Daily and seasonal profiles of gut melatonin and their temporal relationship with pineal and serum melatonin in carp Catla catla under natural photo-thermal conditions

Abstract

A temporal relationship between the daily and seasonal profiles of melatonin (N-acetyl-5-methoxytryptamine) in three different parts of gut, pineal, and serum as well as the density of arylalkylamine N-acetyltransferase (AANAT) protein, the key regulator of melatoninergic pathway in the pineal and respective regions of gut has been sought in a tropical carp Catla catla under natural photo-thermal conditions. The tissue samples were collected at four different clock hours in a daily cycle and the same was repeated in four different seasons in an annual cycle. In a daily cycle, concentrations of melatonin as well as the band intensity of a ∼23 kDa AANAT protein in each segment of gut, irrespective of sampling months, exhibited a peak at midday, while both the variables in the pineal and melatonin in serum showed a peak either in late dark phase (in March) or at midnight (in the remaining seasons). The simple correlation coefficient analysis of values revealed a negative correlation between the melatoninergic system in the gut and the pineal. Notably, seasonal fluctuations of photoperiod as well as water temperature exhibited a negative correlation with the daily peak values of pineal and serum melatonin, but no significant correlation with the respective values of gut melatonin. In conclusion, attainment of a daily peak in melatonin in the gut, unlike in the pineal and serum, does not seem to be a dark-dependent phenomenon.

Keywords:

• carp
• gut
• melatonin
• photo-thermal conditions
• pineal
• temporal pattern

Acknowledgement

Financial assistance from the Council of Scientific and Industrial Research, Govt. of India, New Delhi (37(1390)/09/EMR-II) is gratefully acknowledged.