Daily profiles of serum and gastrointestinal melatonin in response to daytime or night-time supply of tryptophan-rich diet in carp (Catla catla)

Abstract

Influences of daytime (~10:00 h) or night-time (~22:00 h) supply of L-tryptophan (Trp)-rich diet on daily rhythm features of melatonin and arylalkylamine-N-acetyltransferase (AANAT) protein (key regulator of melatonin biosynthesis) in gastrointestinal (gut) tissue extracts, and melatonin in serum were studied in carp (Catla catla). Analysis of obtained data revealed that the mesor and amplitude values of both melatonin and AANAT in gut tissue-extracts were higher in daytime-fed fish than those supplied with food at night, and their acrophase varied from ~2 h in the daytime-fed carp to ~10 h in night-time-fed fish. Notably, initiation of stimulatory response of melatonin and AANAT in gut to Trp-rich diet varied from ~2 h (following food supply in day) to ~6 h (after food supply during night). However, in either case, their elevated levels were maintained for ~12 h. Trp-rich diet also caused increase in serum melatonin levels, and the duration of such response varied with the time of food supply. Collectively, present study not only demonstrates the role of Trp-rich diet as a potential inducer of gut melatoninergic system and modulator of daily serum melatonin profiles, but underlines the importance of the time of food supply as a determining factor of its influence as well.