Day-night difference in β3-adrenoceptor agonist-induced energy expenditure: Contribution of brown fat thermogenesis and physical activity.

β3-adrenergic receptor (β3-AR) agonist, a drug that reduces body fat, stimulates lipomobilization from white adipose tissue (WAT) and thermogenesis in brown adipose tissue (BAT). To test the day-night difference in the effects of β3-AR agonist, in the present study, we examined the responses of lipomobilization and energy expenditure to CL316,243 (CL) during the daytime at 10:00 and nighttime at 22:00 in mice kept in a 12 h light-dark cycle with lights on from 07:00. CL injection increased plasma free fatty acid to the same extent at 10:00 and 22:00. In contrast, CL injection increased total oxygen consumption more markedly at 10:00 than 22:00. Physical activity was suppressed by CL injection especially at 22:00. Correcting total oxygen consumption by the suppressive effect on physical activity, oxygen consumption dependent on BAT thermogenesis was estimated. This revealed that the effect of CL on BAT thermogenesis was not different between 10:00 and 22:00. Thus, we concluded that there is no day-night difference in the CL effects on lipomobilization from WAT and thermogenesis in BAT. The stronger effect of CL on total energy expenditure in the daytime was largely due to a more suppressive effect on physical activity in the nighttime.: