LOWER VARIABILITY IN FEMALE AS COMPARED TO MALE LABORATORY MICE - INVESTIGATIONS ON CIRCADIAN-RHYTHMS

The aim of the present paper was to investigate the estrous cycle of f emale laboratory mice (Haz : ICR) and its possible influence on the re sults of biomedical, particularly chronobiological studies. Furthermor e gender specific differences in intra- and interindividual variabilit ies were analysed on the basis of circadian patterns of locomotor acti vity, body temperature, food intake, blood glucose, serum insulin, liv er glycogen and jejunal maltase activity. Most estrous cycles lasted f or 5 days. The variability was high however and increased with increas ing numbers of females living together per group. An interindividual c ycle synchronization was not observed. For all seven parameters invest igated pronounced 24-h-rhythms were found. Infradian changes were cons iderably lower than the circadian oscillations and were observed at si milar levels in female and in male animals. Analyses of variance of th e seven measurements on the base of the same day times revealed a bett er reproducibility and a higher stability of circadian rhythms in fema le mice (kept both individually and in groups) compared to males. This will have an impact on the results of investigations carried out at a fixed time of the day as well. The causes of the differences were tho ught to be associated with the social behaviour of the animals. The pr esented results show that, at least for chronobiological investigation s carried out on social species, female animals were recommended.