Influence of dietary protein restriction on cell number, cell size and growth of mouse organs during the course of aging.

Groups of male Swiss albino mice on diets of 4%, 8% and 26% protein were sacrificed at 6, 12, 42 and 84 weeks of age to determine the extent to which cell number and cell size were influenced by dietary protein restriction in the course of aging. The results show that cell number is reduced by low protein diets only in liver and kidney: that is, in expanding cell populations. Cell number in the static cell populations of brain and heart was not influenced by diet. Increase in organ size is brought about by a variety of mechanisms. Heart size increases in mice on a higher protein diet by means of increase in cell size; a cellular hypertrophy. Liver size increases both through cell addition and formation of larger polyploid cells. The kidney was the only organ in which there was a continuous addition of new cells of constant size throughout the life span. Dietary protein restriction reduced the rate of cell size increase and of growth. Although it slowed the growth process, it did not alter any of the aging or growth patterns.