Determination of calcium salt solubility with changes in pH and PCO2, simulating varying gastrointestinal environments

Abstract

The amount of calcium available for absorption is dependent, in part, on its sustained solubility in the gastrointestinal (GI) tract. Many calcium salts, which are the calcium sources in supplements and food, have pH-dependent solubility and may have limited availability in the small intestine, the major site of absorption. The equilibrium solubility of four calcium salts (calcium oxalate hydrate, calcium citrate tetrahydrate, calcium phosphate, calcium glycerophosphate) were determined at controlled pH values (7.5, 6.0, 4.5 and < or = 3.0) and in distilled water. The solubility of calcium carbonate was also measured at pH 7.5, 6.0 and 4.5 with two CO(2) environments (0.3 and 152 mmHg) above the solution. The precipitation profile of CaCO(3) was calculated using in-vivo data for bicarbonate and pH from literature and equilibrium calculations. As pH increased, the solubility of each calcium salt increased. However, in distilled water each salt produced a different pH, affecting its solubility value. Although calcium citrate does have a higher solubility than CaCO(3) in water, there is little difference when the pH is controlled at pH 7.5. The partial pressure of CO(2) also played a role in calcium carbonate solubility, depressing the solubility at pH 7.5. The calculations of soluble calcium resulted in profiles of available calcium, which agreed with previously published in-vivo data on absorbed calcium. The experimental data illustrate the impact of pH and CO(2) on the solubility of many calcium salts in the presence of bicarbonate secretions in the intestine. Calculated profiles using in-vivo calcium and bicarbonate concentrations demonstrate that large calcium doses may not further increase intestinal calcium absorption once the calcium carbonate solubility product has been reached.

Comparative Study Between the Effect of Histamine Receptor Antagonists of Type Ii (Famotidine) and Proton Pump Inhibitors (Omeprazole) on the Efficacy of Calcium Carbonate as Phosphate Binder in Haemodialysis Patient

“…In the present study, famotidine aggravated the condition of the patients by augmenting hypocalcaemia state after 4 mo. This effect is supported by Goss et al, 2007 who explained that at neutral pH, calcium carbonate is practically insoluble in water, but although the solubility of calcium salts may be highly pH dependent, calcium absorption is unaffected by alterations in gastric acid secretion [20] In this study, it has also been found that famotidine with caco . 3 did not show any significant change in serum PTH, which contradicted by the study of Bricker, who suggested that original proposal was that phosphate retention as a result of reductions in glomerular filtration rate would cause transient decreases in the levels of calcium, which would, in turn, trigger an increase in PTH secretion and a new steady state would be achieved, with restoration of normal calcium and phosphate levels but, with the consequence that high levels of PTH now would be required to maintain homeostasis [21] The present study shows a significant decrease in serum ALP level upon administration of famotidine in combination with caco .…”

Parathyroid hormone (PTH) rapidly enhances CFTR-mediated HCO3− secretion in intestinal epithelium-like Caco-2 monolayer: a novel ion regulatory action of PTH

“…Unlike the well-buffered apical solution in a Ussing chamber (i.e., the estimated PTH-induced HCO 3 Ϫ flux of ϳ135 pmol·s Ϫ1 ·cm Ϫ2 was not large enough to shift the [HCO 3 Ϫ ]-to-PCO 2 ratio of the buffer solution), the unbuffered ileal fluid would have been alkalinized by the robust HCO 3 Ϫ secretion. Since the ileum is the principal site for phosphate absorption (45), this PTH action could be of physiological significance because phosphate should precipitate as nonabsorbable complexes in the ileal alkaline lumen (11,24), thus fulfilling the classical hypophosphatemic action of PTH (54). On the other hand, in lower vertebrates, the PTH function with regard to HCO 3 Ϫ secretion and the responsive gastrointestinal segment may differ from that in mammals.…”

Protein intake, calcium balance and health consequences

“…Calcium absorption occurs primarily in the duodenum where gastric acid secretion permits to obtain a pH o6.0 necessary for the solubilization of calcium salts from ingested food (Goss et al, 2007). Gastric acid production is not only stimulated by the parasympathetic nervous system but also by chemical signals, nutrients, including Ca 2 þ (Hade and Spiro, 1992;Geibel and Wagner, 2006) and some amino acids (Konturek et al, 1978;Strunz et al, 1978).…”