INTESTINAL-ABSORPTION OF IMMUNOMODULATORY LAMINARAN AND DERIVATIVES IN ATLANTIC SALMON, SALMO-SALAR L

Radiolabelled (I-125, H-3) immunomodulatory laminaran (isolated from Laminaria hyperborea), a beta(1,6)-branched beta(1,3)-D-glucan and different radiolabelled sulphated analogues of laminaran were administered peranally to Atlantic salmon, Salmo salar L.. Intestinal absorption and tissue distribution were examined by means of radioactive tracer techniques. The intestinal uptake was highest with native laminaran and laminaran with a low degree of sulphatation, while highly sulphated laminarans were poorly absorbed. The tissue distribution analysis revealed high amounts of radiolabelled compound in the liver, and anterior and posterior kidney, whereas the spleen contained low amounts. Peak serum and organ concentrations were reached about 30 min after administration. The results were confirmed by autoradiography of tissue sections from salmon after peranal administration of radiolabelled laminaran. Finally, the peranal administration of fluorescence labelled laminaran revealed epithelial supranuclear fluorescent vacuoles containing laminaran. It is concluded that native laminaran and slightly sulphated laminaran are absorbed from the posterior intestine and that they are distributed to tissues rich in immunocompetent cells. Thus, these compounds may have potential as immunomodulatory feed additives.