Permeability of the salmon (Oncorhynchus tshawytscha) posterior intestine in vive to two hydrophilic markers

This study characterised the permeability of the salmonid posterior intesti ne in vivo, to two hydrophilic markers of different molecular weight, both in the presence and absence of sodium deoxycholate (SDA), and determined th e influence of mucosal secretions. The posterior intestine of chinook salmo n was cannulated with a balloon catheter and the lumen infused with a solut ion of fluorescein and C-14-mannitol. In treated fish, the solution also co ntained 5.0 mmol . l(-1) SDA. Blood samples from the dorsal aorta were take n at regular time intervals over 3 h. Clearances and volumes of distributio n were assessed by intravenous administration of the markers to another gro up of fish. In the absence of SDA, low permeabilities were recorded for bot h markers; however, permeabilities for both were significantly greater in t he treated groups. Both solutes had volumes of distribution similar to valu es reported elsewhere. Metabolism of fluorescein by the liver resulted in i ts plasma clearance. In contrast, elimination of mannitol was negligible du ring the study period, probably due to the lowered glomerular filtration ra tes observed in sea water adapted fish. Compared to in vitro investigations , in vivo mucus secretions were significantly lower and solute delivery acr oss the epithelium was higher. Results from these in vivo investigations ha ve implications for the oral delivery of peptides to salmonids.