Pineal N-acetyltransferase activity in hamsters maintained in shortened light cycles

P. K. Rudeen, R. J. Reiter

Research output: Contribution to journalArticlepeer-review

5 Scopus citations


Pineal serotonin N-acetyltransferase activity (NAT) was compared among Syrian hamsters maintained in light: dark (LD) cycles of 14:10 or 2:22 or in an interrupted (LD 1/4:5 3/4 × 4) photoperiodic cycle. In hamsters maintained in a LD 14:10 photoperiod, the zenith of pineal NAT activity occurs at 04:00 h, approximately 8 hours after the onset of the dark phase. When the onset of the dark phase was advanced by 8 hours (in hamsters maintained in LD 2:22 cycles), the pineal NAT activity was advanced by an equivalent length of time. Hamster pineal NAT activity was sup-pressed throughout a 24-hour period when the animals were maintained in darkness interrupted with brief periods of light at 6 h intervals (LD 1/4:5 3/4 × 4). The results suggest that melatonin syn-thesis is determined according to when light occurs during the photoperiodic cycle rather than by the total amount of darkness or the dark: light ratio to which animals are exposed in a 24-hour period.

Original languageEnglish (US)
Pages (from-to)19-23
Number of pages5
JournalJournal of Endocrinological Investigation: Official Journal of the Italian Scociety of Endocrinology
Issue number1
StatePublished - Jan 1979


  • N-acetyltransferase
  • light-dark cycles
  • pineal gland

ASJC Scopus subject areas

  • Endocrinology, Diabetes and Metabolism
  • Endocrinology


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