Sodium-Dependent Phosphate Uptake in the Jejunum Is Post-Transcriptionally Regulated in Pigs Fed a Low-Phosphorus Diet and Is Independent of Dietary Calcium Concentration

Abstract

In rodents, severe dietary P restriction increases active phosphate absorption by the intestine. However, it remains unknown if moderate dietary P restriction has a similar effect. Weanling pigs (n = 32; body weight 7.4 +/- 0.55 kg) were used in a 2 x 2 factorial design and fed dietary available P (aP) concentrations of 0.23 or 0.40% and Ca concentrations of 0.58 or 1.00% for 14 d. Diets were formulated on an aP basis instead of a total P basis, because pigs are unable to absorb phytate-P present in corn and soybean meal. Jejunal segments were mounted in modified Ussing chambers for determination of Na(+)-dependent nutrient transport. Intestinal mucosal scrapings were taken for RNA isolation and brush border membrane (BBM) vesicle isolation. Na(+)-dependent phosphate uptake and gene expression of Na-phosphate cotransporter IIb (NaPi-IIb), SGLT-1 (sodium/glucose cotransporter-1), and calbindin D(9k) and protein expression of NaPi-IIb were evaluated. Na(+)-dependent phosphate transport increased (P < 0.05) 46% as dietary aP concentration was decreased. However, increased Na(+)-dependent phosphate uptake was not accompanied by increased NaPi-IIb mRNA expression. Expression of NaPi-IIb protein in the BBM increased (P < 0.01) 84% in pigs fed low-P diets compared with pigs fed adequate-P diets. No dietary Ca effects or aP x Ca interactions were detected for Na-dependent P uptake, mRNA or protein expression of NaPi-IIb, or mRNA expression of calbindin D(9k). These data suggest that restricting dietary aP concentration by only 43% stimulates Na(+)-dependent phosphate uptake and expression of the NaPi-IIb protein in the BBM of the small intestine and through a post-transcriptional mechanism.

Effects of dietary supplementation of exogenous multi-enzyme mixture containing carbohydrases and phytase on growth performance, energy and nutrient digestibility, and selected mucosal gene expression in the small intestine of weanling pigs fed nutrient deficient diets

“…However, the NC diet did not result in a higher NaPiIIb mRNA expression in this study. This is also in agreement with Saddoris et al (2010). Previously uncharacterized species differences in the regulation of NaPiIIb expression during low dietary P may exist, and this may be responsible for the lack of a change in the expression of NaPiIIb in the pigs on the NC diet.…”

“…Previously uncharacterized species differences in the regulation of NaPiIIb expression during low dietary P may exist, and this may be responsible for the lack of a change in the expression of NaPiIIb in the pigs on the NC diet. As Saddoris et al (2010) reported, the increased NaPiIIb protein abundance in the brush border membranes in pigs fed low P diet was not accompanied by an increased NaPiIIb mRNA expression. Further work is needed to determine if enzymes could influence NaPiIIb protein abundance, especially since there was no enzyme effect on NaPiIIb mRNA expression.…”

The effect of phosphorus restriction during the weaner-grower phase on compensatory growth, serum osteocalcin and bone mineralization in gilts

“…Weaner pigs subjected to moderate dietary P restrictions can adapt by increasing absorption efficiency of P through stimulation of P uptake in the small intestine, however increases in absorption efficiency are not enough to maintain performance to that of pigs fed adequate P diets (Saddoris et al, 2010). Thus, the observed decrease in ADG and ADFI from 10 to 50 kg BW when fed a low-P diet was not surprising.…”

Molecular Mechanisms for Regulation of Intestinal Calcium and Phosphate Absorption by Vitamin D

“…Using in situ loops of intestine [106], brush border membrane vesicles [106,108], and Ussing chambers [113] investigators have shown that dietary phosphate restriction can increase phosphate transport efficiency, e.g. in pig jejunum, phosphate transport is 90% higher in animals fed a 0.25% phosphorus diet compared to a 0.4% phosphorus diet.…”