Splanchnic bed utilization of glutamine and glutamic acid in humans.

To study the fate of enterally delivered nonessential amino acids, glutamine and glutamate, 14 healthy adults were infused in the postabsorptive state with [2-15N]glutamine and [15N]glutamate for 7 h by intravenous (iv) and nasogastric (ng) tube routes. The amount of enterally delivered tracer that was sequestered by the splanchnic bed on the first pass was 54 +/- 4 and 88 +/- 2% for the [2-15N]glutamine and [15N]glutamate tracers, respectively. Only 46 and 12% of the ng glutamine and glutamate tracers entered systemic blood, respectively. The relative amount of 15N transferred from glutamate to glutamine, the transaminating amino acids leucine, isoleucine, valine, and alanine, and to proline was significantly higher when the [15N]glutamate was infused by the ng vs. iv route. The same was also true for [2-15N]glutamine, which presumably transferred 15N after it was converted to glutamate. Thus we conclude that the splanchnic bed sequesters over one-half of the glutamine and almost all of the glutamate delivered to it in the postabsorptive state. There is production of transaminating amino acids in the splanchnic bed, and the splanchnic bed produces simultaneously both glutamine from glutamate and glutamate from glutamine.