Gut Exchange of Glucose and Lactate in Basal State and After Oral Glucose Ingestion in Postoperative Patients

Glucose uptake by the intestine and its conversion into 3-carbon compounds in the human intestine in the basal state and after an oral glucose load are not understood. Consequently, we studied the arterial and portal venous concentration differences (A-PV) for glucose and glucogenic substrates in the basal state and 3 h after the ingestion of a 100-g glucose load with the catheter technique. Five patients were studied 3–11 days after surgery for gallbladder disease or cancer of the colon or liver. A-PV for glucose in the basal state was 0.12 ± 0.02 mM (P < 0.01), indicating net glucose uptake by extrahepatic splanchnic tissues. No net exchange of lactate or pyruvate was detected, but there was release of alanine and uptake of glutamine. After glucose ingestion, glucose was released by the gut, reflecting absorption of the load (mean A-PV for glucose −2.10 ± 0.04 mM, P < 0.01). The arterial glucose concentration rose gradually from 4.6 ± 0.1 mM before glucose ingestion to a plateau at 9.5 ± 0.7 mM from 90 to 180 min. Glucose ingestion was accompanied by net lactate and alanine release (A-PV −0.16 ± 0.06 mM and −48 ± 7 μM, respectively), whereas A-PV for pyruvate did not change. We conclude that, in postoperative patients, there is a significant net glucose uptake by the gastrointestinal tract in the basal state. Glucose ingestion is accompanied by a small release of lactate and alanine from the intestine. However, the estimated net gut formation of lactate and alanine can play only a minor role in the disposal of an oral glucose load.