This paper describes a new method for evaluating glucose metabolism in man using an oral glucose load. The procedure permits the calculation of a blood glucose disappearance rate constant (K) and thereby makes it possible to compare quantitatively the response to oral and intravenous glucose administration in a given individual. Ten metabolically normal adult humans were studied under carefully controlled conditions. Each received similar amounts (20 g) of glucose both orally and intravenously (2–7 days apart) by constant infusion for 1 hr. The effects on blood glucose disappearance rate constants (K) and plasma insulin concentrations (immunoassay) during and for 1 hr following the infusion were compared. Blood glucose concentrations and K values with the 2 routes of glucose administration were similar. In contrast, plasma insulin responses showed a significant difference: oral glucose resulted in a significant and sustained rise, whereas intravenous glucose was associated with a smaller and transient increase. The plasma insulin increase with intravenous glucose is considered to be due to the wellknown effect of hyperglycemia on insulin secretion. The greater and more sustained increase in plasma insulin with oral glucose is interpreted as evidence for an additional stimulus to insulin secretion, possibly a gastrointestinal or liver factor triggered by alimentary glucose.

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