HISTOCHEMICAL-STUDY ON XANTHINE-OXIDASE ACTIVITY IN THE NORMAL RABBITCORNEA AND LENS AND AFTER REPEATED IRRADIATION OF THE EYE WITH UVB RAYS

In the normal rabbit cornea and lens the activity of xanthine oxidase, an enzyme belonging to oxidases generating reactive oxygen species (R OS), is present in the corneal epithelium as well as endothelium and l ens epithelium. Repeated irradiation of the eyes with UVB rays (5 min 1x daily, for 1 to 4 days) caused a gradual increase of xanthine oxida se activity, particularly in the corneal epithelium. Application of ca talase, a scavenger of hydrogen peroxide, to the eye surface during th e irradiation diminished the increase of xanthine oxidase activity. On the contrary, the pretreatment of the rabbit eyes with 3-aminotriazol e, an inhibitor of catalase, for 3 days before the irradiation enhance d the increase of xanthine oxidase activity. In comparison to untreate d eyes, protracted irradiation of the eyes with UVB rays (up to 10 day s) caused a decrease of xanthine oxidase activity in the same cell lay ers of the cornea and lens, It is suggested that xanthine oxidase is i nvolved in the generation of ROS in the anterior eye segment during ea rly irradiation of the eyes with UVB rays and participates in its dama ge. Prolonged repeated irradiation of the eye (5 min 1x daily for 5 to 10 days) caused a decrease of xanthine oxidase activity in the cornea and lens which is attributed to profound damage of the whole anterior eye segment.