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Horm Metab Res 2002; 34(8): 441-445
DOI: 10.1055/s-2002-33602
Original Basic

© Georg Thieme Verlag Stuttgart · New York

Stimulatory Effects of LH on Release of Melatonin and Activities of its Synthesizing Enzymes NAT and HIOMT in Organ-Cultured Pineal Glands of Female Rats

T.  Hosaka 1 , T.  Mimuro 1 , N.  Hamada 1 , M.  T.  Itoh 2 , B.  Ishizuka 1
  • 1Department of Obstetrics and Gynecology, St. Marianna University School of Medicine, Kawasaki, Japan
  • 2Department of Chemistry, St. Marianna University School of Medicine, Kawasaki, Japan
Further Information

Publication History

Received: 7 January 2002

Accepted after revision: 14 May 2002

Publication Date:
25 September 2002 (online)

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Abstract

The pineal hormone melatonin (N-acetyl-5-methoxytryptamine) exerts antigonadotropic effects in some mammalian species. To evaluate the effect of luteinizing hormone (LH) on melatonin release and its synthesizing enzyme activities in pineal glands, pineals of adult female rats undergoing diestrus were organ-cultured in a medium containing 10-12, 10-10 or 10-8 M LH for 6 h. Melatonin release increased significantly in pineals cultured with 10-12 and 10-10 M LH, as compared to control values. Similarly, the activity of arylalkylamine N-acetyltransferase (NAT), the key regulatory enzyme in melatonin biosynthesis, was significantly higher in pineals cultured with 10-12 and 10-10 M LH for 6 h, while LH at 10-8 M had no effect. Although LH at 10-10 M increased pineal hydroxyindole-O-methyltransferase (HIOMT) activity, which catalyzes the final step of melatonin biosynthesis, LH at 10-12 and 10-8 M had no effect. These results demonstrate that at relatively low physiological levels, LH stimulates pineal melatonin synthesis and release, mainly by increasing NAT activity.

Key words

Melatonin - Arylalkylamine N-Acetyltransferase - Hydroxyindole-O-Methyltransferase - Luteinizing Hormone - Pineal Gland - Organ Culture - Female Rats

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T. Hosaka, M.D.

Department of Obstetrics and Gynecology · St. Marianna University School of Medicine

Sugao, Miyamae-ku · Kawasaki 216-8511 · Japan ·

Phone: + 81 (44) 977-8111, ext. 3327

Fax: + 81 (44) 977-2944