Assessment of the postprandial pattern of glucose metabolism in nondiabetic subjects and patients with non-insulin-dependent diabetes mellitus using a simultaneous infusion of [2 3H] and [3 3H] glucose

Abstract

Glucose turnover determined with tritiated isotopes of glucose is subject to potential error due to glucose/glucose-6-phosphate cycling and/or cycling through glycogen. To determine the extent to which these processes alter the apparent pattern of postprandial glucose metabolism, we measured glucose turnover simultaneously with [2 3H] glucose (an isotope that minimally cycles through glycogen but is extensively detritiated during glucose/glucose-6-phosphate cycling) and [3 3H] glucose (an isotope that is not detritiated during glucose/glucose-6-phosphate cycling but can cycle through glycogen). Glucose turnover was measured in patients with non-insulin-dependent diabetes mellitus (NIDDM) and nondiabetic subjects both before and after ingestion of a carbohydrate meal isotopically with labeled [6 14C] glucose. In the postabsorptive state hepatic glucose appearance was higher ( P < .05) when determined with [2 3H] glucose than with [3 3H] glucose in the diabetic patients, but not in the nondiabetic subjects. After glucose ingestion the integrated responses of glucose appearance, systemic entry of ingested glucose, and hepatic glucose release all were higher ( P < .05) when determined with [2 3H] glucose compared to [3 3H] glucose in both the diabetic and nondiabetic subjects. However, the absolute differences between glucose turnover measured with [2 3H] and [3 3H] glucose were similar in the diabetic and nondiabetic subjects. Both isotopes provided a similar assessment of postprandial carbohydrate metabolism, indicating that either isotope can be used with equal efficacy to compare postprandial carbohydrate metabolism in patients with NIDDM and nondiabetic subjects.