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The entry of urea into the lumen of the gastrointestinal tract is facilitated by the urea transporter protein UT-B1. This stage is crucial to our intestinal wellbeing as it is the first step in the urea nitrogen salvaging mechanism which is necessary for healthy gut bacteria. In a previous study a 35kDa glycosylated signal of UT-B1 was strongly expressed in the ascending colon whereas it was almost absent in the descending colon. Our aim was to investigate the expression of UT-B in the whole gastrointestinal tract. To investigate whetherthere are multiple UT-B isoforms in the Cl tract, a number of primer sets were designed from the human UT-B gene. UT-B1 has been identified as the major, if not sole UT-B urea transporter at the RNA level. Using an antibody raised against bovine UT-B1 we found that the small intestine had the strongest 35kDa signal. Surprisingly the ileum had the highest percentage glycosylation, which deglycosy-lated to 30kDa as expected. There was a significant decrease in the amount of glycosylated UT-B1 from the ileum to the left colon. This may show importance of UT-B further up the GI tract than previously thought. In the rat we found that UT-B was solely expressed in the large intestine. According to our results, unlike the rat, UT-B1 is expressed throughout the human GI tract. It is highly glycosylated in the ileum, which suggests it is functionally active here. Further investigation is needed to establish the physiological significance of these findings. [ABSTRACT FROM AUTHOR]