Magnesium deficiency improves glucose homeostasis in the rat: studies in vivo and in isolated islets in vitro

The serum mineral levels, glucose disappearance rate (k(g)), total area und er the glucose (BG) and insulin (DeltaI) curves, and static insulin secreti on were compared among rats fed a Mg-deficient diet for 6 (DF-6) or 11 (DF- 11) weeks, and rats fed a control diet for the same periods (CO-6 and CO-11 groups). No change in glucose homeostasis was observed among DF-6, CO-6 an d CO-11 rats. DF-11 rats showed an elevated k(g) and a reduced BG and Delta I. For evaluating the effect of supplementation, rats fed a control or Mg-d eficient diet for 6 weeks were then fed a Mg-supplemented diet for 5 weeks (SCO and SDF groups respectively). The serum Mg levels in SDF rats were sim ilar to those in CO-11 and SCO rats. but higher than in the DF-11 group. SD F rats showed similar k(g), DeltaG and DeltaI compared with the CO-11 and S CO groups. However, a significantly lower k(g) and higher DeltaG and hi wer e observed in SDF compared with DF-11 rats. Basal and 8.3 mmol glucose/l-st imulated insulin secretion by islets from DF-II rats were higher than by is lets from CO-11 rats. These results indicate that moderate Mg depletion for a long period may increase the secretion and sensitivity to insulin, while Mg supplementation in formerly Mg-deficient rats may prevent the increase in sensitivity and secretion of insulin.