Cellular dynamics of corneal wound re-epithelialization in the rat. II. DNA synthesis of the ocular surface epithelium following wounding.

To determine the fate of ocular surface epithelial cells in response to corneal injury, epithelial cells undergoing DNA synthesis were labeled at discrete time points following abrasion. A 3-mm diameter epithelial defect was made in the center of the rat cornea. One hour prior to sacrifice, animals received an intraperitoneal injection of [3H]-thymidine. DNA synthesis in the regenerating epithelium was of low abundance (< 2%). The undamaged corneal epithelium had a labeling index (LI) that was markedly elevated from unwounded specimens in the first 48 h after abrasion. The LIs of suprabasal cells were increased at 24 h and 36 h; these cells were believed to be displaced basal epithelial cells. Basal and suprabasal cells of the limbus and conjunctiva exhibited increases in LIs from unwounded subjects at singular timepoints (within 24 h of injury). These results, using rigorous statistical analysis, show that DNA synthesis is not impeded--but rather often accelerated--following denuding of the corneal epithelium. Re-epithelialization is not dependent on DNA synthesis in the regenerating region, but appears to be related to an increase in DNA synthesis (along with centripetal migration) in the adjacent, undamaged epithelium. The increase in DNA synthesis occurring in the limbus and conjunctiva does not directly supply cells to the regenerating region within the 72 h required for epithelial restitution, but is conjectured to serve in replenishing ocular surface epithelial cells used in the repair process.