Lens lactate dehydrogenase inactivation after UV-B irradiation: An in vivomeasure of UVR-B penetration

PURPOSE. TO elucidate the spatial distribution of inactivation of lactate d ehydrogenase (LDH) in ultraviolet-B radiation (UVR-B)- exposed eyes. To det ermine the in vivo penetration depth of UVR-B in the lens. METHODS. LDH activity in cornea and lens was investigated with an enzyme hi stochemical technique. Thirty rats were exposed in vivo to UVR-B of approxi mately 300 nm, and the eyes were enucleated and frozen at 0, 2, and G hours after exposure. LDH activity in frozen sections was determined quantitativ ely in the corneal epithelium and four different regions in the lens. UVR-B penetration depth was estimated by using a calculated Lambertian absorptio n coefficient. RESULTS. The LDH activity was decreased in the cornea and the outer anterio r lens cortex at all three time points. The average decrease in enzyme acti vity in the time range was 35% in the cornea and 20% in the outer anterior lens cortex. UVR-B inhibition of LDH was immediate and not dependent on an inflammatory reaction within the eye. Penetration depth, corresponding to 1 /e(2) (similar to 14%) residual UVR-B intensity, was 0.45 mm. CONCLUSIONS. UVR-B does not exhibit any significant effect on LDH activity in the major part of the lens, and this is attributed to the shallow penetr ation (0.45 mm) of UVR-B into the anterior parts of the lens.