A Light and Electron Microscopic Study of the Permeability of the Rabbit Iris Vessels to Horseradish Peroxidase in Experimental Uveitis

Abstract

Experimental uveitis has been produced in two groups of albino rabbits by a single intravitreal injection of antigen. The animals in group I were immunized by injection of 10 mg of human serum albumin, whereas those belonging to group I1 received 50 mg. To study the blood-aqueous barrier to proteins in the iris vessels of these eyes, horseradish peroxidase has been used as a protein tracer by light and electron microscopy. The tracer was injected intravenously at different time intervals (1-30 min) before enucleation.In group I, no leakage of peroxidase from the iris vessels was demonstrated in any eyes except one. The diffusion of peroxidase was halted by thc zonulae occludentes of the vascular endothelium, and there was no evidence of vesicular transport of peroxidase through the endothelial cells. In the more heavy inflamed eyes belonging to group 11, a prominent inflammatory cell infiltration was found in the iris. In these eyes leakage of peroxidase through the interendothelial clefts of the iris vessels was demonstrated.

A contemporary concept of the blood–aqueous barrier

“…Notwithstanding the early EM studies that left open the possibility that the iris vessels and ciliary epithelium were “leaky”, a host of studies, completed in several species, showed that iris vessels and the non-pigmented ciliary epithelium were impermeable to horseradish peroxidase. (Vegge, 1971a,b, Smith, 1971, Smith and Rudt, 1973; Uusitalo, Palkama and Stjernschantz, 1973; Raviola, 1974, Pederson, 1974; Freddo and Raviola, 1982a) (Figure 1 – top). The outcomes of these studies established that the anatomical equivalents of the BAB, as it was originally described, were the tight junctions of the iris vasculature and the non-pigmented ciliary epithelium (Raviola, 1977, Bill, 1986).…”

THE PERMEABILITY OF THE RABBIT CILIARY EPITHELIUM TO HORSERADISH PEROXIDASE IN EXPERIMENTAL UVEITIS An electron microscopic study

“…This is in contrast to the findings in experimental uveitis of the present type. Here the iris vessels seem less affected than the ciliary epithelium (Pedersen 1974). This is believed to reflect differences in the pathogenesis of the breakdown of the blood-aqueous barrier in these conditions.…”