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.INFORMATION on the water exchange of rats deprived of food is sparse and inconsistent. Cumming and Morrison [1956, 1960] reported a marked and fairly consistent increase in urine volume of rats totally deprived of food for 48 hr. and little change in average intake of water but very variable individual changes. Dicker [1949] reported an abrupt decrease of urine volume; other reports [e.g. Mefferd and Hale, 1961;Nocenti and Cizek, 1964] give urine volume only at a later stage of deprivation or without control (fed) values. Bauman, Guyot-Jeannin and Dobrowolski [1964] reported the occurrence of a very dilute urine immediately after deprivation of food, but did not report urine volumes. Evidence or statements on water intake indicate, variously, little change, abrupt fall, slow decline or irregular decline of intake during deprivation of food [e.g. Cizek and Nocenti, 1965;Finger and Reid, 1952;LeMagnen, 1956;Nims and Sutton, 1954;Strominger, 1947] Water of Gut Contents. -The food and water intakes and urine volumes of forty-five ChR-CD rats were recorded; Eighteen rats were then killed after ad lib. feeding and eighteen after 24 hr. and nine after 48 hr. of deprivation of food. The gut contents were removed and weighed wet and dry, and faeces of the deprived animals were collected, dried and weighed. Faeces as collected are partly air dried; the water eliminated in fresh faeces was calculated as twice the dry weight of the faeces [Cumming and Morrison, 1960;Radford, 1959].All values are expressed as mean/rat ± standard error except when explicitly stated otherwise. RESULTSWater Exchange of Three Strains of Rat During Total Deprivation of Food for 2 Days Urine volume increased on 90 per cent of the occasions when food was withheld with water allowe...
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