Oxidation of glutamine by the splanchnic bed in humans.
Level 3 - non-randomized controlled study
Small crossover physiological tracer study in healthy human volunteers
PubMed 10751191 · doi:10.1152/ajpendo.2000.278.4.E593
What was done
Five postabsorptive healthy volunteers completed two 7-hour dual-tracer infusions of [1,2-13C2]glutamine and [ring-2H5]phenylalanine. On each occasion, tracers were administered for 3.5 hours intravenously and 3.5 hours via nasogastric tube in a crossed-over sequence. Splanchnic first-pass uptake, whole-body glutamine flux, tracer oxidation (via exhaled 13CO2), and conversion into plasma glucose were quantified at isotopic plateau.
What was found
First-pass splanchnic extraction removed 27 ± 2% of enteral phenylalanine and 64 ± 2% of enteral glutamine. Total glutamine flux was 303 ± 8 µmol·kg⁻¹·h⁻¹. Exhaled 13CO2 recovery was 73 ± 2% for enteral versus 58 ± 1% for intravenous tracer. The fraction of enteral glutamine oxidized directly on first pass by the splanchnic bed was 53 ± 2%, accounting for 83% of the extracted tracer. Incorporation into plasma glucose was 7% for intravenous and 10% for nasogastric glutamine.
Why it matters
This study provides direct human quantitative evidence that the major metabolic fate of enterally absorbed glutamine during first-pass splanchnic transit is energy production via oxidation, with only a small portion directed toward gluconeogenesis.
Limits
The study is restricted by a very small sample size (n = 5) and evaluated only healthy subjects in the postabsorptive state. Splanchnic measurements reflect combined gut and liver metabolism without distinguishing gut-specific mucosal oxidation from hepatic uptake.
Cited by
- partial When ingested orally, the gut and liver consume the vast majority of glutamine, resulting in very little entering the bloodstream.