Background: In dogs, spontaneous Cushing’s syndrome is most often pituitary-dependent and caused by hypersecretion of adrenocorticotropic hormone (ACTH), resulting in increased adrenocortical glucocorticoid secretion similar to horses. In horses with Cushing’s syndrome (or pituitary pars intermedia dysfunction [PPID]) a thyrotropin-releasing hormone (TRH) stimulation test can be used for diagnosis, as TRH administration results in increased circulating ACTH and cortisol concentrations in affected horses.

Objective: The aim of this study was to investigate the effect of TRH administration on the circulating ACTH and cortisol concentrations in dogs with pituitary-dependent hypercortisolism (PDH).

Methods: Ten clinically normal control dogs and 10 dogs with PDH, all client owned, underwent a TRH stimulation test with measurement of plasma concentrations of ACTH and cortisol, before and after intravenous administration of 10 μg TRH/kg bodyweight.

Results: Plasma ACTH concentration did not rise significantly after TRH stimulation, neither in PDH dogs nor in clinically normal dogs. In contrast, the plasma cortisol concentration did increase significantly after TRH stimulation in both groups (p = .003 in PDH and p < .001 in control). Immunohistochemistry of normal adrenal glands demonstrated the presence of TRH receptors in the whole adrenal cortex.

Conclusions: The results of this study demonstrate that the TRH stimulation test should be rejected as a tool to diagnose PDH in dogs. The observed TRH-induced increase in plasma cortisol concentration without a significant rise in plasma ACTH concentration may be explained by a direct effect of TRH on adrenocortical cells mediated by adrenocortical TRH receptors.

背景：在狗中，自发性库欣综合症通常是垂体依赖性的，是由促肾上腺皮质激素（ACTH）分泌过多引起的，导致与马相似的肾上腺皮质糖皮质激素分泌增加。在患有库欣综合症（或垂体中间部功能障碍[PPID]）的马中，可使用促甲状腺激素释放激素（TRH）刺激试验进行诊断，因为TRH给药会导致患病马的循环ACTH和皮质醇浓度增加。

目的：本研究旨在探讨TRH给药对垂体依赖型高皮质病（PDH）犬循环中ACTH和皮质醇浓度的影响。

方法： 10只临床上正常的对照犬和10只PDH犬（全部归客户所有）在静脉内施用10μgTRH / kg体重之前和之后进行了TRH刺激试验，测量了ACTH和皮质醇的血浆浓度。

结果： TRH刺激后，无论是PDH犬还是临床正常犬，血浆ACTH浓度均未显着升高。相比之下，两组TRH刺激后血浆皮质醇浓度确实显着增加（ PDH中p = 0.003  ，对照中p <.001）。正常肾上腺的免疫组织化学表明整个肾上腺皮质中存在TRH受体。

结论：这项研究的结果表明，TRH刺激试验不应作为诊断狗中PDH的工具。TRH对肾上腺皮质TRH受体介导的肾上腺皮质细胞的直接影响可能解释了观察到的TRH诱导的血浆皮质醇浓度增加而血浆ACTH浓度没有明显增加。