Gonadotropin-Releasing Hormone Increases Melatonin Release in the Pineal Gland of the Female Rat In Vitro

Abstract

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.

Key words

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

References

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