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This Article Full Text Full Text (PDF) All Versions of this Article: 91/3/531    most recent expphysiol.2005.032516v1 Alert me when this article is cited Alert me if a correction is posted Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Marks, J. Articles by Debnam, E. S. Search for Related Content PubMed PubMed Citation Articles by Marks, J. Articles by Debnam, E. S. Related Collections GI & Epithelial

¹ Department of Physiology² Centre for Nephrology³ Department of Biochemistry & Molecular Biology, Royal Free and University College Medical School, London, UK⁴ Institute of Physiology, University of Zurich, Zurich, Switzerland

Previously, it was thought that intestinal phosphate transport occurred exclusively in the proximal small intestine of rodents and humans. However, a recent study has demonstrated that the ileum of mice contributes significantly to the absorption of dietary phosphate, but it is not known whether this region is also an important site of phosphate absorption in the rat. In the present study, we have investigated the mRNA and protein levels of the sodium–phosphate cotransporter, NaPi-IIb, in three regions of rat and mouse small intestine, and related its expression levels to the rate of net phosphate absorption, as measured using the in situ intestinal loop technique. 1,25-Dihydroxyvitamin D₃ is an important physiological regulator of intestinal phosphate absorption that increases phosphate transport in both the duodenum and jejunum of the rat. Based on the recently proposed regional profile of phosphate absorption along the mouse small intestine, we have re-evaluated the effects of 1,25-dihydroxyvitamin D₃ using three distinct regions of the mouse and rat small intestine. Our studies have revealed important differences in the intestinal handling of phosphate between mice and rats. In mice, maximal phosphate absorption occurs in the ileum, which is paralleled by the highest expression levels of NaPi-IIb mRNA and protein. In contrast, in rats maximal absorption occurs in the duodenum with very little absorption occurring in the ileum, which is similar to the pattern reported in humans. However, in both rodent species only the jejunum shows an increase in phosphate absorption in response to treatment with 1,25-dihydroxyvitamin D₃.

(Received 7 October 2005; accepted after revision 23 January 2006; first published online 23 January 2006)
Corresponding author J. Marks: Department of Physiology, Royal Free and University College Medical School, Royal Free Campus, Rowland Hill Street, London NW3 2PF, UK. Email: j.marks{at}medsch.ucl.ac.uk

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