Gonadotropin-releasing hormone increases melatonin release in the pineal gland of the female rat in vitro.
To evaluate the effect of gonadotropin-releasing hormone (GnRH) on melatonin ( N-acetyl-5-methoxytryptamine) release and its synthesizing enzyme activities in pineal glands, pineals from adult female rats during diestrus were organ-cultured in a medium containing 10 -12, 10 -10, or 10 -8 M GnRH for 6 h. Melatonin release increased significantly in pineals cultured with 10 -10 and 10 -8 M GnRH compared to controls. However, in pineal glands that were organ-cultured in a medium containing 10 -12 to 10 -8 M GnRH, the activity of arylalkylamine N-acetyltransferase, which is the key regulatory enzyme in melatonin biosynthesis, showed no significant difference from controls. Likewise, GnRH at these concentrations had no significant effect on the activity of pineal hydroxyindole- O-methyltransferase, which catalyzes the final step of melatonin biosynthesis. These results show that GnRH stimulates pineal melatonin release, but suggest that GnRH does not affect its melatonin synthesis.
Department of Chemistry, St. Marianna University School of Medicine, Sugao, Miyamae-ku, Kawasaki, Japan. itohmt@marianna-u.ac.jp
M T
MT
Itoh
T
T
Hosaka
T
T
Mimuro
N
N
Hamada
B
B
Ishizuka
D000121:Acetylserotonin O-Methyltransferase / Q000378:metabolism; D000818:Animals; D001191:Arylamine N-Acetyltransferase / Q000378:metabolism; D003470:Culture Media; D004031:Diestrus; D005260:Female; D007987:Gonadotropin-Releasing Hormone / Q000008:administration & dosage / Q000494:pharmacology*; D008550:Melatonin / Q000096:biosynthesis / Q000378:metabolism*; D009924:Organ Culture Techniques; D010870:Pineal Gland / Q000187:drug effects* / Q000201:enzymology / Q000378:metabolism*; D051381:Rats; D017208:Rats, Wistar
D003470:Culture Media; D007987:Gonadotropin-Releasing Hormone; D000121:Acetylserotonin O-Methyltransferase; D001191:Arylamine N-Acetyltransferase; D008550:Melatonin