Melatonin receptors in spermatozoa and melatonin metabolism in the male reproductive tract

Studies carried out by the BIOFREZ group of the University of Zaragoza have shown that:

  • Melatonin is a hormone which controls and promotes most of photoperiod dependent processes, varying their concentrations relative to the day/night cycle.
  • Semen quality would be conditioned, in many species, by the presence of endogenous melatonin, which directly and indirectly acts on some of the most important elements that influence sperm quality parameters, specifically sperm motility and reducing or delaying apoptosis (Casao, Mendoza et al. 2010).
  • Our group has determined the presence of endogenous melatonin in sheep seminal plasma, the concentration being not influenced by the period day/night unlike the present in blood plasma (Casao, Cebrián et al. 2010). Thus, whereas during the day disappears from the bloodstream, its concentration remains unchanged in seminal plasma.
  • We have determined the existence of melatonin receptors MT1 and MT2 in sheep sperm membrane (Vicente Carrillo, Arto et al. 2012) and we have demonstrated that modulation of this hormone on sperm capacitation is mainly done by the MT2  receptor (Casao, Luna et al. 2012).

All this means a high specificity of the melatonin metabolism in the male genital tract, which directly could affect sperm quality. The observed levels of this hormone in seminal plasma may be due to mechanisms that protect the hormone from degradation or because of the presence of specific biosynthetic pathways. It could also be that both pathways, anabolic and catabolic exist “per se” in the male genital tract, regulating melatonin concentration and consequently the subsequent action of melatonin on sperm and possibly also on the accessory sex glands.
Based on this background, the objective of this project is to elucidate the possible existence of metabolic biosynthetic and/or degradation pathways of melatonin in the male genital tract and to determine whether these metabolic pathways and melatonin concentration itself play the same role in dependent species photoperiod (sheep, horse) than in other apparently unaffected by it (pig, dog , cattle ), and also if there are melatonin receptors in the membrane of sperm from different species. The knowledge of the existence of sperm receptors for melatonin in different species and the possible existence of anabolic pathways and / or catabolic for this hormone in the male genital tract , together with the analysis of the action of melatonin on the sperm, are aspects fundamental to the management and preparation of semen doses. In addition, to establish protocols for handling animals , photoperiod dependent or not , which have a direct impact on semen quality . Therefore, the main objective of this project is to elucidate the existence of their own metabolism for melatonin in the male genital tract in different species, and to establish the correlation between the presence of this hormone in the seminal plasma and the proper maturation and sperm quality .

This project is being carried out by the BIOFREZ group of the University of Zaragoza (Principal Investigator of the project: J. A. Cebrián-Pérez), the Group for the Study of Reproduction of the Autonomous University of Barcelona and IMAPOR (Animal Reproduction Group) in the University of León (ULE).

The group at the ULE (IMAPOR) consists of:

Felipe Martínez Pastor (Reprobío)

J. C. Domínguez

M. E. Alonso

J. R. González-Montaña