Extensive gut metabolism limits the intestinal absorption of excessive supplemental dietary glutamate loads in infant pigs

Glutamate (Glu) is a major intestinal oxidative fuel, key neurotransmitter, and may be a useful dietary supplement to augment health of the infant gut. We quantified the metabolic fate of various supplemental dietary Glu intakes in young pigs surgically implanted with vascular, intraduodenal (ID), or intragastric (IG) catheters and a portal blood flow probe. Piglets were acutely fed a range of dietary Glu intakes using a basal milk formula (100%) supplemented with varying amounts of monosodium Glu (up to 400%) via ID or IG routes. We quantified the gastrointestinal metabolic fate of dietary Glu using [U-13C] Glu tracer. The Glu net absorption in the basal 100% group was low in both ID and IG groups, ranging from 13 to 17% of intake. Enteral Glu supplementation significantly increased the absolute absorption rate and arterial concentration of Glu. In both the ID and IG groups, enteral [13 C]Glu absorption was limited (<5% tracer input) at the basal Glu intake (100%) but increased nearly 4-fold (-20% input) in the 300% intake group. A substantial fraction (33-50%) of the enteral [C-13]Glu input was oxidized by the gut to (CO2)-C-13 in both the 100 and 300% intake groups. We conclude that extensive gut metabolism limits the absorption of supplemental dietary Glu even at excessive intakes.