Leakage of blood-retinal barrier due to damaging effect of protamine sulfate on the endothelium.

The effect of the polycations, protamine sulfate and poly-L-lysine, on the blood-retinal barrier of rat retinal vessels were studied by retrograde perfusion through the aorta or by intracarotid perfusion of the polycation followed by the protein tracer, hemoglobin. Protamine sulfate induced swelling of cytoplasmic organelles and diffuse staining of many endothelial cells by tracer molecules which subsequently entered the subendothelial and perivascular areas. Polylysine caused some diffuse staining but no leakage of tracer through the endothelial cell. Occasionally, tracer was found in the interendothelial junction after protamine perfusion. The results indicate that surface charge is important for maintaining membrane integrity of the endothelial cells and that breakdown of the blood-retinal barrier may be due to the cytotoxic effect of protamine on the endothelial cell.