Circannual variability in adrenocorticotropic hormone responses to administration of thyrotropin-releasing hormone in clinically normal horses in Australia

Byrne, D.P., Secombe, C.J., Tan, R.H.H., Perera, D.I., Watts, S.P., and Wearn, J.G. (2018) Circannual variability in adrenocorticotropic hormone responses to administration of thyrotropin-releasing hormone in clinically normal horses in Australia. The Veterinary Journal, 238. pp. 58-62.

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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 10 min post-TRH in September and March were 51.4 pg/mL (95% confidence interval, CI, 46.4-56.4 pg/mL) and 248.5 pg/mL (95% CI 170.2-326.9 pg/mL), respectively. The median percentage change in ACTH concentrations in March was 361.9%. In Townsville, the mean ACTH concentrations 30 min post-TRH in September and April were 35.3 pg/mL (95% CI 29.6-40.9 pg/mL) and 112.3 pg/mL (95% CI 93.4-131.2 pg/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.

Item ID: 55704
Item Type: Article (Research - C1)
ISSN: 1532-2971
Keywords: adrenocorticotropic hormone, equine, pituitary pars intermedia dysfunction, reference values, thyrotropin-releasing hormone
Funders: Murdoch University Veterinary Trust
Date Deposited: 26 Sep 2018 08:19
FoR Codes: 07 AGRICULTURAL AND VETERINARY SCIENCES > 0707 Veterinary Sciences > 070799 Veterinary Sciences not elsewhere classified @ 100%
SEO Codes: 83 ANIMAL PRODUCTION AND ANIMAL PRIMARY PRODUCTS > 8303 Livestock Raising > 830306 Horses @ 100%
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