Temporal Dependence of Modulation of Radiation–Induced Cataractogenesis by Estrogen

Abstract

Abstract: : Purpose: We have previously demonstrated that estrogen (17–Beta estradiol, E2) may increase the severity and decrease the latent period for cataractogenesis in rats irradiated with 10–15 Gy of 60 Cobalt Gamma rays. However, the effects of estrogen on radiation –induced cataractogenesis are unclear. The current study was designed to determine whether timing of estrogen administration is important in the modulation of cataractogenesis. Methods: Sialastic capsules containing 20 mg of E2 were implanted into ovariectomized 56 day old Sprague–Dawley rats 1 week prior to, or immediately post irradiation. Untreated, Ovariectomized animals served as controls. The right orbit of all the animals was then irradiated with 15 Gy of 60 Cobalt gamma–rays using a Gamma Knife. The degree of lens opacification was measured at 2–4 week intervals using a slit lamp. Results: Nearly all animals (94%) receiving a continuous course of E2 therapy developed cataracts within 240 days, while only 60% of animals receiving E2 post irradiation developed significant lens opacities. Administration of E2 in rats after irradiation reduced final cataract incidence compared to those that received continuous estrogen therapy. Implantation of E2 after irradiation also resulted in a decrease in the severity of the cataracts that did develop. The treatment also significantly increased the latent period for development of significant lens opacity and inhibited progression towards significant opacity. Conclusions: The time–course and final incidence of cataract formation is dependent on when E2 is administered relative to irradiation.

Keywords: cataract • radiation therapy • pathology: experimental