The effects of long warm and cold ambient exposures on food intake water intake and body weight in the capsaicin desensitized rat.

Seventeen Sprague Dawley rats received, subcutaneously, 250 mg . kg-1 of capsaicin divided into 10 increasing doses (10-50 mg . kg-1) and administered on 7 successive days. Nine controls were treated with an isotonic saline solution using the same protocol. The rats spent, in succession, 5 weeks at 20 degrees C, 6 weeks at 33.5 degrees C, 6 weeks at 8 degrees C, 4 weeks at 30 degrees C and, finally, 5 weeks at 20 degrees C ambient temperature. Their mean food intake (FI), water intake (WI) and body weights were recorded daily. In the 2 groups of rats, FI was inversely related to ambient temperature. However, during the first few days of the exposures, FI in treated rats was greater than controls in the warm environment and less in the cold environment. In controls, WI increased linearly with ambient temperature in the warm environment. This relation was not found in treated rats: they drank less water than controls and lost body weight. During the first days at 8 degrees C ambient temperature, rectal temperature decreased in treated rats and two animals died. The results are similar to those described for rats with hypothalamic lesions. They may also be related to a peripheral effect of the drug.