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Department of Molecular Physiology and Biophysics, Vanderbilt University School of Medicine, Nashville, Tennessee 37232-0615
Portal glucose delivery in the conscious dog augments net
hepatic glucose uptake (NHGU). To investigate the possible role of
altered autonomic nervous activity in the effect of portal glucose
delivery, the effects of adrenergic blockade and acetylcholine (ACh) on
hepatic glucose metabolism were examined in 42-h-fasted conscious dogs.
Each study consisted of an equilibration (
120 to
20
min), a control (
20 to 0 min), and a
hyperglycemic-hyperinsulinemic period (0 to 300 min). During the
last period, somatostatin (0.8 µg · kg
1 · min
1)
was infused along with intraportal insulin (1.2 mU · kg
1 · min
1)
and glucagon (0.5 ng · kg
1 · min
1).
Hepatic sinusoidal insulin was four times basal (73 ± 7 µU/ml) and
glucagon was basal (55 ± 7 pg/ml). Glucose was infused peripherally (0-300 min) to create hyperglycemia (220 mg/dl). In test protocol, phentolamine and propranolol were infused intraportally at 0.2 µg and
0.1 µg · kg
1 · min
1
from 120 min on. ACh was infused intraportally at 3 µg · kg
1 · min
1
from 210 min on. In control protocol, saline was given in place of the
blockers and ACh. Hyperglycemia-hyperinsulinemia switched the net
hepatic glucose balance
(mg · kg
1 · min
1)
from output (2.1 ± 0.3 and 1.1 ± 0.2) to uptake (2.8 ± 0.9 and 2.6 ± 0.6) and lactate balance
(µmol · kg
1 · min
1)
from uptake (7.5 ± 2.2 and 6.7 ± 1.6) to output (3.7 ± 2.6 and 3.9 ± 1.6) by 120 min in the control and test protocols,
respectively. Therefter, in the control protocol, NHGU tended to
increase slightly (3.0 ± 0.6 mg · kg
1 · min
1
by 300 min). In the test protocol, adrenergic blockade did not alter
NHGU, but ACh infusion increased it to 4.4 ± 0.6 and 4.6 ± 0.6 mg · kg
1 · min
1
by 220 and 300 min, respectively. These data are consistent with the
hypothesis that alterations in nerve activity contribute to the
increase in NHGU seen after portal glucose delivery.
hepatic blood flow; lactate
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