Estimation of Glucose Turnover in Rats in vivo with Tritium Labeled Glucoses

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Abstract
Starved and starved-refed rats were injected i.v. with labeled glucose (a mixture of [2-3H]-, [3-3H]- and [U-14C]glucose with either [5-3H]- or [6-3H]glucose), and the decay of the specific activity of [14C]glucose was followed. Glucose was degraded to obtain the 3H/14C ratios for 3 isotope combinations in the same sample. The apparent rates of replacements, apparent C recycling and the body glucose mass were calculated for the different tracers. The 3H/14C ratio from [2-3H, -U-14C]glucose declined much faster than that of the other tracers. Apparent recycling as calculated in fasted rats was 28% for [2-3H, U-14C]-, 18% for [5-3H, U-14C]-, 17% for [3-3H, U-14C] and 14% for [6-3H, U-14C]glucoses. The values in fed rats showed a similar pattern. It was estimated that in fasted rats 85-90% of the 3HOH liberated from injected [2-3H]glucose is formed by catabolism in the periphery and the rest by recycling in the liver between glucose and G-6-P. Detritiation of other labels by hepatic recycling accounts for a very small fraction of the total 3HOH yield.

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