Distribution of water losses among fluid compartments of tissues under thermal dehydration in the rat.

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Abstract
Dehydration amounting to .apprx. 10% of body weight was induced in adult male rats by exposure to a hot, dry environment (D.B.T. [daily base temperature], 36.degree. C; R.H. [relative humidity], 20%) over 6-8 h. The volumes of total water (TW), extracellular fluid (ECF) and plasma (PV) were determined both on individual tissues and on the whole body using the constant dry weight as well as 51Cr-EDTA and 125I-RIHSA [radioiodinated human serum albumin] dilution methods. Total body water (TBW), intracellular (ICF) and interstitial (ISF) fluid volumes were calculated from these data. The 10% loss of body weight caused a decrease in TBW by 17% from the control value; 41% of this loss was from ICF, 47% from ISF and 12% from PV. The decrese of ISF was proportional to that of PV and the water loss from ICF was caused by an increase in plasma osmolality. As to the water loss from organs, 40% of the whole body water loss came from muscle, 30% from skin, 14% from bone and 14% from viscera. The G.I. [gastrointestinal] trace had the highest tendency to lose water while the brain and liver showed the least. Evidently, under heat-induced dehydration, both the extra- and intracellular fluid compartments of muscle and skin play an important role in the compensation of water loss and in the maintenance of circulation to the brain and liver.