INFLAMMATION-INDUCED CHANGES IN ADENOSINE 3',5'-CYCLIC-MONOPHOSPHATE PRODUCTION BY CILIARY EPITHELIAL-CELL BILAYERS

Despite extensive evidence implicating the cytokines interleukin-1 (IL -1) and tumor necrosis factor-alpha (TNF alpha) in the intraocular inf lammatory response, little is known about their effects on signal tran sduction in anterior uveal tissue. Since these cytokines have been sho wn to alter the adenylyl cyclase system in nonocular tissues, we teste d the hypothesis that IL-1 beta and TNF alpha, affect the anterior uve a by altering production of the intracellular second messenger adenosi ne 3',5'-cyclic monophosphate (cAMP) in ciliary epithelial bilayers. T his was accomplished by measuring the levels of cAMP in bilayers ex vi vo, following intraocular inflammation induced by intravitreal injecti on of IL-1 beta, TNF alpha or bacterial endotoxin, and in vitro, follo wing exposure to IL-1 beta, TNF alpha or bacterial endotoxin. Although cAMP production was enhanced in bilayers from IL-1 beta-, TNF alpha- or endotoxin-inflamed eyes, ex vivo, exposure of normal bilayers to IL -1 beta (15 U ml(-1)), TNF alpha (20 U ml(-1)), or a low concentration of endotoxin (0.01 mu g ml(-1)) for 4 hr, in vitro, had no effect on cAMP production. The inability of IL-1 beta, TNF alpha, or the low con centration of endotoxin to increase cAMP production by bilayers, in vi tro, suggests that the enhanced cAMP production observed with inflamed bilayers, ex vivo, was not due to a direct action of these inflammato ry agonists on the ciliary epithelial bilayer. Although direct exposur e to cytokines or endotoxin did not change cAMP production, treatment with IL-1 beta, TNF alpha, or a higher concentration of endotoxin (1 m u g ml(-1)) did affect signal transduction mechanisms. For example, ex posure to IL-1 beta, TNF alpha, or a higher concentration of endotoxin rendered normal bilayers unresponsive to isoproterenol. A similar abs ence of response to isoproterenol was also seen with bilayers from TNF alpha-inflamed eyes. This insensitivity to beta-receptor stimulation is apparently a consequence of receptor downregulation or functional u ncoupling of the receptor from the transducing G protein, since in eac h case of isoproterenol insensitivity, bilayers exhibited forskolin re sponses indistinguishable from the appropriate control tissues. Since cAMP production by the epithelial cell bilayer was increased in three different models of intraocular inflammation, augmented production of this second messenger is likely to occur during uveitis of diverse eti ology. Enhanced cAMP production by inflamed epithelial bilayers may co ntribute to some general aspect of the uveitic response such as altere d intraocular pressure or possibly serve to enhance efflux of fluid fr om swollen anterior uveal tissue.