Treating ocular inflammation (uveitis) has proven a difficult task, due at least in part to the numerous mediators involved and an inadequate understanding of its regulation. Tumor necrosis factor (TNF) and interleukin-1 (IL-1) are two functionally related cytokines with potent inflammatory effects outside the eye and recently-demonstrated phlogistic effects in the eye. We suggest that TNF and IL-1 are key mediators of uveitis by virtue of their effects on uveal tissue via two distinct mechanisms: 1) They provoke secondary release of eicosanoids (metabolites of arachidonic acid) and platelet-activating factors (PAF); 2) They interact directly with uveal cells, affecting cellular levels of cyclic nucleotides through specific binding to cell surface-""""""""G"""""""" protein-linked receptors. Part I of this hypothesis will be addressed by injecting TNF and IL-1 into the vitreal chamber of the rabbit eye and characterizing their effects in terms of dose-response, time course and cytokine levels and interactions. Eicosanoid contributions will be assessed by determining those that increase during cytokine-induced uveitis and then measuring the ability of cyclooxygenase (indomethacin, naproxen) and combined cyclooxygenase/lipoxygenase (SK&F 86002) inhibitors to alter cytokine- induced effects. PAF will be measured in aqueous humor extracts by release of [3H]-serotonin from platelets and its role in cytokine-induced uveitis assessed by determining the effect of a specific PAF receptor antagonist (SRI 63-441) and the ability of intravitreally-injected PAF and PAF/eicosanoid combinations (those which increase during cytokine-induced uveitis) to reproduce the effects of combinations (those which increase during cytokine-induced uveitis) to reproduce the effects of intravitreally-injected cytokines. In part II of this hypothesis the ability of cytokines, in vitro, to induce adenosine 3',5'-cyclic monophosphate (cAMP) production by individual preparations of iris, ciliary body and ciliary processes, and the ability of agents that influence adenylate cyclase activity to alter cytokine-induced cAMP production, in vitro, will be measured. These agents include Gs protein activators (F-; guanosine 5'-[beta, g-imino]triphosphate), a Gi inhibitor (pertussis toxin), protein kinase C (PKC) activators (4beta-phorbol 12-myristate 13- acetate) and inhibitors (H7; staurosporin) and adenylate cyclase activators (forskolin; Mn2+). These studies will provide valuable insight into the mechanisms by which TNF and IL-1 regulate production of the secondary messenger, cAMP, and pivotal substance controlling membrane permeability and aqueous humor production. It is important that the ocular effects of TNF and IL-1, the specific substances secondarily mediating these effects, and the influence of these cytokines on uveal cyclic nucleotide production be elucidated since new pharmacological modalities will soon be available for possible use in the treatment of uveitis.
