Effect of Degree of Polymerization of Silicic Acid on the Gastrointestinal Absorption of Silicate in Rats

Three varieties of sodium aluminosilicate gels with known distributions of molecular forms of silicic acid were orally administered to rats. One preparation was composed chiefly of low molecular weight silicic acids, another preparation of soluble polysilicic acids, and the third preparation of insoluble polysilicic acids. Urinary silicic acid excretion was regarded as corresponding to silicic acid absorption, after oral administration of these silicate preparations, and the relation between silicic acid absorption and degree of polymerization was studied. Among various silicic acids formed upon acid hydrolysis of silicates in the stomach, orthosilicic acid in particular was absorbed, while polysilicic acids, regardless of solubility, were hardly absorbable. It seems likely that silicic acids are absorbed from the digestive tract through the lipoid membrane pore route, the mechanism being common in the permeation of hydrophilic molecules. The possible mechanism of formation of calculi composed of silicic acid is discussed.