Evidence that the gastrointestinal tract is involved in glucose homeostasis

Experiments were carried out on fasted anaesthetized dogs. A vein draining a segment of the upper jejunum was cannulated for blood flow measurement and blood samples were obtained for measurement of glucose content of the arterial blood and venous blood from the upper jejunal segment. Glucose uptake was calculated as the product of jejunal blood flow and the difference between arterial and venous glucose levels (A-V glucose). Blood pressure was recorded continuously. The upper jejunum had a resting glucose uptake of 16 +/- 28 mg/min. When adrenaline (1 microgram/kg or 5 micrograms/kg) injection, glucagon (3 micrograms/kg or 8 micrograms/kg) injection or glucose (10 mg/kg/min or 20 mg/kg/min) infusion was given intravenously, glucose uptake increased 600-700%, 700-900%, and 560-600%, respectively at the peak of their responses. These increases in glucose uptake were much greater than increases in blood flow at the peak of responses to adrenaline, glucagon or glucose. Insulin (5 i.mu/kg or 8 i.mu/kg) injection, however, caused a negative glucose uptake of about 400%, i.e., the gut pushed glucose into the blood stream in response to insulin-induced hypoglycaemia. These results indicate that the jejunum plays a modulatory role in glucose homeostasis.