Salt consumption and body fluid balance during cold exposure in rats

We investigated the effect of exposure to cold on salt consumption and the role of salt consumption on the maintenance of body fluid balance in male Wistar rats. The rats were provided with both tap water and NaCl solution ad lib during 16-h exposure to cold (10 degrees C) and normal (25 degrees C) air temperature conditions. The concentration of the NaCl solution was 0.9% for one group (0.9% NaCl group; n = 7) and 1.8% for the other (1.8% NaCl group; n = 6). At 10 degrees C, weight loss was greater than that at 25 degrees C, and fluid and Na balance were negative in the 0.9% NaCl group. However, the calculated Na concentration of the fluid consumed in the 0.9% NaCl group was about 135 mEq/l Na (0.8% NaCl) at both 10 degrees C and 25 degrees C. In the 1.8% NaCl group, the values indicating fluid and Na balance under both temperature conditions were similar, while the calculated concentration of Na in fluid consumed at 10 degrees C (187 mEq/l Na: 1.1% NaCl) was higher than that at 25 degrees C (153 mEq/l Na: 0.9% NaCl). These results suggest that the consumption of hypertonic NaCl solution indicating increased salt appetite during exposure to cold counteracts the loss of body fluid and Na via urine.