Calcium and oxalic acid kinetics differ in rats

Small molecular weight calcium salts, if absorbed intact, could provide a n utritional source of calcium in subjects with impaired absorption of calciu m by the saturable pathway. An understanding of the mechanism of absorption of calcium oxalate (as a representative salt) may be important nutritional ly and therapeutically. The aim of the present study was to develop models to study absorption, distribution and retention of calcium and oxalate in r ats as a basis for studying calcium oxalate absorption. Labeled compounds ( Ca-45 and [C-14]-oxalic acid) were administered to separate groups of rats orally (n = 8-11) or intravenously (n = 3-5) and blood was sampled for up t o 240 min. Data were analyzed using SAAM/CONSAM. Calcium kinetics were fitt ed by a model with three compartments in the body and one absorption pathwa y from the intestine. By contrast, oxalic acid kinetics were fitted by two pools in the body and two absorption pathways from the intestine. Calcium a nd oxalic acid, therefore, demonstrate different absorption and distributio n kinetics in rats.