[Circadian studies with young and old rats (author's transl)]

8 and 28 months old, male Sprague-Dawley rats (36 animals in each group) were used to determine the rectal temperature, various organ weights (referred to the body weight and the brain weight), various blood parameters and the concentration of Ca and Mg in the plasma and the myocard as a function of the time of the day. The values were approximated to the function y = M + A cos (omega t + phi) (y = parameter value, M = mesor, mean value of the day, A = amplitude, omega = angular velocity, t = hour of the day, phi = acrophase, when y has its highest value). The approximations were significant at 6 out of 45 parameters in both groups (rectal) temperature, pancreas weight related to the body weight, leucocyte number/mm3, GPT, Mg and Ca/Mg in the plasma). 17 parameters could be approximated only at the young rats, 1 parameter only at the old animals. In some cases large age correlated alterations of the amplitude could be observed. The mesor changed only at the pancreas weight related to the body weight. The acrophase shifted only at the leucocyte number/mm3. These variations can lead to wrong interpretations when only mean values are used for age comparisons.