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Dysregulation of the biological clock disrupts the homeostasis of physiological functions, which may lead to the development of various disorders. To investigate the relationship between biological rhythms and disorders, an efficient monitoring method of the biological clock is necessary. In this study, we analyzed the circadian rhythmicity profile of bile acids in urine and investigated whether urinary bile acid (UBA) could reflect the circadian rhythm in liver physiology. Male Wistar-Hannover rats were maintained in metabolic cages under ad lib feeding and later subjected to restricted feeding (in which rats were fed only during light periods). Excreted urine was collected in each session, and bile acid contents were analyzed via an enzyme-based total bile acid assay. UBA content showed diurnal fluctuations under both ad lib and restricted feeding conditions and reached a peak during the dark period of ad lib feeding. In contrast, with restricted feeding, the peak was observed during light periods. Restricted feeding induced an 8-12 h phase shift. Diurnal fluctuation and phase shift by restricted feeding are distinctive features controlled by biological clocks in peripheral tissues. Since bile acids are synthesized in the liver, we propose that UBA might reflect the circadian fluctuation in liver physiology.

identifier:JOS-2434432X-3-60