Parathion (O,O-dimethyl-O-p-nitrophenyl phosphorothioate) induces pineal melatonin synthesis at night

Ahmed M. Attia, Russel J. Reiter, Karl Arne Stokkan, Mostafa H. Mostafa, Salah A. Soliman, Abdel Khalek H. El-Sebae

Research output: Contribution to journalArticlepeer-review

5 Scopus citations


The effects of parathion on male rat pineal N-acetyltransferase (NAT) activity, hydroxyindole-O-methyltransferase (HIOMT) activity and pineal and serum melatonin levels at the end of light period (2000 h) and at night (2300 h and 0100 h) were studied. Additionally, pineal levels of 5-hydroxytryptophan (5-HTP), serotonin (5-HT), and 5-hydroxyindole acetic acid (5-HIAA) were estimated. Parathion was administered intragastrically at total doses (over 6 days) of either 6.5 or 13 mg/kg. Control rats received vehicle (corn oil) only. During the study, the rats were exposed to light:dark cycles of 14:10 with light off at 2100 h. Pineal NAT activity was increased at 0100 h following parathion administration at both doses, but HIOMT activity was unaffected. Pineal and serum melatonin levels were increased at night (2300 h and 0100 h) after the 13 mg/kg dose of parathion while the lower dose increased pineal melatonin only at 0100 h. Also, both doses decreased 5-HTP at 2000 h while the lower dose increased it at 2300; 5-HT was significantly decreased at 2300 h and 5-HIAA levels were lower but only significantly so for the 13 mg/kg dose at 2000 h. The results indicate that parathion has significant effects on pineal melatonin synthesis by mechanisms which remain unknown.

Original languageEnglish (US)
Pages (from-to)553-557
Number of pages5
JournalBrain Research Bulletin
Issue number4
StatePublished - Apr 1991


  • Hydroxyindole-O-methyltransferase (HIOMT)
  • Indoleamines
  • Melatonin
  • N-Acetyltransferase (NAT)
  • Parathion
  • Pineal gland

ASJC Scopus subject areas

  • Neuroscience(all)


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