Phosphorus intake regulates intestinal function and polyamine metabolism in uremia

Abstract

This study found that 5/6-nephrectomized uremic rats showed secondary hyperparathyroidism as reflected by an increase in their serum parathyroid hormone (PTH) level in association with a decrease in serum 1,25-dihydroxyvitamin D [1,25-(OH)2D]. These changes recovered partially upon phosphorus restriction. Calcium absorption and gene expression of calbindin-D9k were decreased in uremia and were also improved by phosphorus restriction. In uremia, intestinal spermidine/spermine N1-acetyltransferase activity was decreased, while ornithine decarboxylase (ODC) activity and its gene expression were potentiated. Enhancement of c-fos and c-jun gene expressions was also observed in uremia. These phenomena suggest that the intestinal villus may proliferate in uremia. Phosphorus restriction prevented increases in the expression of ODC, c-fos and c-jun observed in uremia. Since phosphorus restriction caused a rise in the serum 1,25-(OH)2D level, the role of 1,25-(OH)2D in uremia-induced intestinal dysfunction was examined. A single injection of 1,25-(OH)2D3 to uremic rats caused an increase in the steady-state calbindin-D9k mRNA level, and decreases in steady state c-fos and ODC mRNA levels, suggesting that the deficiency of 1,25-(OH)2D3 is responsible for intestinal dysfunction in uremia. In conclusion, altered polyamine metabolism caused by 1,25-(OH)2D deficiency is intimately involved in intestinal dysfunction and the development of the proliferative state of the intestinal villus in uremia.