Acutely decreased thermoregulatory energy expenditure or decreased activity energy expenditure both acutely reduce food intake in mice

Despite the suggestion that reduced energy expenditure may be a key contributor to the obesity pandemic, few studies have tested whether acutely reduced energy expenditure is associated with a compensatory reduction in food intake. The homeostatic mechanisms that control food intake and energy expenditure remain controversial and are thought to act over days to weeks. We evaluated food intake in mice using two models of acutely decreased energy expenditure: 1) increasing ambient temperature to thermoneutrality in mice acclimated to standard laboratory temperature or 2) exercise cessation in mice accustomed to wheel running. Increasing ambient temperature (from 21°C to 28°C) rapidly decreased energy expenditure, demonstrating that thermoregulatory energy expenditure contributes to both light cycle (40±1%) and dark cycle energy expenditure (15±3%) at normal ambient temperature (21°C). Reducing thermoregulatory energy expenditure acutely decreased food intake primarily during the light cycle (65±7%), thus conflicting with the delayed compensation model, but did not alter spontaneous activity. Acute exercise cessation decreased energy expenditure only during the dark cycle (14±2% at 21°C; 21±4% at 28°C), while food intake was reduced during the dark cycle (0.9±0.1 g) in mice housed at 28°C, but during the light cycle (0.3±0.1 g) in mice housed at 21°C. Cumulatively, there was a strong correlation between the change in daily energy expenditure and the change in daily food intake (R² = 0.51, p<0.01). We conclude that acutely decreased energy expenditure decreases food intake suggesting that energy intake is regulated by metabolic signals that respond rapidly and accurately to reduced energy expenditure.     

Increased resting energy expenditure after 40 minutes of aerobic but not resistance exercise

Objective: Resting energy expenditure (REE) is increased 24 hours after high‐intensity aerobic exercise lasting 60 minutes, whereas results have been inconsistent after resistance training and aerobic exercise of shorter duration. The objective of the study was to compare the effects of 40 minutes of high‐intensity aerobic vs. resistance exercise on REE 19 to 67 hours after exercise. Research Methods and Procedures: REE was compared 19, 43, and 67 hours after 40 minutes of aerobic training (AT; 80% maximum heart rate) or resistance training (RT; 10 repetitions at 80% maximum strength, two sets and eight exercises). Twenty‐three black and 22 white women were randomly assigned to AT, RT, or no training (controls). Exercisers trained 25 weeks. REE was measured after a 12‐hour fast. Results: There was a significant time × group interaction for REE when adjusted for fat‐free mass and fat mass, with post hoc tests revealing that the 50‐kcal difference between 19 and 43 hours (1310 ± 196 to 1260 ± 161 kcal) and the 34‐kcal difference between 19 and 67 hours (1310 ± 196 to 1276 ± 168 kcal) were significant for AT. No other differences were found, including RT (19 hours, 1256 ± 160; 43 hours, 1251 ± 160; 67 hours, 1268 ± 188 kcal). Urine norepinephrine increased with training only in AT. After adjusting for fat‐free mass, REE Δ between 19 and both 43 and 67 hours was significantly related to urine norepinephrine (r = 0.76, p < 0.01 and 0.68, p < 0.03, respectively). Discussion: Consistent with findings on longer duration AT, these results show that 40 minutes of AT elevates REE for 19 hours in trained black and white women. This elevation did not occur with 40 minutes of RT. Results suggest that differences are, in part, due to increased sympathetic tone.     

Increased resting energy expenditure in cystic fibrosis

To explore the hypothesis that there is an increased metabolic rate in cystic fibrosis, resting energy expenditure was measured by indirect calorimetry in 23 subjects with cystic fibrosis in a stable clinical state and in 42 normal control subjects. Resting energy expenditure was found to be elevated by an average of 0.45 MJ/24 h [95% confidence interval (CI) = 0.26-0.64, t = 4.91, P less than 0.001] (108 kcal/24 h), or 9.2% above expected values derived from the regression relating resting energy expenditure to whole body weight and sex in control subjects. When related to lean body mass, values were still elevated by 0.36 MJ/24 h (95% CI = 0.18-0.53, t = 4.15, P less than 0.001) (86 kcal/24 h), or 7.2%. The increased values were found to be independent of age, sex, or body size. There were significant correlations between increased values and poor pulmonary function as measured by the ratio of the forced expiratory volume in 1 s to forced vital capacity (r = -0.44, P less than 0.05) and subclinical infection as indicated by the blood leukocyte count (r = 0.40, P less than 0.05). However, the correlations were low, suggesting that other factors may contribute to the increased resting energy expenditure, possibly including the putative metabolic defect in cystic fibrosis.     

Increased energy expenditure, decreased adiposity, and tissue-specific insulin sensitivity in protein-tyrosine phosphatase 1B-deficient mice

Protein-tyrosine phosphatase 1B (PTP-1B) is a major protein-tyrosine phosphatase that has been implicated in the regulation of insulin action, as well as in other signal transduction pathways. To investigate the role of PTP-1B in vivo, we generated homozygotic PTP-1B-null mice by targeted gene disruption. PTP-1B-deficient mice have remarkably low adiposity and are protected from diet-induced obesity. Decreased adiposity is due to a marked reduction in fat cell mass without a decrease in adipocyte number. Leanness in PTP-1B-deficient mice is accompanied by increased basal metabolic rate and total energy expenditure, without marked alteration of uncoupling protein mRNA expression. In addition, insulin-stimulated whole-body glucose disposal is enhanced significantly in PTP-1B-deficient animals, as shown by hyperinsulinemic-euglycemic clamp studies. Remarkably, increased insulin sensitivity in PTP-1B-deficient mice is tissue specific, as insulin-stimulated glucose uptake is elevated in skeletal muscle, whereas adipose tissue is unaffected. Our results identify PTP-1B as a major regulator of energy balance, insulin sensitivity, and body fat stores in vivo.     

Reduction in postprandial energy expenditure during pregnancy.

Energy expenditure was measured during pregnancy in seven primigravid women at 12-15, 25-28, and 34-36 weeks and after the cessation of lactation. On each occasion the resting metabolic rate and the increase in metabolic rate after ingestion of a liquid test meal were measured by indirect calorimetry. In absolute terms the resting metabolic rate increased steadily during pregnancy but when expressed per unit of body weight no change was found. The energetic response to a mixed constituent meal was significantly reduced by 28% in the middle trimester of pregnancy. These findings suggest a possible maternal adaptation to increase energetic efficiency at a time when the energy demands of the fetus are high.     

Increased thermoregulatory responsiveness in cold adapted but not in hyperthyroid hypermetabolic rats

Cold-adapted (CA) rats, unlike non-adapted (NA) ones, give exaggerated metabolic response to acute cold exposure, with paradoxical "overshoot" core temperature (Tc) rise in the cold, and they also give enhanced hyperthermia to central injection of prostaglandin E1 (PGE1). The adaptation-dependent differences might be explained either by the high thermogenic capacity of peripheral tissues in CA rats or by differences in the central processing of regulatory signals. If high tissue metabolism sufficiently explains the extreme responses of CA animals, other hypermetabolic states (with high resting metabolic rate, RMR), e.g. hyperthyroidism, should also be accompanied by enhanced reactions. In the present study thermoregulatory responses to acute cold exposure or to PGE1 were compared in hypermetabolic CA, similarly hypermetabolic thyroxine-treated (T4) and control non-hypermetabolic NA rats (mean RMR = 8.12, 8.47 and 6.03 W kg(-1), respectively). Cold exposure was followed by paradoxical core temperature (Tc) rise of 0.5 to 0.7 degrees C only in CA rats, but by Tc fall (0.8 to 2.1 degrees C) in NA and T4 animals. Identical central stimuli (PGE1) induced larger elevations of Tc and metabolic rate in CA rats than in similarly hypermetabolic T4 or in non-hypermetabolic NA animals (mean Tc rise of 1.9 degrees C in CA vs. 0.9 degrees C in T4 and 1.0 degrees C in NA rats). Vasodilatation thresholds were also similar in NA and T4, but lowered in CA animals. A hypermetabolic status, per se, does not seem to explain the enhanced thermoregulatory responsiveness of CA animals, adaptation-induced central regulatory changes may be more important for the "overshoot" phenomenon.     

An energy 'sources' and 'fractions' approach to the mechanical energy expenditure problem--III. Mechanical energy expenditure reduction during one link motion

Mechanical energy economy and transformation during one link motion are analyzed on the basis of the theory developed in the previous publications (parts I and II of this series, J. Biomechanics 19, 287-300). The 'compensation coefficient' characterizing mechanical energy economy is introduced. The attempts to estimate MEE using only energy curves and neglecting the powers of real sources of energy implicitly lead to replacement of real force and moment systems by the systems reduced to the centers of mass. But such an unintentional substitution of imaginary sources for real ones, specifically, the reduction of forces acting on the link to the equivalent system, changes estimates of mechanical energy expenditure (MEE). That is why the methods of calculating MEE economy based on the determination of so-called 'quasi-mechanical' work (the sum of the kinetic and potential energy increases per one cycle of motion) are not correct. There are two mechanisms to reduce the MEE using the antiphase fluctuations (corresponding to energy transformations) of the (a) rotational and translational fractions of the total energy (at the expense of the F-sources); (b) potential and kinetic energies (at the expense of the mg-source).     

Effect of whole-body electromyostimulation on energy expenditure during exercise

The application of whole-body electromyostimulation (WB-EMS) in the area of fat reduction and body shaping has become more popular recently. Indeed, some studies prove positive outcomes concerning parameters related to body composition. However, there are conflicting data as to whether EMS relevantly impacts energy expenditure (EE) during or after application. Thus, the main purpose of the study was to determine the acute effect of WB-EMS on EE. Nineteen moderately trained men (26.4 ± 4.3 years) were randomly assigned to a typically used low-intensity resistance exercise protocol (16 minutes) with (85 Hz) and without WB-EMS. Using a crossover design, the same subjects performed both tests after completely recovering within 7 days. Energy expenditure as the primary endpoint of this study was determined by indirect calorimetry. The EE during low-intensity resistance exercise with adjuvant WB-EMS was significantly higher (p = 0.008) than that during the control condition (412 ± 60 vs. 352 ± 70 kcal; effect size; d = 0.92). This study clearly demonstrates the additive effect of WB-EMS on EE in moderately trained subjects during low-intensity resistance exercise training. Although this effect was statistically significant, the fast and significant reductions of body fat observed in recent studies suggest that the effect of WB-EMS on EE may still be underestimated by indirect calorimetry because of the inability of indirect calorimetry to accurately assess EE during "above-steady state conditions." Although from a statistically point of view WB-EMS clearly impacts EE, the relatively small effect did not suggest a broad application of this device in this area. However, taking other positive outcomes of this technology into account, WB-EMS may be a time-saving option at least for subjects unwilling or unable to exercise conventionally.     

Increased lipolysis and energy expenditure in a mouse model with severely impaired glucagon secretion

Background

Secretion of insulin and glucagon is triggered by elevated intracellular calcium levels. Although the precise mechanism by which the calcium signal is coupled to insulin and glucagon granule exocytosis is unclear, synaptotagmin-7 has been shown to be a positive regulator of calcium-dependent insulin and glucagon secretion, and may function as a calcium sensor for insulin and glucagon granule exocytosis. Deletion of synaptotagmin-7 leads to impaired glucose-stimulated insulin secretion and nearly abolished Ca²⁺-dependent glucagon secretion in mice. Under non-stressed resting state, however, synaptotagmin-7 KO mice exhibit normal insulin level but severely reduced glucagon level.

Methodology/Principal Findings

We studied energy expenditure and metabolism in synaptotagmin-7 KO and control mice using indirect calorimetry and biochemical techniques. Synaptotagmin-7 KO mice had lower body weight and body fat content, and exhibited higher oxygen consumption and basal metabolic rate. Respiratory exchange ratio (RER) was lower in synaptotagmin-7 KO mice, suggesting an increased use of lipid in their energy production. Consistent with lower RER, gene expression profiles suggest enhanced lipolysis and increased capacity for fatty acid transport and oxidation in synaptotagmin-7 KO mice. Furthermore, expression of uncoupling protein 3 (UCP3) in skeletal muscle was approximately doubled in the KO mice compared with control mice.

Conclusions

These results show that the lean phenotype in synaptotagmin-7 KO mice was mostly attributed to increased lipolysis and energy expenditure, and suggest that reduced glucagon level may have broad influence on the overall metabolism in the mouse model.     

Effect of endurance training on gross energy expenditure during exercise

We compared the effect of endurance exercise training on gross energy expenditure (GEE) during steady-state exercise in 20 younger men (31.2 +/- 0.6 years) and 20 middle-aged men (49.2 +/- 1.1 years). The subjects trained for eight months. The training program consisted of three 45-min walking and jogging exercise sessions per week at an intensity of approximately 60-85% of the heart rate at peak VO2. We administered bicycle ergometer tests at 0, 4, and 8 months into training. Participants exercised at a power output of 100 W for 10 min using a pedaling frequency of 50 rpm. We determined GEE (kcal/min) by measuring the oxygen consumption and respiratory exchange ratio. We found a significant reduction (p less than 0.05) in GEE (0.7-1.3 kcal/min) following 4 months of endurance training in both age groups, with a further reduction (p less than 0.05) noted in only the middle-aged group at month 8. We found no difference (p greater than 0.05) in GEE between the younger and middle-aged men. We conclude that chronic exercise may modify GEE during a submaximal exercise bout and that this adaptation is similar in magnitude in younger and middle-aged men.     

Effects on energy expenditure of facial cooling during exercise.

Estimated energy expenditures for men during Arctic manhauling expeditions were 29-33 MJ day-1, higher than those documented for other hard-working groups and exceeding predicted energy costs for such activities. Although physiological effects from generalised cooling were unlikely, cold exposure of the face could have influenced exercise metabolism via autonomic stimulation. This hypothesis was examined by measuring oxygen consumption, energy expenditure, respiratory exchange ratio (R) and cardiovascular changes during rest and exercise, with and without exposure of the face to air at--20 degrees C. Measurements were made in five subjects during 15 min of rest followed by continuous exercise on a cycle ergometer consisting of 15-min periods at 75, 100, 125 and 150 W external work. The cold air caused a profound fall in facial temperatures and small falls in mean skin and rectal temperatures (P less than 0.001). These changes were associated with a small increase in the mean oxygen consumption over all levels of rest and exercise (0.86 l min-1 vs 0.82 l min-1, P less than 0.001) and a corresponding increase in mean energy expenditure (294 W vs 283 W, P less than 0.05). Cold air also caused an increase in mean resting R values (1.00 vs 0.88, P less than 0.01) but a decrease in the mean R value for all levels of exercise (0.85 vs 0.91, P less than 0.05). Pulse rates were unchanged but systolic and diastolic blood pressures were relatively elevated throughout the cold face experiments (P less than 0.001).     

Increased reproductive capacity and physical defense but decreased tannin content in an invasive plant

Abstract Plant invasions create novel plant–insect interactions. The EICA (evolution of increased competitive ability) hypothesis proposes that invasive plants will reallocate resources from defense to growth and/or reproduction because they have escaped from their co‐evolved insect natural enemies. Testing multiple herbivory by monophagous and oligophagous herbivores and simultaneous measurement of various plant traits will provide new insights into the evolutionary change of invasive plants. In this context, we conducted a common garden experiment to compare plant growth and reproduction, chemical and physical defense, and plant responses to herbivory by different types of herbivores between invasive North American populations and native East Asian populations of mile‐a‐minute weed, Persicaria perfoliata. We found that invasive mile‐a‐minute exhibited lower biomass, flowered earlier and had greater reproductive output than plants from the native range. Compared with native populations, plants from invasive populations had lower tannin content, but exhibited higher prickle density on nodes and leaves. Thus our results partially support the EICA hypothesis. When exposed to the monophagous insect, Rhinoncomimus latipes and the oligophagous insects, Gallerucida grisescens and Smaragdina nigrifrons, more damage by herbivory was found on invasive plants than on natives. R. latipes, G. grisescens and S. nigrifrons had strong, moderate and weak impacts on the growth and reproduction of mile‐a‐minute, respectively. The results indicate that mile‐a‐minute may have evolved a higher reproductive capacity in the introduced range, and this along with a lack of oligophagous and monophagous herbivores in the new range may have contributed to its invasiveness in North America.