title: Effect of oral melatonin administration on sex hormone, prolactin, and thyroid hormone concentrations in adult dogs.
abstract: OBJECTIVE
  To determine the effect of oral melatonin (MT) administration on serum concentrations of sex hormones, prolactin, and thyroxine in dogs.
  
  
  METHODS
  Prospective study.
  
  
  METHODS
  8 male and 8 female adult sexually intact dogs.
  
  
  METHODS
  5 male and 5 female dogs were treated with MT (1.0 to 1.3 mg/kg [0.45 to 0.59 mg/lb] of body weight), PO, every 12 hours for 28 days; the other 6 dogs were used as controls. Blood samples were collected on days 0, 14, and 28, and serum concentrations of estradiol-17 beta, progesterone, testosterone, androstenedione, 17-hydroxyprogesterone (17-HP), dihydroepiandrostenedione sulfate (DHEAS), prolactin, and thyroxine were determined. On day 5, serum MT concentrations were measured before and periodically for up to 8 hours after MT administration in 4 treated dogs.
  
  
  RESULTS
  Female dogs treated with MT had significant decreases in serum estradiol, testosterone, and DHEAS concentrations between days 0 and 28. Male dogs treated with MT had significant decreases in serum estradiol and 17-HP concentrations between days 0 and 28. Serum MT concentrations increased significantly after MT administration and remained high for at least 8 hours. Prolactin and thyroxine concentrations were unaffected by treatment.
  
  
  CONCLUSIONS
  Melatonin is well absorbed following oral administration and may alter serum sex hormone concentrations.
authors.affiliation: Department of Small Animal Clinical Sciences, College of Veterinary Medicine, University of Tennessee, Knoxville 37901, USA.
authors.forename: P F
authors.initials: PF
authors.lastname: Ashley
authors.forename: L A
authors.initials: LA
authors.lastname: Frank
authors.forename: L P
authors.initials: LP
authors.lastname: Schmeitzel
authors.forename: E M
authors.initials: EM
authors.lastname: Bailey
authors.forename: J W
authors.initials: JW
authors.lastname: Oliver
mesh_terms: D019326:17-alpha-Hydroxyprogesterone / Q000097:blood; D000042:Absorption; D000284:Administration, Oral; D000818:Animals; D003687:Dehydroepiandrosterone / Q000097:blood; D004285:Dogs / Q000097:blood* / Q000254:growth & development; D004958:Estradiol / Q000097:blood; D005260:Female; D012739:Gonadal Steroid Hormones / Q000097:blood*; D006197:Hair / Q000187:drug effects / Q000254:growth & development; D008297:Male; D008550:Melatonin / Q000008:administration & dosage / Q000097:blood / Q000494:pharmacology*; D011388:Prolactin / Q000097:blood*; D011446:Prospective Studies; D013739:Testosterone / Q000097:blood; D013974:Thyroxine / Q000097:blood*
chemical_list: D012739:Gonadal Steroid Hormones; D013739:Testosterone; D003687:Dehydroepiandrosterone; D004958:Estradiol; D019326:17-alpha-Hydroxyprogesterone; D011388:Prolactin; D008550:Melatonin; D013974:Thyroxine