The Conservation of Water by Young Adult Rats with Restricted Water Supplies

Abstract

The purpose of this work was to study the water balance of laboratory rats under restricted water conditions, with particular attention to insensible water loss. Young adult female rats were fed liquid diets by gavage in amounts which maintained constant body weights. The diets were identical except for their water content which was 61.5, 48.3 and 38.7% of the diets. CO2 production, O2 consumption and urine osmotic pressure determinations were made in addition to complete water balance studies. The rats adapted to these reduced water intakes without apparent difficulty and reduction of water to 28.1% of the diet during another short trial was also tolerated. A mean urine osmotic pressure of 3855 milliosmoles/liter was found when the diet contained 28.1% water. When the diet contained 38.7% water, the mean urine osmotic pressure was 3581 millisomoles/liter in the main trial and rechecked at 3276 milliosomoles/liter. The greatest saving of water, over the range of water restriction, was made by reduction of urine volume. Decreased dietary water was associated with a decreased proportion of water in the feces. The insensible water loss was less in grams, grams per liter of O2 uptake or grams per liter of CO2 production when water was restricted.