How Ole-Jakob, Nordøy Erling S
Department of Arctic Biology and Institute of Medical Biology, University of Tromsø, Breivika, Tromsø 9037, Norway.
J Comp Physiol B. 2007 Jul;177(5):535-42. doi: 10.1007/s00360-007-0152-9. Epub 2007 Mar 21.
The purpose of this study was to answer the question of whether dehydrated harp seals (Phoca groenlandica) are able to obtain a net gain of water from the intake of seawater. Following 24 h of fasting, three subadult female harp seals were dehydrated by intravenous administration of the osmotic diuretic, mannitol. After another 24 h of fasting, the seals were given 1,000 ml seawater via a stomach tube. Urine and blood were collected for measurement of osmolality and osmolytes, while total body water (TBW) was determined by injections of tritiated water. In all seals, the maximum urinary concentrations of Na(+) and Cl(-) were higher than in seawater, reaching 540 and 620 mM, respectively, compared to 444 and 535 mM in seawater. In another experiment, the seals were given ad lib access to seawater for 48 h after mannitol-induced hyper-osmotic dehydration. In animals without access to seawater, the mean blood osmolality increased from 331 to 363 mOsm kg(-1) during dehydration. In contrast, the blood osmolality, hematocrit and TBW returned to normal when the seals were permitted ad lib access to seawater after dehydration. In conclusion, this study shows that harp seals have the capacity to gain net water from mariposa (voluntarily drinking seawater) and are able to restore water balance after profound dehydration by drinking seawater.
本研究的目的是回答脱水的竖琴海豹（格陵兰海豹）是否能够通过摄入海水获得净水分增加的问题。在禁食24小时后，通过静脉注射渗透性利尿剂甘露醇使三只亚成年雌性竖琴海豹脱水。在另外禁食24小时后，通过胃管给海豹喂食1000毫升海水。收集尿液和血液以测量渗透压和渗透溶质，同时通过注射氚标记水来测定总体水（TBW）。在所有海豹中，Na⁺和Cl⁻的最大尿浓度均高于海水，分别达到540和620 mM，而海水中为444和535 mM。在另一项实验中，在甘露醇诱导的高渗性脱水后，让海豹自由饮用海水48小时。在无法获取海水的动物中，脱水期间平均血液渗透压从331升高至363 mOsm kg⁻¹。相比之下，脱水后当允许海豹自由饮用海水时，血液渗透压、血细胞比容和总体水恢复正常。总之，本研究表明竖琴海豹有能力从饮用海水（自愿饮用海水）中获得净水分，并且能够通过饮用海水在严重脱水后恢复水平衡。
