Effect of solubility on the gastrointestinal absorption of aluminum from various aluminum compounds in the rat.

The present study was carried out to determine whether the insoluble property of most aluminum compounds was the reason for the limited absorption of this element from the gastrointestinal tract. Aluminum compounds of varying degrees of solubility were studied. At pH 3, more than 25% of the aluminum from all of the compounds studied (with the exception of sucralfate [13%]) was in solution. At pH 6, the solubility of aluminum in Al(OH)3 and sucralfate was less than 1%; it was 15% in AlCl3 and 33% in aluminum lactate. Aluminum solubility did not change with a change in pH for the citrate compounds, which varied between 38%, with sucralfate plus citric acid, and 91%, with aluminum citrate. The fraction of the administered dose of aluminum absorbed as estimated by urinary excretion after gastric gavage was 0.015% for sucralfate and Al(OH)3, 0.037% for AlCl3 and aluminum lactate, and greater than 0.80% for all aluminum compounds administered with citrate. A similar relationship was found between the solubility of the aluminum compounds and absorption, as determined by calculated absorption from the changes in plasma aluminum levels. Solubility alone, however, could not totally explain the effect of citrate on aluminum absorption. The solubility of aluminum in aluminum lactate and sucralfate plus citric acid were the same at pH 6. Absorption of aluminum from aluminum lactate, however, was only 1.6% as much as that found for sucralfate plus citric acid.(ABSTRACT TRUNCATED AT 250 WORDS)