CARBOHYDRATE-METABOLISM IN MG-SUFFICIENT AND MG-DEFICIENT RATS TREATED WITH STREPTOZOTOCIN AND INSULIN

Sprague-Dawley rats weighing 190 to 270 g were rendered Mg-deficient b y feeding a diet with low Mg2+ content (Mg-D, 80 ppm Mg) and deionized water ad libitum. Controls were fed the same diet and drinking water containing 20 mM Mg aspartate HC1 (Mg-S). On day 14, half of the anima ls in each group received an intraperitoneal injection of 75 mg/kg bod y weight (BW) streptozotocin (STZ) and the other half a placebo. On da y 35 subgroups were given a subcutaneous injection of 4 IU/kg BW human insulin. Blood was taken on day 7 (before STZ), 28 (14 days after STZ ) and 35 (3 h after administration of insulin or the placebo) and anal yzed for Mg2+ and glucose. Urine was collected before and after STZ an d also analyzed for glucose and electrolytes. Treatment with STZ resul ted in polyphagia, polydipsia and loss of BW. Mg2+ uptake via food and drinking water increased by a factor of 2 to 5. Mortality started to occur on the 3(rd) day after STZ injection and was significantly highe r in Mg-deficient(61.1%) than in Mg-sufficient (3.8%) animals. Blood g lucose maximally increased on day 28, i.e. 14 days after STZ applicati on (772 mg% in Mg-deficient and 546 mg% in Mg-sufficient rats). Accord ingly, glycosuria was 45% higher in Mg-deficient diabetic rats, and ur inary electrolyte excretion increased considerably in ail diabetic rat s which was partly due to polyphagia and polydipsia. Insulin reduced b lood glucose in the diabetic Mg-sufficient and Mg-deficient rats by ab out the same amount. Liver glycogen in Mg-sufficient and Mg-deficient rats was reduced by STZ and restored by insulin. The effects of insuli n on blood glucose and liver glycogen were not significantly different in Mg-sufficient and Mg-deficient rats.