Stacey Michael J, Woods David R, Brett Stephen J, Britland Sophie E, Fallowfield Joanne L, Allsopp Adrian J, Delves Simon K
Department of Surgery and Cancer, Imperial College London, London, United Kingdom.
Department of Military Medicine, Royal Centre for Defence Medicine, Birmingham, United Kingdom.
Physiol Rep. 2018 Sep;6(18):e13851. doi: 10.14814/phy2.13851.
Acclimatization favors greater extracellular tonicity from lower sweat sodium, yet hyperosmolality may impair thermoregulation during heat stress. Enhanced secretion or action of vasopressin could mitigate this through increased free water retention. Aims were to determine responses of the vasopressin surrogate copeptin to dehydrating exercise and investigate its relationships with tonicity during short and long-term acclimatization. Twenty-three participants completed a structured exercise programme following arrival from a temperate to a hot climate. A Heat Tolerance Test (HTT) was conducted on Day-2, 6, 9 and 23, consisting of 60-min block-stepping at 50% VO peak, with no fluid intake. Resting sweat [Na ] was measured by iontophoresis. Changes in body mass (sweat loss), core temperature, heart rate, osmolality (serum and urine) and copeptin and aldosterone (plasma) were measured with each Test. From Day 2 to Day 23, sweat [Na ] decreased significantly (adjusted P < 0.05) and core temperature and heart rate fell. Over the same interval, HTT-associated excursions were increased for serum osmolality (5 [-1, 9] vs. 9 [5, 12] mosm·kg ), did not differ for copeptin (9.6 [6.0, 15.0] vs. 7.9 [4.3, 14.7] pmol·L ) and were reduced for aldosterone (602 [415, 946] vs. 347 [263, 537] pmol·L ). Urine osmolality was unchanging and related consistently to copeptin at end-exercise, whereas the association between copeptin and serum osmolality was right-shifted (P = 0.0109) with acclimatization. Unchanging urine:serum osmolality argued against increased renal action of vasopressin. In conclusion, where exercise in the heat is performed without fluid replacement, heat acclimatization does not appear to enhance AVP-mediated free water retention in humans.
适应性变化有利于因汗液钠含量降低而使细胞外张力增加，但在热应激期间高渗状态可能会损害体温调节。血管加压素分泌增加或作用增强可通过增加自由水潴留来缓解这种情况。本研究旨在确定血管加压素替代物 copeptin 对脱水运动的反应，并研究其在短期和长期适应过程中与张力的关系。23 名参与者在从温带气候地区抵达炎热气候地区后完成了一项结构化运动计划。在第 2、6、9 和 23 天进行了耐热性测试（HTT），包括以 50% 最大摄氧量进行 60 分钟的台阶试验，期间不摄入液体。通过离子电渗法测量静息时的汗液[Na]。每次测试时测量体重变化（汗液流失）、核心温度、心率、渗透压（血清和尿液）以及 copeptin 和醛固酮（血浆）。从第 2 天到第 23 天，汗液[Na]显著下降（校正 P < 0.05），核心温度和心率下降。在相同时间段内，HTT 相关的血清渗透压升高（5 [-1, 9] 与 9 [5, 12] mosm·kg） copeptin 无差异（9.6 [6.0, 15.0] 与 7.9 [4.3, 14.7] pmol·L），醛固酮降低（602 [415, 946] 与 347 [263, 537] pmol·L）。运动结束时尿渗透压不变且始终与 copeptin 相关，而随着适应，copeptin 与血清渗透压之间的关联向右偏移（P = 0.0109）。尿渗透压与血清渗透压不变表明血管加压素的肾脏作用未增强。总之，在炎热环境中进行无液体补充的运动时，热适应似乎并未增强人体中 AVP 介导的自由水潴留。
