Glucose metabolism during exercise in man: the role of insulin in the regulation of glucose utilization.
The present study was designed to characterize further the role of insulin in the regulation of glucose utilization during a 2-h exercise at 40% VO2max in 14 h fasted, healthy subjects. Endogenous insulin and glucagon were suppressed by somatostatin infusion and replaced singly or in combination to match the hormonal concentrations observed during similar exercise in saline-treated control subjects. Glucose kinetics were determined by a tracer method using D-[2,3,4,6,6-2H]glucose. In the exercising controls, during the last hour of the exercise, plasma glucose remained stable (4.26 +/- 0.06 mmol/L) and glucose utilization (Rd) increased significantly (p < 0.05) from 12.2 +/- 0.2 to 28.6 +/- 1.3 mumol.kg-1.min-1. During insulin deficiency without glucagon replacement, plasma glucose was maintained at 3.74 +/- 0.10 mmol/L by dextrose infusion, but with glucagon replacement plasma glucose increased to 6.69 +/- 0.24 mmol/L (p < 0.05). These hormonal changes were associated with an increase in Rd to 18.6 +/- 1.1 mumol.kg-1.min-1 (p = ns versus resting controls) and to 37.9 +/- 1.9 mumol.kg-1.min-1 (p < 0.05 versus resting controls), respectively. When insulin was replaced without glucagon replacement, plasma glucose was maintained at 3.85 +/- 0.06 mmol/L by dextrose infusion and Rd increased significantly (p < 0.05) from the resting value to 25.9 +/- 0.7 mumol.kg-1.min-1. When insulin was replaced together with glucagon, the plasma glucose (4.29 +/- 0.15 mmol/L) and the Rd (32.1 +/- 0.9 mumol.kg-1.min-1, p < 0.05 versus the resting value) obtained were similar to the values from the saline exercising control. Glucose metabolic clearance rate (MCR) significantly increased (p < 0.05) during exercise in all protocols. When insulin was made deficient, MCR increased 2-fold (p < 0.05) during exercise (2.7 to 4.8 and 5.4 mL.kg-1.min-1, respectively, with and without glucagon deficiency). However, when insulin was present, with and without glucagon deficiency, it increased further to 6.7 and 7.5 mL.kg-1.min-1, respectively, and values were different (p < 0.05) from glucose MCRs during insulin deficiencies. It is concluded that in 14 h fasted, healthy subjects, exercise per se can stimulate whole body glucose uptake even when insulin is made deficient. Insulin is necessary, however, for optimal glucose utilization during prolonged mild intensity exercise.
Lavoie
C
C
Research Group on Diabetes and Metabolic Regulation, Clinical Research Institute of Montréal, Canada.
Ducros
F
F
Bourque
J
J
Langelier
H
H
Chiasson
J L
JL
D000328:Adult; D001786:Blood Glucose / Q000187:drug effects / Q000378:metabolism; D015444:Exercise / Q000502:physiology*; D005215:Fasting / Q000378:metabolism; D005230:Fatty Acids, Nonesterified / Q000097:blood; D005934:Glucagon / Q000097:blood; D005947:Glucose / Q000378:metabolism*; D006801:Humans; D007328:Insulin / Q000097:blood / Q000502:physiology*; D008297:Male; D010187:Pancreatic Hormones / Q000097:blood / Q000378:metabolism; D013004:Somatostatin / Q000494:pharmacology
D001786:Blood Glucose; D005230:Fatty Acids, Nonesterified; D007328:Insulin; D010187:Pancreatic Hormones; D013004:Somatostatin; D005934:Glucagon; D005947:Glucose