Fig. 4.

Diurnal changes in energy expenditure, respiratory quotient, and UCP1 expression in BAT from male Fischer 344 rats consuming a control or methionine-restricted diet (MR) for 9 (4, A and B) or 20 mo (4, C and D). At 32 days of age, rats were randomly assigned to receive a control diet containing 0.86% methionine (control group) or a diet with methionine restricted to 0.17% (MR). The diets were provided ad libitum, and cohorts (8–10 rats/cohort) of each group consumed their respective diets for 9 or 20 mo after weaning. After 9 and 20 mo, rats from the respective control and MR cohorts were adapted to the calorimetry chambers for 24 h prior to measurement of O₂ consumption and CO₂ production at 30-min intervals for the following 3 days. Thereafter, body composition of each rat was determined by DEXA scanning as described in materials and methods and used to express EE per unit of fat-free mass. Average EE was calculated for each animal in each group for the period when lights were on (7 AM–7 PM), when lights were off (7 PM–7 AM), and averaged over both periods to assess total daily EE. The means were compared by ANOVA at each age (Table 1). UCP1 mRNA (E) and protein expression (F) were measured in BAT after 3 (experiment 2), 9, and 20 mo on the respective diets. The responses were compared by ANOVA. ^a,bMeans at each time point with letters that differ denote P < 0.05.