Atmosphere and Ocean Research Institute, The University of Tokyo, Kashiwa, Chiba 277-8564, Japan,
Zoolog Sci. 2024 Feb;41(1):132-139. doi: 10.2108/zs230085.
Vertebrates have expanded their habitats during evolution, which accompanies diversified routes for water acquisition. Water is acquired by oral intake and subsequent absorption by the intestine in terrestrial and marine animals which are subjected to constant dehydration, whereas most water is gained osmotically across body surfaces in freshwater animals. In addition, a significant amount of water, called metabolic water, is produced within the body by the oxidation of hydrogen in organic substrates. The importance of metabolic water production as a strategy for water acquisition has been well documented in desert animals, but its role has attracted little attention in marine animals which also live in a dehydrating environment. In this article, the author has attempted to reevaluate the role of metabolic water production in body fluid regulation in animals inhabiting desiccating environments. Because of the exceptional ability of their kidney, marine mammals are thought to typically gain water by drinking environmental seawater and excreting excess NaCl in the urine. On the other hand, it is established that marine teleosts drink seawater to enable intestinal water and ion absorption, and the excess NaCl is excreted by branchial ionocytes. In addition to the oral route, we suggest through experiments using eels that water production by lipid metabolism is an additional route for water acquisition when they encounter seawater. It seems that metabolic water production contributes to counteract dehydration before mechanisms for water regulation are reversed from excretion in freshwater to acquisition in seawater.
脊椎动物在进化过程中扩展了它们的栖息地，伴随着多样化的水分获取途径。陆地和海洋动物通过口腔摄入和随后的肠道吸收来获取水分，这些动物经常处于脱水状态，而大多数水则通过淡水动物的体表面渗透来获取。此外，体内由有机基质中的氢氧化产生大量被称为代谢水的水分。代谢水产生作为获取水分的策略的重要性在沙漠动物中得到了很好的证明，但它在同样生活在脱水环境中的海洋动物中的作用却很少受到关注。在本文中，作者试图重新评估代谢水产生在生活在干燥环境中的动物体液调节中的作用。由于其肾脏的特殊能力，海洋哺乳动物通常被认为是通过饮用环境海水并在尿液中排泄多余的 NaCl 来获得水分的。另一方面，已经确定海洋硬骨鱼通过饮用海水来实现肠道水和离子吸收，多余的 NaCl 则通过鳃离子细胞排泄。除了口腔途径，我们通过对鳗鱼的实验表明，当它们遇到海水时，通过脂质代谢产生水是获取水分的另一种途径。似乎代谢水的产生有助于在水调节机制从淡水的排泄转变为海水的获取之前，对抗脱水。
