The rat oocyte synthesises melatonin

Area of Science:

• Reproductive Biology
• Endocrinology
• Molecular Biology

Background:

• Melatonin, an indoleamine, is primarily known for its synthesis in the pineal gland.
• Previous research suggests potential melatonin synthesis within the ovary.
• The enzymes arylalkylamine N-acetyltransferase (AANAT) and acetylserotonin O-methyltransferase (ASMT) are crucial for melatonin production.

Purpose of the Study:

• To investigate the expression of AANAT and ASMT in the adult rat ovary.
• To determine if melatonin is synthesized within ovarian cells, particularly oocytes.

Main Methods:

• Reverse transcription-polymerase chain reaction (RT-PCR) to detect AANAT and ASMT mRNA.
• Western blotting to confirm the presence of AANAT protein.
• Immunohistochemistry to localize AANAT protein within ovarian tissues.
• Incubation of isolated oocytes with serotonin to assess melatonin production.

Main Results:

• Both AANAT and ASMT mRNAs were detected in the adult rat ovary.
• AANAT protein (24kDa) was identified in the ovary, similar to the pineal gland.
• AANAT protein was localized to oocytes, corpus luteum, medulla, and mast cells.
• Oocytes exhibited increasing AANAT levels during follicular development and metabolized serotonin to melatonin.

Conclusions:

• The enzymes necessary for melatonin synthesis are present and active in the adult rat ovary.
• Melatonin is synthesized directly from serotonin within oocytes.
• Oocyte-derived melatonin may influence oocyte growth, maturation, and function, potentially via antioxidant or calmodulin antagonist mechanisms.