Background: Precise knowledge of the rate of glucose absorption after meal feeding requires invasive methods in humans.
Objective: This study aimed to validate in an animal model a technique combining the euglycemic hyperinsulinemic clamp and oral carbohydrate loading (OC-Clamp) as a noninvasive procedure to quantify the posthepatic appearance of glucose after oral carbohydrate loading.
Design: Twenty-one pigs were fitted with arterial, jugular, portal, and duodenal catheters and a portal blood flow probe. At glucose clamp steady state, duodenal glucose (0.9 g/kg; DG-Clamp) and oral carbohydrate (140 g corn or mung bean starch as part of a mixed meal; OC-Clamp) were administered while the glucose infusion was progressively reduced to compensate for the incremental posthepatic appearance of glucose. [3-3H]glucose was used to assess the glucose turnover rate.
Results: Hepatic glucose production was totally suppressed by insulin infusion, and the whole-body glucose turnover rate remained stable during glucose absorption. The incremental portal appearance of glucose after the DG load was not altered by hyperinsulinemia, and the cumulative posthepatic appearance of glucose was 63 +/- 3% (x +/- SEM) of the DG load. The net hepatic portal appearance of glucose remained constant during absorption (34 +/- 3% of the load). After the OC load, the respective portal appearance rates of glucose were significantly different between carbohydrate sources; however, the rates paralleled those of the posthepatic appearance of glucose. Again, net hepatic glucose uptake expressed as portal appearance was similar for both carbohydrates.
Conclusions: The results validate the OC-Clamp method to monitor the posthepatic appearance of glucose after carbohydrate ingestion and to discriminate between different carbohydrate sources. The results suggest that the technique be used in humans.