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.
Itoh
M T
MT
Department of Chemistry, St. Marianna University School of Medicine, Sugao, Miyamae-ku, Kawasaki, Japan. itohmt@marianna-u.ac.jp
Hosaka
T
T
Mimuro
T
T
Hamada
N
N
Ishizuka
B
B
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