Effect of Bicarbonate Feeding on Intestinal Absorption of Calcium and Vitamin D Metabolism in Rats

1. The effect of bicarbonate (NaHCO₃) feeding on intestinal absorption of calcium and phosphorus and vitamin D metabolism was investigated. Gut sac uptake of ⁴⁵Ca and [³²P]phosphate in vitro, as well as the plasma level of vitamin D metabolites, was determined in rats fed with NaHCO₃ for 9 days and their pair-fed controls.

2. Duodenal uptake of ⁴⁵Ca and [³²P]phosphate by alkalotic rats was less than duodenal uptake by controls. 1,25(OH)₂D plasma level was much higher in alkalotic rats than in their controls, and 25(OH)D slightly higher than in controls.

3. These data suggest that NaHCO₃ feeding causes a substantial increase in 1,25(OH)₂D plasma level, but interferes with calcium and phosphorus absorption in the duodenum.