ENERGY BUDGETS IN FREE-LIVING GREEN IGUANAS IN A SEASONAL ENVIRONMENT

Using a variety of techniques we estimated energy expenditure and allocation of energy in free-living green iguanas (Iguana iguana) in a seasonal environment on Curacao, Netherlands Antilles. 1) Daily energy expenditure (DEE) was measured by means of the doubly labeled water (DLW) technique, using O-18 and deuterium (H-2). The method was validated in green iguanas at ambient temperature and humidity levels occurring on Curacao. Energy expenditures from the DLW method differed by 2.1 +/- 8.2% compared to respirometry and balance methods. This value falls within the range of deviations found in other validation studies, and indicates that the DLW method is acceptable in green iguanas even at high ambient humidity. 2) Average DEE was 71.7 kJ . kg-1.d-1. There were no significant differences in DEE between males and females, although males tended to have higher metabolic rates during the mating season. Energy expenditure on a yearly basis including clutch production in females did not differ between females and males, indicating comparable annual levels of energy expenditure between the sexes. 3) Temperature dependence of standard metabolic rate (SMR) and resting metabolic rate (RMR) were determined by respirometry experiments. RMR increased with temperature with a Q10 of 2.24. In combination with field body temperatures SMR and RMR of free-living iguanas could be determined. SMR amounted to 15-22% of the DEE. DEE was 1.8-2.8 times RMR. 4) The energy expenditure above RMR was allocated between activities involving locomotion and stationary activities. DEE in combination with behavioral data revealed an indirect measure of the costs linked to locomotion in the field, including climbing (255 kJ.km-1.kg-1). Locomotion with a climbing component imposed six times the costs of horizontal walking. Although time spent locomoting was only a very small fraction of the total time, the costs linked to locomotor activities amounted to almost-equal-to 23% of the daily energy expenditure. Postural adjustment costs were almost-equal-to 33% of the DEE. Locomotion could explain 78% of the observed variation in DEE. If other activities, such as foraging and social activities, were included in multiple regression analyses, 96% of the variation in DEE could be explained. 5) Body condition of males decreased during the mating period (March/April), while most of the decrease in body condition of females occurred during the time of oviposition (May/June). Time spent in social activities was higher during the mating period, especially so in males, but time devoted to other activities (locomotion, foraging) did not differ significantly between the seasons. Comparison between the sexes revealed that males spent more time locomoting than females, throughout the year. 6) Differences in body condition in the course of the year were not due to differences in DEE, but were mainly a result of differences in metabolizable energy intake. Though on a yearly basis energy expenditure was equal in both sexes, energy allocation differed between the sexes. Females devoted almost-equal-to 15% of their annual energy budget to the production of eggs, while males showed heightened social activity during the mating phase and spent twice as much time in locomotor activities than females

The effect of warmth acclimation on behaviour, thermophysiology and perception

Public and commercial buildings tend to overheat and considerable energy is consumed by air-conditioning and ventilation. However, many occupants remain unsatisfied and consequently exhibit thermoregulatory behaviour (TRB), e.g. opening windows or controlling the air-conditioning. This, in turn, might negatively influence the building energy use. This paper hypothesizes that warmth acclimation influences thermophysiology, perception and TRB in a warm environment. Therefore, the effect of warmth acclimation on TRB, physiology and perception is investigated. Twelve participants underwent a so-called SWITCH protocol before and after warmth acclimation (7 days, 6h/day, about 33 degrees C, about 22% RH). During SWITCH, the participants chose between a warm (37 degrees C) and a cold (17 degrees C) condition. TRB was determined by the number of switches and the time spent in a specific condition. Mean skin temperature was recorded to assess behavioural thresholds. Thermal comfort and sensation were indicated on visual analogue scales (VAS). After acclimation, the upper critical behavioural threshold significantly increased from 35.2 +/- 0.6 to 35.5 +/- 0.5 degrees C (p0.05) and the range of mean skin temperatures at which no behaviour occurred significantly widened (3.6 +/- 0.7 to 4.2 +/- 0.6;

Brown Adipose Tissue in Morbidly Obese Subjects

BACKGROUND: Cold-stimulated adaptive thermogenesis in brown adipose tissue (BAT) to increase energy expenditure is suggested as a possible therapeutic target for the treatment of obesity. We have recently shown high prevalence of BAT in adult humans, which was inversely related to body mass index (BMI) and body fat percentage (BF%), suggesting that obesity is associated with lower BAT activity. Here, we examined BAT activity in morbidly obese subjects and its role in cold-induced thermogenesis (CIT) after applying a personalized cooling protocol. We hypothesize that morbidly obese subjects show reduced BAT activity upon cold exposure. METHODS AND FINDINGS: After applying a personalized cooling protocol for maximal non-shivering conditions, BAT activity was determined using positron-emission tomography and computed tomography (PET-CT). Cold-induced BAT activity was detected in three out of 15 morbidly obese subjects. Combined with results from lean to morbidly obese subjects (n = 39) from previous study, the collective data show a highly significant correlation between BAT activity and body composition (P<0.001), respectively explaining 64% and 60% of the variance in BMI (r = 0.8; P<0.001) and BF% (r = 0.75; P<0.001). Obese individuals demonstrate a blunted CIT combined with low BAT activity. Only in BAT-positive subjects (n = 26) mean energy expenditure was increased significantly upon cold exposure (51.5±6.7 J/s versus 44.0±5.1 J/s, P = 0.001), and the increase was significantly higher compared to BAT-negative subjects (+15.5±8.9% versus +3.6±8.9%, P = 0.001), indicating a role for BAT in CIT in humans. CONCLUSIONS: This study shows that in an extremely large range of body compositions, BAT activity is highly correlated with BMI and BF%. BAT-positive subjects showed higher CIT, indicating that BAT is also in humans involved in adaptive thermogenesis. Increasing BAT activity could be a therapeutic target in (morbid) obesity

Brown adipose tissue activity after a high-calorie meal in humans.

BACKGROUND: Studies in rodents have shown that brown adipose tissue (BAT) is activated on food intake, thereby reducing metabolic efficiency. OBJECTIVE: The current study investigated whether a single high-calorie, carbohydrate-rich meal activates BAT in lean human adults. DESIGN: BAT activity was studied in 11 lean adult men [age: 23.6 +/- 2.1 y; body mass index (BMI; in kg/m2): 22.4 +/- 2.1] after consumption of a high-calorie, carbohydrate-rich meal (1622 +/- 222 kcal; 78% carbohydrate, 12% P, 10% F). BAT activity during 2 h of mild cold exposure served as a positive control experiment. BAT activity was assessed by [18F]fluorodeoxyglucose (FDG)-positron emission tomography-computed tomography. Energy expenditure was measured by indirect calorimetry. RESULTS: Postprandial [18F]FDG uptake was significantly higher in BAT [1.65 +/- 0.99 mean standard uptake value (SUVmean)] than in subcutaneous (0.35 +/- 0.15 SUVmean; P < 0.05) and visceral (0.49 +/- 0.24 SUVmean; P < 0.05) white adipose tissue and liver (0.95 +/- 0.28 SUVmean; P < 0.05). Postprandial BAT activity was lower than cold-induced BAT activity (7.19 +/- 2.09 SUVmean). However, postprandial BAT activity may have been underestimated because of high postprandial [18F]FDG uptake in skeletal muscle compared with cold (1.36 +/- 0.31 compared with 0.59 +/- 0.07 SUVmean, P < 0.05), which reduces [18F]FDG bioavailability for BAT and other tissues. No direct relation was found between BAT and diet-induced thermogenesis (DIT). CONCLUSIONS: Glucose uptake in BAT increases after a meal in humans, which indicates a role for BAT in reducing metabolic efficiency. However, the quantitative contribution of BAT to DIT relative to other tissues, such as skeletal muscle, remains to be investigated. This trial was registered at www.controlled-trials.com as ISRCTN21413505

Hot-water immersion does not increase postprandial muscle protein synthesis rates during recovery from resistance-type exercise in healthy, young males

The purpose of this study was to assess the impact of postexercise hot-water immersion on postprandial myofibrillar protein synthesis rates during recovery from a single bout of resistance-type exercise in healthy, young men. Twelve healthy, adult men (age: 23 ± 1 y) performed a single bout of resistance-type exercise followed by 20 min of water immersion of both legs. One leg was immersed in hot water [46°C: hot-water immersion (HWI)], while the other leg was immersed in thermoneutral water (30°C: CON). After water immersion, a beverage was ingested containing 20 g intrinsically L-[1-13C]-phenylalanine and L-[1-13C]-leucine labeled milk protein with 45 g of carbohydrates. In addition, primed continuous L-[ring-2H5]-phenylalanine and L-[1-13C]-leucine infusions were applied, with frequent collection of blood and muscle samples to assess myofibrillar protein synthesis rates in vivo over a 5-h recovery period. Muscle temperature immediately after water immersion was higher in the HWI compared with the CON leg (37.5 ± 0.1 vs. 35.2 ± 0.2°C; P < 0.001). Incorporation of dietary protein-derived L-[1-13C]-phenylalanine into myofibrillar protein did not differ between the HWI and CON leg during the 5-h recovery period (0.025 ± 0.003 vs. 0.024 ± 0.002 MPE; P = 0.953). Postexercise myofibrillar protein synthesis rates did not differ between the HWI and CON leg based upon L-[1-13C]-leucine (0.050 ± 0.005 vs. 0.049 ± 0.002%/h; P = 0.815) and L-[ring-2H5]-phenylalanine (0.048 ± 0.002 vs. 0.047 ± 0.003%/h; P = 0.877), respectively. Hot-water immersion during recovery from resistance-type exercise does not increase the postprandial rise in myofibrillar protein synthesis rates. In addition, postexercise hot-water immersion does not increase the capacity of the muscle to incorporate dietary protein-derived amino acids in muscle tissue protein during subsequent recovery

The influence of bright and dim light on substrate metabolism, energy expenditure and thermoregulation in insulin-resistant individuals depends on time of day

AIMS/HYPOTHESIS: In our modern society, artificial light is available around the clock and most people expose themselves to electrical light and light-emissive screens during the dark period of the natural light/dark cycle. Such suboptimal lighting conditions have been associated with adverse metabolic effects, and redesigning indoor lighting conditions to mimic the natural light/dark cycle more closely holds promise to improve metabolic health. Our objective was to compare metabolic responses to lighting conditions that resemble the natural light/dark cycle in contrast to suboptimal lighting in individuals at risk of developing metabolic diseases. METHODS: Therefore, we here performed a non-blinded, randomised, controlled, crossover trial in which overweight insulin-resistant volunteers (n = 14) were exposed to two 40 h laboratory sessions with different 24 h lighting protocols while staying in a metabolic chamber under real-life conditions. In the Bright day–Dim evening condition, volunteers were exposed to electric bright light (~1250 lx) during the daytime (08:00–18:00 h) and to dim light (~5 lx) during the evening (18:00–23:00 h). Vice versa, in the Dim day–Bright evening condition, volunteers were exposed to dim light during the daytime and bright light during the evening. Randomisation and allocation to light conditions were carried out by sequential numbering. During both lighting protocols, we performed 24 h indirect calorimetry, and continuous core body and skin temperature measurements, and took frequent blood samples. The primary outcome was plasma glucose focusing on the pre- and postprandial periods of the intervention. RESULTS: Spending the day in bright light resulted in a greater increase in postprandial triacylglycerol levels following breakfast, but lower glucose levels preceding the dinner meal at 18:00 h, compared with dim light (5.0 ± 0.2 vs 5.2 ± 0.2 mmol/l, n = 13, p=0.02). Dim day–Bright evening reduced the increase in postprandial glucose after dinner compared with Bright day–Dim evening (incremental AUC: 307 ± 55 vs 394 ± 66 mmol/l × min, n = 13, p=0.009). After the Bright day–Dim evening condition the sleeping metabolic rate was identical compared with the baseline night, whereas it dropped after Dim day–Bright evening. Melatonin secretion in the evening was strongly suppressed for Dim day–Bright evening but not for Bright day–Dim evening. Distal skin temperature for Bright day–Dim evening was lower at 18:00 h (28.8 ± 0.3°C vs 29.9 ± 0.4°C, n = 13, p=0.039) and higher at 23:00 h compared with Dim day–Bright evening (30.1 ± 0.3°C vs 28.8 ± 0.3°C, n = 13, p=0.006). Fasting and postprandial plasma insulin levels and the respiratory exchange ratio were not different between the two lighting protocols at any time. CONCLUSIONS/INTERPRETATION: Together, these findings suggest that the indoor light environment modulates postprandial substrate handling, energy expenditure and thermoregulation of insulin-resistant volunteers in a time-of-day-dependent manner. TRIAL REGISTRATION: ClinicalTrials.gov NCT03829982. FUNDING: We acknowledge the financial support from the Netherlands Cardiovascular Research Initiative: an initiative with support from the Dutch Heart Foundation (CVON2014–02 ENERGISE). GRAPHICAL ABSTRACT: [Image: see text] SUPPLEMENTARY INFORMATION: The online version contains peer-reviewed but unedited supplementary material available at 10.1007/s00125-021-05643-9

Temperature and surgical wound heat loss during orthopedic surgery: computer simulations and measurements

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