Aging of liver: morphological and biochemical changes.

Light-microscopically there are no significant age-dependent changes in the liver, due to the slight increase in biochemically determined connective tissue components. Electron-microscopical comparison of young and old animals show a larger size and decreased numbers of liver cell mitochondria in older animals. Collagen synthesis in liver is accelerated during growth, as demonstrated by assay of the [3H] proline incorporation rates and of the specific activity of hydroxyproline, corresponding to a decrease in the prolyl hydroxylase activity with age. The neutral salt-soluble collagen fraction may be regarded as a parameter for collagen synthesis, which is activated during the growth period and then remains constant without age and sex differences. Not much is known about the significance of these changes with increasing age or about their initiating factors, although there are parallel findings for liver intoxication and inflammation.