Distribution of intravenously and perorally administeredAeromonas salmonicidalipopolysaccharide in Atlantic salmon,Salmo salarL.

The uptake and distribution ofAeromonas salmonicidalipopolysaccharide (LPS) in Atlantic salmon,Salmo salarL., was investigated. The purified LPS molecule was radiolabelled by bromine oxidation and subsequent sodium borotritide reduction, or fluorescein labelled. After intravenous injection, high amounts of radiolabelled LPS was found in the spleen, liver, anterior and posterior kidneys at 30 min and 2 h. Twenty four hours after i.v. administration, the spleen still contained high amounts of radioactivity, the liver contained increased amounts while the anterior and posterior kidneys showed reduced contents of radioactivity compared with the findings 30 min and 2 h after administration. After peroral administration, relatively less radioactive LPS accumulated in the liver compared with the spleen and kidneys at 0·5, 1, 4 and 24 h. At 24 and 48 h after administration the anterior intestine contained high amounts of radioactivity while the posterior intestine contained low amounts. Histological examinations of tissue sections revealed accumulation of fluorescein-labelled LPS in kidney sinusoidal endothelial cells and macrophages and in splenic ellipsoid sheath cells (macrophages and reticular cells). Liver endothelial cells also showed accumulation of FITC-LPS.