HORSERADISH-PEROXIDASE - A RELIABLE OR A MISLEADING TOOL FOR THE INVESTIGATIONS ON THE ORIGIN OF THE PROTEINS OF THE AQUEOUS-HUMOR

The concept of the blood-aqueous barrier is largely based on the use o f horseradish peroxidase (HRP). The present investigation was designed to check its reliability as a macromolecular tracer, especially with regard to the transport of plasma proteins. Rabbits were killed 5 min to 24 h after being intravenously injected with HRP. The tracer diffus ed rapidly, reaching the aqueous humor of the eye in 3 min or less and was detected at high concentration in the narrow space between the ou ter epithelial layer of the ciliary epithelium and the wall of the per vious capillaries in the stroma of the processes. HRP appeared to migr ate from the blood to the posterior chamber, permeating the tight junc tions, viz., the anatomical basis of the blood-aqueous barrier. It was detected at higher concentration at the anterior surface of the iris, at short time intervals; this was interpreted as penetration of the t racer from the aqueous humor of the anterior chamber. The choroid was also labeled in continuation with the reaction in the stroma of the pa rs plana of the ciliary body which, in turn, sometimes reached the iri s root. Therefore, the pervious blood vessels of the choroid could be a source of macromolecules for the iris root. HRP also induced the for mation of lysosomes in the ciliary epithelium. This can hardly be acce pted as the way in which plasma proteins are physiologically transport ed to the aqueous humor. However, the pathway of HRP migration over sh ort time intervals seems to be in agreement with previous research ind icating: that the entrance of serum albumin into the posterior chamber is the first step of its incorporation into the aqueous humor.