| Summary: | PepT1 (Peptide Transporter 1, SLC15A1) is a proton-coupled peptide transporter responsible for uptake of short peptides and peptide-like drugs from the intestinal lumen into enterocytes. A PepT1-type transporter has recently been sequenced for Atlantic cod and found to be expressed along the whole post-gastric intestine including pyloric caeca. In the present thesis the effect of dietary inclusion of peptides and amino acids on expression of PepT1 mRNA in different regions of juvenile Atlantic cod intestine was investigated. Five groups of cod weighing 10-15 grams were fed for 46 days with a diet containing approximately 42% crude protein, either as fishmeal (FM diet) or 30 % of the fish meal substituted by either whole fish hydrolysate (FH diet), retenate after ultra filtration of fish hydrolysate (UFR diet), retenate after nano filtration of fish hydrolysate (NFR diet) or a mix of free amino acids (FAA diet). After 14 days (T1) and at the end of the experiment (46 days; T3), three fish were sampled from each group and the intestine divided into five segments, namely pyloric caeca (S1) and the remainder of the intestine from the pyloric caeca to the anus divided into four equally long segments (S2 to S5). Total RNA isolated from each segment was subjected to a two-step quantitative RT-PCR using SYBR green and Atlantic cod elongation factor 1 alpha as reference gene. For all diets PepT1 was found to be expressed in all segments, suggesting that for juvenile Atlantic cod the whole intestine is involved in peptide absorption. The different groups of fish showed a similar PepT1 mRNA expression in all segments, but differences in regional expression were found. At T3 the regional expression profile showed statistical differences in PepT1 expression between segments in the FAA and UFR fed fish (diets included amino acids or larger sized peptides). Both groups had a higher expression in S2 and S3 (mid intestine) then pyloric caeca (S1) and S5. A similar trend was also observed for the UFR at T1, while the FAA fed fish ...
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