title: Pineal melatonin synthesis is decreased in type 2 diabetic Goto-Kakizaki rats.
abstract: OBJECTIVE
  It is not well understood why the amplitude of melatonin rhythms is reduced in diabetic animals and humans. This paper addresses the differences in the pineal melatonin synthesis of type 2 diabetic Goto-Kakizaki (GK) rats compared to non-diabetic Wistar rats (8 and 50 weeks old).
  
  
  METHODS
  Plasma melatonin concentrations and the pineal content of melatonin and its precursors (tryptophan, 5-hydroxytryptophan, serotonin, and N-acetylserotonin) were quantified at the middle of the day and night. Additionally, the expression of melatonin synthesizing enzymes, pineal noradrenaline content, and pineal protein content were considered, and the melatonin secreting capacity of pineal glands was studied in vitro.
  
  
  RESULTS
  The pineal glands of diabetic GK rats have a different expression pattern of melatonin synthesizing enzymes. The amount of all precursors of melatonin is reduced in pineal glands of diabetic GK rats. The pineal glands of diabetic GK rats contain less noradrenaline, indicating a reduced stimulation of nighttime melatonin synthesis. The pineal glands of diabetic GK rats produce less melatonin in reaction to noradrenaline in vivo and in vitro. The pineal glands of diabetic GK rats contain less protein, probably a consequence of diabetic neuropathy.
  
  
  CONCLUSIONS
  This is the first time that melatonin synthesis is examined in a type 2 diabetic rat model. The present data unveiled several reasons for a reduced melatonin secretion in diabetic animals and presents an important link in the interaction between melatonin and insulin.
authors.affiliation: Institute of Anatomy and Cell Biology, Martin Luther University Halle-Wittenberg, Grosse Steinstrasse 52, 06097 Halle, Germany.
authors.forename: Thomas
authors.initials: T
authors.lastname: Frese
authors.forename: Andreas Gunter
authors.initials: AG
authors.lastname: Bach
authors.forename: Eckhard
authors.initials: E
authors.lastname: Mühlbauer
authors.forename: Klaus
authors.initials: K
authors.lastname: Pönicke
authors.forename: Hans-Jürgen
authors.initials: HJ
authors.lastname: Brömme
authors.forename: André
authors.initials: A
authors.lastname: Welp
authors.forename: Elmar
authors.initials: E
authors.lastname: Peschke
mesh_terms: D000818:Animals; D030801:Animals, Genetically Modified; D003924:Diabetes Mellitus, Type 2 / Q000503:physiopathology*; D004195:Disease Models, Animal; D015536:Down-Regulation; D008550:Melatonin / Q000235:genetics / Q000378:metabolism*; D010870:Pineal Gland / Q000378:metabolism*; D012313:RNA / Q000378:metabolism; D051381:Rats; D011922:Rats, Mutant Strains; D017208:Rats, Wistar; D020133:Reverse Transcriptase Polymerase Chain Reaction
chemical_list: D012313:RNA; D008550:Melatonin