In the liver, clock genes are proposed to drive metabolic rhythms. These gene rhythms are driven by the suprachiasmatic
nucleus (SCN) mainly by food intake and via autonomic and hormonal pathways. Forced activity during the normal rest
phase, induces also food intake, thus neglecting the signals of the SCN, leading to conflicting time signals to target tissues
of the SCN. The present study explored in a rodent model of night-work the influence of food during the normal sleep
period on the synchrony of gene expression between clock genes and metabolic genes in the liver. Male Wistar rats were
exposed to forced activity for 8 h either during the rest phase (day) or during the active phase (night) by using a slow
rotating wheel. In this shift work model food intake shifts spontaneously to the forced activity period, therefore the
influence of food alone without induced activity was tested in other groups of animals that were fed ad libitum, or fed
during their rest or active phase. Rats forced to be active and/or eating during their rest phase, inverted their daily peak of
Per1, Bmal1 and Clock and lost the rhythm of Per2 in the liver, moreover NAMPT and metabolic genes such as Ppara lost
their rhythm and thus their synchrony with clock genes. We conclude that shift work or food intake in the rest phase leads
to desynchronization within the liver, characterized by misaligned temporal patterns of clock genes and metabolic genes.
This may be the cause of the development of the metabolic syndrome and obesity in individuals engaged in shift work.