Absorption of calcium oxalate does not require dissociation in rats

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