Effects of diabetes on intestinal magnesium absorption in the rat

Control and streptozotocin-diabetic rats were studied at 5, 12, and 32 days after induction of diabetes. Magnesium absorption was measured by in situ perfusion of duodenum and ileum. At 5 days, duodenal mucosal growth is similar in controls and diabetics. At 12 days, mucosal growth is 50% greater in diabetics, and at 32 days, 100% greater. Ileal mucosal growth followed the same pattern but was half that of duodenum. Therefore, absorption data were expressed per centimeter segment length to define absorptive capacity of the segment and per gram dry weight of mucosa to define absorptive specific activity. Mean absorptive specific activity was lower in diabetics than controls at all time intervals. The difference was significant only for duodenum of diabetics at 32 days, when magnesium absorption declined to half that of controls. In contrast, absorptive capacity for both segments remained the same in both groups, attributable to the greater mucosal growth in diabetics. These findings for magnesium contrast with effects of diabetes on calcium transport: specific absorption and segment absorptive capacity are depressed in diabetics at both 5 and 11 days. Thus, although transport of magnesium and calcium usually tend to change in parallel in diabetes, transport of magnesium is depressed later and to a lesser degree than calcium, and segment transport capacity is maintained. The findings suggest differences in mechanism of regulation of magnesium and calcium transport.