DIETARY ALUMINUM-CHLORIDE REDUCES THE AMOUNT OF INTESTINAL CALBINDIN-D-28K IN CHICKS FED LOW-CALCIUM OR LOW PHOSPHORUS DIETS

The mechanism of aluminum (Al) toxicity may involve disturbances in ca lcium (Ca) metabolism. Aluminum compounds have been reported to reduce vitamin D-dependent Ca absorption in chicks, rats and humans. To inve stigate the mechanism by which Al reduces Ca absorption, we studied th e effect of dietary aluminum chloride (AlCl3) on the relative amounts of intestinal calbindin D-28K in chicks fed diets varying in Ca and ph osphorus concentration. AlCl3 was added so that Al constituted 0, 0.15 or 0.3 g/100 g of diets that were either adequate, low in Ca, low in P, or contained supplemental P. Diets were fed for 2 wk. Intestinal ca lbindin D-28K levels were assayed using SDS-PAGE and Ca-45 binding to Western blots. Added dietary Al greatly reduced the amount of intestin al calbindin in chicks fed adequate diets, low Ca diets, or low P diet s. When diets with supplemental P were fed, little calbindin was evide nt with or without added Al. Tibia ash, body weight and food intake we re also reduced (P < 0.05) by added Al. These results indicate that di etary AlCl3 inhibits vitamin D-dependent Ca absorption by reducing the amount of intestinal calbindin D-28K. Aluminum, therefore, may interf ere with the body's ability to regulate intestinal calbindin D-28K lev els. This could have implications for other tissues that contain subst antial levels of calbindin D-28K.