Methods for measuring gluconeogenesis in vivo.

Recent developments in stable isotope technology have led to the conception of new protocols for measuring the contribution of gluconeogenesis to glucose production in humans. Earlier techniques were subject to variable underestimations resulting from isotopic exchanges occurring during the transfer of carbon label from the tracer to glucose. This review concentrates on four novel techniques: (1) mass isotopomer distribution analysis of glucose labelled from [13C]glycerol or [13C]lactate; (2) mass isotopomer distribution analysis of glucose and lactate during infusion of [U-13C6]glucose; (3) 2H-enrichment of body water by ingestion of 2H2O, and measuring the 2H-labelling on C5 and C2 of glucose, and (4) difference between glucose turnover and rate of hepatic glycogenolysis measured by nuclear magnetic resonance spectroscopy. The advantages and limitations of the four protocols are discussed. The 2H2O technique is the most practical; it is not subject to artifacts resulting from isotopic exchanges, and is not affected by zonation of hepatic metabolism.