Motzfeldt Jensen Mette, Almasi Charlotte, Florian Sørensen Hans Christian, Andersen Stine Linding, Andersen Stig
M Motzfeldt Jensen, Department of Clinical Medicine, Aalborg University Hospital, Aalborg, Denmark.
C Almasi, Department of Nuclear Medicine, Aalborg University Hospital, Aalborg, Denmark.
Eur Thyroid J. 2024 Dec 1;14(1). doi: 10.1530/ETJ-24-0272.
Thyroid hormones and sympathetic stimulation are needed for activating Brown adipose tissue (BAT) during cold exposure. Studies of human cold exposure have demonstrated both increased production and raised clearance of triiodothyronine (T3). Greenlandic hunters provide a unique model for evaluating metabolic effects of cold exposure.
We aimed to explore the dynamics of thyroid hormones when blocking sympathetic activity in Greenlandic hunters during winter to inspire knowledge on mechanisms of BAT activation.
We conducted a 7-day field study of Greenlandic hunters (n=7) in East Greenland in February. The sympathetic system was blocked using a non-selective beta blocker for seven consecutive days. A group of non-hunter Greenlanders (n = 8) from the same settlement were included for parallel sampling. All participants were healthy men. Blood samples were drawn daily for measurement of TSH, thyroid hormone levels, and thyroglobulin.
Hunters had higher serum thyroglobulin, TSH, and high fT3/fT4 ratio compared to controls. Blocking the sympathetic activity was followed by changes in serum thyroglobulin and fT3 with an initial decrease and subsequent restoration of levels, while TSH and fT4 showed a gradual increase over the course of the study. The fT3/fT4 ratio showed a continuous and marked decrease.
We hypothesise that when blocking the sympathetic system, TSH increases to uphold the production of T3 needed for maintaining BAT activity. Additionally, alterations of fT3/fT4-ratio support a hypothesis of adrenergic stimulation promoting T3 over T4 secretion from the thyroid via the adrenergic nerve terminals in the thyroid.
在寒冷暴露期间，甲状腺激素和交感神经刺激是激活棕色脂肪组织（BAT）所必需的。对人类寒冷暴露的研究表明，三碘甲状腺原氨酸（T3）的产生增加且清除率提高。格陵兰猎人提供了一个评估寒冷暴露代谢效应的独特模型。
我们旨在探索在冬季阻断格陵兰猎人的交感神经活动时甲状腺激素的动态变化，以增进对BAT激活机制的了解。
2月，我们在东格陵兰对格陵兰猎人（n = 7）进行了为期7天的实地研究。使用非选择性β受体阻滞剂连续7天阻断交感神经系统。来自同一定居点的一组非猎人格陵兰人（n = 8）被纳入进行平行采样。所有参与者均为健康男性。每天采集血样以测量促甲状腺激素（TSH）、甲状腺激素水平和甲状腺球蛋白。
与对照组相比，猎人的血清甲状腺球蛋白、TSH和高fT3/fT4比值更高。阻断交感神经活动后，血清甲状腺球蛋白和fT3发生变化，最初水平下降，随后恢复，而TSH和fT4在研究过程中逐渐升高。fT3/fT4比值持续且显著下降。
我们假设，当阻断交感神经系统时，TSH会增加以维持维持BAT活动所需的T3的产生。此外，fT3/fT4比值的改变支持了一种假设，即肾上腺素能刺激通过甲状腺中的肾上腺素能神经末梢促进甲状腺分泌T3而非T4。
