Lack of correlation between sodium-lithium countertransport activity and insulin action in non-insulin-dependent diabetes mellitus

An association between maximal sodium-lithium countertransport (SLC) activity and insulin action has been reported in diabetic patients with hypertension. It is currently not known whether such a relationship occurs in NIDDM patients in the absence of hypertension. To address this question, we studied SLC activity and insulin action in normotensive people with NIDDM and matched non-diabetic controls. Insulin was infused in a manner mimicking insulin concentrations normally observed in non-diabetic subjects following food ingestion while glucose was clamped at ∼5 mmols. Both the glucose infusion rate required to maintain euglycemia and the tracer determined rate of glucose disappearance were lower (P<0.05) in the diabetic than non-diabetic subjects indicating insulin resistance. However, maximal SLC activity was not significantly correlated (r = -0.01 to 0.29) with either the glucose infusion rate required to maintain euglycemia or insulin induced glucose disappearance in either the diabetic or non-diabetic subjects. We conclude that SLC activity is not an index of insulin action in NIDDM.