Basal Metabolic Rate In Mammals Research Articles

Metabolic rates of three gazelle species (Nanger soemmerringii, Gazella gazella, Gazella spekei) adapted to arid habitats

The basal metabolic rate of mammals correlates with body mass, but deviations from this regression have been observed and explanations comprise ecological adaptations, reproductive strategies or phylogeny. Certain mammalian groups, adapted to arid environments, show comparatively lower metabolic rates. To expand existing datasets and to investigate metabolic rates in ruminants adapted to arid environments, we conducted respiration measurements with three gazelle species (Gazella spekei, G. gazella and N. soemmerringii, total n=16). After an adaptation period to a diet of fresh lucerne offered ad libitum, subjects were put separately into respiration boxes for 24h where they had free access to food and water. Oxygen consumption and carbon dioxide production were measured with a modular system of gas analyzers and pumps. Mean and resting metabolic rate (RMR) were calculated by accounting for the entire measurement phase or the lowest 20 oxygen measurements, respectively. N. soemmerringii had the lowest relative RMR values and the highest respiratory coefficients compared to the other species. Measured values were compared to expected RMR values calculated based on body mass. Gazella spekei and G. gazella showed higher RMR values than expected, while the RMR of N. soemmerringii was in the range of expected values. Our results indicate that not all mammals adapted to aridity have lower metabolic rates under conditions of unlimited resources and that in these cases other physiological adaptations might be of higher importance. Further extensions of the datasets could allow explaining which deviations of metabolic rate from the body mass regressions result from convergent adaptations.

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 (alpha) of a mammal is proportional to the inverse of its mass-corrected basal metabolic rate: alpha proportional (B / M)-1 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.

N−3 polyunsaturated fatty acids impair lifespan but have no role for metabolism

Although generally considered as beneficial components of dietary fats, polyunsaturated fatty acids (PUFA) have been suspected to compromise maximum lifespan (MLSP) in mammals. Specifically, high amounts of phospholipid PUFAs are thought to impair lifespan due to an increase in the susceptibility of membranes to lipid peroxidation and its damaging effect on cellular molecules. Also, there is evidence from in vitro studies suggesting that highly unsaturated PUFAs elevate basal metabolic rate (BMR). Previous comparative studies in this context were based on small sample sizes, however, and, except for one study, failed to address possible confounding influences of body weight and taxonomic relations between species. Therefore, we determined phospholipid membrane composition in skeletal muscle from 42 mammalian species to test for a relation with published data on MLSP, and with literature data on BMR (30 species). Using statistical models that adjust for the effects of body weight and phylogeny, we found that among mammals, MLSP indeed decreases as the ratio of n-3 to n-6 PUFAs increases. In contrast to previous studies, we found, however, no relation between MLSP and either membrane unsaturation (i.e. PUFA content or number of double bonds) or to the very long-chain, highly unsaturated docosahexaenoic acid (DHA). Similarly, our data set gave no evidence for any notable relation between muscle phospholipid fatty acid composition and BMR, or MLSP and BMR in mammals. These results contradict the 'membrane pacemaker theory of aging', that is, the concept of a direct link between high amounts of membrane PUFAs, elevated BMR, and thus, impaired longevity.

Nucleotypic Effect in Homeotherms: Body-Mass-Corrected Basal Metabolic Rate of Mammals is Related to Genome Size

Nucleotypic Effect in Homeotherms: Body-Mass-Corrected Basal Metabolic Rate of Mammals is Related to Genome Size

78 THE WHOLE BODY TURNOVER RATES OF rRNA AND tRNA ARE CORRELATED WITH THE BASAL METABOLIC RATE IN MAMMALS OF DIFFERENT SIZE

We have developed a noninvasive method to determine whole body turnover rates of tRNA, rRNA and mRNA in mammals by measuring specific, quantitatively excreted modified RNA catafaolites (nucleosides, nucleobases) in urine by HPLC. An investigation of the turnover rates of rRNA and tRNA in pigs, human adults, preterm infants, sheep, goats, rats, hamsters, mice ranging in mean body weight from 126 kg (pigs) to 0.028 kg (mice) reveals that the rRNA and tRNA turnover rates per unit body weight correlate with the basal metabolic rates (BMR) per unit body weight (calculated by the formula: BMR (kJ × d−1) = 240 × kg body weight0.74). The correlation coefficient between the BMR of the 7 species and the rRNA turnover rates is 0.995; that between the BMR of 6 species (mice excluded) and the tRNA turnover rates is 0.998. We believe that our method for determining the whole body turnover rates of different RNA classes will be useful to assess the metabolic state in mammals. This method could turn out to be useful for early diagnosis and thus for the prevention of metabolic stress (e.g. caused by food deficiency and/or infections) as well as for monitoring therapeutic success.

Basal Metabolic Rates in Mammals: Allometry, Phylogeny and Ecology

Basal metabolic rate in mammals increases allometrically with body weight, irrespective of the taxonomic level chosen for analysis. Species' deviations from the allometric curve (relative basal metabolic rates) are associated with differences in diet, habitat and taxonomic affinity. When correlations with taxonomy are controlled for, the only consistently significant association that remains is the higher relative basal metabolic rates of vertebrate eaters. Key-words: Basal metabolic rates, diet and habitat, mammals, comparative studies

Relation of Thyroxine Secretion Rate to Age and Growth Rate in the Cockerel

IT IS well established that thyroid hormone increases basal metabolic rate in mammals and birds (Belasco and Murlin, 1941; McCartney and Shaffner, 1950). Basal metabolic rate is high in the young chicken and decreases with advancing age (Barott and Pringle, 1946). It has been reported that thyroxine secretion rate is higher in the young mice and chickens than in the adult ones (Hurst and Turner, 1948; Grad and Hoffman, 1955; Schultze and Turner, 1945). The present work was undertaken to elucidate the relationship of thyroxine secretion rate to age and to growth rate in the chicken. MATERIALS AND METHODSCockerels of White Leghorn (W.L.) and the crossbred between White Cornish males and White Leghorn females (W.C.×W.L.), bred at the National Institute of Animal Industry, were used. The birds hatched in early April were reared in electric brooders at 30°C. until 3 weeks of age and 25°C. until 9 weeks of…

Total cytochrome oxidase activity and its relation to basal and maximal metabolism.

THE study of the values of the basal metabolic rate in mammals and its relation to body-weight has been the object of many papers and reviews since the middle of the nineteenth century. On the other hand, very few data are available concerning the upper limit of animal metabolism; only individual values are found in the literature concerning the maximal metabolism of some mammals and man. The incompleteness of the available data and their suitability for comparative purposes are connected with the difficulty in obtaining the state of maximal performance in animals. In addition, in many of the animals used, maximal oxygen consumption can be obtained only under simultaneous application of work and lowered temperatures, so that the working and thermoregulatory capacity of the animals are used as well. In these conditions, however, a rapid decrease of metabolism occurs as a result of cooling the animals, as I have already shown1; it is very difficult, therefore, to find out the period of greatest oxygen consumption. Nearly all the data in the literature seem to be affected by this error, and the results obtained are, therefore, probably lower than true maximal values.