title: Validation of a low-dose ACTH stimulation test in healthy adult horses.
abstract: OBJECTIVE
  To determine the lowest ACTH dose that would induce a maximum increase in serum cortisol concentration in healthy adult horses and identify the time to peak cortisol concentration.
  
  
  METHODS
  Evaluation study.
  
  
  METHODS
  8 healthy adult horses.
  
  
  METHODS
  Saline (0.9% NaCl) solution or 1 of 4 doses (0.02, 0.1, 0.25, and 0.5 μg/kg [0.009, 0.045, 0.114, and 0.227 μg/lb]) of cosyntropin (synthetic ACTH) were administered IV (5 treatments/horse). Serum cortisol concentrations were measured before and 30, 60, 90, 120, 180, and 240 minutes after injection of cosyntropin or saline solution; CBCs were performed before and 30, 60, 120, and 240 minutes after injection.
  
  
  RESULTS
  For all 4 doses, serum cortisol concentration was significantly increased, compared with the baseline value, by 30 minutes after administration of cosyntropin; no significant differences were detected among maximum serum cortisol concentrations obtained in response to administration of doses of 0.1, 0.25, and 0.5 μg/kg. Serum cortisol concentration peaked 30 minutes after administration of cosyntropin at a dose of 0.02 or 0.1 μg/kg, with peak concentrations 1.5 and 1.9 times, respectively, the baseline concentration. Serum cortisol concentration peaked 90 minutes after administration of cosyntropin at a dose of 0.25 or 0.5 μg/kg, with peak concentrations 2.0 and 2.3 times, respectively, the baseline concentration. Cosyntropin administration significantly affected WBC, neutrophil, and eosinophil counts and the neutrophil-to-lymphocyte ratio.
  
  
  CONCLUSIONS
  Results suggested that in healthy horses, administration of cosyntropin at a dose of 0.1 μg/kg resulted in maximum adrenal stimulation, with peak cortisol concentration 30 minutes after cosyntropin administration.
authors.affiliation: Department of Clinical Sciences, College of Veterinary Medicine, Auburn University, Auburn, AL 36849, USA. stewaaj@auburn.edu
authors.forename: Allison J
authors.initials: AJ
authors.lastname: Stewart
authors.forename: Ellen N
authors.initials: EN
authors.lastname: Behrend
authors.forename: James C
authors.initials: JC
authors.lastname: Wright
authors.forename: Linda G
authors.initials: LG
authors.lastname: Martin
authors.forename: Robert J
authors.initials: RJ
authors.lastname: Kemppainen
authors.forename: Katherine A
authors.initials: KA
authors.lastname: Busch
authors.forename: R Reid
authors.initials: RR
authors.lastname: Hanson
mesh_terms: D000324:Adrenocorticotropic Hormone / Q000008:administration & dosage* / Q000494:pharmacology*; D000818:Animals; D004305:Dose-Response Relationship, Drug; D005260:Female; D006736:Horses / Q000097:blood*; D006854:Hydrocortisone / Q000097:blood* / Q000378:metabolism*; D008297:Male
chemical_list: D000324:Adrenocorticotropic Hormone; D006854:Hydrocortisone