Yamanaka Yujiro, Motoshima Hidemasa, Uchida Kenji
Laboratory of Life & Health Sciences, Graduate School of Education, Hokkaido University, Sapporo, Japan.
Research and Education Center for Brain Science, Hokkaido University, Sapporo, Japan.
Neuropsychopharmacol Rep. 2019 Mar;39(1):41-47. doi: 10.1002/npr2.12042. Epub 2018 Nov 27.
The hypothalamic-pituitary-adrenal (HPA) axis responds to changing environmental demands including psychological stressors. The aim of the present study was to assess whether the time of day effects on the acute response of HPA axis activity to acute psychological stress.
We studied 27 healthy young subjects. The subjects were participated two experiments as follows. In the first experiment, subjects were instructed to keep their regular sleep schedule for 2 weeks which were measured by using a wrist-worn activity monitor. Afterward, to evaluate a diurnal rhythm of salivary cortisol, eight saliva samples were collected during waking period every 2 hours from when the subjects woke up. In the second experiment, the subjects were randomly assigned to two groups. The Trier Social Stress Test (TSST) was performed either in the morning (n = 14) or in the evening (n = 13). We measured diurnal rhythm of salivary cortisol and stress response of salivary cortisol and heart rate by the TSST. Morning and evening tests were started at 2 hours and 10 hours after woke up, respectively.
All subjects showed a normal diurnal rhythm of salivary cortisol concentration, with a peak in the morning immediately after awaking and a minimum in the evening. The salivary cortisol response after the TSST was significantly increased from the prestress level in the morning but not in the evening.
The HPA response to acute psychological stress was more pronounced in the morning than in the evening, correlating with the circadian regulation of cortisol synthesis.
下丘脑 - 垂体 - 肾上腺（HPA）轴对包括心理应激源在内的不断变化的环境需求做出反应。本研究的目的是评估一天中的时间是否会影响HPA轴活动对急性心理应激的急性反应。
我们研究了27名健康的年轻受试者。受试者参与了以下两个实验。在第一个实验中，受试者被要求保持两周的正常睡眠时间表，通过佩戴在手腕上的活动监测器进行测量。之后，为了评估唾液皮质醇的昼夜节律，从受试者醒来时起，在清醒期间每2小时收集8份唾液样本。在第二个实验中，受试者被随机分为两组。分别在上午（n = 14）或晚上（n = 13）进行特里尔社会应激测试（TSST）。我们通过TSST测量唾液皮质醇的昼夜节律以及唾液皮质醇和心率的应激反应。上午和晚上的测试分别在醒来后2小时和10小时开始。
所有受试者唾液皮质醇浓度均呈现正常的昼夜节律，醒来后立即在早晨达到峰值，晚上达到最低值。TSST后唾液皮质醇反应在上午从应激前水平显著增加，而在晚上则没有。
HPA轴对急性心理应激的反应在早晨比晚上更明显，这与皮质醇合成的昼夜调节相关。
