THE METABOLISM OF VARIOUSLY C14-LABELED GLUCOSE IN MAN AND AN ESTIMATION OF THE EXTENT OF GLUCOSE METABOLISM BY THE HEXOSE MONOPHOSPHATE PATHWAY

Abstract

Studies of glucose metabolism utilizing radioactive glucose have been reported in several animal species (1-3) including normal and diabetic man (4-6). In these studies the tracer employed has been glucose with the C14 uniformly distributed throughout the six carbon atoms. From the reactions of glucose catabolism in the Embden-Meyerhof pathway, Krebs ' tricarboxylic acid cycle and the hexose monophosphate pathway, it is apparent that the individual carbon atoms of glucose may have different rates of oxidation to carbon dioxide as well as different metabolic fates in the body. Previous studies (7, 8) of ribose metabolism have shown that the hexose monophosphate pathway exists in man. The studies reported here have been performed with glucose labeled with C14 located in specific carbon atoms, in order to ascertain differences in metabolism of individual parts of the sugar. From the results obtained an attempt is made to quantitate in man the extent of glucose metabolism via the hexose monophosphate pathway. METHODS Three normal male and one female volunteer, aged 18 to 21 years, served as subjects for these experiments. All were maintained on a diet containing 300 g of carbohydrate and were fasted overnight prior to and throughout the performance of the study. An intravenous glucose tolerance test performed according to Amatuzio, Stutzman, Vanderbilt and Nesbitt (9) revealed normal glucose tolerance in all of the subjects. Glucose-i-C14, specific activity (SA) 2.67 /Ac per mg, and glucose-2-C"4, SA 5.56 /Ac per mg, were purchased from the Volk Radiochemical Co.; glucose-U-C14, SA 2.06,uc per mg, from Nuclear Chicago; and glucose-6-C4,