Lens Epithelial Cell Proliferation and Migration in Radiation Cataracts

The left eyes of young and adult mice and rats were exposed to 2400 r of gamma radiation from a Co/sup 60/ source administered at the rate of 40 r/min. The right eyes of the animals served as controls. Thymidine--tritium is incorporated into the deoxyribonucleic acid (DNA) in the synthesis phase of cell division. The number of epithelial cells labeled per section of lens and the number of grains found per cell were taken as a measure of nucleic acid synthesis. The change in position of labeled cells with time was taken as an indication of cell movement. Initially, the grain count per cell decreased temporarily and then remained near the control level after irradiation. Frequency of cell labeling remained constant for several weeks and then increased moderately. The germinative zone remained in the normal pre-equatorial position even though there was considerable cell damage evident in the epithelium and cortex regions of the lens. Cells from the germinative zone in the adult rat moved slowly after irradiation. These labeled cells were not found to enter the lens cortex until after the cataract was well advanced or complete. In younger animals cell migration was fast enough so that labeled cells movedmore » into the lens and migrated toward the posterior pole sometimes before the cataract was complete. In the mouse these labeled cells migrated toward the posterior pole just under the lens capsule to form plaques. Lens fiber damage in all cases was well advanced before cells in the zone of DNA synthesis at the time of irradiation migrated and reached the area of opacity in the lens cortex. Previous work on radiation cataract formation has been critically reviewed, and a postulated sequence of events leading to the cataract has been put forth. In this sequence of events, damage to the newly forming lens fibers at the time of irradiation is seen as directly leading to the cataract. (auth)« less