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Comparison of hair follicle histology between horses with pituitary pars intermedia dysfunction and excessive hair growth and normal aged horses.
Abstract: 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.
© 2013 The Authors. Veterinary Dermatology © 2013 ESVD and ACVD.
Publication Date: 2013-01-22 PubMed ID: 23331700DOI: 10.1111/j.1365-3164.2012.01080.xGoogle Scholar: Lookup The Equine Research Bank provides access to a large database of publicly available scientific literature. Inclusion in the Research Bank does not imply endorsement of study methods or findings by Mad Barn.
- Journal Article
- Research Support
- Non-U.S. Gov't
Summary
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This research explores the influence of pituitary pars intermedia dysfunction (PPID) on hair growth in older horses, and the impact of treatment with pergolide mesylate on the condition. It found that PPID results in excessive hair growth due to the persistence of active hair follicles, and that treatment with pergolide can improve shedding and decrease active hair follicle count to virtually normal levels.
Objectives and Methods
- The primary aim of this study was to compare the stages of hair follicles in horses affected by PPID that display excessive hair growth, with those in normal, elderly horses.
- The research also aimed to study the impact of the drug pergolide mesylate on hair follicle stages after six months of treatment in PPID-affected horses.
- The study was conducted on twelve horses: eight horses with PPID and four healthy, age-matched horses serving as controls.
- Diagnosis of PPID was based on changes in the hair coat condition and supporting results from overnight dexamethasone suppression tests.
- Skin biopsies from the neck and rump of both PPID-affected horses and control horses were collected. This procedure was repeated after a period of six months in horses treated with pergolide.
- The number of hair follicles in two stages – active growth (anagen) and rest (telogen) stage – were counted in the skin biopsy samples.
Results
- The baseline biopsies taken before treatment showed an increased percentage of active hair follicles and a decreased percentage of resting hair follicles in PPID-affected horses compared to control horses.
- Contrarily, after pergolide treatment, a marked improvement in shedding was found in all PPID-affected horses, bringing the percentages of active and resting follicles to levels comparable with non-treated control horses.
Conclusions
- The study found that the unusual hair growth seen in PPID-affected horses stems from the persistence of active hair follicles.
- Furthermore, the use of pergolide was shown to enhance shedding and decrease anagen follicle count (active hair growth) in horses with PPID, essentially normalizing the hair growth cycle.
Cite This Article
APA
Innerå M, Petersen AD, Desjardins DR, Steficek BA, Rosser EJ, Schott HC.
(2013).
Comparison of hair follicle histology between horses with pituitary pars intermedia dysfunction and excessive hair growth and normal aged horses.
Vet Dermatol, 24(1), 212-7.e7.0E47.
https://doi.org/10.1111/j.1365-3164.2012.01080.x Publication
Researcher Affiliations
- 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.
MeSH Terms
- Aging
- Animals
- Dopamine Agonists / therapeutic use
- Female
- Hair / growth & development
- Hair Follicle / pathology
- Horse Diseases / metabolism
- Horses
- Male
- Pergolide / therapeutic use
- Pituitary Diseases / drug therapy
- Pituitary Diseases / pathology
- Pituitary Diseases / veterinary
- Pituitary Gland, Intermediate
Citations
This article has been cited 9 times.- Kirkwood NC, Hughes KJ, Stewart AJ. Prospective Case Series of Clinical Signs and Adrenocorticotrophin (ACTH) Concentrations in Seven Horses Transitioning to Pituitary Pars Intermedia Dysfunction (PPID). Vet Sci 2022 Oct 17;9(10).
- Kirkwood NC, Hughes KJ, Stewart AJ. Pituitary Pars Intermedia Dysfunction (PPID) in Horses. Vet Sci 2022 Oct 10;9(10).
- Nitzsche AM, Fey K, Büttner K, Gröf M, Staszyk C. The Gingiva of Horses With Pituitary Pars Intermedia Dysfunction: A Macroscopic Anatomical Evaluation. Front Vet Sci 2021;8:786971.
- Fortin JS, Hetak AA, Duggan KE, Burglass CM, Penticoff HB, Schott HC 2nd. Equine pituitary pars intermedia dysfunction: a spontaneous model of synucleinopathy. Sci Rep 2021 Aug 6;11(1):16036.
- Tsuchiya T, Noda R, Ikeda H, Maeda M, Sato F. Relationship between endogenous plasma adrenocorticotropic hormone concentration and reproductive performance in Thoroughbred broodmares. J Vet Intern Med 2021 Jul;35(4):2002-2008.
- Fortin JS, Benskey MJ, Lookingland KJ, Patterson JS, Howey EB, Goudreau JL, Schott HC 2nd. Restoring pars intermedia dopamine concentrations and tyrosine hydroxylase expression levels with pergolide: evidence from horses with pituitary pars intermedia dysfunction. BMC Vet Res 2020 Sep 25;16(1):356.
- Spelta CW. Equine pituitary pars intermedia dysfunction: current perspectives on diagnosis and management. Vet Med (Auckl) 2015;6:293-300.
- Parmantier S, Kyriazopoulou P, McClendon M, Adams A, Murphy BA. Influence of Extended Photoperiod Using Blue Light Masks on Hypertrichosis, Coat Condition and General Health Parameters in Horses with Pituitary Pars Intermedia Dysfunction. Animals (Basel) 2025 Oct 5;15(19).
- Schott HC 2nd, Strachota JR, Marteniuk JV, Refsal KR. Long-Term Response of Equids With Pituitary Pars Intermedia Dysfunction to Treatment With Pergolide. J Vet Intern Med 2025 May-Jun;39(3):e70109.
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