REDUCTION IN RATE OF OCCURRENCE OF AGE-RELATED LESIONS IN DIETARY RESTRICTED LABORATORY MICE

This report describes the results of a study to find differences in the distribution of pathologic lesions between 40% dietary restricted (DR) and ad libitum (AL) fed mice of four genotypes, C57BL/6NNia, DBA/2NNia, B6D2F1NNia and B6C3FlNNia. Representative samples of all organs were studied from 1134 mice killed at 12, 18, 24 and 30 months of age. Approximately half were female, half male. All mice were fed a natural ingredient diet, NIH-31 and were maintained under pathogen free conditions. A total of 135 lesions was observed. The rate of occurrence of each of 35 common lesions is described for each age/genotype/sex in the study. Fifteen lesions are described in detail. Highly significant differences were found between mice of the same age, sex and genotype in the two diet groups in the percent rate of occurrence of total lesions, total tumors, and total lymphoid nodules of various organs. These parameters generally increased with age in both diet groups. For example, of female mice of all genotypes at 24 months, 51% AL and 13% DR mice had tumors. These percentages were 123% and 17% respectively at 30 months. The evidence presented here suggests that total tumors, total lymphoid nodules, total lesions, and absence of lesions are all useful measures of aging, independent of the life span, that reflect the long known effect of dietary restriction on reducing the rate of aging. These parameters, however, only partially reflected the longer life span of hybrid as compared with inbred mice.