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Research Group on Diabetes and Metabolic Regulation, Research Center, Centre Hospitalier de l'Université de Montréal, Hôtel-Dieu Pavilion Department of Medicine, University of Montréal, Montreal, Quebec H2W 1T8; and Department of Physical Activities, Université du Québec à Trois-Rivières, Trois-Rivières, Quebec, Canada G9A 5H7
This study was designed to characterize the impact of endurance
training on the hepatic response to glucagon. We measured the effect of
glucagon on hepatic glucose production (HGP) in resting trained
(n = 8) and untrained
(n = 8) healthy male subjects (maximal
rate of O2 consumption: 65.9 ± 1.6 vs. 46.8 ± 0.6 ml O2 · kg
1 · min
1,
respectively, P < 0.001). Endogenous
insulin and glucagon were suppressed by somatostatin (somatotropin
release-inhibiting hormone) infusion (450 µg/h) over 4 h. Insulin
(0.15 mU · kg
1 · min
1)
was infused throughout the study, and glucagon (1.5 ng · kg
1 · min
1)
was infused over the last 2 h. During the latter period, plasma glucagon and insulin remained constant at 138.2 ± 3.1 vs. 145.3 ± 2.1 ng/l and at 95.5 ± 4.5 vs. 96.2 ± 1.9 pmol/l in
trained and untrained subjects, respectively. Plasma glucose increased and peaked at 11.4 ± 1.1 mmol/l in trained subjects and at 8.9 ± 0.8 mmol/l in untrained subjects
(P < 0.001). During glucagon stimulation, the mean increase in HGP area under the curve was 15.8 ± 2.8 mol · kg
1 · min
1
in trained subjects compared with 7.4 ± 1.6 mol · kg
1 · min
1
in untrained subjects (P < 0.01)
over the first hour and declined to 6.8 ± 2.8 and 4.9 ± 1.4 mol · kg
1 · min
1
during the second hour. In conclusion, these observations indicate that
endurance training is associated with an increase in HGP in response to
physiological levels of glucagon, thus suggesting an increase in
hepatic glucagon sensitivity.
exercise; endurance training; insulin-to-glucagon ratio
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