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- and
-adrenergic receptor stimulation
on hepatic glucose production during heavy exercise
Department of Molecular Physiology and Biophysics and Diabetes Research and Training Center, Vanderbilt University School of Medicine, Nashville, Tennessee 37232
The role of catecholamines in the control of
hepatic glucose production was studied during heavy exercise in dogs,
using a technique to selectively block hepatic
- and
-adrenergic
receptors. Surgery was done >16 days before the study, at which time
catheters were implanted in the carotid artery, portal vein, and
hepatic vein for sampling and the portal vein and vena cava for
infusions. In addition, flow probes were implanted on the portal vein
and hepatic artery. Each study consisted of a 100-min equilibration, a
30-min basal, a 20-min heavy exercise (~85% of maximum heart rate), a 30-min recovery, and a 30-min adrenergic blockade
test period. Either saline (control; n = 7) or
(phentolamine)- and
(propranolol)-adrenergic blockers
(Blk; n = 6) were infused in the
portal vein. In both groups, epinephrine (Epi) and norepinephrine (NE)
were infused in the portal vein during the blockade test period to
create supraphysiological levels at the liver. Isotope ([3-3H]glucose)
dilution and arteriovenous differences were used to assess hepatic
function. Arterial Epi, NE, glucagon, and insulin levels were similar
during exercise in both groups. Endogenous glucose production
(Ra) rose similarly during
exercise to 7.9 ± 1.2 and 7.5 ± 2.0 mg · kg
1 · min
1
in control and Blk groups at time = 20 min. Net hepatic glucose output
also rose to a similar rate in control and Blk groups with exercise.
During the blockade test period, arterial plasma glucose and
Ra rose to 164 ± 5 mg/dl and
12.0 ± 1.4 mg · kg
1 · min
1,
respectively, but were essentially unchanged in Blk. The attenuated response to catecholamine infusion in Blk substantiates the
effectiveness of the hepatic adrenergic blockade. In conclusion, these
results show that direct hepatic adrenergic stimulation does not
participate in the increase in Ra,
even during the exaggerated sympathetic response to heavy exercise.
catecholamine; adrenergic blockade; endogenous glucose production
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