Interstitial glucose concentration and glycemia: implications for continuous subcutaneous glucose monitoring

The changes in plasma glucose concentration and in interstitial glucose con centration, determined with a miniaturized subcutaneous glucose sensor, wer e investigated in anesthetized nondiabetic rats. Interstitial glucose was e stimated through two different calibration procedures. First, after a gluco se load, the magnitude of the increase in interstitial glucose, estimated t hrough a one-point calibration procedure, was 70% of that in plasma glucose . We propose that this is due to the effect of endogenous insulin on periph eral glucose uptake. Second, during the spontaneous secondary decrease in p lasma glucose after the glucose load, interstitial glucose decreased faster than plasma glucose, which may also be due to the effect of insulin on per ipheral glucose uptake. Third, during insulin-induced hypoglycemia, the dec rease in interstitial glucose was less marked than that of plasma glucose, suggesting that hypoglycemia suppressed transfer of glucose into the inters titial tissue; subsequently, interstitial glucose remained lower than plasm a glucose during its return to basal value, suggesting that the stimulatory effect of insulin on peripheral glucose uptake was protracted. If these ob servations obtained in rats are relevant to human physiology, such discrepa ncies between plasma and interstitial glucose concentration may have major implications for the use of a subcutaneous glucose sensor in continuous blo od glucose monitoring in diabetic patients.