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HORMONES AND SIGNALING
Department of Pharmacy, Kyoto University Hospital, Faculty of Medicine, Kyoto University, Kyoto, Japan
Submitted 26 April 2006 ; accepted in final form 19 May 2006
We previously demonstrated that starvation markedly increased the amount of mRNA and protein levels of the intestinal H+/peptide cotransporter (PEPT1) in rats, leading to altered pharmacokinetics of the PEPT1 substrates. In the present study, the mechanism underlying this augmentation was investigated. We focused on peroxisome proliferator-activated receptor
(PPAR
), which plays a pivotal role in the adaptive response to fasting in the liver and other tissues. In 48-h fasted rats, the expression level of PPAR
mRNA in the small intestine markedly increased, accompanied by the elevation of serum free fatty acids, which are endogenous PPAR
ligands. Oral administration of the synthetic PPAR
ligand WY-14643 to fed rats increased the mRNA level of intestinal PEPT1. Furthermore, treatment of the human intestinal model, Caco-2 cells, with WY-14643 resulted in enhanced PEPT1 mRNA expression and uptake activity of glycylsarcosine. In the small intestine of PPAR
-null mice, augmentation of PEPT1 mRNA during fasting was completely abolished. In the kidney, fasting did not induce PEPT1 expression in either PPAR
-null or wild-type mice. Together, these results indicate that PPAR
plays critical roles in fasting-induced intestinal PEPT1 expression. In addition to the well-established roles of PPAR
, we propose a novel function of PPAR
in the small intestine, that is, the regulation of nitrogen absorption through PEPT1 during fasting.
Caco-2; SLC15A1; starvation; glycylsarcosine; small intestine
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