A spontaneous increase of salt intake and changes of colonic temperature in mice exposed to cold

The effect of repeated short-term exposure to cold on spontaneous salt (NaCl) intake and colonic temperature was investigated in two experiments on mice. In Experiment 1, half of a group of test animals were exposed to cold (7-9 degrees C; 6h/day; 4 days), and half of both the exposed and non-exposed animals were allowed to choose between drinking water with (0.9%) and without (0%) NaCl. Food and fluids were provided all day long during the experiment. Mice provided with NaCl solution showed increased salt intake with cold exposure. Colonic temperature of mice was measured twice a day at the beginning and the end of cold exposure. Different changes in colonic temperature among the groups were observed at the end of cold exposure. In mice exposed to cold and provided with NaCl solution, colonic temperatures stayed unchanged, whereas in those without NaCl solution colonic temperatures decreased significantly after cold exposure. In Experiment 2, all the mice were exposed to cold as in Experiment 1. Four patterns of feeding of food and fluids were applied to groups of eight mice each: removal of food and fluids during cold; removal during 9 h before cold and during cold; removal during cold and during 9 h after cold, and feeding all day long. Half the mice in each feeding pattern were allowed to choose NaCl fluids (0% & 0.9%). Colonic temperature was measured as in Experiment 1. In all the feeding patterns, colonic temperature was significantly lower in the mice without NaCl solution than those with NaCl solution. Among four feeding patterns in mice with NaCl solution, colonic temperature was significantly higher in the case of feeding all day long than in the other three patterns.