Effect of fast duration on disposition of an intraduodenal glucose load inthe conscious dog

The effects of prior fast duration (18 h, n = 8; 42 h, n = 8) on the glycem ic and tissue-specific responses to an intraduodenal glucose load were stud ied in chronically catheterized conscious dogs. [3-H-3]glucose was infused throughout the study. After basal measurements, glucose spiked with [U-C-14 ]glucose was infused for 150 min intraduodenally. Arterial insulin and gluc agon were similar in the two groups. Arterial glucose (mg/dl) rose similar to 70% more during glucose infusion after 42 h than after an 18-h fast. The net hepatic glucose balance (mg kg(-1) min-l) was similar in the two group s (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% oxidiz ed, and 8% lactate release after a 42-h fast; it was 23% glycogen, 21% oxid ized, and 56% lactate release after an 18-h fast. Net hindlimb glucose upta ke was similar between groups. The appearance of intraduodenal glucose duri ng glucose infusion (mg/kg) was 900 +/- 50 and 1,120 +/- 40 after 18- and 4 2-h fasts (P < 0.01). Conclusion: glucose administration after prolonged fa sting induces higher circulating glucose than a shorter fast (increased app earance of intraduodenal glucose); Liver and hindlimb glucose uptakes and t he hormonal response, however, are unchanged; finally, an intrahepatic redi stribution of carbons favors glycogen deposition.