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Abstract
The intestinal absorption of calcium (Ca) from Ca ascorbate (Ca-AsA) was investigated in normal rats. Each animal was perorally administered either 5 mg (low dose) or 10 mg (high dose) of Ca in 1 ml of distilled water as Ca-AsA, Ca carbonate (CaCO^sub 3^), or Ca chloride (CaCl^sub 2^), which were intrinsically labeled with ^sup 45^Ca using ^sup 45^CaCl^sub 2^. The amount of radioactivity in plasma was measured periodically up to 34 h after dosing, and pharmacokinetic parameters were calculated from the radioactivity in plasma. The time taken to reach the maximum ^sup 45^Ca level (T^sub max^) did not differ among the three groups. The area under the plasma ^sup 45^Ca level/time curve (AUC∞) value for the Ca-AsA group was significantly higher than those for the CaCO^sub 3^ and the CaCl^sub 2^ groups. The radioactivity at T^sub max^ (C^sub max^) for the Ca-AsA group was significantly higher than those for the CaCO^sub 3^ and the CaCl^sub 2^ groups for the low dose, and comparable with or significantly higher than those for the CaCl^sub 2^ and CaCO^sub 3^ groups for the high dose. Similar results were observed for whole-body ^sup 45^Ca retention. Radioactivity in the femur 34 h after dosing was the highest in the Ca-AsA group and the lowest in the CaCO^sub 3^ group. The rank order of solubility in water, the first fluid (pH 1.2, JP-1) of JPXIII disintegration medium, acetate buffer solution (pH 4.0), triethanolamine-malate buffer solution (pH 7.0) and ammonium chloride buffer solution (pH 10.0) at 37°C was CaCl^sub 2^ > Ca-AsA > CaCO^sub 3^. In contrast, the rank order of the solubility in the second fluid (pH 6.8, JP-2) of JPXIII disintegration medium at 37°C was Ca-AsA > CaCl^sub 2^ > CaCO^sub 3^. These results indicate that the absorbability of Ca from Ca-AsA is almost comparable with, or higher than, that from CaCl^sub 2^ and significantly higher than that from CaCO^sub 3^ because of its high degree of solubility in the intestine. Therefore, Ca-AsA would be useful as a Ca supplement with relatively high absorption from intestine.[PUBLICATION ABSTRACT]