Protein synthesis and antioxidant capacity in aging mice: effects of long-term voluntary exercise.

Exercise increases metabolic rate and the production of reactive oxygen species (ROS) but also elevates protein turnover. ROS cause damage to macromolecules (e.g., proteins) and thereby contribute to aging. Protein turnover removes and replaces damaged proteins. The balance between these two responses may underlie beneficial effects of physical activity on aging. Effects of lifelong exercise on antioxidant enzyme activities and fractional synthesis rate of protein (FSRP) were examined at various ages (2-26 mo) in heart, liver, and muscle of mice that had been selectively bred for high wheel-running activity, housed with (S+) or without (S-) a running wheel, and their random-bred controls (C+) housed with running wheels. FSRP decreased with age and increased in muscle of young, but not old, activity-selected mice. Enzyme activity of superoxide dismutase and glutathione peroxidase decreased with age and showed a peak at 10 mo of age in liver. Selection for wheel-running activity did not affect antioxidant enzyme activity. Daily energy expenditure correlated positively with antioxidant levels in liver. This might indicate that oxidative stress (ROS production) increases with metabolic rate, driving upregulation of antioxidant enzymes. Alternatively, the elevated energy expenditure may reflect the energetic cost of elevated protection, consistent with the disposable-soma hypothesis and with other studies showing positive links between energy expenditure and life span. Long-term elevations in voluntary exercise did not result in elevations in antioxidant enzyme activities or protein synthesis rates.

Does growth rate determine the rate of metabolism in shorebird chicks living in the Arctic?

We measured resting and peak metabolic rates (RMR and PMR, respectively) during development of chicks of seven species of shorebirds: least sandpiper (Calidris minutilla; adult mass 20-22 g), dunlin (Calidris alpina; 56-62 g), lesser yellowlegs (Tringa flavipes; 88-92 g), short-billed dowitcher (Limnodromus griseus; 85-112 g), lesser golden plover (Pluvialis dominicana; 150-156 g), Hudsonian godwit (Limosa haemastica; 205-274 g), and whimbrel (Numenius phaeopus; 380 g). We tested two opposing hypotheses: the growth rate-maturity hypothesis, which posits that growth rate in chicks is inversely related to functional maturity of tissues, and the fast growth rate-high metabolism hypothesis, which suggests that rapid growth is possible only with a concomitant increase in either RMR or PMR. We have found no evidence that chicks of shorebirds with fast growth rates have lower RMRs or lower PMRs, as would be predicted by the growth rate-maturity hypothesis, but our data suggested that faster-growing chest muscles resulted in increased thermogenic capacity, consistent with the fast growth-high metabolism hypothesis. The development of homeothermy in smaller species is a consequence primarily of greater metabolic intensities of heat-generating tissues. The maximum temperature gradient between a chick's body and environment that can be maintained in the absence of a net radiative load increased rapidly with body mass during development and was highest in least sandpipers and lowest among godwits. Chicks of smaller species could maintain a greater temperature gradient at a particular body mass because of their higher mass-specific maximum metabolic rates.

Energetics of growth in semi-precocial shorebird chicks in a warm environment: the African black oystercatcher, Haematopus moquini.

We studied prefledging growth, energy expenditure and time budgets of African Black Oystercatcher, Haematopus moquini, chicks on Robben Island, Western Cape, South Africa. The aim of the study was to investigate the effect of parental feeding on the growth and energetics of semi-precocial shorebird chicks. Chicks reached mean fledging mass, 463 g, in 40 days. The growth rate coefficient of African Black Oystercatcher chicks was 2% below the predicted value for a shorebird species of their body mass, but it was smaller than that of other precocial and semi-precocial shorebirds to date. Resting metabolic rate (RMR, measured through respirometry), daily metabolisable energy (DME), defined as daily energy expenditure (DEE, measured with doubly labelled water) plus energy deposited into tissue (E(tis)), and total metabolisable energy (TME) of African Black Oystercatcher chicks were similar to those expected for a species of their body size. DEE was not influenced by weather (ambient temperature, operative temperature and wind speed), therefore, variations in DEE may be explained by body mass alone. The relative RMR of the African Black Oystercatcher was greater, their TME was approximately the same, their average daily metabolisable energy (ADME) was less, and they spent less time foraging (short periods of parental feeding) and more time inactive than three precocial species in the Western Cape. Therefore, the semi-precocial mode of development of African Black Oystercatcher chicks reduced energy costs from thermoregulation and activity, and they were able to grow relatively faster than precocial, self-feeding shorebird species in similar climatic conditions. The growth rate coefficient of African Black Oystercatcher chicks was smaller than that of Eurasian Oystercatcher, Haematopus ostralegus, chicks, which may be a consequence of differences in body size and latitudinal effects.

Water and heat balance during flight in the rose-colored starling (Sturnus roseus).

Water imbalance during flight is considered to be a potentially limiting factor for flight ranges in migrating birds, but empirical data are scarce. We studied flights under controlled ambient conditions with rose-colored starlings in a wind tunnel. In one experiment, we measured water fluxes with stable isotopes at a range of flight speeds (9-14 m s(-1)) at constant temperature (15 degrees C). In a second experiment, we measured evaporation rates at variable ambient temperatures (Ta = 5 deg -27 deg C) but constant speed (12 m s(-1)). During all flights, the birds experienced a net water loss. On average, water influx was 0.98 g h(-1) (SD = 0.16; n = 8), and water efflux was 1.29 g h(-1) (SD = 0.14; n = 8), irrespective of flight speed. Evaporation was related to temperature in a biphasic pattern. At temperatures below 18.2 degrees C, net evaporation was constant at 0.36 g h(-1) (SD = 0.18; n = 10), rising at higher temperatures with a slope of 0.11 per degree to about 1.5 g h(-1) at 27 degrees C. We calculated the relative proportion of dry and evaporative heat loss during flight. Evaporative heat loss at Ta < 18.2 deg C was 14% of total heat production during flight, and dry heat loss accounted for 84%. At higher temperatures, evaporative heat loss increased linearly with T(a) to about 25% at 27 degrees C. Our data suggest that for prolonged flights, rose-colored starlings should adopt behavioral water-saving strategies and that they cannot complete their annual migration without stopovers to replenish their water reserves.

Assessment of the amount of body water in the Red Knot (Calidris canutus): an evaluation of the principle of isotope dilution with 2H, (17)O, and (18)O as measured with laser spectrometry and isotope ratio mass spectrometry.

We have used the isotope dilution technique to study changes in the body composition of a migratory shorebird species (Red Knot, Calidris canutus) through an assessment of the amount of body water in it. Birds were quantitatively injected with a dose of water with elevated concentrations of 2H, (17)O, and (18)O. Thereafter, blood samples were taken and distilled. The resulting water samples were analysed using an isotope ratio mass spectrometry (for 2H and (18)O only) and a stable isotope ratio infrared laser spectrometry (2H, (17)O, and (18)O) to yield estimates of the amount of body water in the birds, which in turn could be correlated to the amount of body fat. Here, we validate laser spectrometry against mass spectrometry and show that all three isotopes may be used for body water determinations. This opens the way to the extension of the doubly labelled water method, used for the determination of energy expenditure, to a triply labelled water method, incorporating an evaporative water loss correction on a subject-by-subject basis or, alternatively, the reduction of the analytical errors by statistically combining the (17)O and (18)O measurements.

Nutritional bias as a new mode of adjusting sex allocation.

Sex biases in the allocation of resources to offspring occur in a broad range of taxa. Parents have been shown to achieve such biases either by producing numerically more of one sex or by providing the individuals of one sex with a greater quantity of resources. In addition, skews in allocation could occur if the offspring of one sex receive resources of higher quality (greater nutritional or energetic value by weight or volume), although this mode of adjustment has, to our knowledge, never been demonstrated. We compared the types of prey and the metabolizable energy provisioned to male and female nestlings in one of the most sexually size dimorphic of all birds, the brown songlark, Cinclorhamphus cruralis. Within broods, we found that males not only received more prey than their smaller sisters, but also prey of apparently higher quality. This dietary disparity could result either from mothers actively discriminating between the sexes when providing prey or from competition among siblings. We suggest that sex differences in offspring diet quality may occur in a wide range of other taxa and function as an additional mechanism of sex allocation adjustment.

Exercising for life? Energy metabolism, body composition, and longevity in mice exercising at different intensities.

Studies that have found a positive influence of moderate, nonexhaustive exercise on life expectancy contradict the rate-of-living theory, which predicts that high energy expenditure in exercising animals should shorten life. We investigated effects of exercise on energy metabolism and life span in male mice from lines that had been selectively bred for high voluntary wheel-running activity and from the nonselected control lines. Mice were divided into the following three groups (n = 100 per group): active high-runner mice (housed with wheels; HR+), sedentary high-runner mice (no wheels provided; HR-), and active control mice (C+). Sixty animals from each group were left undisturbed throughout their lives to create survival curves. In the remaining 40 animals in each group, energy metabolism and body composition was measured at 2, 10, 18, or 26 mo of age. Wheel-running activity was increased by approximately 50% throughout life in HR+ mice compared with C+ mice, and mass-specific daily energy expenditure was increased by approximately 30% in HR+ mice compared with both C+ mice and HR- mice. Median life span was similar in HR+ mice and HR- mice (740 and 733 d, respectively), and it was significantly shorter in these mice than it was in C+ mice (828 d). Thus, increasing the amount of voluntary aerobic exercise (as a result of selective breeding or housing with wheels) did not result in extended life span in mice, and we found no evidence for a direct link between energy expenditure and life span.

Comparison of methods to assess body fat in non-obese six to seven-year-old children.

BACKGROUND & AIM: Different non-invasive methods exist to evaluate total body fat in children. Most methods have shown to be able to confirm a high fat percentage in children with overweight and obesity. No data are available on the estimation of total body fat in non-obese children. The aim of this study is to compare total body fat, assessed by different methods in non-obese children. METHODS: We compared total body fat, assessed by isotope dilution, dual energy X-ray, skinfold thickness, bioelectrical impedance analysis, combination of these methods as well as BMI in 30 six to seven-year-old children. RESULTS: The children had a mean BMI of 16.01kg/m(2) (range 13.51-20.32) and five children were overweight according to international criteria. Different methods showed rather different absolute values for total body fat. Bland-Altman analysis showed that the difference between the DEXA method and isotope dilution was dependent on the fat percentage. Children with the same BMI show a marked variation in total body fat ranging from 8% to 22% as estimated from the isotope dilution method. CONCLUSION: Non-invasive methods are presently not suited to assess the absolute amount of total body fat in 6-7 years old children.

Metabolism and aging: effects of cold exposure on metabolic rate, body composition, and longevity in mice.

The proposition that increased energy expenditure shortens life has a long history. The rate-of-living theory (Pearl 1928 ) states that life span and average mass-specific metabolic rate are inversely proportional. Originally based on interspecific allometric comparisons between species of mammals, the theory was later rejected on the basis of comparisons between taxa (e.g., birds have higher metabolic rates than mammals of the same size and yet live longer). It has rarely been experimentally tested within species. Here, we investigated the effects of increased energy expenditure, induced by cold exposure, on longevity in mice. Longevity was measured in groups of 60 male mice maintained at either 22 degrees C (WW) or 10 degrees C (CC) throughout adult life. Forty additional mice were maintained at both of these temperatures to determine metabolic rate (by stable isotope turnover, gas exchange, and food intake) as well as the mass of body and organs of subsets of animals at four different ages. Because energy expenditure might affect longevity by either accumulating damage or by instantaneously affecting mortality rate, we included a third group of mice exposed to 10 degrees C early in life and to 22 degrees C afterward (CW). Exposure to cold increased mean daily energy expenditure by ca. 48% (from 47.8 kJ d(-1) in WW to 70.6 kJ d(-1) in CC mice, with CW intermediate at 59.9 kJ d(-1)). However, we observed no significant differences in median life span among the groups (WW, 832 d; CC, 834 d; CW, 751 d). CC mice had reduced body mass (lifetime mean 30.7 g) compared with WW mice (33.8 g), and hence their lifetime energy potential (LEP) per gram whole-body mass had an even larger excess than per individual. Greenberg ( 1999 ) has pointed out that the size of the energetically costly organs, rather than that of the whole body, may be relevant for the rate-of-living idea. We therefore expressed LEP also in terms of energy expenditure per gram dry lean mass or per gram "metabolic" organ mass (i.e., heart, liver, kidneys, and brain). No matter how it was expressed, LEP in CC mice significantly exceeded that of WW mice. This result demonstrates that increased energy expenditure does not shorten life span and adds evidence to the intraspecific refutation of the rate-of-living theory. We suggest that increased energy expenditure has both positive and negative effects on different factors determining life span and that the relationship between energy turnover and longevity is fundamentally nonmonotonic.

Evaluation of the deuterium dilution method to estimate body composition in the barnacle goose: accuracy and minimum equilibration time.

We examined body composition in barnacle geese (Branta leucopsis) by proximate carcass analysis and by deuterium isotope dilution. We studied the effect of isotope equilibration time on the accuracy of total body water (TBW) estimates and evaluated models to predict fat-free mass (FFM) and fat mass (FM) from different measurements varying in their level of invasiveness. Deuterium enrichment determined at 45, 90, and 180 min after isotope injection did not differ significantly. At all sampling intervals, isotope dilution spaces (TBW(d)) consistently overestimated body water determined by carcass analysis (TBW(c)). However, variance in the deviation from actual TBW was higher at the 45-min sampling interval, whereas variability was the same at 90 and 180 min, indicating that 90 min is sufficient time to allow for adequate equilibration. At 90 min equilibration time, deuterium isotope dilution overestimated TBW(c) by 7.1% +/= 2.6% (P < 0.001, paired t-test, n=20). This overestimate was consistent over the range of TBW studied, and TBW(c) could thus be predicted from TBW(d) (r2=0.976, P<0.001). Variation in TBW(c) and TBW(d) explained, respectively, 99% and 98% of the variation in FFM. FM could be predicted with a relative error of ca. 10% from TBW estimates in combination with body mass (BM). In contrast, BM and external body measurements allowed only poor prediction. Abdominal fat fresh mass was highly correlated to total FM and, if the carcass is available, allows simple means of fat prediction without dissecting the entire specimen.

Energy expenditure during flight in relation to body mass: effects of natural increases in mass and artificial load in Rose Coloured Starlings.

Rose Coloured Starlings (Sturnus roseus) flew repeatedly for several hours in a wind tunnel while undergoing spontaneous variation in body mass. The treatments were as follows: flying unrestrained (U), with a control harness of 1.2% of their body mass (C), or with a harness of 7.4% of their body mass, which was either applied immediately before the flight (LS) or at least 9 days in advance (LL). Energy expenditure during flight (ef in W) was measured with the Doubly Labelled Water method. Flight costs in L(S) and LL were not significantly different and therefore were pooled (L). The harness itself did not affect ef, i.e. U and C flights were not different. ef was allometrically related with body mass m (in g). The slopes were not significantly different between the treatments, but ef was increased by 5.4% in L compared to C flights (log10(ef) = 0.050 + 0.47 x log10(m) for C, and log10(ef) = 0.073 + 0.47 x log10(m) for L). The difference in ef between C, LS and LL was best explained by taking the transported mass m transp (in g) instead of m into account (log10(ef) = -0.08 + 0.54 x log10(m transp)). Flight costs increased to a lesser extent than expected from interspecific allometric comparison or aerodynamic theory, regardless of whether the increase in mass occurred naturally or artificially. We did not observe an effect of treatment on breast muscle size and wingbeat frequency. We propose that the relatively low costs at a high mass are rather a consequence of immediate adjustments in physiology and/or flight behaviour than of long-term adaptations.

Female mice respond differently to costly foraging versus food restriction.

Experimental manipulation of foraging costs per food reward can be used to study the plasticity of physiological systems involved in energy metabolism. This approach is useful for understanding adaptations to natural variation in food availability. Earlier studies have shown that animals foraging on a fixed reward schedule decrease energy intake and expenditure. However, the extent to which these changes depend on decreased food intake or increased foraging costs per se has never been tested. We manipulated foraging costs per food reward in female Hsd:ICR(CD-1) laboratory mice, comparing animals faced with low (L) and high (H) foraging costs to non-foraging animals receiving a food restriction (R) matched to the intake of H animals. Mice in the H group ran as much as L mice did but ate significantly less. They concurrently reduced daily energy expenditure and resting metabolic rate, decreased the size of major metabolic organs and utilized body fat stores; mass-specific resting metabolic rate did not differ between groups. We found evidence that these alterations in energy balance may carry fitness costs. As a secondary response to our experimental treatment, H females and, eventually, some R females ceased to show signs of estrous cyclicity. Surprisingly, results of an immune challenge with keyhole limpet hemocyanin showed that primary immune response did not differ between L and H groups, and was actually higher in R mice. Our results demonstrate that high foraging costs per se--the combination of high activity and low food intake--have pronounced physiological effects in female mice.

Wheel-running activity and energy metabolism in relation to ambient temperature in mice selected for high wheel-running activity.

Interrelationships between ambient temperature, activity, and energy metabolism were explored in mice that had been selectively bred for high spontaneous wheel-running activity and their random-bred controls. Animals were exposed to three different ambient temperatures (10, 20 and 30 degrees C) and wheel-running activity and metabolic rate were measured simultaneously. Wheel-running activity was decreased at low ambient temperatures in all animals and was increased in selected animals compared to controls at 20 and 30 degrees C. Resting metabolic rate (RMR) and daily energy expenditure (DEE) decreased with increasing ambient temperature. RMR did not differ between control and selected mice, but mass-specific DEE was increased in selected mice. The cost of activity (measured as the slope of the relationship between metabolic rate and running speed) was similar at all ambient temperatures and in control and selected mice. Heat generated by running apparently did not substitute for heat necessary for thermoregulation. The overall estimate of running costs was 1.2 kJ/km for control mice and selected mice.

Behavioural and physiological responses to increased foraging effort in male mice.

Free-living animals must forage for food and hence may face energetic constraints imposed by their natural environmental conditions (e.g. ambient temperature, food availability). Simulating the variation in such constraints, we have experimentally manipulated the rate of work (wheel running) mice must do to obtain their food, and studied the ensuing behavioural and physiological responses. This was done with a line of mice selectively bred for high spontaneous wheel running and a randomly bred control line that vary in the amount of baseline wheel-running activity. We first determined the maximum workload for each individual. The maximum workload animals could engage in was around 23 km d(-1) in both control and activity-selected mice, and was not associated with baseline wheel-running activity. We then kept mice at 90% of their individual maximum and measured several physiological and behavioural traits. At this high workload, mice increased wheel-running activity from an average of 10 to 20 km d(-1), and decreased food intake and body mass by approximately 20%. Mass-specific resting metabolic rate strongly decreased from 1.43 to 0.98 kJ g(-1) d(-1), whereas daily energy expenditure slightly increased from 2.09 to 2.25 kJ g(-1) d(-1). Costs of running decreased from 2.3 to 1.6 kJ km(-1) between baseline and workload conditions. At high workloads, animals were in a negative energy balance, resulting in a sharp reduction in fat mass as well as a slight decrease in dry lean mass. In addition, corticosterone levels increased, and body temperature was extremely low in some animals at high workloads. When challenged to work for food, mice thus show significant physiological and behavioural adjustments.

Energy expenditure and wing beat frequency in relation to body mass in free flying Barn Swallows (Hirundo rustica).

Many bird species steeply increase their body mass prior to migration. These fuel stores are necessary for long flights and to overcome ecological barriers. The elevated body mass is generally thought to cause higher flight costs. The relationship between mass and costs has been investigated mostly by interspecific comparison and by aerodynamic modelling. Here, we directly measured the energy expenditure of Barn Swallows (Hirundo rustica) flying unrestrained and repeatedly for several hours in a wind tunnel with natural variations in body mass. Energy expenditure during flight (e (f), in W) was found to increase with body mass (m, in g) following the equation e (f) = 0.38 x m (0.58). The scaling exponent (0.58) is smaller than assumed in aerodynamic calculations and than observed in most interspecific allometric comparisons. Wing beat frequency (WBF, in Hz) also scales with body mass (WBF = 2.4 x m (0.38)), but at a smaller exponent. Hence there is no linear relationship between e (f) and WBF. We propose that spontaneous changes in body mass during endurance flights are accompanied by physiological changes (such as enhanced oxygen and nutrient supply of the muscles) that are not taken into consideration in standard aerodynamic calculations, and also do not appear in interspecific comparison.

Estimating expenditure on male and female offspring in a sexually size-dimorphic bird: a comparison of different methods.

The parents of sexually size-dimorphic offspring are often assumed to invest more resources producing individuals of the larger sex. A range of different methods have been employed to estimate relative expenditure on the sexes, including quantifying sex-specific offspring growth, food intake, energy expenditure and energy intake, in addition to measures of parental food provisioning and energy expenditure. These methods all have the potential to provide useful estimates of relative investment, but each has particular problems of interpretation, and few studies have compared the estimates derived concurrently from more than two of these measures. In this study we compared these surrogate measures of parental investment in the brown songlark Cinclorhamphus cruralis, which exhibits one of the most extreme cases of sexual size dimorphism among birds. At 10 days of age we found that male chicks, on average, were 49% heavier, received 42% more prey items, expended 44% more energy and ingested 50% more metabolizable energy than their sisters. Furthermore, we created, experimentally, both all-male and all-female broods of 10-day-old chicks and found that mothers delivered 43% more prey items and expended 27% more energy when provisioning all-male broods, providing the first direct evidence for a change in parental energy expenditure in relation to brood sex ratio. These data reveal remarkable agreement between these estimates of investment and suggest that all may provide quantitatively useful information on sex allocation. However, the lower variance associated with estimates of relative mass and energy intake suggest that these methods may be of greater utility, although this may primarily reflect the shorter period over which our provisioning data were collected.

Metabolic costs of avian flight in relation to flight velocity: a study in Rose Coloured Starlings (Sturnus roseus, Linnaeus).

The metabolic costs of flight at a natural range of speeds were investigated in Rose Coloured Starlings (Sturnus roseus, Linnaeus) using doubly labelled water. Eight birds flew repeatedly and unrestrained for bouts of 6 h at speeds from 9 to 14 m s(-1) in a low-turbulence wind tunnel, corresponding to travel distances between 200 and 300 km, respectively. This represents the widest speed range where we could obtain voluntarily sustained flights. From a subset of these flights, data on the wing beat frequency (WBF) and intermittent flight behaviour were obtained. Over the range of speeds that were tested, flight costs did not change with velocity and were on an average 8.17+/-0.64 W or 114 W kg(-1). Body mass was the only parameter with a significant (positive) effect on flight costs, which can be described as EE(f)=0.741 M(0.554). WBF changed slightly with speed, but correlated better with body mass. Birds showed both types of intermittent flight, undulating and bounding, but their frequencies did not systematically change with flight speed.

Field metabolic rates of phytophagous bats: do pollination strategies of plants make life of nectar-feeders spin faster?

Recently, it was argued that extrinsic factors, such as high foraging costs, lead to elevated field metabolic rates (FMR). We tested this suggestion by comparing the FMR of nectar-feeding and fruit-eating bats. We hypothesized that the foraging effort per energy reward is higher for nectar-feeding mammals than for fruit-eating mammals, since energy rewards at flowering plants are smaller than those at fruiting plants. Using the doubly labelled water method, we measured the FMR of nectar-feeding Glossophaga commissarisi and fruit-eating Carollia brevicauda, which coexisted in the same rainforest habitat and shared the same daytime roosts. Mass-specific FMR of G. commissarisi exceeded that of C. brevicauda by a factor of almost two: 5.3+/-0.6 kJ g(-1) day(-1) for G. commissarisi and 2.8+/-0.4 kJ g(-1) day(-1) for C. brevicauda. Since nectar-feeding bats imbibe nectar droplets of only 193 J energy content during each flower visit, a G. commissarisi bat has to perform several 100 flower visits per night to meet its energy requirement. The fruit-eating C. brevicauda, on the other hand, needs to harvest only 3-12 Piper infructescenses per night, as the energy reward per Piper equals ca. 6-30 kJ. We argue that the flowering and fruiting plants exert different selective forces on the foraging behaviour and energetics of pollinators and the seed dispersers, respectively. A comparison between nectar-feeding and non-nectar-feeding species in various vertebrate taxa demonstrates that pollinators have elevated FMRs.

Respiratory water loss during rest and flight in European Starlings (Sturnus vulgaris).

Respiratory water loss in Starlings (Sturnus vulgaris) at rest and during flight at ambient temperatures (T(amb)) between 6 and 25 degrees C was calculated from respiratory airflow and exhaled air temperature. At rest, breathing frequency f (1.4+/-0.3 Hz) and tidal volume Vt (1.9+/-0.4 ml) were independent of T(amb), but negatively correlated with each other. Mean ventilation at rest was 156+/-28 ml min(-1) at all T(amb). Exhaled air temperature (T(exh)) at rest increased with T(amb) (T(exh) = 0.92.T(amb)+12.45). Respiratory water loss at rest averaged 0.18+/-0.09 ml h(-1) irrespective of T(amb). In flying Starlings f was 4.0+/-0.4 Hz and independent of T(amb). Vt during flight averaged 3.6+/-0.4 ml and increased with T(amb) (Vt = 0.06.T(amb)+2.83) as, correspondingly, did ventilation. T(exh) during flight increased with T(amb) (T(exh) = 0.85.T(amb)+17.29). Respiratory water loss during flight (average REWL(f) = 0.74+/-0.22 ml h(-1)) was significantly higher than at rest and increased with T(amb). Our measurements suggest that respiratory evaporation accounts for most water loss in flying Starlings and increases more than cutaneous evaporation with rising ambient temperature.

Socio-economic and environmental factors influence energy utilization in Brazilian breast-fed infants.

Energy intake recommendations for infants are based on data from industrialized countries. FAO/WHO/UNU expressed the need for studies on total energy expenditure (TEE) and basal metabolic rate from developing countries covering current and changing lifestyles. For this observational study, 65 infants of differing socioeconomic status (SES) (n = 32 middle SES, n = 33 low SES) were selected in Pelotas, southern Brazil, aiming to: 1) compare TEE, minimum observable energy expenditure (MOEE), activity energy expenditure (AEE) between breast-fed infants 8.7 mo of age from middle and low SES; and 2) investigate the effect of potential mediating factors on TEE and AEE. TEE and total body water were measured with doubly labeled water, MOEE with respiration calorimetry, breast milk intake using the dose-to-the-mother deuterium-oxide turnover method, food intake using 1-d food weighing, and prevalence of overweight using BMI Z-scores. TEE adjusted for ethnicity was 257 (95% CI 232-281) kJ/(kg . d) in middle SES infants vs. 318 (95%CI 294-342) kJ/(kg . d) in low SES infants (P = 0.001). MOEE did not differ between groups and the difference in TEE was therefore attributed to AEE (P = 0.008). The effect of SES on AEE was mediated by the number of persons per bedroom (crowding). Prevalence of overweight tended to be higher in middle SES infants (P = 0.054) than in low SES infants. The difference in TEE and AEE between SES groups emphasizes the importance of an accurate description of the SES of any population in which TEE is studied and questions the extent to which TEE data from middle-class infants in transitional countries should be considered normative.