The influence of acidity in the intestine upon the absorption of calcium salts by the blood

If calcium compounds are present in sufficient amounts in the diet, their solubility in the intestinal contents would be a limiting factor for absorption. Apparently calcium chloride and calcium lactate are quite easily absorbed. Salvesen 1 observed that calcium lactate could supply the entire calcium requirement of parathyroidectomized dogs even on a meat diet. Calcium lactate is quite soluble (about 10 per cent) compared with carbonates, phosphates, and most organic salts of calcium.

The solubility of organic calcium salts generally is favored by acidity. It has been suggested 2 that the acidity of the intestine is a factor in calcium absorption. Inouye 3 remarks that lactose feeding favors the maintenance of a sufficiently high blood calcium concentration to prevent tetany in parathyroidectomized dogs, and that this diet favors an acidophile flora. The diffusible calcium salts of milk are increased by acidification, as well as by tryptic digestion. 4

In order 'to secure evidence on the absorption of calcium salts from the intestine these experiments were performed. Under anesthesia the intestines of dogs and rabbits were injected with CaC1₂, solutions buffered at several hydrogen ion concentrations. Blood samples were removed at the start and at successive periods, and the serum Ca determined by the method of Kramer and Tisdall 5 It has been shown 6 that serum calcium constitutes practically the entire blood calcium.

CaC1₂ solutions were selected as the most soluble of calcium salts, buffering of the acid solutions being accomplished by citrate mixtures. In general, alkaline buffers are objectionable because of the insolubility of their calcium compounds, but the glycocoll mixture was finally used. Possibly because of digestion, the pH of such a solution was not stable, and moved rapidly toward an acid condition in the intestine.

Rabbits did not prove such suitable subjects for the experiments because of the variability found in their normal serum.