title: α-Melanocyte--stimulating hormone and adrenocorticotropin concentrations in response to thyrotropin-releasing hormone and comparison with adrenocorticotropin concentration after domperidone administration in healthy horses and horses with pituitary pars intermedia dysfunction.
abstract: OBJECTIVE
  To compare endogenous ACTH and α-melanocyte-stimulating hormone (α-MSH) concentrations after administration of thyrotropin-releasing hormone (TRH) and to compare ACTH concentrations after TRH administration with those following domperidone administration in healthy horses and horses with pituitary pars intermedia dysfunction (PPID).
  
  
  METHODS
  Prospective case series.
  
  
  METHODS
  69 clinically normal horses and 47 horses with or suspected to have PPID.
  
  
  METHODS
  ACTH concentrations were measured during 108 TRH stimulation tests in 88 horses, and α-MSH concentrations were measured during 56 TRH stimulation tests in 50 horses. In 28 of these horses, ACTH concentrations after domperidone administration were measured and test results were compared. The pituitary gland was histologically examined in all horses that were euthanatized.
  
  
  RESULTS
  ACTH and α-MSH concentrations increased in all horses after TRH administration, with a greater and more prolonged increase in horses with PPID. Percentage increase was significantly greater for α-MSH concentration than for ACTH concentration. The change in ACTH concentration after domperidone administration was less consistent in differentiating clinically normal horses from those with PPID than was the response to TRH.
  
  
  CONCLUSIONS
  Results suggested that ACTH concentration in response to TRH administration was useful for the diagnosis of PPID in horses and appeared more accurate than response to domperidone administration. Use of an α-MSH concentration ≥ 30 or 50 pmol/L did not appear superior to use of an ACTH concentration ≥ 36 pg/mL for the diagnosis of PPID, either before or 30 minutes after TRH administration.
authors.affiliation: Department of Clinical Studies, New Bolton Center, School of Veterinary Medicine, University of Pennsylvania, Kennett Square, PA 19348, USA. jbeech@vet.upenn.edu
authors.forename: Jill
authors.initials: J
authors.lastname: Beech
authors.forename: Dianne
authors.initials: D
authors.lastname: McFarlane
authors.forename: Sue
authors.initials: S
authors.lastname: Lindborg
authors.forename: Janice E
authors.initials: JE
authors.lastname: Sojka
authors.forename: Raymond C
authors.initials: RC
authors.lastname: Boston
mesh_terms: D000324:Adrenocorticotropic Hormone / Q000097:blood*; D000818:Animals; D004294:Domperidone / Q000494:pharmacology*; D018492:Dopamine Antagonists / Q000494:pharmacology; D006728:Hormones / Q000494:pharmacology; D006734:Horse Diseases / Q000097:blood*; D006736:Horses; D010900:Pituitary Diseases / Q000097:blood / Q000378:metabolism / Q000662:veterinary*; D052716:Pituitary Gland, Intermediate; D013973:Thyrotropin-Releasing Hormone / Q000494:pharmacology*; D000521:alpha-MSH / Q000097:blood*
chemical_list: D018492:Dopamine Antagonists; D006728:Hormones; D004294:Domperidone; D000521:alpha-MSH; D013973:Thyrotropin-Releasing Hormone; D000324:Adrenocorticotropic Hormone