Circannual variability in adrenocorticotropic hormone responses to administration of thyrotropin-releasing hormone in clinically normal horses in Australia.
Abstract: Thyrotropin releasing hormone (TRH)-stimulation testing for pituitary pars intermedia dysfunction (PPID) in horses is only recommended at certain times of the year. Current diagnostic cut-off values reflect testing in the northern hemisphere during this time. The aims of this study were to evaluate TRH stimulation testing during two different phases of the circannual pituitary cycle and to determine whether diagnostic cut-off values developed in the northern hemisphere are appropriate in Australia. Thirteen clinically normal horses at Perth, Western Australia, and 23 horses at Townsville, Queensland, Australia, had TRH stimulation tests performed at two different time points during the circannual pituitary cycle. At both locations, post-TRH adrenocorticotropic hormone (ACTH) concentrations were significantly different between testing time points (Perth: P=0.001; Townsville: P<0.0001). In Perth, the mean ACTH concentrations 10min post-TRH in September and March were 51.4pg/mL (95% confidence interval, CI, 46.4-56.4pg/mL) and 248.5pg/mL (95% CI 170.2-326.9pg/mL), respectively. The median percentage change in ACTH concentrations in March was 361.9%. In Townsville, the mean ACTH concentrations 30min post-TRH in September and April were 35.3pg/mL (95% CI 29.6-40.9pg/mL) and 112.3pg/mL (95% CI 93.4-131.2pg/mL), respectively. The median percentage change in ACTH concentrations in April was 144.7%. The ACTH cut-off value after TRH stimulation in normal horses in September in Perth and Townsville was similar to the values established in the northern hemisphere. However, TRH stimulation testing in March/April was highly variable at both locations.
Crown Copyright © 2018. Published by Elsevier Ltd. All rights reserved.
Publication Date: 2018-07-19 PubMed ID: 30103916DOI: 10.1016/j.tvjl.2018.07.008Google Scholar: Lookup
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- Journal Article
- Adrenocorticotropic Hormone (ACTH)
- Animal Health
- Animal Science
- Clinical Study
- Comparative Study
- Diagnosis
- Diagnostic Technique
- Disease Diagnosis
- Endocrine System
- Epidemiology
- Equine Health
- Geographical Differences
- Hormones
- Horses
- Physiology
- Pituitary Pars Intermedia Dysfunction
- Thyroid Hormones
- Thyrotropin-Releasing Hormone
- Veterinary Medicine
- Veterinary Research
Summary
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This study evaluates the variability in the responses to Thyrotropin releasing hormone stimulation testing in horses in two Australian locations during different times of the year. The results were then compared to diagnostic cut-off values from the northern hemisphere to determine their suitability in the Australian context.
Research Methodology
- Thirteen clinically normal horses in Perth, Western Australia, and twenty-three horses in Townsville, Queensland, Australia were selected for this study. Each horse underwent Thyrotropin releasing hormone (TRH) stimulation tests at two separate times during the circannual pituitary cycle.
- The adrenocorticotropic hormone (ACTH) levels of the horses were measured before and after the TRH stimulation tests, with a significant difference found between the testing time points at both locations.
Findings from Perth, Western Australia
- The ACTH concentrations 10 minutes post-TRH in September and March averaged at 51.4pg/mL and 248.5pg/mL, respectively.
- In March, there was seen an average increase of 361.9% in ACTH levels compared to the initial September readings.
Findings from Townsville, Queensland, Australia
- The ACTH concentrations 30 minutes post-TRH in September and April averaged at 35.3pg/mL and 112.3pg/mL, respectively.
- In April, there was seen an average increase of 144.7% in ACTH levels compared to the initial September readings.
Correlation with Northern Hemisphere Cut-Off Values
- The ACTH cut-off value after TRH stimulation in normal horses in September in both Perth and Townsville was similar to the values established in the northern hemisphere.
- However, the TRH stimulation testing in the later phase (March/April) saw highly variable readings in both locations, indicating possible regional variations.
Conclusion
- The research suggests that while the diagnostic cut-off values from the northern hemisphere may be applicable for Australian horses during certain periods, they may not be reliable across all months.
- It points towards the need for region-specific diagnostic cut-offs for TRH stimulation tests to accurately determine potential pituitary pars intermedia dysfunction in horses.
Cite This Article
APA
Byrne DP, Secombe CJ, Tan RHH, Perera DI, Watts SP, Wearn JG.
(2018).
Circannual variability in adrenocorticotropic hormone responses to administration of thyrotropin-releasing hormone in clinically normal horses in Australia.
Vet J, 238, 58-62.
https://doi.org/10.1016/j.tvjl.2018.07.008 Publication
Researcher Affiliations
- College of Veterinary Medicine, School of Veterinary and Life Sciences, Murdoch University, Perth, Western Australia, Australia.
- College of Veterinary Medicine, School of Veterinary and Life Sciences, Murdoch University, Perth, Western Australia, Australia. Electronic address: csecombe@murdoch.edu.au.
- Discipline of Veterinary Clinical Sciences, College of Public Health, Medical and Veterinary Sciences, James Cook University, Townsville, Queensland, Australia.
- School of Engineering and IT, Murdoch University, Perth, Western Australia, Australia.
- Discipline of Veterinary Clinical Sciences, College of Public Health, Medical and Veterinary Sciences, James Cook University, Townsville, Queensland, Australia.
- Discipline of Veterinary Clinical Sciences, College of Public Health, Medical and Veterinary Sciences, James Cook University, Townsville, Queensland, Australia.
MeSH Terms
- Adrenocorticotropic Hormone / blood
- Adrenocorticotropic Hormone / drug effects
- Animals
- Australia
- Horse Diseases / diagnosis
- Horses / metabolism
- Pituitary Diseases / diagnosis
- Pituitary Diseases / veterinary
- Thyrotropin-Releasing Hormone / pharmacology
- Time Factors
Citations
This article has been cited 5 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).
- Kam YN, McKenzie K, Coyle M, Bertin FR. Repeatability of a thyrotropin-releasing hormone stimulation test for diagnosis of pituitary pars intermedia dysfunction in mature horses. J Vet Intern Med 2021 Nov;35(6):2885-2890.
- Horn R, Stewart AJ, Jackson KV, Dryburgh EL, Medina-Torres CE, Bertin FR. Clinical implications of using adrenocorticotropic hormone diagnostic cutoffs or reference intervals to diagnose pituitary pars intermedia dysfunction in mature horses. J Vet Intern Med 2021 Jan;35(1):560-570.
- Menzies-Gow NJ. Equine Pituitary Pars Intermedia Dysfunction. Vet Sci 2025 Aug 20;12(8).
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