title: The rat oocyte synthesises melatonin.
abstract: Melatonin (N-acetyl-5-methoxytryptamine) is an indoleamine originally identified in the pineal gland, where it is synthesised enzymatically from serotonin (5-hydroxytryptamine) by the sequential action of arylalkylamine N-acetyltransferase (AANAT) and acetylserotonin O-methyltransferase (ASMT; also known as hydroxyindole O-methyltransferase). Melatonin directly affects ovarian functions and previous studies have suggested that melatonin is synthesised in the ovary. In the present study, we examined whether AANAT and ASMT are expressed in the adult rat ovary. Reverse transcription-polymerase chain reaction analyses demonstrated that both AANAT and ASMT mRNAs are expressed in the ovary. Western blotting for AANAT protein showed that the ovary, like the pineal gland, contains this enzymatic protein with a molecular mass of 24kDa. Immunohistochemistry revealed that the AANAT protein is localised to the oocyte, corpus luteum and medulla, including mast cells. AANAT protein was found in oocytes at all stages of follicular development, and its levels in oocytes increased progressively throughout follicular development. Furthermore, isolated oocytes metabolised exogenous serotonin to melatonin. These findings demonstrate that melatonin is synthesised from serotonin in oocytes. Melatonin synthesised in the oocyte may be implicated in its own growth or maturation, for example, by acting as a calmodulin antagonist or an antioxidant.
authors.affiliation: Department of Obstetrics and Gynaecology, St. Marianna University School of Medicine, Sugao, Miyamae-ku, Kawasaki 216-8511, Japan.
authors.forename: Kenichiro
authors.initials: K
authors.lastname: Sakaguchi
authors.forename: Masanori T
authors.initials: MT
authors.lastname: Itoh
authors.forename: Noriyuki
authors.initials: N
authors.lastname: Takahashi
authors.forename: Wataru
authors.initials: W
authors.lastname: Tarumi
authors.forename: Bunpei
authors.initials: B
authors.lastname: Ishizuka
mesh_terms: D000121:Acetylserotonin O-Methyltransferase / Q000378:metabolism*; D000818:Animals; D047068:Arylalkylamine N-Acetyltransferase / Q000378:metabolism*; D053898:Biosynthetic Pathways / Q000502:physiology*; D015153:Blotting, Western; D017931:DNA Primers / Q000235:genetics; D005260:Female; D007150:Immunohistochemistry; D008550:Melatonin / Q000096:biosynthesis*; D009865:Oocytes / Q000378:metabolism*; D051381:Rats; D017208:Rats, Wistar; D020133:Reverse Transcriptase Polymerase Chain Reaction; D014048:Tolonium Chloride
chemical_list: D017931:DNA Primers; D014048:Tolonium Chloride; D000121:Acetylserotonin O-Methyltransferase; D047068:Arylalkylamine N-Acetyltransferase; D008550:Melatonin