title: Comparison of hair follicle histology between horses with pituitary pars intermedia dysfunction and excessive hair growth and normal aged horses.
abstract: BACKGROUND
  Pituitary pars intermedia dysfunction (PPID) in older equids is commonly recognized by a long hair coat that fails to shed.
  
  
  OBJECTIVE
  The aim of this study was to compare hair follicle stages in PPID-affected horses with excessively long hair coats with the stages of normal aged horses (controls) and to compare hair follicle stages in PPID-affected horses after 6 months of treatment with pergolide mesylate with those of control horses.
  
  
  METHODS
  Eight PPID-affected horses and four normal, age-matched, control horses.
  
  
  METHODS
  Skin biopsies were collected from the neck and rump of PPID-affected and control horses. A diagnosis of PPID was established based on hair coat changes and supportive overnight dexamethasone suppression test results. Skin biopsies were repeated after 6 months of treatment with pergolide. The number of hair follicles in anagen (A) or telogen (T) was counted for each skin biopsy using transverse sections.
  
  
  RESULTS
  Pretreatment biopsies had a greater percentage of A follicles (neck 96%, rump 95%) and a lower percentage of T follicles (neck 4%, rump 5%) in PPID-affected horses than in control horses (A, neck 15%, rump 25%; and T, neck 85%, rump 75%). After treatment with pergolide, all PPID-affected horses had improved shedding, and the percentages of A follicles (neck 69%, rump 70%) and T follicles (neck 31%, rump 30%) were not different from untreated control horses (A, neck 68%, rump 82%; and T, neck 32%, rump 18%).
  
  
  CONCLUSIONS
  These findings document that excessive hair growth (hypertrichosis) in PPID-affected horses is due to persistence of hair follicles in A. Furthermore, treatment with pergolide improved shedding and reduced the percentage of A follicles in PPID-affected horses.
authors: Department of Small Animal Clinical Sciences, Diagnostic Center for Population and Animal Health, College of Veterinary Medicine, Michigan State University, East Lansing, MI 48824, USA.
authors: Marie
authors: M
authors: Innerå
authors: Annette D
authors: AD
authors: Petersen
authors: Danielle R
authors: DR
authors: Desjardins
authors: Barbara A
authors: BA
authors: Steficek
authors: Edmund J
authors: EJ
authors: Rosser
authors: Harold C
authors: HC
authors: Schott
mesh_terms: D000375:Aging; D000818:Animals; D018491:Dopamine Agonists / Q000627:therapeutic use; D005260:Female; D006197:Hair / Q000254:growth & development*; D018859:Hair Follicle / Q000473:pathology*; D006734:Horse Diseases / Q000378:metabolism*; D006736:Horses; D008297:Male; D010479:Pergolide / Q000627:therapeutic use; D010900:Pituitary Diseases / Q000188:drug therapy / Q000473:pathology / Q000662:veterinary*; D052716:Pituitary Gland, Intermediate
chemical_list: D018491:Dopamine Agonists; D010479:Pergolide