Duodenal aluminum absorption in the rat: effect of vitamin D

Aluminum absorption by the duodenum was studied with an in vivo isolated gut segment technique in vitamin D-deficient and vitamin D-replete rats. Aluminum uptake could be resolved into saturable and nonsaturable components. Both groups demonstrated an identical nonsaturable mechanism with an aluminum uptake of approximately 23% of the amount perfused per 100 mg dry intestinal weight. Saturable absorption was significantly lower in the vitamin D-deficient group (Jmax 6.9 +/- 1.4 microM X h-1 X 100 mg dry wt-1) than in the vitamin D-replete group (Jmax 13.0 +/- 2.7 microM X h-1 X 100 mg dry wt-1) (P less than 0.05). The presence of aluminum in the perfusion solutions reduced duodenal calcium absorption by 33% (P less than 0.02) in the vitamin D-replete group but not the vitamin D-deficient group. These results suggest that aluminum is absorbed in the duodenum by both a nonsaturable mechanism and a vitamin D-dependent saturable mechanism, for which it may compete with calcium.