Glucose homeostasis in magnesium-deficient rats

Glucose homeostasis was studied in rats fed diets containing 750,200, or 100 mg/kg Mg for 6 to 8 weeks, from the age of 4 weeks. Weight gain of the rats receiving 200 and 100 mg/kg diets was decreased. This resulted from both a lower food intake and reduced effectiveness of the ingested food. Fed or fasting plasma glucose levels were similar in the three groups. During an intravenous glucose tolerance test, the rate of glucose disappearance was higher in Mg 100 rats than in controls. By contrast, during an oral glucose tolerance test, the rise in plasma glucose was greater and more sustained in Mg 100 rats. During both tests, the insulin response was markedly lower in Mg-deficient rats than in controls. This could be partially due to the reduced insulin content of the pancreas of these animals. The impairment of tolerance to oral glucose was corrected by 5 weeks on a high-Mg diet. After intravenous injection of insulin, the fall in plasma glucose levels was also slightly more pronounced in Mg 100 rats. During no test did we observe a significant difference between glucose or insulin responses in Mg 200 or Mg 750 rats. These results, thus, show that chronic Mg deficiency alters several parameters of glucose homeostasis in the rat.