Role of the Oropharynx in Regulation of Glycemia

Previous studies have demonstrated that reflexes originating from the oral cavity at the start of food intake are necessary to ensure a normal glucose tolerance. In our experiment, the underlying mechanisms of these reflexes were studied in conscious, freely moving rats bearing chronic catheters. A double-isotope technique was used to measure, under non-steady-state conditions, rates of total glucose appearance (total R_a), total glucose disappearance (R_d), gut glucose absorption (gut R_a), hepatic glucose production (HGP), and the metabolic clearance rate of glucose (MCR_g). In random order, 1 wk apart, rats either spontaneously drank 1 ml of a 60% glucose solution or were given the same dose into the stomach via a chronic gastric catheter. Glycemia and insulinemia were lower when glucose was taken orally than when the same amount of the substrate was administered intragastrically. Total R_a after glucose administration was the same in both groups throughout the experiment. Despite lower insulin and glucose values, the increase in R_d was initially higher in the oral group than in the intragastric group. This was accompanied by initial higher MCR_g values in the oral group than in animals that received the glucose load directly into their stomachs. We conclude that a series of reflexes elicited by oral glucose ingestion improve glucose tolerance by increasing the efficiency of glucose disposal in the early stages after a glucose load, with a smaller amount of insulin released.