thiourea and Uveitis--Anterior

Dimethylthiourea, a potent scavenger of toxic oxygen metabolites such as the hydroxyl radical, hypochlorous acid, and hydrogen peroxide, was tested for its ability to inhibit an experimentally induced inflammatory response. Inflammation was induced in one eye of male New Zealand white rabbits by intravitreal injection of 10 ng Escherichia coli endotoxin; the contralateral eye received an equal volume of pyrogen-free saline vehicle. Dimethylthiourea was administered intraperitoneally to these animals at 0, 300, 450 and 600 mg kg-1. At 24 h post-endotoxin injection, all vehicle-injected eyes appeared normal with the exception of a small, but significant increase in aqueous humor protein concentration in the 600 mg kg-1 dimethylthiourea group. In endotoxin-injected eyes, treatment with dimethylthiourea, especially at the highest dose, significantly reduced iridal hyperemia, aqueous humor cell number and protein and prostaglandin-E concentrations, and the ex vivo release of prostaglandin-E from the lens. The ability of dimethylthiourea to significantly inhibit the inflammatory response to intravitreally-injected endotoxin suggests that toxic oxygen metabolites may play an important role in the initiation and/or propagation of this form of acute anterior uveitis. Furthermore, the data are consistent with an important interaction between toxic oxygen and arachidonic acid metabolites.

Topics: Animals; Endotoxins; Escherichia coli; Male; Rabbits; Thiourea; Uveitis, Anterior; Vitreous Body

Topical application of the H2-histamine receptor agonist, dimaprit (S-[4-N,N-dimethylaminopropyl]isothiourea), produced eosinophil chemotaxis into the anterior segment of rabbit eyes only when an H2-antagonist was co-administered. Nordimaprit (S-[4-N,N-dimethylaminoethyl]isothiourea), a structural homologue of dimaprit that lacked activity at histamine receptors, produced eosinophil chemotaxis whether or not an H2-antagonist was co-administered. Onset of eosinophil chemotaxis began after 2 or more days of treatment, and was accompanied by corneal edema, opacification, and ocular inflammation. There was no concurrent eosinophilia in the peripheral blood or in the conjunctiva. The response occurred in pigmented and albino rabbit eyes, and was facilitated by prior co-administration of proparacaine eye drops. Another dimaprit homologue without activity at histamine receptors, homodimaprit (S-[4-N,N-dimethylaminobutyl]isothiourea), did not produce eosinophil chemotaxis when applied topically, nor did the H2-agonists impromidine, histamine, or 4-methylhistamine, whether co-administered with an H2-antagonist or not. It was concluded that dimaprit and nordimaprit produced a selective eosinophil chemotaxis unrelated to H1- and H2-histamine receptor activity. However, the H2-agonist activity of dimaprit appeared to inhibit this response unless neutralized by an H2-antagonist. Topical application of dimaprit with an H2-antagonist or nordimaprit alone may allow large numbers of non-degranulated eosinophils, free of other cell types, to be harvested from the aqueous humor.

Topics: Animals; Chemotaxis, Leukocyte; Cimetidine; Dimaprit; Eosinophils; Eye Color; Intraocular Pressure; Propoxycaine; Rabbits; Receptors, Histamine H2; Thiourea; Uveitis, Anterior