Aluminum effects upon calbindin D9k-linked duodenal calcium transport in diabetic male rats.

In order to elucidate if the inhibition mechanisms of Aluminum (Al) on intestinal calcium flux involve some possible action on calbindin-D9k, a series of in vivo and in vitro experiments were carried out in normal and in streptozotocin-induced diabetic male rats. The dose-response curves obtained from the in vitro studies indicate that, in the diabetic group (which has a lower content of calbindin-D9k), the effect of Al on JCa(ms) has a small dependence on rising Al concentration (0-10 microM). The parameters obtained from those curves: Emax (maximum reduction percentage of JCa(ms)) and ED50 (Al concentration that produces half of the highest inhibition) were significantly diminished in this group compared to control. Both s.c. injections of calcitriol (D3) at doses of 0.08 and 0.40 microg/kg body wt. per day and insulin (10 IU/kg body wt. per day), increase the inhibitory effect of Al to levels that did not differ from controls. In vivo gavage of 60 mg/kg body wt. per day of aluminum chloride for 1 week reveals that the degree of reduction of intestinal CaBP9k by Al is directly correlated to duodenal content of this protein (r2 = 0.683, P = 0.022).

Sex-related differences in the effect of aluminum on calcium transport in the small intestine of the rat.

Everted sacs of distinct segments of small intestine from male and female rats were incubated with 2 microM of aluminum (Al). In duodenum, Al significantly diminished calcium flux (JCams) in cycling females (31%, P < 0.01) and in males (17%, P < 0.05). Incubation under anaerobic conditions nullified the inhibition of Al on JCams both in male and in female duodenal sacs. Jejunal and ileal JCams measured under aerobic conditions were not modified by the presence of Al in mucosal fluid compared to Al-free controls, neither in males nor in cycling females. In ovariectomized female rats treated with estrogen the studies of dose-response curves showed that the sensitivity to the effect of Al on JCams was raised (the dose that produced half maximum response diminished) with increasing 17 beta-estradiol serum levels, without changes in the maximum response. In castrated male rats injected with testosterone, the effect of Al on duodenal JCams was found to be independent of testosterone levels. In summary, our results demonstrated that the Al inhibition on duodenal JCams was influenced by sexual hormone levels in females but was independent of them in males.