We used hepatic balance and tracer ([3H]
glucose) techniques to examine the impact of "breakfast" on hepatic
glucose metabolism later in the same day. From 0-240 min, 2 groups of conscious dogs (n = 9 dogs/group) received a duodenal infusion of
glucose (GLC) or saline (SAL), then were fasted from 240-360 min. Three dogs from each group were euthanized and tissue collected at 360 min. From 360-600 min, the remaining dogs underwent a hyperinsulinemic (4× basal) hyperglycemic clamp (arterial
blood glucose 146 ± 2 mg/dL) with portal GLC infusion. The total GLC infusion rate was 14% greater in dogs infused with GLC than in those receiving SAL (AUC360-600min 2,979 ± 296 vs. 2,597 ± 277 mg/kg, respectively). The rates of hepatic
glucose uptake (5.8 ± 0.8 vs. 3.2 ± 0.3 mg ⋅ kg-1 ⋅ min-1) and
glycogen storage (4.7 ± 0.6 vs. 2.9 ± 0.3 mg ⋅ kg-1 ⋅ min-1) during the clamp were markedly greater in dogs receiving GLC compared with those receiving SAL.
Hepatic glycogen content was ∼50% greater,
glycogen synthase activity was ∼50% greater,
glycogen phosphorylase activity was ∼50% lower, and the amount of phosphorylated
glycogen synthase was 34% lower, indicating activation of the
enzyme, in dogs receiving GLC compared with those receiving SAL. Thus, morning GLC primed the liver to extract and store more
glucose in the presence of hyperinsulinemic
hyperglycemia later in the same day, indicating that breakfast enhances the liver's role in
glucose disposal in subsequent same-day meals.