Circulating Hypothalamic-Pituitary-Adrenal Axis Hormones and Insulin Concentrations in Horses and Ponies.
Abstract: Mechanisms resulting in breed predispositions to insulin dysregulation (ID) are poorly characterized. Cortisol antagonizes insulin, and free, biologically active cortisol can be increased in ID. Breed-related differences in serum free cortisol fraction (FCF) could contribute to ID, but FCF has not been quantified in equidae predisposed to ID, such as ponies. To compare FCF and other hypothalamic-pituitary-adrenal (HPA) axis hormones between horses and ponies during health and ID. We hypothesized: (1) FCF is higher in ponies than horses in health, and is higher still in ponies with ID and obesity; and (2) FCF is positively correlated with insulin in horses and ponies during health and ID. Thirty-three horses and 24 ponies were sampled before morning feeding in their normal routine. Plasma ACTH and insulin and serum total cortisol concentrations and FCF were measured. ID was defined as evidence of hyperinsulinemia at rest or after oral sugar administration. Data were compared with Mann-Whitney tests and Spearman correlation analysis (P < 0.05). Total cortisol, free cortisol, insulin concentrations, and FCF were comparable in healthy horses (n = 24) and ponies (n = 12), but ACTH concentrations were 29% higher in ponies than in horses (P = 0.016). In animals with ID, total cortisol, free cortisol, and insulin concentrations were similar between horses and ponies, but FCF was increased 40% in ponies (n = 12) compared to horses (n = 9). These data demonstrate differences in insulin, ACTH, and free cortisol during health and ID between ponies and horses.
Copyright © 2021. Published by Elsevier Inc.
Publication Date: 2021-11-14 PubMed ID: 35219029DOI: 10.1016/j.jevs.2021.103810Google Scholar: Lookup
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- Journal Article
- Research Support
- Non-U.S. Gov't
Summary
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The research investigates the relationship and differences in the hormones of the hypothalamic-pituitary-adrenal axis and insulin levels between ponies and horses, both in healthy conditions and under insulin dysregulation (ID). The study found differences in the values of some hormones, including insulin, ACTH, and free cortisol among both animals during health and ID.
Objective of the Research
- The research was carried out to understand the mechanisms that result in breed predispositions to insulin dysregulation (ID) which is yet to be well defined.
- Because cortisol is known to counter insulin and could be increased in ID, the researchers also aimed to explore if differences in serum free cortisol fraction (FCF) between horses and ponies could contribute to ID.
Method
- A total of 33 horses and 24 ponies were sampled before their morning feed as part of their usual routine.
- The plasma ACTH and insulin and serum total cortisol concentrations along with FCF were measured in each subject.
- Insulin dysregulation (ID) was identified by the presence of hyperinsulinemia, either at rest or after oral sugar administration.
- Data obtained were analyzed and compared using the Mann-Whitney test and Spearman correlation analysis.
Findings
- It was observed that total cortisol, free cortisol, insulin concentrations, and FCF were similar in both healthy horses and ponies.
- However, ACTH concentrations were about 29% higher in ponies than in horses.
- In animals with ID, total cortisol, free cortisol, and insulin concentrations were again found to be similar between horses and ponies.
- Interestingly, in case of ID, FCF was found to be 40% higher in ponies compared to horses.
Conclusion
- The research demonstrated that there are differences in levels of insulin, ACTH, and free cortisol between ponies and horses both during health and in conditions of ID.
- The study hence provides valuable insights into the hormonal differences between horses and ponies, both under normal conditions and in states of insulin dysregulation.
Cite This Article
APA
Vaughn SA, Norton NA, Hart KA.
(2021).
Circulating Hypothalamic-Pituitary-Adrenal Axis Hormones and Insulin Concentrations in Horses and Ponies.
J Equine Vet Sci, 111, 103810.
https://doi.org/10.1016/j.jevs.2021.103810 Publication
Researcher Affiliations
- Department of Large Animal Medicine, College of Veterinary Medicine, University of Georgia, Athens, GA.
- Department of Large Animal Medicine, College of Veterinary Medicine, University of Georgia, Athens, GA.
- Department of Large Animal Medicine, College of Veterinary Medicine, University of Georgia, Athens, GA. Electronic address: khart4@uga.edu.
MeSH Terms
- Adrenocorticotropic Hormone
- Animals
- Horse Diseases
- Horses
- Hydrocortisone
- Hypothalamo-Hypophyseal System
- Insulin
- Insulin, Regular, Human
- Pituitary-Adrenal System
Citations
This article has been cited 3 times.- Menzies-Gow NJ. Equine Pituitary Pars Intermedia Dysfunction. Vet Sci 2025 Aug 20;12(8).
- Vaughn SA, Lemons MB, Hart KA. The Effect of Season and Breed on Hypothalamic-Pituitary-Adrenal Axis Hormones, Metabolic Hormones, and Oxidative Markers in Ponies and Horses. J Vet Intern Med 2025 Mar-Apr;39(2):e70047.
- Kellon EM, Gustafson KM. Hypertriglyceridemia in equines with refractory hyperinsulinemia treated with SGLT2 inhibitors. Open Vet J 2023 Mar;13(3):365-375.
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