Daily Variation of Body Temperature, Liver Catalase Activity, and Plasma Iron Concentration in Normal and Tumor-Bearing Rats

Summary A comparison was made between the daily variations observed in body temperature, liver catalase activity, and plasma iron concentration in normal and tumor-bearing rats. All three of these measurements were found to have a 24-hr rhythm in normal Holtzman and Fischer rats. With rats bearing either the Walker 256 carcinoma or a 20-methylcholanthrene-induced tumor, these daily cyclic rhythms were altered. It is suggested that care must be exercised in choosing the time of day to compare normal and tumor-bearing animals.