Summary
The purpose of this study was to further document the role of locally released norepinephrine
(NE) in the control of metabolic and endocrine responses to exercise in rats. Post-ganglionic
blockade with bretylium (20 mg · kg-1, i.v.) reduced NE release from sympathetic nerve endings and triggered a compensatory
increase in epinephrine (E) release from the adrenal medulla, as reflected by plasma
NE and E concentrations at rest and exercise (E/NE ratio = 2.92±0.53 and 2.48±0.51
vs 0.62±0.15 and 1.48±0.18 in control rats; mean±SE). Following bretylium administration
a reduction in running time to exhaustion (28 m · min-1, 8% slope: 33±2 min vs 74±10 min) was associated with 1) a faster decrease in blood
glucose concentration (3.58±0.80 mM vs 8.09±0.38 mM in control rats exercised for
33 min); and 2) an increased glycogen store utilization in fast-twitch muscles (superficial
vastus lateralis and gastrocnemius lateralis). Glycogen utilization was not modified
in soleus muscle and in the liver. Taken together these results suggest that post-ganglionic
blockade increased carbohydrate store and peripheral blood glucose utilization. This
could reflect an impairment in fat mobilization and utilization which might be secondary
to a reduction of NE release in the adipose tissue and/or in the endocrine pancreas.
Key-Words
Bretylium
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Epinephrine
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Norepinephrine
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Pancreatic Hormones
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Carbohydrate Stores
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Blood Glucose
