Diurnal variation in oxygen consumption of laboratory rats

Oxygen consumption (VO2) was measured in Porton albino rats using a closed circuit apparatus. The groups studied were controls, cold-adapted animals, and those which had accumulated brown adipose tissue as a result of a cafeteria diet with a high energy content. It was possible to show in each group studied a difference in VO2 according to the time of day at which it was measured. This was consistent within each group studied. The diurnal variation shown (higher in the morning than in the afternoon) is characteristic of nocturnal animals. Measurement of VO2 then must be made within the same time-period or integrated over 24 h. Spurious correlations may otherwise occur.