Cell cycle specific effects of selenium on the lens epithelium studied in vivo by the direct chemical approach.

We attempted to separate S phase from post-S phase effects of selenium upon the lens epithelium by exposing the lens in vivo to selenium either during S phase synthesis of DNA or immediately after completion of DNA synthesis. Incorporation of 3H-thymidine into lens epithelial cell DNA is complete within about 3 hours after intraperitoneally injecting this substrate. Young rats were given selenium either 5 hours before injecting 3H-thymidine (selenium present at the time of labeled-DNA synthesis) or 5 hours after 3H-thymidine (selenium present immediately after completion of S phase). By measuring changes in the distribution of 3H-DNA between the epithelium and lens body for 14 days after injection we estimated migration times and rates of differentiation of the labeled cell population. When selenium was present during DNA synthesis, DNA labeling was decreased by 70%, net migration time (movement from the germinative zone to the equator) was markedly prolonged and the rate of differentiation was slightly accelerated. Selenium had little affect on these parameters if first present immediately after S phase. We conclude that selenium insult to the lens epithelium is largely confined to germinative epithelial cells in S or pre-S phases of the cell cycle.