title: The effect of geographic location, breed, and pituitary dysfunction on seasonal adrenocorticotropin and α-melanocyte-stimulating hormone plasma concentrations in horses.
abstract: BACKGROUND
  Plasma α-melanocyte-stimulating hormone (α-MSH) and adrenocorticotropin (ACTH) concentrations in horses vary with season, confounding diagnostic testing for pituitary pars intermedia dysfunction (PPID).
  
  
  OBJECTIVE
  The goals of this study were to determine whether seasonal variation in plasma α-MSH and ACTH concentrations in horses is influenced by geographic location, breed, or PPID.
  
  
  METHODS
  Healthy light breed horses residing in Florida, Massachusetts, and Finland (n = 12 per group); healthy Morgan horses (n = 13); healthy ponies (n = 9) and horses with PPID (n = 8).
  
  
  METHODS
  Monthly plasma α-MSH and ACTH concentrations were measured by radioimmunoassay. Nonlinear regression analysis was used to estimate the time of peak hormone concentrations. Mean hormone concentrations in fall and nonfall months were compared.
  
  
  RESULTS
  The fall peak plasma α-MSH concentration occurred earlier in horses residing at more northern locations. Mean seasonal α-MSH concentrations were similar in all healthy groups at all locations, but in the fall, plasma ACTH concentrations were higher in horses living in more southern locations. Plasma ACTH but not α-MSH concentrations were higher in Morgan horses compared with light breed horses from the same location. Hormone concentrations of ponies did not differ from those of horses during either season. Concentrations of both hormones were high in the fall compared with the spring in horses with PPID.
  
  
  CONCLUSIONS
  These findings suggest geographic location of residence and breed may affect the onset, amplitude, or both of the seasonal peak of pars intermedia (PI) hormones and should be considered when performing diagnostic testing for PPID. Horses with PPID maintain seasonal regulation of PI hormone output.
authors: Department of Physiological Sciences, Center for Veterinary Health Sciences, Oklahoma State University, Stillwater, OK 74078, USA. diannem@okstate.edu
authors: D
authors: D
authors: McFarlane
authors: M R
authors: MR
authors: Paradis
authors: D
authors: D
authors: Zimmel
authors: B
authors: B
authors: Sykes
authors: B W
authors: BW
authors: Brorsen
authors: A
authors: A
authors: Sanchez
authors: K
authors: K
authors: Vainio
mesh_terms: D000324:Adrenocorticotropic Hormone / Q000097:blood*; D000818:Animals; D005260:Female; D005387:Finland; D005431:Florida; D006736:Horses / Q000097:blood*; D008297:Male; D008404:Massachusetts; D052716:Pituitary Gland, Intermediate / Q000503:physiopathology*; D012044:Regression Analysis; D012621:Seasons; D000521:alpha-MSH / Q000097:blood*
chemical_list: D000521:alpha-MSH; D000324:Adrenocorticotropic Hormone