N-Acetyltransferase activity, hydroxyindole-O-methyltransferase activity, and melatonin levels in the Harderian glands of the female Syrian hamster: Changes during the light: Dark cycle and the effect of 6-parachlorophenylalanine administration

Armando Menendez-Pelaez, Kimberly A. Howes, Aldo Gonzalez-Brito, Russel J. Reiter

Research output: Contribution to journalArticle

60 Scopus citations


The activities of NAT and HIOMT and the melatonin content of the Harderian glands of female Syrian hamsters were studied. When hamsters were kept under a light:dark cycle of 14:10 (lights on at 06.00 h), NAT activity exhibited a sharp, short term rise at one hour after lights on. Simultaneously, the activity of HIOMT, which forms melatonin, exhibited a rapid decline. Melatonin levels, like HIOMT activity, also showed a precipitous drop at one hour after light onset. After the respective changes, both NAT and HIOMT activity reverted back to night time levels. Melatonin levels remained depressed for several hours but by 1400 h (8 hours after lights on), nighttime melatonin values were re-established. Treatment of female hamsters with PCPA, a trytophan hydroxylase inhibitor, led to depressed levels of Harderian melatonin without affecting the activities of either NAT or HIOMT.

Original languageEnglish (US)
Pages (from-to)1231-1238
Number of pages8
JournalBiochemical and Biophysical Research Communications
Issue number3
Publication statusPublished - Jun 30 1987


ASJC Scopus subject areas

  • Biophysics
  • Biochemistry
  • Molecular Biology
  • Cell Biology

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