EFFECTS OF INSULIN ON PLASMA MAGNESIUM IN NONINSULIN-DEPENDENT DIABETES-MELLITUS - EVIDENCE FOR INSULIN-RESISTANCE

Insulin influences both glucose metabolism and magnesium homeostasis i n humans. The present studies sought to determine whether insulin-indu ced stimulation of magnesium uptake is impaired in noninsulin-dependen t diabetes mellitus (NIDDM) and enhanced by acute hyperglycemia. To do so, we measured plasma magnesium concentrations in diabetic and nondi abetic subjects on two occasions: once when glucose concentrations wer e maintained constant and once when glucose concentrations were varied to mimic a postprandial pattern. The same amount of insulin was infus ed on both occasions in a manner that reproduced the systemic insulin concentrations normally observed after glucose ingestion. During the p randial insulin infusion, the decrement in the plasma magnesium concen tration was lower (P < 0.05) in the diabetic patients than that in the nondiabetic subjects during both the euglycemic (4.1 +/- 0.9 vs. 7.8 +/- 1.3 mmol/L 8 h) and hyperglycemic (1.7 +/- 1.1 vs. 6.6 +/- 1.4 mmo l/L 8 h) studies. Glucose disappearance also was lower (P < 0.05) in t he diabetic patients than that in the nondiabetic subjects, and the in sulin-induced decrement in plasma magnesium was correlated (P < 0.01) with glucose disappearance. On the other hand, despite higher (P < 0.0 5) rates of disappearance in the hyperglycemic than euglycemic experim ents, the decrement in plasma magnesium did not differ in either group on either occasion. We conclude that insulin resistance in subjects w ith NIDDM impairs the ability of insulin to stimulate magnesium as wel l as glucose uptake.