Use of [3-3H]glucose and [6-14C]glucose to measure glucose turnover and glucose metabolism in humans

Abstract

[3-3H]glucose is frequently used to measure glucose turnover in humans. If fructose 6-phosphate-fructose 1,6-diphosphate cycling (Fpc) is negligible in both liver and muscle, then [3-3H]- and [6-14C]glucose (corrected for Cori cycle activity) should provide equivalent measures of glucose turnover. In addition, if glycogenolysis is fully suppressed, then [14C]lactate specific activity should equal that of [6-14C]glucose from which it was derived, and oxidation of [6-14C]glucose, as measured by rate of generation of 14CO2, should equal total glucose oxidation (i.e., that derived from intra- and extracellular pools) as measured by indirect calorimetry. To address these questions, glucose turnover was measured simultaneously with [3-3H]- and [6-14C]glucose in the basal state and in presence of low (approximately 200 pM) and high (approximately 750 pM) insulin concentrations. Glucose turnover rates measured with [3-3H]- and [6-14C]glucose were equivalent at all insulin concentrations, indicating that Fpc had no detectable effect on measurement of glucose appearance. [14C]lactate specific activity was lower (P less than 0.01) than that of [6-14C]glucose in the basal state but not during either low- or high-dose insulin infusion, implying that all lactate was derived from extracellular glucose. On the other hand, glucose oxidation as measured by rate of generation of 14CO2 was lower (P less than 0.05) than glucose oxidation as measured by indirect calorimetry during both insulin infusions, implying either that suppression of glycogenolysis was not complete in all tissues or that one or both of these techniques do not accurately measure glucose oxidation.(ABSTRACT TRUNCATED AT 250 WORDS)

Coping with an exogenous glucose overload: glucose kinetics of rainbow trout during graded swimming

“…Therefore, it is a measure of the highest possible rate of glucose oxidation when nonoxidative disposal is nil. In the resting state, mammals only oxidize about 50% of R d as reported for rats (43%) (5), dogs (30 -50%) (31,44), and humans (40 -60%) (16,21). However, during exercise, this can increase to close to 100% as in humans (4).…”

Glutamine: a major gluconeogenic precursor and vehicle for interorgan carbon transport in man.

“…The arterialized glutamine concentration (648±34 jsmol/liter) was approximately twofold greater than that of alanine (325±33 .tmol/liter, P < 0.001) and more than 10-fold greater than that of glutamate (52±5 gmol/liter). The difference in circulating glutamine and alanine concentrations was a consequence (Table III), of both a greater rate of glutamine appearance (5.76±0.26 vs. 4.40±0.33 Htmolkg -' min -' for alanine, P < 0.01 ) and a lower rate of glutamine clearance from plasma (9.3±0.8 vs. 14.7±1.3 ml kg-lmin1 for alanine, P < 0.001).…”

“…However, more plasma glucose is converted to plasma lactate than comes from plasma lactate (3)(4)(5), and glycerol be-comes a quantitatively important gluconeogenic precursor only when there is accelerated lipolysis such as after prolonged fasting (6), and in diabetes mellitus (7). Consequently, under normal circumstances, amino acids are largely responsible for the net addition of carbons to the glucose pool which are not immediately derived from plasma glucose.…”

Pushing the limits of glucose kinetics: how rainbow trout cope with a carbohydrate overload

“…Therefore, it is a measure of the highest possible rate of glucose oxidation when non-oxidative disposal is nil. In the resting state, mammals only oxidize about 50% of R d glucose as reported for rats (43%) (Brooks and Donovan, 1983), dogs (30-50%) (Paul and Bella Issekutz, 1967;Wasserman et al, 1992) and humans (40-60%) (Glamour et al, 1995;Katz et al, 1992). The fraction of R d glucose actually oxidized in resting trout has never been measured, but is most likely less than 100%, as in mammals.…”