Effect of fast duration on disposition of an intraduodenal glucose load in the conscious dog.

UNLABELLED: The effects of prior fast duration (18 h, n = 8; 42 h, n = 8) on the glycemic and tissue-specific responses to an intraduodenal glucose load were studied in chronically catheterized conscious dogs. [3-3H]glucose was infused throughout the study. After basal measurements, glucose spiked with [U-14C]glucose was infused for 150 min intraduodenally. Arterial insulin and glucagon were similar in the two groups. Arterial glucose (mg/dl) rose approximately 70% more during glucose infusion after 42 h than after an 18-h fast. The net hepatic glucose balance (mg. kg-1. min-1) was similar in the two groups (basal: 1.8 +/- 0.2 and 2.0 +/- 0.3; glucose infusion: -2.2 +/- 0.5 and -2.2 +/- 0.7). The intrahepatic fate of glucose was 79% glycogen, 13% oxidized, and 8% lactate release after a 42-h fast; it was 23% glycogen, 21% oxidized, and 56% lactate release after an 18-h fast. Net hindlimb glucose uptake was similar between groups. The appearance of intraduodenal glucose during glucose infusion (mg/kg) was 900 +/- 50 and 1,120 +/- 40 after 18- and 42-h fasts (P < 0.01).
CONCLUSION: glucose administration after prolonged fasting induces higher circulating glucose than a shorter fast (increased appearance of intraduodenal glucose); liver and hindlimb glucose uptakes and the hormonal response, however, are unchanged; finally, an intrahepatic redistribution of carbons favors glycogen deposition.