ENHANCED PROSTAGLANDIN SYNTHESIS AFTER ULTRAVIOLET-B EXPOSURE MODULATES DNA-SYNTHESIS OF LENS EPITHELIAL-CELLS AND LOWERS INTRAOCULAR-PRESSURE IN-VIVO

Purpose. To study the functional significance of prostaglandin synthes is after ultraviolet-B (UVB) exposure of cultured human lens epithelia l cells and rabbit eyes in vivo. Methods. Prostaglandin E(2) (PGE(2)) was assayed using a radioimmunoassay (RIA) and mass spectroscopy. An i mmortalized human lens epithelial cell line (HLE-B3) was exposed to UV irradiation, and the synthesis of PGE(2) was compared with the rabbit lens epithelial cell line N/N1003A. Intact human lenses were exposed to UVB in organ culture. [H-3]Thymidine incorporation was measured in cultured lens epithelial cells by incubation with the radiolabel. The effects of isobutyl methyl xanthine (IBMX), an inhibitor of phosphodie sterase and of dibutyryl cyclic adenosine monophosphate (cAMP), an ana log of cAMP, on PGE(2) synthesis and DNA synthesis, were determined. R abbit eyes were exposed to UVB radiation in vivo. Intraocular pressure was measured at specific times after exposure. Aqueous humor was remo ved from rabbit eyes, and its PGE(2) content was measured by RTA. Resu lts. Cultured human lens epithelial cells (HLE), like rabbit lens epit helial cells (RLE), showed a dose-dependent increase in basal PGE(2) s ynthesis 24 hours after UVB exposure. However, the amount of PGE(2) sy nthesis was 2000-fold higher in the rabbit cells. Ultraviolet-B radiat ion enhanced the incorporation of [H-3] thymidine in lens epithelial c ells. Pretreatment of cells with indomethacin reduced PGE(2) synthesis and [H-3]thymidine incorporation. The human and rabbit cells responde d in a similar manner to changes in DNA synthesis after UVB exposure. The addition of IBMX or dbcAMP to indomethacin-treated, UVB-exposed ce lls restored DNA synthesis toward the levels observed in the UVB-expos ed cells. An increase in the concentration of cAMP was observed in len s epithelial cells exposed to exogenous PGE(2). PGE(2) synthesis in in tact human lenses also increased twofold 24 hours after UVB exposure. Exposure of the rabbit eye in vivo to an optimal dose of UVB produced an increase in the PGE(2) levels of the lens and the aqueous humor. Me asurements of the intraocular pressure (IOP) of the animals showed a d ecrease in IOP by 2.21 +/- 0.66 and 6.45 +/- 0.79 mm Hg (mean +/- SEM, P = 0.004, t-test) at 6 and 24 hours after WE exposure, respectively. The decrease in IOP was prevented by pretreatment with indomethacin. Exposure of the rabbit lens to UVB radiation in vivo enhanced [H-3]thy midine incorporation twofold into the lens. Pretreatment of rabbits wi th indomethacin before exposure reduced this response. Conclusions. Re sults indicate that UVB exposure enhances PGE(2) synthesis in HLE cult ures as well as in rabbit lenses irradiated in vivo. This increased PG E(2) synthesis is related to the increase in DNA synthesis observed af ter UVB treatment. The modulation of DNA synthesis in cultured lens ep ithelial cells after UVB exposure may be mediated by a cAMP-dependent mechanism.