Lens epithelium and radiation cataracts. II. Interphase death in the meridional rows

X irradiation of the lens of a young rat with doses exceeding 2 Gy (200 rad) causes the fragmentation of the nuclei of some of the cells of the meridional rows (MR). The karyopyknosis, which seems to begin as a blebbing of the nucleus, is the result of a direct effect on the cells which were in the MR at the moment of irradiation. The numbers of fragmented nuclei, when observed at the peak time of 12 hr after irradiation, reveal a strong dose dependence. Four Gray will produce less than one such damaged nucleus in 10 rows while 24 Gy exposures result in one fragmented nucleus for every two rows. Time-course analysis revealed that the time of onset is inversely correlated to dose. Fragmented nuclei were observed 4.5 hr following 24 Gy and appeared only at the 9-hr interval following 6 Gy. From the first to the third day after irradiation, the numbers of fragmented nuclei per MR were independent of dose. The fact that the nonmitotic cells of the meridional rows are affected suggests that the pathology is one which has classically been described as interphase death. The details of these observations and a discussion of their role in the overall phenomenon of radiation cataractogenesis are presented