Concentration-dependent morphologic effects of cytochalasin B in the aqueous outflow system

Cytochalasin B at concentrations of 1, 5, 10, 15, 20, or 40 microgram/ml was continuously exchange-perfused into the eyes of nine living Macaca mulatta monkeys while intraocular pressure (IOP) was maintained at 25 mm Hg for 30 min. Pressures were then slowly reduced to 4 mm Hg to permit blood to reflux into Schlemm's canal as a tracer, and the eyes were fixed while maintained at 4 mm Hg IOP. Tissues were examined in all eyes by light and transmission electron microscopy. At concentrations of 1, 5, and 10 microgram/ml cytochalasin B, the integrity of the endothelial lining of the trabecular wall of Schlemm's canal was maintained. At 15 microgram/ml cytochalasin B, 6% of the length of the endothelial lining was disrupted; at 20 microgram/ml, 54%; and at 40 microgram/ml, 83%. There was a washout of extracellular material at the site of breaks and also a reflux of blood from Schlemm's canal into the trabecular meshwork in the same regions.