in moderately cold environments (0 ° C ≤ ta ≤ + 15 ° C)

Six female and 33 male workers of the food industry (16–55 years), divided into three groups according to climatic conditions at the workplaces, were monitored during a typical shift. Fourteen subjects worked continuously in 0–7 °C, 18 in 13–15 °C and seven moved frequently between these climatic areas. Mean metabolic rates, heart rates, rectal temperatures and skin temperatures at the trunk and at the feet were similar between each of the three groups. Considerable differences between estimated clothing insulations worn and calculated required clothing insulations (IREQ neutral) were statistically analyzed. The results suggest that — apart from a limited overestimation — this discrepancy is mainly related to the difference between time-adjusted averages of metabolic rates of the single activities and the respective daily minimum suggesting the need for an adequate weighting for the metabolic rates, particularly if workers are at least temporarily exposed to air temperatures of more than 7–13 °C.

O-19-275 - Induction of immediate early genes after traumatic focal brain injury in the rat: Effects of mannitol on c-fos mRNA expression

To test whether camelids, as an artiodactyl family, are characterised by comparatively low energy expenditure, we collated literature data from experiments where at least one camelid and one ruminant species received the same diet, and literature data on camelid metabolism and energy requirements. Additionally, we measured the maintenance and resting metabolism in five alpacas, six llamas and five Bactrian camels by chamber respirometry. Irrespective of whether dry matter intake was expressed as g kg−0.75 day−1, g kg−0.9 day−1, or g kg−1.0 day−1, camelids ingested significantly less food than domestic ruminants (data available for sheep and goats). Although metabolic rates and energy requirements reported for camelids vary over a large range, they are generally below the ‘average’ basal mammal metabolism, and below published energy requirements for ruminants. The mean metabolic rates measured in this study were 215 ± 68, 261 ± 33 and 248 ± 51 kJ kg−0.75 day−1 for alpacas, llamas and Bactrian camels, respectively. The corresponding resting metabolic rates averaged at 144 ± 64, 164 ± 38 and 192 ± 48 kJ kg−0.75 day−1. These findings confirm that camelids in general are characterised by relatively low metabolism and food intake, which might explain why this previously diverse group is currently limited to arid environments with low food resources where a reduced metabolism represents an advantage.

Decline in Pelagic Cephalopod Metabolism With Habitat Depth Reflects Differences in Locomotory Efficiency.

The metabolic rates of 33 species of pelagic cephalopods from California and Hawaii were measured and correlated with minimum depth of occurrence. Mean metabolic rates ranged from 0.07 {mu}mol O2g-1 h-1 for the deep-living vampire squid, Vampyroteuthis infernalis, to 8.79 {mu}mol O2 g-1 h-1 for Gonatus onyx, a vertically migrating squid. An individual of V. infernalis, which lives within the oxygen minimum layer off California, had the lowest mass-specific metabolic rate ever measured for a cephalopod (0.02 {mu}mol O2g-1 h-1, 1050 g wet weight). For species collected in sufficient quantity and size range, metabolism was related to body size. Critical partial pressures of oxygen (Pc) were determined for Hawaiian and Californian cephalopods. Pc values for Hawaiian animals were considerably higher than for those taken off California, a trend that corresponds to the higher levels of environmental oxygen in the Hawaiian waters. Buffering capacity ({beta}) of mantle muscle, assayed in eight cephalopod species, was used to estimate the capacity for glycolytic energy production. Mean {beta} ranged from 1.43 slykes for a bathypelagic octopod, Japetella heathi, to 77.08 slykes for an epipelagic squid. Sthenoteuthis oualaniensis. Significant declines with increasing depth of occurrence were observed for both metabolism and {beta}. The decline in metabolic parameters with depth is interpreted as a decreased reliance on locomotory abilities for predator/prey interactions in the light-limited deep sea. The decline in metabolism with depth observed for pelagic cephalopods was significantly steeper than that previously observed for either pelagic fishes or crustaceans. We suggest that since strong locomotory abilities are not a priority in the deep sea, deeper-living cephalopods may rely more heavily on means of locomotion that are more efficient than jet propulsion via mantle contractions--means such as fin swimming or medusoid swimming utilizing the arms and extensive webbing present in many deep-living species. The greater efficiency of deeper-living cephalopods may be responsible for the observation that the decline in metabolic rates with depth is more pronounced for pelagic cephalopods than for fishes or crustaceans.

Thermogenesis associated with spontaneous activity: an important component of thermoregulatory needs in rats.

1. Quantification of the energy cost of spontaneous activity in freely moving lean and obese Zucker rats was performed at 28 degrees C and during acute cold exposure (from 28 to 5 degrees C). 2. An open-circuit metabolic chamber was supplemented with an ultrasensitive ergometric platform equipped with six undirectional accelerometers and with an opto-electronic device for location of the rat's centre of mass. 3. Resting and mean metabolic rates during control and cold-exposure periods were similar in both groups of rats. The 'extra thermogenesis' (ET), i.e. the difference between mean and resting metabolic rate, amounted to 11.7 +/- 1.1 and 8.6 +/- 0.7% of resting metabolic rate at 28 degrees C, and 39.7 +/- 2.9 and 34.1 +/- 2.9% of resting metabolic rate during cold exposure for lean and obese rats, respectively. 4. During the control period obese rats moved 3.71 +/- 0.61 m h-1 and lean rats 8.69 +/- 0.57 m h-1, but during cold exposure the distance moved by obese rats increased 3.58 +/- 0.33-fold whereas that moved by lean rats only increased 1.40 +/- 0.06-fold. The external work performed during spontaneous activity seldom reached 1.0% of the increase in metabolic rate. 5. In obese rats, weight was a good predictor of the distance covered, and cold exposure induced the same percentage increase in both distance and ET. Activity-associated thermogenesis of obese rats was the predominant thermogenic source that substituted for their atrophied brown fat thermogenesis whereas in lean rats with active brown fat these correlations were not found.

Diet Alters Metabolic Rate in the Yellow-Bellied Marmot (Marmota flaviventris) during Hibernation

We investigated the hypothesis that dietary composition can alter metabolic rate in the marmot. We provided marmots with two different diets: Purina standard Rodent Chow (no. 5001) and an essential fatty acid deficient (EFAD) diet (Purina chow no. 5803C). Metabolic rate was determined by indirect calorimetry during the summer and winter season. The mean metabolic rate measured during the summer was 7.54 mL O₂ min⁻¹ kg⁻¹ 0.62 for the control group and 7.43 mL O₂ min⁻¹ kg⁻¹ ± 0.34 for the EFAD animals. Both animal groups gained weight during the summer; body weights peaked in September. Fatty acid analysis of white adipose tissue from each group revealed significant differences (P < 0.01) in percent composition of fatty acid species 16:1, 18:1, 18:2, 18:3, and 20:0. Winter mean metabolic rates for the control group were significantly lower (P < 0.05) than they were for EFAD animals for all stages of hibernation (entrance, deep hibernation, and arousal). Average total hibernating bout length for the control group was 7.76 d, which is significantly higher (P < 0.05) than the 5.72 d for the EFAD group. These results support the hypothesis that essential fatty acids alter the metabolic rate in marmots and are necessary for normal thermoregulation during hibernation.

Effects of feeding frequency on metabolism of juvenile walleye

The effects of feeding frequency (1, 2, 3, or 15 times daily) on oxygen consumption (OC, mg O 2 kg −1 h −1) and ammonia excretion, (AE, mg TAN kg −1 h −1) of walleye ( Stizostedion vitreum) are described. Walleye were reared at a practical culture density of 35·4 kg m −3 in a single-pass system at 23·2°C. Diurnal variation in metabolic rates were related to feeding, not to photoperiod. Minimum OC rates occurred 30 min before the first feeding of the day, which was the longest average time since the last feeding. Metabolic rates increased immediately after feeding. The maximum rates for OC were 36–49% higher than the minimum rates, and 14–22% higher than the 24-h mean rate. Maximum rates for AE were 137–409% higher than the minimum rates, and 39–87% higher than the mean rates. There was a highly significant difference in the mean metabolic rates related to feeding frequency. The mean OC rate for 1 feeding day −1 (222·0 mg O 2 kg −1 h −1) was greater than the mean rates for 2, 3 and 15 feedings day −1. The OC rate for 1 feeding day −1 was 50·6% greater than the rate for 15 feedings day −1 (147·4 mg O 2 kg −1 h −1), the lowest mean rate. Mean and maximum oxygen/feed ratio (OFR, kg O 2 kg −1 feed fed day −1), varied inversely with feeding frequency. The mean ammonia/feed ratio (AFR) was similar for all but the 3 feedings day −1 treatment, but the maximum AFRs for 2 and 15 feedings day −1 were lower than the AFRs for 1 and 3 feedings day −1. AE was directly proportional to OC; the regression equations were highly significant, but specific for feeding frequency.