Anne Marie Bakke-McKellep

Effects of dietary soyabean meal, inulin and oxytetracycline on intestinal microbiota and epithelial cell stress, apoptosis and proliferation in the teleost Atlantic salmon (Salmo salar L.).

Soyabean meal (SBM)-induced enteritis in the distal intestine of the teleost Atlantic salmon (Salmo salar L.) and other salmonids may be considered a model for diet-related mucosal disorders in other animals and man. The role of the intestinal microbiota in its pathogenesis was explored. Compared to diets containing fishmeal (FM) as the sole protein source, responses to extracted SBM or the prebiotic inulin, with or without oxytetracycline (OTC) inclusion, were studied following a 3-week feeding trial. Intestinal microbiota, organosomatic indices and histology, as well as immunohistochemical detection of proliferating cell nuclear antigen (PCNA), heat shock protein 70 (HSP70) and caspase-3-positive cells in the distal intestine, were studied. Distal intestine somatic indices (DISI) were higher in inulin and lower in SBM compared to FM-fed fish. The low DISI caused by SBM corresponded with histological changes, neither of which was affected by OTC, despite a significant decrease in adherent bacteria count. Image analysis of PCNA-stained sections showed a significant increase in the proliferative compartment length in SBM-fed fish, accompanied by apparent increases in reactivity to HSP70 and caspase-3 along the mucosal folds, indicating induction of cellular repair and apoptosis, respectively. Fish fed the SBM diet had higher total number as well as a more diverse population composition of adherent bacteria in the distal intestine. Thus SBM-induced enteritis is accompanied by induction of distal intestinal epithelial cell protective responses and changes in microbiota. Putative involvement of bacteria in the inflammatory response merits further investigation.

In vitro uptake and interaction between arginine and lysine in the intestine of Atlantic salmon (Salmo salar)

Abstract The kinetics and interactions of the in vitro uptake of the amino acids lysine and arginine were studied in the mid intestine of Atlantic salmon by the everted sleeve method. Since an imbalance of amino acids may affect feed utilisation and growth by metabolic and/or absorptive mechanisms, knowledge of the uptake dynamics of the two amino acids is relevant. The maximum rate of transport (Vmax) and apparent affinity value (Kt) for carrier-mediated arginine uptake were lower as compared to the kinetic parameters for carrier-mediated lysine uptake. Carrier-mediated uptake of arginine showed a Vmax of 0.22 nmol mg−1 min−1 and a Kt of 3.5 mM and a permeability coefficient (P) of 0.014 nmol mg−1 min−1 mM−1 for the non-saturable uptake. Carrier-mediated uptake of lysine showed a Vmax of 0.50 nmol mg−1 min−1 and Kt of 13.7 mM and a P of 0.010 nmol mg−1 min−1 mM−1 for the non-saturable uptake. Interactions were revealed, as the total uptake of one amino acid was affected by the presence of the other amino acid in the incubation solution, suggesting that the amino acids share a common carrier. Lysine had both a stimulatory and inhibitory effect on the uptake of arginine, depending on the relative concentration of the two amino acids. Arginine had an inhibitory effect on lysine uptake, regardless of concentration.