bims-ciryme Biomed News
on Circadian rhythms and metabolism
Issue of 2021‒03‒21
two papers selected by
Gabriela Da Silva Xavier
University of Birmingham

  1. Neuroendocrinology. 2021 Mar 18.
      Background Dysregulation of metabolic regulatory hormones often occurs during the progress of obesity. Key regulatory hormone Insulin-GH balance has recently been proposed to maintain metabolism profiles. Time-restricted feeding (TRF) is an effective strategy against obesity without detailed research on pulsatile GH releasing patterns. Methods TRF was performed in an over-eating MC4RKO obese mouse model using normal food. Body weight and food intake were measured. Series of blood samples were collected for 6 h pulsatile GH profile, glucose tolerance test and insulin tolerance test at 5, 8, and 9 weeks of TRF, respectively. Indirect calorimetric recordings were performed by Phenomaster system at 6 weeks for 1 week and body composition was measured by Nuclear magnetic resonance spectroscopy (NMR). Substrate and energy metabolism related gene expression were measured in terminal liver and subcutaneous white adipose tissues. Results TRF increased pulsatile GH secretion in dark phase and suppressed hyperinsulinemia in MC4RKO obese mice to reach a reduced insulin/GH ratio. This was accompanied by the improvement in insulin sensitivity, metabolic flexibility, glucose tolerance and decreased glucose fluctuation, together with appropriate modification of gene expression involved in substrate metabolism and adipose tissue browning. NMR measurement showed that TRF decreased fat mass but increased lean mass. Indirect calorimeter recording indicated that TRF decreased the respiratory exchange ratio (RER) reflecting consumption of more fatty acid in energy production in light phase and increased the oxygen consumption during activities in dark phase. Conclusions TRF effectively decreases hyperinsulinemia and restores pulsatile GH secretion in the overeating obese mice with significant improvement in substrate and energy metabolism and body composition without reducing total caloric intake.
  2. J Biol Rhythms. 2021 Mar 15. 748730421998469
      Plants and animals use circadian and photoperiodic timekeeping mechanisms to respond to daily and seasonal changes in light:dark and appropriately coordinate their development. Although the mechanisms that may connect the circadian and photoperiodic clock are still unclear in many species, researchers have been using Nanda-Hamner protocols for decades to elucidate how seasonal time is measured and determine whether seasonal responses have a circadian basis in a given species. In this brief tutorial we describe how to design and interpret the results of Nanda-Hamner experiments, and provide suggestions on how to use both Nanda-Hamner protocols and modern molecular experiments to better understand the mechanisms of seasonal timekeeping.
    Keywords:  Nanda-Hamner protocol; circadian rhythms; external coincidence model; hourglass model; photoperiodism