The effect of age and diet on biochemical characteristics of the tissues of mice

Weanling male B6D2F1 mice were divided among the following four dietary groups. One group was fed 24% protein ad libitum. Another group was fed 4% protein ad libitum. The third and fourth groups were fed the 24% protein diet ad libitum for twenty-four hours on Monday and Wednesday, and for eight hours on Friday. The third group was sacrificed following a 24 hour feeding period, while the fourth group was sacrificed following a 24 hour fasting period. The animals were sacrificed at approximately 14, 29, and 33 months of age and a variety of enzymes as well as protein and DNA of livers, kidneys, spleens, hearts and brains were determined. Liver was most affected by age and dietary restriction. Dietary restriction reduced age regressions. A linear relationship existed in the various organs between cellular size, estimated by the concentration of DNA, and either cellular protein or most enzymatic activities. Age and dietary restriction resulted in small cells in liver but not the other organs. When cells of the same size were compared, animals fed the low protein diet exhibited hepatic cellular protein and enzymatic activities lower than that of controls whereas those starved during intermittent feeding had values considerably higher. The data suggest two independent mechanisms perhaps associated with protein synthesis, which increase life span and may result in differential effects on age-associated changes.