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The effect of fasting and refeeding on mRNA expression of PepT1 and gastrointestinal hormones regulating digestion and food intake in zebrafish (Danio rerio)

Koven, William, Schulte, Patricia
Fish physiology and biochemistry 2012 v.38 no.6 pp. 1565-1575
Danio rerio, aquariums, cholecystokinin, compensatory growth, digestion, digestive tract, fish, food deprivation, food intake, gastrin-releasing peptide, gene expression, ghrelin, messenger RNA, microvilli, polymerase chain reaction, protons, quantitative analysis, refeeding, ribosomal RNA, satiety, secretion, transporters, tripeptides
In vertebrates, a significant part of ingested protein is absorbed as di- and tripeptides through a brush border membrane proton/oligopeptide transporter protein called PepT1. The aim of the present study was to determine the effect of short-term food deprivation and refeeding in adult zebrafish (Danio rerio) on gastrointestinal mRNA expression of PepT1 as well as on the satiety hormones cholecystokinin (CCK), gastrin-releasing peptide (GRP) and ghrelin (GHR) in order to elucidate a potential mechanism driving compensatory growth. Sixty adult zebrafish were stocked in a 40-L aquarium and fed daily a commercial flake diet to satiation for 10 days where the digestive tracts (DT) of sampled fish (n = 5) were dissected out. Samplings were repeated following 1, 2 and 5 days of food deprivation and after 1, 2 and 5 days of refeeding. The RNA was extracted from all sampled DTs and analyzed by quantitative real-time PCR for the mRNA expression of PepT1, rRNA 18S, CCK, GRP and GHR. PepT1 mRNA expression increased with successive refeedings reaching a level approximately 8 times higher than pre-fast levels. CCK, GRP and GHR mRNA levels also decreased during fasting, but increased only to pre-fasting levels with refeeding. Overall, the results suggest that PepT1 may be a contributing mechanism to compensatory growth that could influence CCK secretion and GRP and GHR activity.