PHYSIOLOGICAL BASIS OF THIRST
PHYSIOLOGICAL BASIS OF THIRST
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DOI：
10.1038/ki.1976.74
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发表时间：
1976-01-01
影响因子：
19.6
通讯作者：
FITZSIMONS, JT
中科院分区：
文献类型：
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作者：
FITZSIMONS, JT
水在很大程度上是生命的一部分，以至于不可能想象一个陆地生物没有确保充足供应的机制。在真正的陆地脊椎动物中，哺乳动物、鸟类和爬行动物已经很好地定义了口渴的机制，尽管还没有完全弄清楚。两栖动物一般不喝水，但它们会根据需要通过皮肤吸收水分。目前尚不清楚它们是否有一种由脱水激活的“水驱动”，这类似于高等脊椎动物的口渴，但尽管有主要负面报道，似乎一些两栖动物至少在脱水时确实会寻找水。有趣的是，催乳素具有诱导未成熟的蝾螈寻找水分并呈现繁殖形式的作用，据报道，它会引起人类志愿者的口渴和盐渴[1]，并在没有补偿减少生理盐水或水的摄入量的情况下，在兔子中保留钠和水[2]。催乳素诱导的水驱动作用可能与水平衡关系不大，因为它的目的几乎可以肯定主要是生殖。然而，这种行为，生活在干旱地区的两栖动物为了到达潮湿的底土而进行的洞穴活动，以及大量关于两栖动物寻找水的报道，表明两栖动物在脱水时可能会经历一种类似于高等脊椎动物口渴的感觉[3]。甚至在鱼类中，似乎也有因需要而喝水的情况。在海水中，鳗鱼和其他海洋硬骨鱼一样，是一种退行性硬骨鱼，它不断地饮水，以补充身体表面因渗透而失去的水分，但一旦进入淡水，它就会停止饮水。然而，在淡水中，可以通过注入高渗盐水(止渴的细胞刺激)或去除血液(止渴的细胞外刺激)来使其饮用[4]。因此，鳗鱼在对细胞和细胞外脱水的反应中表现出饮酒行为，这一点与哺乳动物相似。与哺乳动物不同，鳗鱼的饮水似乎是一种反射，因为它在切除前脑和中脑后仍在继续。讨论鱼是否感到口渴，一种有意识的感觉，或者喝水的行为是否完全是无意识的，这是没有什么意义的。由于鱼生活在水中，确保足够的饮水量所需的神经机制可能比陆地动物简单得多，在陆地动物中，首先寻找水，然后摄取水的行为要复杂得多。正是这种行为的复杂性可以解释陆地动物饮酒的脑化现象。重要的是，鱼类已经进化出在脱水状态下诱导水摄取所需的神经组织和其他机制。从鱼类的基本反射饮酒到陆生脊椎动物表现出的更复杂的寻找和消费水的行为，在系统发育过程中的进展反映在饮水行为的个体发育中。六天大的乳鼠因细胞或细胞外脱水而口渴，它们可以很容易地吞下放在嘴里的水，但它们不能为自己寻找水。因此，它们与淡水鱼相似。然而，当它们长大两周时，它们表现出与口渴的成年人相同的找水行为。成人饮酒行为的发展似乎并不依赖于个人的后天经验，尽管可以想象，成人之间的数量差异可能源于不同的后天经验或缺陷。
Water is so much a part of life that it is impossible to imagine a terrestrial organism not provided with mechanisms to ensure sufficient supplies. Among the truly terrestrial vertebrates, the mammals, birds and reptiles have well defined, albeit incompletely worked out, mechanisms of thirst. The amphibia in general do not drink but they absorb water according to need across the skin. It is not clear whether they have a “water drive” activated by dehydration which would be analogous to thirst in the higher vertebrates, but despite mainly negative reports it seems probable that some amphibians, at least, do seek out water when they are dehydrated. It is interesting that prolactin, which has the effect of inducing immature newts to seek water and assume their reproductive form, has been reported to cause thirst and salt craving in human volunteers [1] and retention of sodium and water without compensatory reduction of either saline or water intake in rabbits [2]. The prolactin-induced “water drive” effect in the newt may have little to do with water balance since its purpose is almost certainly mainly reproductive. Nevertheless, such behavior, the burrowing that amphibia inhabiting the arid regions engage in in order to reach the damp subsoil, as well as the numerous reports that amphibia seek water, suggest that amphibia may experience a sensation akin to thirst in the higher vertebrates when dehydrated [3].Even among the fish there appear to be situations where drinking of water is provoked by need. In sea water the eel, a catadromous teleost, like other marine teleosts, drinks continuously in order to replace the water lost by osmosis across the body surface, but as soon as it enters fresh water it stops drinking. However, in fresh water it can be made to drink by infusing hypertonic saline (a cellular stimulus to thirst) or by removing blood (an extracellular stimulus to thirst) [4]. The eel therefore resembles the mammal in showing drinking behavior in response to both cellular and extracellular dehydration. Unlike the mammal, drinking by the eel appears to be reflex since it continues after removal of the prosencephalon and mesencephalon. There is little purpose in discussing whether the fish experiences thirst, a conscious sensation, or whether the act of drinking is entirely unconscious. Since the fish lives in water, the neural mechanisms needed to ensure that enough is drunk could be simpler than in a terrestrial animal where the much more complicated behavior of first seeking and then ingesting water is required. It is this complexity of behavior that could account for the encephalization of drinking in the terrestrial animal. What is important is that the fishes have already evolved the neural organization and other mechanisms necessary to induce intake of water in states of dehydration.The progression during phylogeny from essentially reflex drinking in the fish to the much more complicated behavior of seeking and consuming water shown by the terrestrial vertebrates is reflected in the ontogeny of drinking behavior [5]. Six-day-old suckling rats made thirsty by cellular or extracellular dehydration will readily swallow water placed in the mouth, but they are not capable of seeking water for themselves. They therefore resemble freshwater fish. When they are two weeks older, however, they show the same water-seeking behavior as thirsty adults. The development of adult drinking behavior does not appear to depend on individual postnatal experience though it is conceivable that quantitative differences between adults may stem from different postnatal experiences to deficits.