Bacterial endotoxin (lipopolysaccharide; LPS) is known to alter systemic vascular permeability, but this effect is difficult to monitor and quantitate in vivo. The ocular vessels of the rabbit are particularly sensitive to LPS. Using a slit lamp equipped with a fluorophotometer, we have adapted a method to quantitate endotoxin-induced ocular vascular permeability by measuring the accumulation of fluorescein isothiocyanate-conjugated albumin into the anterior chamber of the eye. After intravenous administration of Salmonella typhimurim LPS, the anterior chamber fluorescence and blood fluorescence were measured at intervals of 15 min and 1 h, respectively, over 4 h. In controls, maximal fluorescence in the anterior chamber was 3.1 ± 0.8% of blood fluorescence. Doses of LPS as low as 0.25 Fg/kg produced an ocular/serum fluorescence ratio of 17.6 ± 4.9. A dose of 2.5 pLg of LPS per kg tended to produce a higher ratio (68.0 ± 7.1) than a larger dose of 50 p,g/kg (30.5 ± 16.6). Permeability changes began within 30 min after on August 5, 2020 by guest http://iai.asm.org/ Downloaded from
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