基础代谢产热的分子机制

本文综述了基础代谢的功能,发生,产热的途径以及各产热途径对基础代谢率（basal metabolic rate,BMR)的贡献,基础条件下整个机体的能量消耗用来维持两种功能：服务功能和细胞维持功能,基础代谢的产生是由体内的解偶联反应引起的,产热过程涉及到细胞内的非线粒体呼吸,质子漏和ATP周转反应,产生的热量分别占BMR的10％,20－30％和60％－70％。ATP周转反应包括Na^ -K^ 泵,Ca^2 泵,肌肉收缩,蛋白质周转,糖异生和尿素合成等,各产热反应对细胞呼吸的贡献只有组织特异性,却没有种属特异性,因而它们对BMR的贡献不仅与自身活性有关,还与体内各器官的相对重量有关。     

On the relation between basal and maximum metabolic rate in mammals

Basal and maximum metabolic rates, measured by oxygen consumption, for 18 species of wild mammals have been obtained from a search of literature records. The mass exponent of the allometric regression equation for maximum metabolic rate is significantly higher than that for BMR (0.841 and 0.745, respectively; P less than 0.05) in the group of animals examined. No significant correlation between mass-independent basal and maximum metabolic rates has been found. These results do not support the 'aerobic capacity' model of the origin of endothermy.     

The influence of foraging mode and arid adaptation on the basal metabolic rates of burrowing mammals

Two competing but nonexclusive hypotheses to explain the reduced basal metabolic rate (BMR) of mammals that live and forage underground (fossorial species) are examined by comparing this group with burrowing mammals that forage on the surface (semifossorial species). These hypotheses suggest that the low BMR of fossorial species either compensates for the enormous energetic demands of subterranean foraging (the cost-of-burrowing hypothesis) or prevents overheating in closed burrow systems (the thermal-stress hypothesis). Because phylogentically informed allometric analysis showed that arid burrowing mammals have a significantly lower BMR than mesic ones, fossorial and semifossorial species were compared within these groups. The BMRs of mesic fossorial and semifossorial mammals could not be reliably distinguished, nor could the BMRs of large (>77 g) arid fossorial and semifossorial mammals. This finding favours the thermal-stress hypothesis, because the groups appear to have similar BMRs despite differences in foraging costs. However, in support of the cost-of-burrowing hypothesis, small (<77 g) arid fossorial mammals were found to have a significantly lower BMR than semifossorial mammals of the similar size. Given the high mass-specific metabolic rates of small animals, they are expected to be under severe energy and water stress in arid environments. Under such conditions, the greatly reduced BMR of small fossorial species may compensate for the enormous energetic demands of subterranean foraging.     

The influence of basal metabolic rate on blood pressure among indigenous Siberians

Hypertension is an important global health issue and is currently increasing at a rapid pace in most industrializing nations. Although a number of risk factors have been linked with the development of hypertension, including obesity, high dietary sodium, and chronic psychosocial stress, these factors cannot fully explain the variation in blood pressure and hypertension rates that occurs within and between populations. The present study uses data collected on adults from three indigenous Siberian populations (Evenki, Buryat, and Yakut [Sakha]) to test the hypothesis of Luke et al. (Hypertension 43 (2004) 555-560) that basal metabolic rate (BMR) and blood pressure are positively associated independent of body size. When adjusted for body size and composition, as well as potentially confounding variables such as age, smoking status, ethnicity, and degree of urbanization, BMR was positively correlated with systolic blood pressure (SBP; P < 0.01) and pulse pressure (PP; P < 0.01); BMR showed a trend with diastolic blood pressure (DBP; P = 0.08). Thus, higher BMR is associated with higher SBP and PP; this is opposite the well-documented inverse relationship between physical activity and blood pressure. If the influence of BMR on blood pressure is confirmed, the systematically elevated BMRs of indigenous Siberians may help explain the relatively high blood pressures and hypertension rates documented among native Siberians in the post-Soviet period. These findings underscore the importance of considering the influence of biological adaptation to regional environmental conditions in structuring health changes associated with economic development and lifestyle change.     

Age at first reproduction and growth rate are independent of basal metabolic rate in mammals

This study tested an emergent prediction from the Metabolic Theory of Ecology (MTE) that the age at first reproduction (α) of a mammal is proportional to the inverse of its mass-corrected basal metabolic rate: The hypothesis was tested with multiple regression models of conventional species data and phylogenetically independent contrasts of 121 mammal species. Since age at first reproduction is directly influenced by an individual’s growth rate, the hypothesis that growth rate is proportional to BMR was also tested. Although the overall multiple regression model was significant, age at first reproduction was not partially correlated with either body mass, growth rate or BMR. Similarly, growth rate was not correlated with BMR. Thus at least for mammals in general, there is no evidence to support the fundamental premise of the MTE that individual metabolism governs the rate at which energy is converted to growth and reproduction at the species level. The exponents of the BMR allometry calculated using phylogenetic generalized least squares regression models were significantly lower than the three-quarter value predicted by the MTE. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Standard metabolic rate and thermoregulation of five species of Mongolian small mammals

Summary Oxygen consumption was measured over a range of ambient temperatures in 5 species of Mongolian small mammals:Microtus brandti, Alticola argentatus, Phodopus sungorus, Meriones unguiculatus, andOchotoma daurica (Tables 1 and 2). The measurements were made in the field, the animals being adjusted to natural environmental conditions. All the species studied coexist in the same arid steppe ecosystem. A variety of climatic adaptations was found.Abbreviations BMR basal metabolic rate - T _a ambient temperature     

Fluctuating selection on basal metabolic rate

BMR (Basal metabolic rate) is an important trait in animal life history as it represents a significant part of animal energy budgets. BMR has also been shown to be positively related to sustainable work rate and maximal thermoregulatory capacity. To this date, most of the studies have focused on the causes of interspecific and intraspecific variation in BMR, and fairly little is known about the fitness consequences of different metabolic strategies. In this study, we show that winter BMR affects local survival in a population of wild blue tits (Cyanistes caeruleus), but that the selection direction differs between years. We argue that this fluctuating selection is probably a consequence of varying winter climate with a positive relation between survival and BMR during cold and harsh conditions, but a negative relation during mild winters. This fluctuating selection can not only explain the pronounced variation in BMR in wild populations, but will also give us new insights into how energy turnover rates can shape the life‐history strategies of animals. Furthermore, the study shows that the process of global warming may cause directional selection for a general reduction in BMR, affecting the general life‐history strategy on the population level.     

Locomotor mode, maximum running speed, and basal metabolic rate in placental mammals

The locomotor performance (absolute maximum running speed [MRS]) of 120 mammals was analyzed for four different locomotor modes (plantigrade, digitigrade, unguligrade, and lagomorph-like) in terms of body size and basal metabolic rate (BMR). Analyses of conventional species data showed that the MRS of plantigrade and digitigrade mammals and lagomorphs increases with body mass, whereas that of unguligrade mammals decreases with body mass. These trends were confirmed in plantigrade mammals and lagomorphs using phylogenetically independent contrasts. Multiple regression analyses of MRS contrasts (dependent variable) as a function of body mass and BMR contrasts (predictor variables) revealed that BMR was a significant predictor of MRS in the complete data set, as well as in plantigrade and nonplantigrade mammals. However, there was severe multicollinearity in the nonplantigrade model that may influence the interpretation of these models. Although these data show mass-independent correlation between BMR and MRS, they are not necessarily indicative of a cause-effect relationship. However, the analyses do identify a negligible role of body size associated with MRS once phylogenetic and BMR effects are controlled, suggesting that the body size increase in large mammals over time (i.e., Cope's rule) can probably rule out MRS as a driving variable.     

Perinatal adaptation in mammals: the impact of metabolic rate

Mammalian birth is accompanied by profound changes in metabolic rate that can be described in terms of body size relationship (Kleiber's rule). Whereas the fetus, probably as an adaptation to the low intrauterine pO₂, exhibits an “inappropriately” low, adult-like specific metabolic rate, the term neonate undergoes a rapid metabolic increase up to the level to be expected from body size. A similar, albeit slowed, “switching-on” of metabolic size allometry is found in human preterm neonates whereas animals that are normally born in a very immature state are able to retard or even suppress the postnatal metabolic increase in favor of weight gain and O₂ supply. Moreover, small immature mammalian neonates exhibit a temporary oxyconforming behavior which enhances their hypoxia tolerance, yet is lost to the extent by which the size-adjusted metabolic rate is “locked” by increasing mitochondrial density. Beyond the perinatal period, there are no other deviations from metabolic size allometry among mammals except in hibernation where the temporary “switching-off” of Kleiber's rule is accompanied by a deep reduction in tissue pO₂. This gives support to the hypothesis that the postnatal metabolic increase represents an “escape from oxygen” similar to the evolutionary roots of mitochondrial respiration, and that the overall increase in specific metabolic rate with decreasing size might contribute to prevent tissues from O₂ toxicity.     

The influence of weather on habitat use by small mammals

Summer habitat use by three species of forest small mammals was determined using tracking stations Nocturnal weather influenced habitat selection by deer mice and woodland jumping mice but not by red-backed voles Deer mice used all habitats equally on clear nights but were most active in mixed forest on cloudy, rainless nights and most active in a coniferous habitat on rainy nights Jumping mice were most active in mixed forest on clear and rainy nights but shifted to coniferous forest on cloudy dry nights Red-backed voles were most active in the coniferous habitat regardless of weather Microhabitat references within habitats reflected the same preferences as habitat selection Microhabitat selection by jumping mice also changes with weather The mechanism most likely responsible for the observed habitat selection changes is changing insect abundance associated with cloud cover and rainfall     

The influence of heat increment of feeding on basal metabolic rate in Phyllotis darwini (Muridae)

One of the most important prerequisites for obtaining a reliable measure of basal metabolic rate (BMR) in endotherms is that the animal must be in a post-absorptive condition. However, because of the diversity of nutrition and digestion modes in vertebrates, it is not simple to generalize a standard procedure for BMR measurement. Thus, information in this regard must be experimentally obtained by measuring the heat increment of feeding (HIF). We used a repeated-measures design to test for the effects of HIF on BMR in Phyllotis darwini, a granivorous rodent. Our results suggest that, in this species, feeding induces an elevation in O(2) consumption that can persist up to 4 h after the last meal. In addition, and irrespective of the fasting period, measures made with less than 2 h of fasting yield BMR values that are significantly higher than measurements after longer fasting periods (i.e. 3 and 4 h).     

Concurrent resistance and endurance training influence basal metabolic rate in nondieting individuals

Thirty physically active healthy men (20.1 ± 1.6 yr) wererandomly assigned to participate for 10 wk in one of the following training groups: endurance trained (ET; 3 days/wk joggingand/or running), resistance trained (RT; 3 days/wkresistance training), or combined endurance and resistance trained(CT). Before and after training, basal metabolic rate (BMR), percentbody fat (BF), maximal aerobic power, and one-repetition maximum forbench press and parallel squat were determined for each subject.Urinary urea nitrogen was determined pre-, mid-, and posttraining. BMRincreased significantly from pre- to posttraining for RT (7,613 ± 968 to 8,090 ± 951 kJ/day) and CT (7,455 ± 964 to 7,802 ± 981 kJ/day) but not for ET (7,231 ± 554 to 7,029 ± 666 kJ/day).BF for CT (12.2 ± 3.5 to 8.7 ± 1.7%) was significantly reducedcompared with RT (15.4 ± 2.7 to 14.0 ± 2.7%) and ET (11.8 ± 2.9 to 9.5 ± 1.7%). Maximal aerobic power increasedsignificantly for ET (13%) but not RT (0.2%) or CT (7%),whereas the improvements in one-repetition maximum bench press andparallel squat were greater in RT (24 and 23%, respectively) comparedwith CT (19 and 12%, respectively). Urinary urea nitrogen loss wasgreater in ET (14.6 ± 0.9 g/24 h) than in RT (11.7 ± 1.0 g/24h) and CT (11.5 ± 1.0 g/24 h) at the end of 10 wk oftraining. These data indicate that, although RT alone will increase BMRand muscular strength, and ET alone will increase aerobic power anddecrease BF, CT will provide all of these benefits but to a lessermagnitude than RT and ET after 10 wk of training.

     

Perinatal adaptation in mammals: the impact of metabolic rate.

Mammalian birth is accompanied by profound changes in metabolic rate that can be described in terms of body size relationship (Kleiber's rule). Whereas the fetus, probably as an adaptation to the low intrauterine pO2, exhibits an "inappropriately" low, adult-like specific metabolic rate, the term neonate undergoes a rapid metabolic increase up to the level to be expected from body size. A similar, albeit slowed, "switching-on" of metabolic size allometry is found in human preterm neonates whereas animals that are normally born in a very immature state are able to retard or even suppress the postnatal metabolic increase in favor of weight gain and O2 supply. Moreover, small immature mammalian neonates exhibit a temporary oxyconforming behavior which enhances their hypoxia tolerance, yet is lost to the extent by which the size-adjusted metabolic rate is "locked" by increasing mitochondrial density. Beyond the perinatal period, there are no other deviations from metabolic size allometry among mammals except in hibernation where the temporary "switching-off" of Kleiber's rule is accompanied by a deep reduction in tissue pO2. This gives support to the hypothesis that the postnatal metabolic increase represents an "escape from oxygen" similar to the evolutionary roots of mitochondrial respiration, and that the overall increase in specific metabolic rate with decreasing size might contribute to prevent tissues from O2 toxicity.     

On structural theories of basal metabolic rate

Because cells and organisms interface with the environment through surfaces, their design should be governed by surface laws. Yet, basal metabolic rate is not proportional to the 0·67-power of body mass (surface law) but to the 0·75-power of body mass. From the many theories that have derived a surface law, Teissier's dimensional analysis theory was probably the neatest. However, the surface law has been empirically invalidated. Moreover, Teissier assumed that times in the prototype animal and a similar one with different size are in the same ratio as their linear sizes. This is incorrect, however, because heart rates, being inverses of times, should be proportional to the 1/3-power of body mass—but are proportional to the 1/4-power of body mass, which is consistent with a 0·75-power law of basal metabolic rate. McMahon's recent attempt to explain the deviation of the empirical law from a surface law based entirely on structural considerations, is critically examined. It does not appear that purely structural considerations could explain the deviation between the empirical 0·75-law of basal metabolic rate and the surface law.     

A strong response to selection on mass-independent maximal metabolic rate without a correlated response in basal metabolic rate

Metabolic rates are correlated with many aspects of ecology, but how selection on different aspects of metabolic rates affects their mutual evolution is poorly understood. Using laboratory mice, we artificially selected for high maximal mass-independent metabolic rate (MMR) without direct selection on mass-independent basal metabolic rate (BMR). Then we tested for responses to selection in MMR and correlated responses to selection in BMR. In other lines, we antagonistically selected for mice with a combination of high mass-independent MMR and low mass-independent BMR. All selection protocols and data analyses included body mass as a covariate, so effects of selection on the metabolic rates are mass adjusted (that is, independent of effects of body mass). The selection lasted eight generations. Compared with controls, MMR was significantly higher (11.2%) in lines selected for increased MMR, and BMR was slightly, but not significantly, higher (2.5%). Compared with controls, MMR was significantly higher (5.3%) in antagonistically selected lines, and BMR was slightly, but not significantly, lower (4.2%). Analysis of breeding values revealed no positive genetic trend for elevated BMR in high-MMR lines. A weak positive genetic correlation was detected between MMR and BMR. That weak positive genetic correlation supports the aerobic capacity model for the evolution of endothermy in the sense that it fails to falsify a key model assumption. Overall, the results suggest that at least in these mice there is significant capacity for independent evolution of metabolic traits. Whether that is true in the ancestral animals that evolved endothermy remains an important but unanswered question.     

Expenditure freeze: the metabolic response of small mammals to cold environments

There is renewed focus on the ecological determinants of animal metabolism and recent comparative analyses support the physiological expectation that the field metabolic rate (FMR) of homeotherms should increase with declining ambient temperature. However, sustained elevation of FMR during prolonged, seasonal cold could be prevented by intrinsic limits constraining FMR to some multiple of basal metabolic rate (BMR) or extrinsic limits on resource abundance. We analysed previous measures of mammalian FMR and BMR to establish the effect of ambient temperature on both traits and found no support for intrinsic limitation. We also measured the FMR of a northern population of red squirrels (Tamiasciurus hudsonicus) exposed to ambient temperatures much colder than all but one previous study of mammal FMR. These measurements revealed levels of energy expenditure that are, unexpectedly, among the lowest ever recorded in homeotherms and that actually decrease as it gets colder. Collectively, these results suggest the metabolic niche space of cold climate endotherms may be much larger than previously recognized.     

The functional significance of individual variation in basal metabolic rate

Basal metabolic rate (BMR) was established as a common reference point allowing comparable measures across different individuals and species. BMR is often regarded as a minimal rate of metabolism compatible with basic processes necessary to sustain life. One confusing aspect, however, is that BMR is highly variable, both within and between species. A potential explanation for this variability is that while individuals with high BMRs may suffer the disadvantage of having to feed for longer to cover the extra energy demands, this may be offset by advantages that accrue because of the high metabolic rate. One suggested advantage is that high levels of BMR are a consequence of maintaining a morphology that permits high rates of the maximal sustained rate of metabolism (SusMR)--the rate of metabolism that can be sustained for days or weeks. We have been studying the energetics of MF1 laboratory mice during peak lactation to investigate this idea. In this article, we review some of our work in connection with three particular predictions that derive from the hypothesised links among morphology, basal metabolism, and sustained metabolic rate. By comparing groups of individuals, for example, lactating and nonlactating individuals, the patterns that emerge are broadly consistent with the hypothesis that BMR and SusMR are linked by morphology. Lactating mice have bigger organs connected with energy acquisition and utilisation, greater resting metabolic rates in the thermoneutral zone, called RMRt (approximately equivalent to BMR), and high sustainable rates of maximal energy intake. However, when attempts are made to establish these relationships across individuals within lactating mice, the associations that are anticipated are either absent or very weak and depend on shared variation due to body mass. At this level there is very little support for the suggestion that variation in RMRt (and thus BMR) is sustained by associations with SusMR.     

Complications inherent in scaling the basal rate of metabolism in mammals

The scaling of the basal rate of metabolism in mammals is reexamined. Both the power and level of the scaling function are sensitive to various factors that interact with body mass and rate of metabolism, including the precision of temperature regulation, food habits, and activity level. This sensitivity implies that the rate of metabolism is a highly plastic character in the course of evolution. Consequently, the singular effect of mass on the rate of metabolism is most effectively analyzed in ecologically and physiologically uniform sets of species, rather than in taxonomically defined groups, which often are ecologically and physiologically diverse. Otherwise, all fitted curves for mammals integrate a variety of competing factors, thereby reflecting the species used and denying unique analytic significance to the power in scaling relations. Kleiber's eutherian curve may represent a relatively uniform set of data because all the species included were domesticated and because selection for high rates of production (and high rates of metabolism) occurred in the process of domestication. In the analysis of scaling relationships, the standard error of estimate (Sy.x) is a more valuable measure of the residual variation than is (1.0-r2) because r2 is a non-linear measure of the conformation of data to the relation and because Sy.x, unlike r2, is independent of the units used in the scaling relationship. At present the best estimate indicates that total rate of metabolism scales proportionally to approximately m0.60 at small masses (less than 300 g), as long as small species do not enter torpor, and scales proportionally to approximately m0.75 at large masses (greater than or equal to 300 g). Physiological properties other than metabolism are potentially sensitive to secondary factors, so their scaling functions also would be most clearly defined for physiologically uniform groups of species. This view suggests that insight into the significance of scaling relations can be obtained by examining the residual variation around a scaling function as well as by examining conformation to the function.     

The allometry of avian basal metabolic rate: good predictions need good data

Basal metabolic rate (BMR) is often predicted by allometric interpolation, but such predictions are critically dependent on the quality of the data used to derive allometric equations relating BMR to body mass (Mb). An examination of the metabolic rates used to produce conventional and phylogenetically independent allometries for avian BMR in a recent analysis revealed that only 67 of 248 data unambiguously met the criteria for BMR and had sample sizes with n>/=3. The metabolic rates that represented BMR were significantly lower than those that did not meet the criteria for BMR or were measured under unspecified conditions. Moreover, our conventional allometric estimates of BMR (W; logBMR=-1.461+0.669logMb) using a more constrained data set that met the conditions that define BMR and had n>/=3 were 10%-12% lower than those obtained in the earlier analysis. The inclusion of data that do not represent BMR results in the overestimation of predicted BMR and can potentially lead to incorrect conclusions concerning metabolic adaptation. Our analyses using a data set that included only BMR with n>/=3 were consistent with the conclusion that BMR does not differ between passerine and nonpasserine birds after taking phylogeny into account. With an increased focus on data mining and synthetic analyses, our study suggests that a thorough knowledge of how data sets are generated and the underlying constraints on their interpretation is a necessary prerequisite for such exercises.