Extracellular rather than intracellular pathway plays an important role in attenuating thirst and drinking desirability during head-out immersion in hypohydrated men.

本研究的目的是调查的机制，减少口渴的感觉在头伸出水浸泡（HOI）在低水分的受试者。8名男性（19-25岁）在两种不同条件下接受热中性HOI（水温; 34.5 ℃）和热中性空气（室温; 28 ℃），正常水化（Eu-H_2 O和Eu-air）和低水化（Hypo-H_2 O，在高温下运动后体重减轻3.8%，Posm = +10 mosmol/kg和Hypo-air）。在整个实验期间，受试者不允许饮酒。使用Hypo-H_2 O的视觉模拟量表上的口渴感减少低氧组在HOI 10 min时，利尿作用明显减弱，血浆容量持续增加，而Eu-H_2 O组在HOI早期出现短暂的血浆扩张，而在整个HOI期间观察到显著的利尿作用，（P<0.05）血浆心钠素水平持续下降Eu-H_2 O和Hypo-H_2 O均能降低HOI时血浆肾素活性（P<0.05）低氧组HOI时每搏输出量增加显著（P<0.05），而Eu-H_2 O组无显著差异（P> 0.05）HOI时缺氧组与缺氧组比较差异有显著性（P<0.05），因此，更大的增加HOI时每搏输出量的增加（P<0.05）可能提示低氧对机械感受器的刺激作用更强。本研究结果可能支持细胞外途径可能在减少低水化受试者HOI期间的口渴感中起重要作用的假设。

The purpose of this study was to investigate the mechanisms underlying a reduction of thirst sensation during head-out water immersion (HOI) in hypohydrated subjects. Eight males (19-25 yr) were subjected to thermoneutral HOI (water temperature ; 34.5ﾟC) and thermoneutral air (room temperature ; 28ﾟC) under two different conditions, euhydrated (Eu-H_2O and Eu-air) and hypohydrated (Hypo-H_2O, 3.8% weight loss after exercise in heat, Posm = +10 mosmol/kg and Hypo-air). Subjects were not allowed to drink throughout experimental periods. Thirst sensation on a visual analog scale with Hypo-H_2O was decreased (P<0.05) in 10 min of HOI.A significant attenuation of diuresis and a sustained increase in plasma volume occurred throughout HOI with Hypo-H_2O.In Eu-H_2O, however, a transient plasma expansion was observed early during HOI, while a remarkable diuresis was observed throughout HOI.There was a prompt and sustained increase (P<0.05) in the plasma level of atrial natriuretic peptides and a sustained decrease (P<0.05) in the plasma renin activity during HOI in both Eu-H_2O and Hypo-H_2O.Plasma arginine vasopressin decreased (P<0.05) during HOI in Hypo-H_2O but not in Eu-H_2O.The increment of stroke volume was greater (P<0.05) with Hypo-H_2O during HOI.Therefore, a greater increase (P<0.05) in stroke volume during HOI may suggest the greater stimulation of the mechanoreceptors with Hypo-H_2O.Plasma osmolality remained elevated in the presence of an attenuated thirst during HOI.Thus, the present results may support the hypothesis that the extracellular pathways may play an important role in reducing thirst sensation during HOI in hypohydrated subjects.