Dietary factors affecting sodium -dependent phosphate uptake and gene expression of the NaPi -IIb in the small intestine of weanling pigs

Kari L Saddoris, Purdue University

Abstract

Three experiments were conducted to determine the effect of dietary P, Ca, and vitamin D supplementation on Na+-dependent phosphate uptake in the small intestine of weanling pigs. Additionally, mechanisms through which regulation of intestinal P transport occurs were investigated. In Exp. 1, feeding low-P diets to weanling pigs resulted in a 46% increase in Na +-dependent P uptake in the small intestine compared to pigs fed adequate P diets. The increase in Na+-dependent P uptake was accompanied by an 82% increase in abundance of the NaPi-IIb cotransporter protein in brush border membrane vesicles isolated from the jejunum. However, no differences were detected in expression of NaPi-IIb mRNA in the small intestine. This indicates increases in Na+-dependent P uptake in pigs fed a low-P diet occur through a post-transcriptional mechanism. Additionally, this increase was unaffected by dietary Ca concentrations. In Exp. 2, treating Caco-2 cells with 10 nM 1,25(OH)2D3 for 48 h resulted in a 52% increase in Na+-dependent P uptake. However, feeding vitamin D-deficient pigs cholecalciferol concentrations of 1200 IU failed to further stimulate Na+-dependent P uptake over that of pigs fed 350 IU of cholecalciferol. Additionally, no differences were detected in NaPi-IIb mRNA expression in the jejunum. In Exp. 3, we attempted to determine if increases in Na+-dependent P uptake in pigs fed low-P diets occurs via transcriptional, translational, or post-translational mechanisms. Pigs were fed either a low (0.07%) or adequate (0.80%) P diet for 3 d and were i.p. injected with either actinomycin D, cycloheximide, or saline daily. Sodium-dependent P uptake was increased 34% in pigs fed the low-P diet compared to pigs fed the adequate P diet. Additionally, no effects of injection were detected indicating that stimulation of Na+-dependent P uptake can occur in the presence of a transcriptional or translational inhibitor. Overall, consumption of a low-P diet appears to stimulate Na+-dependent transport and abundance of the NaPi-IIb cotransporter on the BBM of enterocytes in the small intestine of weanling pigs through a post-translational mechanism.

Degree

Ph.D.

Advisors

Radcliffe, Purdue University.

Subject Area

Livestock

COinS