Diurnal variation of autophagy in rod visual cells in the rat.

In the process of autophagy, parts of the cell's own cytoplasm are enclosed by membranes and subsequently digested by enzymes. Autophagy is a well-known process found in various tissues under different conditions (See Refs.). Autophagy in visual cells was first documented by Remé and Young (1977) and Remé (1977), and was considered to be a general and important degradative pathway in visual cell metabolism. Recently, La Vail (1976) demonstrated that the shedding of disks from the tips of rod outer segments followed a circadian rhythm in rats. The peak period of disk shedding occurred shortly after the onset of the lighting period. In this study we have demonstrated, by quantitative analysis, that autophagy in rod inner segments follows a diurnal variation. The peak period of autophagic activity occurs about 3 h after the peak period of disk-shedding. Both peak periods take place in daytime, when the animals are less active. This finding further supports our assumption of autophagy being an important pathway in visual cell degradative mechanisms.