Melatonin, an important candidate which regulates the animal reproduction: A review

Photoperiod is a very reliable predictor of future environmental conditions, since it is a very constant environmental clue and based on the period of light the animals may be the long day breeders or short day breeders. Daylight is perceived essentially by the eyes and the information is translated into hormonal (melatonin) stimuli by the pineal gland. The major function of melatonin is thought to be as an extremely potent free radical scavenger which is capable of quenching both reactive oxygen species as well as reactive nitrogen species and this function is receptor independent. However, some receptor mediated functions are also identified such as circadian entrainment, seasonal reproduction and ovarian activity. Two membrane bound melatonin receptors have been identified and characterized, MTNR1A or MT1 and MTNR1B or MT2 and both of them belong to the family of G protein-coupled, seven trans-membrane receptors. Melatonin appears to play key roles in the regulation of the endocrine system which includes regulation of GnRH via receptor mediated activity. MTNR1A modulates the effect of Melatonin on circadian and behavioral function in mice regulates the upstream gonadal response to Melatonin in C57BL and C3H mice and is sufficient and necessary to mediate the effects of Melatonin on reproductive function in hamsters.