Effect of fasting on the peripheral circadian gene expression in rats

The present study found that fasting did not significantly shift the circadian phases of the clock genes (Bmal1, Cry1, Per1, Per2, Per3, Dec1, Dec2, and Rev-erb a) and clock-controlled gene Dbp. However, the mRNA levels of these circadian genes were altered in both a gene-and tissue-specific manner. Bmal1 and Cry1 were insensitive to the fasting signal, because their mRNA levels almost remained unchanged after fasting. On the contrary, the mRNA levels of Per2, Dec1 and Dec2 were not only markedly altered but also altered steadily in the liver and heart, indicating that these three clock genes are sensitive to the stimuli of fasting. As for Per1, Per3 and Rev-erb alpha, they were differently or even contrarily regulated in the liver and heart by the stimuli of fasting, suggesting that these three clock genes may play different roles in the circadian systems of the liver and heart. Thus, the existence of food cues may be important for maintaining a regular circadian level in the peripheral clocks.