Choriocapillaris regeneration in the rabbit. Ultrastructure of new endothelial tube formation.

After experimental destruction of the retinal pigment epithelium (RPE) by intravenous injection of sodium iodate, the rabbit choriocapillaris (CC) atrophies. This report studies the subsequent regeneration of the CC with the goal of identifying sources of new CC and mechanisms by which new endothelial tube is formed. Light and transmission electron microscopic methods were used. The CC appeared to regenerate from three sources: choroidal venules, remnant CC and newly produced cells. Whatever the source, new endothelial tube was formed by extensions of the endothelium that sealed off new lumenal space by junctional complexes. This process was always confined to the tissue space within remnant sleeves of basement membrane left behind by initial atrophy, and which served as a substrate for endothelial movement. The endothelium of new endothelial tube was initially thick and unfenestrated. It became thinner and fenestrated by a process of cavitation, in which cavities continuous with the lumen pushed into the thick endothelial cytoplasm towards its abluminal side. At this site new fenestrae were formed. Fenestrae were initially scattered about the endothelial tube, but with its maturation became localized on the side facing the regenerated RPE.