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

本研究的目的是探讨缺水受试者在头部出水浸泡（HOI）过程中口渴感觉减少的机制。8名男性（19-25岁）在两种不同的条件下进行热中性HOI（水温，34.5ºC）和热中性空气（室温，28ºC），脱水（Eu-H_2O和Eu-air）和低水合（低h_2o，热运动后体重减轻3.8%,Posm = +10 mosmol/kg和低空气）。在整个实验期间，受试者不得饮酒。低氢水视觉模拟量表的口渴感觉在HOI 10 min时降低（P<0.05）。在整个低氧HOI中，利尿明显减弱，血浆容量持续增加。然而，在Eu-H_2O中，在HOI早期观察到短暂的等离子体膨胀，而在整个HOI过程中观察到明显的利尿。Eu-H_2O和sub - h_2o在HOI期间血浆肾素活性持续降低（P<0.05），血浆钠肽水平持续升高（P<0.05）。血浆精氨酸抗利尿激素在低浓度h_2o条件下降低（P<0.05），而在高浓度h_2o条件下无显著差异。在HOI期间，低浓度h_2o对脑卒中容量的增加作用更大（P<0.05）。因此，HOI期间脑卒中容量的较大增加（P<0.05）可能表明低氧水对机械感受器的刺激更大。在HOI期间，在口渴减轻的情况下，血浆渗透压仍然升高。因此，目前的结果可能支持细胞外通路可能在减少缺水受试者在HOI期间的口渴感觉中发挥重要作用的假设。

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.