ALUMINUM FRACTIONATION IN A SIMULATED RAT STOMACH - AN IN-VITRO STUDY

This study is part of a project dealing with the absorption of alumini um in rats from acidified drinking water. The hypothesis of the projec t was that 'labile' forms of aluminium in water might be more availabl e for absorption than aluminium in food. To investigate this hypothesi s, the distribution of species of the metal within the rat stomach mus t 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 concentrat ion of 4.0 mg l(-1) Al was detected as total dissolved aluminium (Al-t ot) after incubation in a simulated rat stomach. The levels of 'quickl y reacting aluminium' (Al-qr) (approximately the sum of Al3+ and its m onomeric hydroxo and sulfate complexes) were very low (<0.2 mg l(-1)), but difficult to quantify precisely in this matrix. The pattern of th e in vitro results was confirmed by measurements in pooled rat stomach s from in vivo experiments. There are obviously considerable amounts o f ligands present in rat feed that bind strongly to aluminium and ther eby affect the distribution of metal species inside the rat stomach. I t 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 fractiona tion measurements within simulated or real gastric systems.