Injured vitreous stimulates DNA synthesis in retinal pigment epithelial cells in culture and within the vitreous

Cultures of rabbit retinal pigment epithelium (RPE) were exposed to normal vitreous and to vitreous injured by intravitreal injection of foreign particles. Counts of labeled RPE nuclei after incubation with³H-thymidine in vitro indicated an increase in DNA synthesis with exposure to normal vitreous and an even greater increase with exposure to injured vitreous. Fractionation of injured vitreous demonstrated that the apparent proliferation stimulus resided in the cell-free supernate. The data suggest that normal vitreous contains a humoral factor that stimulates RPE proliferation and that levels of an active agent increase after vitreal injury. RPE injected into the vitreous also responds by increased DNA synthesis to subsequent vitreal injury. This observation implies that foreign substances in the vitreous, as after vitreal hemorrhage, promote development of extraretinopathies involving RPE by stimulating intravitreal proliferation of invasive RPE cells.