Effect of dietary restriction and stress on body temperature in rats.

Body temperature was measured in 6- and 24-month-old Sprague-Dawley rats that were either kept on a restricted diet or fed ad libitum. The circadian variation of body temperature was similar in 24-month-old restrained, restricted, and control rats. Feeding of rats increased their body temperature. The process of temperature measurement also increased body temperature of rats. This stress-induced increase of temperature was larger in younger than in older rats and was diminished in ad-libitum-fed rats by 24-hr fasting. The stress-induced increase in rats on restricted diet that were fasted 24 hrs before the experiment was similar to that observed in 24-hr-fasted ad-libitum-fed rats. These results show that appropriate controls should be used when the effect of chronic food restriction is being investigated to distinguish between the effect of short-term fasting and long-term food restriction. These results also indicate that the increase of life span induced by dietary restriction in rats is not associated with decreased body temperature as was observed in some strains of mice.