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TRANSFER OF URANIUM THROUGHOUT THE ENTIRE GASTROINTESTINAL TRACT IN RAT.

 Dublineau I, Grison S, Baudelin C, Dudoignon N, Marquette C, Souidi M, Voisin P and Aigueperse J. 33 th annual meeting of the european society for radiation biology, 25-28 aout 2004, Budapest, Hongrie.

Summary

 Objective. The presence of uranium in environment may lead to contamination of human population throughout the entire life mainly by chronic ingestion. The mechanisms of uranium transfer from alimentary bolus to blood are still not well known. The aim of this present study was thus to determine the preferential digestive segments for uranium absorption throughout the entire alimentary tract (oral cavity, small intestine, colon) with in vivo and ex vivo approaches. In addition, some information about the nature of transepithelial pathways (para- or trans-cellular) was done.

Methods. The experiments are performed in Sprague-Dawley rats. After euthanasia (overdose of sodium pentobarbitone), samples of digestive segments  (duodenum, jejunum, ileum, proximal and distal colon) were placed in Ussing chambers to measure tissue transepithelial resistance (RT= PD/Isc in Ohm/cm2) and apparent permeability of uranium (Papp(U) in cm/s) with mucosal-serosal 233U fluxes (2 kBq/4 ml). These experiments were completed by in vivo experiments performed in anaesthetized rat after in situ deposit of uranium (50 kBq/ml) in specific parts of digestive tract and measurements of uranium apparition in peripheral blood (up to 3 hours after) to estimate uranium absorption by each studied segment.

Results. Papp values in small intestine were of 3.0 cm/s for duodenum, 1.6 for jejunum and 2.4 for ileum. In large intestine, values were very different from proximal colon (3.7 cm/s) to distal colon (1.7 cm/s). A negative correlation was found in large intestine between RT and Papp(U) (r2=0.88), which suggests a paracellular pathway for uranium in this part of digestive tract, unlike in small intestine. Results of in vivo experiments indicated uranium absorption by ileum and no uranium absorption by mouth and proximal colon.

Conclusion. The results obtained in the present study indicated no uranium absorption by buccal cavity. Concerning the small intestine, different parts (duodenum, jejunum and ileum) of this segment had the capacity to transport uranium, with a more important passage observed in duodenum. In large intestine, the marked value of Papp(U) obtained ex vivo in proximal colon suggested uranium absorption by this segment, which was not corroborated with in vivo experiments. In conclusion, only small intestine seems to participate to the gastrointestinal absorption of uranium.

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