Hucklebridge F H, Clow A, Abeyguneratne T, Huezo-Diaz P, Evans P
Department of Biomedical Sciences, University of Westminster, London, UK.
Life Sci. 1999;64(11):931-7. doi: 10.1016/s0024-3205(99)00019-3.
The hypothalamic-pituitary-adrenal axis is characterized by a marked circadian cycle with heightened activity in the morning. This is synchronized to awakening such that free cortisol increases two to three fold in the first thirty to forty five minutes following awakening -- the awakening cortisol response. It has been suggested that this activity, by mobilizing energy reserves prepares the body for the metabolic demands of the day. Similar arguments are applied to the cortisol response to psychological challenge. Paradoxically the cortisol response to a psychosocial stressor is abrogated in fasted individuals with low blood glucose. Also cortisol response to a psychosocial stressor is positively correlated to blood glucose levels after glucose load. We examined if the same relationship applies to the awakening cortisol response. There was no correlation between the cortisol response and awakening blood glucose levels. Moreover a group with mean blood glucose at the bottom of the euglycemic range, identified by split at the median for glucose level upon awakening, showed no deficit in cortisol response. Hence the physiology of the awakening response differs to that of a psychological stress response. These data challenge the view that an oxidisable substrate for energy metabolism is permissive for cortisol responses. In addition the present findings do not support a predominantly gluconeogenic role for morning cortisol activation.
下丘脑 - 垂体 - 肾上腺轴的特点是存在明显的昼夜节律周期，早晨活动增强。这种节律与觉醒同步，以至于在觉醒后的最初30至45分钟内，游离皮质醇增加两到三倍——即觉醒皮质醇反应。有人认为，这种活动通过调动能量储备，使身体为一天的代谢需求做好准备。类似的观点也适用于皮质醇对心理挑战的反应。矛盾的是，在血糖低的禁食个体中，皮质醇对心理社会应激源的反应被消除。此外，皮质醇对心理社会应激源的反应与葡萄糖负荷后的血糖水平呈正相关。我们研究了这种关系是否也适用于觉醒皮质醇反应。皮质醇反应与觉醒时的血糖水平之间没有相关性。此外，通过将觉醒时的血糖水平按中位数划分，确定了一组血糖均值处于正常血糖范围下限的人群，该组在皮质醇反应方面没有缺陷。因此，觉醒反应的生理机制与心理应激反应不同。这些数据对能量代谢的可氧化底物有利于皮质醇反应这一观点提出了挑战。此外，目前的研究结果不支持早晨皮质醇激活主要具有糖异生作用的观点。
