Aluminium fractionation in a simulated rat stomach: an in vitro study

This study is part of a project dealing with the absorption of aluminium in rats from acidified drinking water. The hypothesis of the project was that 'labile' forms of aluminium in water might be more available for absorption than aluminium in food. To investigate this hypothesis, the distribution of species of the metal within the rat stomach must be considered. So far, few attempts in this direction have been made. The distribution of aluminium forms in vitro was studied, simulating the conditions present in a rat stomach. The in vitro set-up is based on methods used for drug release studies. The results show that only part of the aluminium (29-54%) added in 'labile' forms at a concentration of 4.0 mg l-1 Al was detected as total dissolved aluminium (Altot) after incubation in a simulated rat stomach. The levels of 'quickly reacting aluminium' (Alqr) (approximately the sum of Al and its monomeric hydroxo and sulfato complexes) were very low (< 0.2 mg l-1), but difficult to quantify precisely in this matrix. The pattern of the in vitro results was confirmed by measurements in pooled rat stomachs from in vivo experiments. There are obviously considerable amounts of ligands present in rat feed that bind strongly to aluminium and thereby affect the distribution of metal species inside the rat stomach. It is believed that phosphoserine, present in the protein casein, is an important ligand for aluminium complexation in this case. The results show that studies of Al absorption should be accompanied by fractionation measurements within simulated or real gastric systems.