Received October 7, 2005
Revised November 16, 2005
Accepted after revision January 23, 2006
GI & Epithelial Physiology [230]
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Intestinal phosphate absorption and the effect of Vitamin D: a comparison of rat with mouse
Joanne Marks 1*,
Surjit K Srai 1,
Jurg Biber 2,
Heini Murer 2,
Robert J Unwin 1,
Edward S Debnam 1
1 Royal Free and University College Medical School
2 University of Zurich
* To whom correspondence should be addressed. E-mail: j.marks{at}medsch.ucl.ac.uk.
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Abstract |
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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 if 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 has been shown to be an important physiological regulator of intestinal phosphate absorption. Earlier studies have established that this hormone 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 on three distinct regions of the mouse and rat small intestine. Our studies have revealed important differences in the intestinal handling of phosphate in 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.
Key Words:
Brush-border membrane, Phosphate, Small intestine
