Abstract
1,25-dihydroxyvitamin D3 [1,25-(OH)2D3] could promote phosphorus (P) absorption in the duodenum of broilers. The vitamin D receptor (VDR) mediates the action of 1,25-(OH)2D3. However, it remains unknown whether and how VDR is involved in promoting P absorption in the duodenum of broilers by 1,25-(OH)2D3. The objective of the current study was to investigate the effect of added 1,25-(OH)2D3 levels on P absorption, mRNA or protein expression levels of VDR, retinoid X receptor (RXR), type IIb sodium-phosphate cotransporter (NaPi-IIb), inorganic phosphate transporter (PiT) 1 and PiT-2, and the enrichments of VDR bound to DNA promoters of the above P transporters in the ligated duodenal loops of Arbor Acres male broilers. The duodenal loops were perfused with solutions (pH = 6.0) containing 0 (control), 12.5, or 25.0 ng/L of 1,25-(OH)2D3 for up to 40 min. The results indicated that the addition of either 12.5 or 25.0 ng/L 1,25-(OH)2D3 to the perfusates increased (P < 0.04) P absorption percentage and rate, as well as the mRNA expression levels of VDR, RXR, NaPi-IIb, and PiT-2, alongside protein expression levels of VDR, NaPi-IIb, and PiT-2, whereas it did not affect (P > 0.10) PiT-1 mRNA and protein expression levels. Moreover, 1,25-(OH)2D3 administration increased (P < 0.01) the enrichments of VDR bound to NaPi-IIb and PiT-2 DNA promoter regions in the ligated duodenal loops of broilers, which were in line with their mRNA expression levels. These findings suggest that 1,25-(OH)2D3 increased P absorption possibly through VDR-mediated transactivation of NaPi-IIb and PiT-2 genes in the duodenum of Arbor Acres male broilers.