The effect of food access schedule and diet composition on the rhythmicity of serum melatonin and pineal N-acetyltransferase activity in rats /

Abstract

Melatonin is a hormone secreted by the pineal gland, which is known to modulate biological rhythms in mammals. This study investigated the effect of food access schedule and dietary composition on serum melatonin and pineal NAT activity in adult male Wistar rats. These rats were maintained on a 12:12 h light:dark schedule with lights on at 0800h. The rats were randomly assigned to two dietary groups. A group was simultaneously fed a protein-rich and carbohydrate-rich granulated diet and the other group fed granulated rat chow. Each dietary group was further divided based on dietary feeding schedules. Animals were fed between 0800--1600 h or fed ad libitum. The study revealed that protein intake of rats fed the dietary choice was lower with the restricted access than in the free access. In rats fed dietary choice, the nocturnal melatonin levels and pineal NAT activity were significantly lower under the restricted access feeding when compared to the ad libitum feeding schedule. This was not observed in rats fed single chow diet. In conclusion our data demonstrate that food composition does affect the nocturnal synthesis of melatonin as well as the activity of the enzyme NAT. This could be via dietary intake of tryptophan, which is a precursor melatonin synthesis in the pineal gland