Effects of topical clonidine on prostaglandin-E(2)-induced aqueous flare elevation in pigmented rabbits

We evaluated the role of topical clonidine on experimental ocular inflammation. Transcorneal diffusion of prostaglandin (PG) E(2), 7. 09 x 10(-2) mmol/l, with the use of a glass cylinder was employed to produce aqueous flare elevation in pigmented rabbits. Clonidine was topically administered and yohimbine was injected intravenously. Aqueous flare was measured with a laser flare cell meter. Topical instillation of 0.25% clonidine inhibited 89% of PGE(2)-induced aqueous flare elevation. Instillation of clonidine at 60 or 30 min before and 10 min after PGE(2) inhibited flare significantly. Pretreatment with intravenous yohimbine decreased the clonidine-induced inhibition of the flare elevation in a dose-dependent manner. It is possible that the anti-inflammatory action of topical clonidine may be mediated partly by alpha(2)-receptors.