Temporal relationship between the daily profiles of gut melatonin, oxidative status and major digestive enzymes in carp Catla catla

Abstract

The present study demonstrated a temporal relationship between the concentrations of melatonin, oxidative status and digestive physiology in the gut of a tropical carp Catla catla. We measured the levels of gut melatonin, malondialdehyde (MDA) – a faithful marker of intracellular stress, different antioxidants and major digestive enzymes in the carp gut at four different clock hours in a daily cycle under natural photo-thermal conditions. A correlation between the gut variables was sought to point their possible functional relationship. Gut melatonin titers displayed significant diurnal variations with a peak at midday. An identical temporal pattern with the highest value at midday and nadir at midnight was noted in the activities of superoxide dismutase, catalase and glutathione peroxidase. In contrast, levels of MDA and reduced glutathione (GSH) were highest at midnight and lowest at midday. The activity of all the studied digestive enzymes (α-amylase, cellulase, protease and lipase) showed significant daily variations with a peak at midday. Gut melatonin concentrations by showing a positive correlation with the activity of both enzymatic antioxidants and digestive enzymes, and a negative correlation with the levels of GSH and MDA indicated their possible physiological interplay in a daily cycle. Collectively, our study presented the first information on the daily profiles of oxidative stress, different antioxidants and digestive enzymes in the gut tissues of any fish species, and suggested their functional relationship with the concentrations of gut melatonin in carp Catla catla.

Key words:

• Antioxidants
• carp
• gut
• melatonin
• stress
• diurnal

Acknowledgements:

Financial assistance from the Council of Scientific and Industrial Research (CSIR), New Delhi (37(1220)/05/ EMR-II) and the Department of Science and Technology (DST), Government of India, (DST/INSPIRE Fellowship/2011/IF110070) is thankfully acknowledged.