Intestinal uptake and organ distribution ofimmunomodulatory aminated β-1,3-d-polyglucose in Atlantic salmon (Salmo salar L.)

Intestinal uptake and organ distribution of aminated β-1,3-d-polyglucose (AG),a potent soluble immunomodulator, were studied in the Atlantic salmon (Salmo salar L.). AG was tritiated or labelled with 125I-tyramine cellobiose and traced after intravenous injection (125I-TC-AG), or after intragastric or rectal administration (125I-TC-AG or [3H]AG) to the Atlantic salmon. Plasma levels and tissue distribution of AG were investigated. AG appeared in blood and various tissues within minutes after rectal or intragastric administration. Histological investigations showed that fluorescence-labelled AG was taken up by epithelial cells in the lower part of the intestine. Blood clearance of intravenously injected 125I-TC-AG was rapid; about 50% of the labelled AG had disappeared from blood after 20 min. The highest amounts of radiolabelled AG following intravenous injection were found in liver, spleen and kidney. Radioactivity per g tissue was equal in head and trunk kidney. Significant amounts of radioactivity were also found in the wall of the hindgut after intestinal administration. The fact that aminated β-1,3-d-polyglucose is transported through epithelial cells in the intestine and cleared from the blood in lymphoid tissues suggests the possible use of this immunomodulating polysaccharide as feed additive in fish culture.