Diurnal Variation of Nuclear Receptors in Mice with or without Fasting

Nuclear receptors such as pregnane X receptor (PXR) and constitutive androstane receptor (CAR) regulate the transcription of transporter and cytochrome P450 (CYP). The diurnal variation was observed in some transporters regulated by nuclear receptors. We investigated whether diurnal variation in PXR and CAR exists in mice. We also examined the effect of food intake on the diurnal rhythm of hepatic PXR and CAR using fed and fasted mice. In liver and small intestine of fed mice, the mRNA levels of PXR and CAR were unchanged between 7:00 AM and 7:00 PM. In contrast to fed mice, fasting mice partly exhibited the diurnal variation in PXR, not in CAR. The mRNA levels of PXR at 7:00 AM were significantly higher than that those at 7:00 PM in liver of fasting mice. These results indicated the different effects of fasting in mice on diurnal variation of PXR in each tissue.