Circadian and seasonal rhythms of melatonin production in mules (Equus asinus × Equus caballus)

Bruno Cozzi, Giovanni Morei, Jean‐Paul ‐P Ravault, Didier Chesneau, Russel J. Reiter

Research output: Contribution to journalArticlepeer-review

18 Scopus citations


Abstract: The present study describes the patterns of melatonin production in the mule (Equus asinus × Equus caballus). Blood was sampled hourly for 24 h from eight mule mares in spring and fall. The data obtained show the presence of a circadian rhythm of production of melatonin, with highest values during the dark phase both in spring and fall. In fall the nightly rise of melatonin production begins earlier in the dark phase and reaches higher quantitative levels than in spring. The morning decline of melatonin production is similar in the two seasons. Maximal levels of nightly melatonin production in the mule are about 10× higher than those described in the horse. The results reported here indicate the persistence of brain structures able to receive and transduce environmental signals in the mule, a genetically sterile mammalian hybrid.

Original languageEnglish (US)
Pages (from-to)130-135
Number of pages6
JournalJournal of pineal research
Issue number3
StatePublished - Apr 1991


  • equidae
  • hybrid
  • pineal gland
  • sterility

ASJC Scopus subject areas

  • Endocrinology


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