Effect of metabolic acidosis on intestinal absorption of calcium and phosphorus

To investigate the effect of metabolic acidosis on intestinal calcium (Ca) and phosphorus (P) absorption and vitamin D metabolism, metabolic balance studies and in vitro gut sac uptake of ⁴⁵Ca and [³²P]phosphate were performed in rats maintained on low-Ca and moderately low-P diet and fed NH₄Cl for 3 or 9 days and pair-fed controls. Plasma 1,25(OH)₂D concentration was measured in the rats fed NH₄Cl for 9 days and their controls. Net Ca and P absorption was 87-92% in the acidotic rats and did not differ from control. Moreover, gut sac uptakes of ⁴⁵Ca and [³²P]phosphate were not different from control. Plasma 1,25(OH)₂D was higher in the ammonium chloride-fed rats than in controls (213 ± 44 vs. 110 ± 12 pg/ml), and serum P was lower in the acidotic animals (4.6 ± 0.7 vs. 7.6 ± 0.3 mg/dl). These data indicate that metabolic acidosis does not depress the augmented intestinal absorption of calcium and phosphorus noted during their dietary deprivation nor reduce the plasma level of 1,25(OH)₂D.