THE WATER EXCHANGE AND POLYURIA OF RATS DEPRIVED OF FOOD

Abstract

Male and female rats void a greatly increased volume of dilute urine for the first 1 or 2 days of deprivation of food with water allowed. The polyuria is not dependent on an increase of water intake and occurs unless intake falls to about 5 g./day. The polyuria also occurs when food intake is restricted to 1/3 normal but not on restriction to 2/3. Almost 2/3 of the excess urine not attributable to increased water intake could be accounted for as water absorbed from diminishing gut contents; the remainder may be derived from depletion of other labile pools of body water. The volume of urine can be restored to control levels and the concentration partially restored by simultaneous deprivation of food and water or by treatment with ‘Pitressin’. On more prolonged deprivation of food with water allowed, urine concentration approached control levels by day 4–6. On prolonged restriction of food, water turnover remained high and urine remained dilute for at least 6 days; concentration could be restored by ‘Pitressin’. It is concluded that the dilute urine of food deprivation and restriction is the result of a self‐imposed water diuresis. The high water turnover represents, by the criterion of the potential concentrating ability of the kidney, an inefficiency of water regulation.