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      Seasonal variation in sleeping metabolic rate, thyroid activity, and leptin.

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      Journal: American journal of physiology. Endocrinology and metabolism
      Publisher: American Physiological Society

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          Abstract

          We investigated seasonal variation in sleeping metabolic rate (SMR) and the possible relation to body composition, thyroid activity, and leptin. Twenty-five healthy volunteers were examined four times during the year: in spring (April, May), summer (July, August), autumn (October, November), and winter (January, February). Body composition was determined using a three-compartment model based on underwater weighing and the deuterium dilution method. SMR was measured during an overnight stay in a respiration chamber. A blood sample was taken for the analysis of free and total thyroxine, TSH, and leptin. SMR showed a significant seasonal variation (P < 0.01) with a maximum in winter (4.54 kJ/min) and a minimum in summer (4.34 kJ/min). The amplitude was 0.10 +/- 0.02 kJ/min, and the phase was November 5th. Season explained 17% of the intraindividual variation in SMR. The circannual rhythm in SMR could not be explained by changes in body composition, thyroid activity, or leptin. Interindividual variation in SMR was explained by fat-free mass (P < 0.001) and leptin (P < 0.001).

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          Most cited references29

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          Thyroid hormone control of thermogenesis and energy balance.

          José D E Sousa E Silva (1995)
          The mechanisms whereby thyroid hormone increases heat production have been analyzed with emphasis in more recent developments. Thyroid hormone increases obligatory thermogenesis as a result of the stimulation of numerous metabolic pathways involved in development, remodeling, and delivery of energy to the tissues. In addition, thyroid hormone may specifically stimulate some thermogenic mechanisms selected during evolution of homeotherms (e.g., Na/K-ATPase, Ca2+ cycling in muscle). Thyroid hormone also plays an essential role in facultative thermogenesis interacting with the sympathetic nervous system (SNS) at various levels. Peripherally, thyroid hormone potentiates the effects of the SNS at the level of the adrenergic receptor and adenylyl cyclase complex as well as distal from this point. Synergistic interactions between T3 and cAMP on the regulation of gene expression have been described. Brown adipose tissue (BAT) T4-5'-deiodinase plays a central role in controlling heat production. When this enzyme is stimulated by norepinephrine in the euthyroid and hypothyroid condition, it provides high concentrations of T3 to BAT; inhibition by T4 in hyperthyroidism may limit brown fat thermogenic responses. Also, thyrotoxicosis uniquely reduces the expression of beta 3-adrenergic receptors in brown adipose tissue, and the increased obligatory thermogenesis of this condition, via afferent neural pathways, may reduce the hypothalamic stimulation of brown fat, providing additional mechanisms to limit brown adipose tissue thermogenesis in hyperthyroidism.
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            A dual-respiration chamber system with automated calibration.

            Antonia F. Ten Brink, Annelot Schoffelen, K Westerterp … (1997)
            This study characterizes respiration chambers with fully automated calibration. The system consists of two 14-m3 pull-type chambers. Care was taken to provide a friendly environment for the subjects, with the possibility of social contact during the experiment. Gas analysis was automated to correct for analyzer drift and barometric pressure variations and to provide ease of use. Methods used for checking the system's performance are described. The gas-analysis repeatability was within 0.002%. Results of alcohol combustion (50-350 ml/min CO2) show an accuracy of 0.5 +/- 2.0 (SD) % for O2 consumption and -0.3 +/- 1.6% for CO2 production for 2- to 24-h experiments. It is concluded that response time is not the main factor with respect to the smallest practical measurement interval (duration); volume, mixing, gas-analysis accuracy, and levels of O2 consumption and CO2 production are at least equally important. The smallest practical interval was 15-25 min, as also found with most chamber systems described in the literature. We chose to standardize 0.5 h as the minimum measurement interval.
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              The Maastricht protocol for the measurement of body composition and energy expenditure with labeled water.

              K Westerterp, Klaske Lichtenbelt, L Wouters (1995)
              An update of practical aspects of the use of labeled water for the measurement of total body water (TBW) and energy expenditure (EE) is presented as applied in Maastricht, The Netherlands. We use a 10-hour equilibration period. The isotopes for the measurement of TBW and EE are routinely administered, after collecting a background urine sample, as a last consumption before the night. Our data show an underestimate of TBW measured with isotope dilution after 4 hours (in the morning), a discrepancy which increases with the size of TBW. No such relation and no significant differences were found after 10-hour (overnight) equilibration. The ratio between the dilution space for deuterium and oxygen-18 is higher than the earlier figure of 1.03, especially in adult subjects with a high body fat content. For an observation period of EE over two weeks, samples from the second and the last voiding on the first, mid, and last day of the observation period are collected. Differences in EE calculated from morning and evening samples within the first and second week allow detection of sampling errors and if so, samples are excluded from the final calculation. Differences of EE between weeks 1 and 2 allow a check for the consistency of the subjects' physical activity level and usually fall within 10% of the average EE over the total observation interval.
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                Author and article information

                Journal
                PubMed ID:: 12857676
                DOI:: 10.1152/ajpendo.00488.2002

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