Liver polyploidy: influence of age and of dietary restriction.

Polyploidy increases with age in mammalian liver. Since dietary restriction increases lifespan, the question posed in this study was whether liver polyploidy would be influenced by dietary protein restriction. Restricted mice were fed a 4% protein diet, while control mice received a 26% protein diet. Polyploidy was determined from measurements of nuclear diameter on liver of 3 week, 1 1/2, 3, 10, 20 and 24-1/2 month old Swiss albino mice. The percentage of polyploid cells increased steadily with age. The rate of increase, expressed as the polyploidization index, was greater in the fully fed control animals as compared to the animals on protein restriction. Protein restriction thus retards the age associated process of polyploidization of liver nuclei. Nuclear diameter increased slightly with age, but was not influenced by protein restriction.