Measurement of glucose turnover--implications for the study of inborn errors of metabolism.

Aspects of glucose metabolism have been investigated quantitatively employing stable isotopes for 20 year. Use of non-recycling [6,6-2H2] or [U-13C] glucose labels provides a value for total hepatic glucose production (glycogenolysis plus gluconeogenesis). Quantitation of gluconeogenesis with isotopic tracers has itself recently been revisited employing protocols and analytical options that purport to overcome the isotope exchanges (dilution) experienced at the level of oxaloacetate when the rate of incorporation of label into glucose from infused alanine, lactate or pyruvate is monitored. Labelled glucose has been employed to investigate metabolic disturbances of glycogen storage disease type I (GSD-I) and type III (GSD-III). Endogenous glucose production and glucose recycling have been studied in both these storage diseases employing a primed-continuous infusion of D-[U-13C] glucose and quantitation of isotope enrichments and isotopomer distribution observed in plasma glucose either by mass spectrometry or nuclear magnetic resonance spectroscopy. General aspects of glucose metabolism as investigated with stable isotopes are presented.