Effect of enteral vs. parenteral glucose delivery on initial splanchnic glucose uptake in nondiabetic humans. Am J Physiol Endocrinol Metab 283: E259-E266, 2002. First published March 27, 2002 10.1152/ajpendo.00178.2001.-To determine if enteral delivery of glucose influences splanchnic glucose metabolism, 10 subjects were studied when glucose was either infused into the duodenum at a rate of 22 mol ⅐ kg Ϫ1 ⅐ min Ϫ1 and supplemental glucose given intravenously or when all glucose was infused intravenously while saline was infused intraduodenally. Hormone secretion was inhibited with somatostatin, and glucose (ϳ8.5 mmol/l) and insulin (ϳ450 pmol/l) were maintained at constant but elevated levels. Intravenously infused [6,6-2 H2]glucose was used to trace the systemic appearance of intraduodenally infused [3-3 H]glucose, whereas UDP-glucose flux (an index of hepatic glycogen synthesis) was measured using the acetaminophen glucuronide method. Despite differences in the route of glucose delivery, glucose production (3.5 Ϯ 1.0 vs. 3.3 Ϯ 1.0 mol ⅐ kg Ϫ1 ⅐ min Ϫ1 ) and glucose disappearance (78.9 Ϯ 5.7 vs. 85.0 Ϯ 7.2 mol ⅐ kg Ϫ1 ⅐ min Ϫ1 ) were comparable on intraduodenal and intravenous study days. Initial splanchnic glucose extraction (17.5 Ϯ 4.4 vs. 14.5 Ϯ 2.9%) and hepatic UDP-glucose flux (9.0 Ϯ 2.0 vs. 10.3 Ϯ 1.5 mol ⅐ kg Ϫ1 ⅐ min Ϫ1 ) also did not differ on the intraduodenal and intravenous study days. These data argue against the existence of an "enteric" factor that directly (i.e., independently of circulating hormone concentrations) enhances splanchnic glucose uptake or hepatic glycogen synthesis in nondiabetic humans. splanchnic glucose metabolism; postprandial hyperglycemia; acetaminophen glucuronide; hepatic glycogen synthesis; enteric signal GLUCOSE CONCENTRATIONS RARELY exceed 8.0-9.0 mmol/l in healthy nondiabetic humans. This is because of a complex interplay in the regulation of glucose metabolism between splanchnic and extrasplanchnic tissues. After carbohydrate ingestion, the splanchnic bed limits the amount of glucose that must be disposed of by peripheral tissues by a variety of mechanisms (20,22,24). These include metabolism of a portion of the ingested glucose by the gut, stimulation of hepatic glucose uptake, and suppression of hepatic (and perhaps renal) glucose production (1, 12, 36). The route of glucose delivery is also important. It is well established that glucose tolerance is better during enteral than during intravenous glucose delivery. This is in part because of increased insulin secretion mediated by neural (commonly referred to as the cephalic phase) and incretin pathways (4,7,21,60). It is less clear whether enteral glucose administration directly (i.e., independently of changes in hormone concentrations) enhances splanchnic glucose uptake in humans.Several studies suggest that it may. DeFronzo et al. (19) used the hepatic catheterization technique in an effort to determine whether the route of glucose delivery influences splanchnic glucose balance. They reported that net splanchnic...