von Ameln H, Laniado M, Röcker L, Kirsch K A
J Appl Physiol (1985). 1985 Jan;58(1):114-20. doi: 10.1152/jappl.1985.58.1.114.
Nine healthy volunteers underwent three experimental procedures in random order. The protocols were 4 h of thermal dehydration followed by 2 h of head-out water immersion, 4 h of thermal dehydration followed by 2 h of chair rest, and 6 h of rest in the supine position. Four hours of heat exposure (50 degrees C) resulted in a body weight loss of approximately 3.5%. Plasma osmolality rose by approximately 5 mosmol/kg, mean arterial pressure (MAP) decreased from 85 to 78 mmHg, and body temperature increased from 36.8 to 38.6 degrees C. As a consequence of the combined action of hypertonicity, hypovolemia, hypotension, and hyperthermia, plasma arginine vasopressin (AVP) increased from 2.1 to 8.1 pg/ml after 4 h thermal dehydration. Changes in body weight, plasma osmolality, body temperature, and MAP were similar after either a subsequent 2 h of water immersion or 2 h of chair rest. However, during chair rest plasma AVP remained elevated (8.4 pg/ml), whereas during immersion plasma AVP decreased from 8.1 to 4.7 pg/ml. This was probably due to the central hypervolemia induced by immersion. Our results support the hypothesis that central hypervolemia rather than hypotonicity is the primary stimulus for AVP suppression during water immersion in dehydrated subjects. During the early immersion period hypoosmolality might contribute to the AVP suppression.
九名健康志愿者按随机顺序接受了三项实验程序。实验方案分别为：4小时热脱水后接着2小时头部浸入水中；4小时热脱水后接着2小时坐在椅子上休息；6小时仰卧休息。4小时的热暴露（50摄氏度）导致体重减轻约3.5%。血浆渗透压上升约5毫摩尔/千克，平均动脉压（MAP）从85毫米汞柱降至78毫米汞柱，体温从36.8摄氏度升至38.6摄氏度。由于高渗、血容量不足、低血压和体温过高的共同作用，热脱水4小时后血浆精氨酸加压素（AVP）从2.1皮克/毫升升至8.1皮克/毫升。随后2小时的头部浸入水中或坐在椅子上休息后，体重、血浆渗透压、体温和MAP的变化相似。然而，坐在椅子上休息时血浆AVP仍保持升高（8.4皮克/毫升），而在浸入水中时血浆AVP从8.1皮克/毫升降至4.7皮克/毫升。这可能是由于浸入水中引起的中枢性血容量过多所致。我们的结果支持这样一种假说，即对于脱水受试者，中枢性血容量过多而非低渗是水浸期间AVP抑制的主要刺激因素。在浸入水的早期，低渗可能有助于AVP的抑制。
