Effect of daytime-restricted feeding in the daily variations of liver metabolism and blood transport of serotonin in rat

The biogenic amine serotonin is a signaling molecule in the gastrointestinal tract, platelets, and nervous tissue. In nervous system, serotonin and its metabolites are under the control of the circadian timing system, but it is not known if daily variations of serotonin exist in the liver. To explore this possibility, we tested if the rhythmic pattern of serotonin metabolism was regulated by daytime restricted feeding (DRF) which is a protocol associated to the expression of the food entrained oscillator (FEO). The DRF involved food access for 2 h each day for 3 weeks. Control groups included food ad libitum (AL) as well as acute fasting and refeeding. Serotonin-related metabolites were measured by high pressure liquid chromatography, the anabolic and catabolic enzymes were evaluated by western blot, qPCR, and immunohistochemistry to generate 24-h profiles. The results showed in the AL group, liver serotonin, tryptophan hydroxylase-1 activity, and protein abundance as well as serotonin in plasma and serum were rhythmic and coordinated. The DRF protocol disrupted this coordinated response and damped the rhythmic profile of these parameters. We demonstrated the daily synthesis and the degradation of serotonin as well as its transport in blood. This rhythm could influence the physiological role played by serotonin in peripheral organs. DRF caused an uncoordinated response in the liver and blood serotonin rhythm. This modification could be a part of the physiology of the FEO.