title: Seasonal variations of melatonin in ram seminal plasma are correlated to those of testosterone and antioxidant enzymes.
abstract: BACKGROUND
  Some breeds of sheep are highly seasonal in terms of reproductive capability, and these changes are regulated by photoperiod and melatonin secretion. These changes affect the reproductive performance of rams, impairing semen quality and modifying hormonal profiles. Also, the antioxidant defence systems seem to be modulated by melatonin secretion, and shows seasonal variations. The aim of this study was to investigate the presence of melatonin and testosterone in ram seminal plasma and their variations between the breeding and non-breeding seasons. In addition, we analyzed the possible correlations between these hormones and the antioxidant enzyme defence system activity.
  
  
  METHODS
  Seminal plasma from nine Rasa Aragonesa rams were collected for one year, and their levels of melatonin, testosterone, superoxide dismutase (SOD), glutathione reductase (GRD), glutathione peroxidase (GPX) and catalase (CAT) were measured.
  
  
  RESULTS
  All samples presented measurable quantities of hormones and antioxidant enzymes. Both hormones showed monthly variations, with a decrease after the winter solstice and a rise after the summer solstice that reached the maximum levels in October-November, and a marked seasonal variation (P < 0.01) with higher levels in the breeding season. The yearly pattern of GRD and catalase was close to that of melatonin, and GRD showed a significant seasonal variation (P < 0.01) with a higher activity during the breeding season. Linear regression analysis between the studied hormones and antioxidant enzymes showed a significant correlation between melatonin and testosterone, GRD, SOD and catalase.
  
  
  CONCLUSIONS
  These results show the presence of melatonin and testosterone in ram seminal plasma, and that both hormones have seasonal variations, and support the idea that seasonal variations of fertility in the ram involve interplay between melatonin and the antioxidant defence system.
authors.affiliation: Departamento de Bioquímica, Facultad de Veterinaria, Instituto Universitario de Investigation en Ciencias Ambientales de Aragón, Universidad de Zaragoza, Spain. adriana@unizar.es
authors.forename: Adriana
authors.initials: A
authors.lastname: Casao
authors.forename: Igor
authors.initials: I
authors.lastname: Cebrián
authors.forename: Mayra Eoda
authors.initials: ME
authors.lastname: Asumpção
authors.forename: Rosaura
authors.initials: R
authors.lastname: Pérez-Pé
authors.forename: José A
authors.initials: JA
authors.lastname: Abecia
authors.forename: Fernando
authors.initials: F
authors.lastname: Forcada
authors.forename: José A
authors.initials: JA
authors.lastname: Cebrián-Pérez
authors.forename: Teresa
authors.initials: T
authors.lastname: Muiño-Blanco
mesh_terms: D000818:Animals; D000975:Antioxidants / Q000378:metabolism*; D002374:Catalase / Q000378:metabolism; D004798:Enzymes / Q000378:metabolism; D005979:Glutathione Peroxidase / Q000378:metabolism; D005980:Glutathione Reductase / Q000378:metabolism; D008297:Male; D008550:Melatonin / Q000032:analysis / Q000378:metabolism*; D012621:Seasons; D012661:Semen / Q000737:chemistry / Q000378:metabolism*; D012756:Sheep / Q000378:metabolism*; D013482:Superoxide Dismutase / Q000378:metabolism; D013739:Testosterone / Q000378:metabolism*
chemical_list: D000975:Antioxidants; D004798:Enzymes; D013739:Testosterone; D002374:Catalase; D005979:Glutathione Peroxidase; D013482:Superoxide Dismutase; D005980:Glutathione Reductase; D008550:Melatonin