A comparative study on the effects of ageing and training on the levels of lipofuscin in various tissues of the rat.

1. A modified procedure, based on the autofluorescent properties of the age pigment, lipofuscin, has been applied to obtain quantitative data on the accumulation of the proteolipid fraction of the pigment in a variety of tissues of the rat (Rattus norvegicus). The tissues investigated included muscle (fast-twitch white and red fibers), heart, brain and spleen. 2. The effects of a life-long treadmill training program on the concentration of lipofuscin in the different tissues, was determined in a cross-sectional study at various ages between 41/2 and 19 months. 3. All the tissues investigated revealed an increase in the concentration of lipofuscin with training. The increase exceeded the increment observed in ageing control animals. 4. It is postulated that the elevated lipofuscin levels observed with physical training reflect an ultrastructural adaptive change in the cells. A relative deficiency of oxygen in the tissues could be the important metabolic factor triggering this mechanism.