School of Veterinary Science, The University of Queensland, Gatton, Queensland, Australia.
Boehringer Ingelheim Pty Ltd, North Ryde, New South Wales, Australia.
J Vet Intern Med. 2020 May;34(3):1350-1356. doi: 10.1111/jvim.15771. Epub 2020 Apr 7.
Determination of plasma adrenocotrophic hormone (ACTH) concentration (endogenous or thyrotropin-releasing hormone [TRH] stimulation test) is the most commonly used diagnostic test for pituitary pars intermedia dysfunction (PPID) in horses. Because ACTH is unstable, samples often are frozen to be shipped to laboratories or to allow for batch analysis of research samples. However, the effect of multiple freeze-thaw cycles on equine ACTH is unknown.
To determine the effects of multiple freeze-thaw cycles on immunoreactive ACTH concentration.
Twenty-eight horses ranging from 10 to 27 years of age were used.
Prospective study. Horses were divided into 4 groups: group 1, PPID-negative, without TRH stimulation; group 2, PPID-negative, with TRH stimulation; group 3, PPID-positive, without TRH stimulation; and group 4, PPID-positive, with TRH stimulation. Whole blood was collected from each horse at baseline or 30 minutes after TRH stimulation. Immunoreactive plasma ACTH concentration was determined using a chemiluminescence assay. Plasma samples then were frozen at -80°C >24 hours, thawed at 4°C and reanalyzed for 5 freeze-thaw cycles. Changes in plasma ACTH concentration were analyzed using a linear mixed-effect model.
Significant effects of freeze-thaw cycles (P = .001) and PPID status (P = .04) on plasma ACTH concentration were observed, but no significant effect of TRH stimulation was identified.
The plasma ACTH concentration is altered by freeze-thaw cycles, and the effect is observed sooner in horses with PPID. To diagnose PPID, multiple freeze-thaw cycles should be avoided when measuring plasma ACTH concentration.
测定血浆促肾上腺皮质激素（ACTH）浓度（内源性或促甲状腺素释放激素[TRH]刺激试验）是目前最常用于马垂体中间叶功能减退症（PPID）的诊断试验。由于 ACTH 不稳定，通常将样本冷冻以运送到实验室或允许批量分析研究样本。然而，多次冻融循环对马 ACTH 的影响尚不清楚。
确定多次冻融循环对免疫反应性 ACTH 浓度的影响。
28 匹马，年龄 10 至 27 岁。
前瞻性研究。将马分为 4 组：组 1，PPID 阴性，无 TRH 刺激；组 2，PPID 阴性，有 TRH 刺激；组 3，PPID 阳性，无 TRH 刺激；组 4，PPID 阳性，有 TRH 刺激。从每匹马采集基础或 TRH 刺激后 30 分钟的全血。使用化学发光测定法测定免疫反应性血浆 ACTH 浓度。将血浆样本在-80°C 下冷冻>24 小时，在 4°C 下解冻，并进行 5 个冻融循环的重新分析。使用线性混合效应模型分析血浆 ACTH 浓度的变化。
观察到冻融循环（P=.001）和 PPID 状态（P=.04）对血浆 ACTH 浓度有显著影响，但未发现 TRH 刺激有显著影响。
冻融循环改变了血浆 ACTH 浓度，并且在 PPID 马中更早观察到这种影响。为了诊断 PPID，在测量血浆 ACTH 浓度时应避免多次冻融循环。
