Abstract
Calcium absorption is thought to occur only if calcium is in a soluble or dissociated form, although experimental evidence is lacking. The intestinal absorption of calcium oxalate, a small, neutral and virtually insoluble calcium salt, was elucidated in the whole body of awake rats. Suspensions of 45Ca ascorbate, 14C-oxalic acid and doubly labeled 45Ca- [14C]-oxalate were given by gavage to separate groups of rats. Following dosing, blood samples were drawn for up to 240 min through a previously inserted intravenous catheter. Serum was assayed for radioactive tracers, and data were then plotted as fraction of dose over time. Calcium absorption was 15% [with a loading of 0.3 mmol (15 mg) calcium], oxalic acid absorption was 22% and Ca-oxalate absorption was 45Ca from calcium ascorbate and 14C from oxalic acid differed, whereas 45Ca and 14C from doubly labeled Ca-oxalate had identical serum appearance profiles. Therefore, we conclude that calcium oxalate was absorbed intact. Addition of excess, unlabeled calcium to the doubly-labeled calcium oxalate did not alter the relationship of the serum level of the two tracers, confirming absorption of calcium oxalate as the intact salt. Thus, calcium bound as a small, neutral, calcium salt such as calcium oxalate does not have to be dissociated prior to absorption. Possibly other small compounds would be similarly absorbed. These results alter our current understanding of calcium bioavailability from foods and therapeutic agents.
| Original language | English |
|---|---|
| Pages (from-to) | 170-173 |
| Number of pages | 4 |
| Journal | Journal of Nutrition |
| Volume | 129 |
| Issue number | 1 |
| State | Published - 1999 |
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All Science Journal Classification (ASJC) codes
- Food Science
- Medicine (miscellaneous)
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Absorption of calcium oxalate does not require dissociation in rats. / Hanes, Denise A.; Weaver, Connie M.; Heaney, Robert P.; Wastney, Meryl.
In: Journal of Nutrition, Vol. 129, No. 1, 1999, p. 170-173.Research output: Contribution to journal › Article
}
TY - JOUR
T1 - Absorption of calcium oxalate does not require dissociation in rats
AU - Hanes, Denise A.
AU - Weaver, Connie M.
AU - Heaney, Robert P.
AU - Wastney, Meryl
PY - 1999
Y1 - 1999
N2 - Calcium absorption is thought to occur only if calcium is in a soluble or dissociated form, although experimental evidence is lacking. The intestinal absorption of calcium oxalate, a small, neutral and virtually insoluble calcium salt, was elucidated in the whole body of awake rats. Suspensions of 45Ca ascorbate, 14C-oxalic acid and doubly labeled 45Ca- [14C]-oxalate were given by gavage to separate groups of rats. Following dosing, blood samples were drawn for up to 240 min through a previously inserted intravenous catheter. Serum was assayed for radioactive tracers, and data were then plotted as fraction of dose over time. Calcium absorption was 15% [with a loading of 0.3 mmol (15 mg) calcium], oxalic acid absorption was 22% and Ca-oxalate absorption was 45Ca from calcium ascorbate and 14C from oxalic acid differed, whereas 45Ca and 14C from doubly labeled Ca-oxalate had identical serum appearance profiles. Therefore, we conclude that calcium oxalate was absorbed intact. Addition of excess, unlabeled calcium to the doubly-labeled calcium oxalate did not alter the relationship of the serum level of the two tracers, confirming absorption of calcium oxalate as the intact salt. Thus, calcium bound as a small, neutral, calcium salt such as calcium oxalate does not have to be dissociated prior to absorption. Possibly other small compounds would be similarly absorbed. These results alter our current understanding of calcium bioavailability from foods and therapeutic agents.
AB - Calcium absorption is thought to occur only if calcium is in a soluble or dissociated form, although experimental evidence is lacking. The intestinal absorption of calcium oxalate, a small, neutral and virtually insoluble calcium salt, was elucidated in the whole body of awake rats. Suspensions of 45Ca ascorbate, 14C-oxalic acid and doubly labeled 45Ca- [14C]-oxalate were given by gavage to separate groups of rats. Following dosing, blood samples were drawn for up to 240 min through a previously inserted intravenous catheter. Serum was assayed for radioactive tracers, and data were then plotted as fraction of dose over time. Calcium absorption was 15% [with a loading of 0.3 mmol (15 mg) calcium], oxalic acid absorption was 22% and Ca-oxalate absorption was 45Ca from calcium ascorbate and 14C from oxalic acid differed, whereas 45Ca and 14C from doubly labeled Ca-oxalate had identical serum appearance profiles. Therefore, we conclude that calcium oxalate was absorbed intact. Addition of excess, unlabeled calcium to the doubly-labeled calcium oxalate did not alter the relationship of the serum level of the two tracers, confirming absorption of calcium oxalate as the intact salt. Thus, calcium bound as a small, neutral, calcium salt such as calcium oxalate does not have to be dissociated prior to absorption. Possibly other small compounds would be similarly absorbed. These results alter our current understanding of calcium bioavailability from foods and therapeutic agents.
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M3 - Article
VL - 129
SP - 170
EP - 173
JO - Journal of Nutrition
JF - Journal of Nutrition
SN - 0022-3166
IS - 1
ER -