AJP - Endocrinology and Metabolism, Vol 256, Issue 6 E811-E817, Copyright © 1989 by American Physiological Society
Disposition of a glucose load in fed rats and rats adapted to a high-carbohydrate diet
C. B. Niewoehner and F. Q. Nuttall
Endocrinology, Metabolism, and Nutrition Section, Veterans Administration Medical Center, Minneapolis 55417.
Current evidence suggests that, during the transition from the fasted to
the fed state, liver glycogen is synthesized primarily from gluconeogenic
precursors rather than from glucose unless the circulating glucose
concentration is high. In the fed state the glucose concentration already
is elevated. We aimed to determine whether administration of an additional
oral glucose load (4 g/kg) to chow- or high-carbohydrate diet-adapted (CHO)
rats would further increase the glucose concentration and result in
increased direct glucose uptake. In the chow- and CHO-fed rats, 70 and 98%
of the administered glucose was absorbed by 120 min. In the chow-fed rats
the glucose concentration entering the liver increased by only 1.0 mM from
8.0 to 9.0 mM; no net hepatic glucose uptake was observed. In the
CHO-adapted rats the entering glucose concentration increased transiently
by 3.5 mM from 8.0 to 11.5 mM. This was associated with net glucose uptake,
which continued until the entering glucose concentration fell below 9.5 mM,
the entering glucose concentration threshold above which net glucose uptake
was observed previously in fasted rats. Net hepatic glucose uptake could
not be correlated with insulin or hepatic intracellular glucose
concentrations. Net glycogen synthesis did not occur in either group. We
could not account for the absorbed glucose by the rise in portal glucose
concentrations or by increased muscle glycogen deposition. The fate of much
of the absorbed glucose remains unknown.
