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1 Department of Molecular Physiology and Biophysics and 2 Diabetes Research and Training Center, Vanderbilt University School of Medicine, Nashville, Tennessee 37232-0615
To test whether hepatic
insulin action and the response to an insulin-induced decrement in
blood glucose are enhanced in the immediate postexercise state as they
are during exercise, dogs had sampling (artery, portal vein, and
hepatic vein) catheters and flow probes (portal vein and hepatic
artery) implanted 16 days before a study. After 150 min of moderate
treadmill exercise or rest, dogs were studied during a 150-min
hyperinsulinemic (1 mU · kg
1 · min
1) euglycemic
(n = 5 exercised and n = 9 sedentary)
or hypoglycemic (65 mg/dl; n = 8 exercised and
n = 9 sedentary) clamp. Net hepatic glucose output
(NHGO) and endogenous glucose appearance (Ra) and utilization (Rd) were assessed with arteriovenous and
isotopic ([3-3H]glucose) methods. Results show that,
immediately after prolonged, moderate exercise, in relation to
sedentary controls: 1) the glucose infusion rate required to
maintain euglycemia, but not hypoglycemia, was higher; 2)
Rd was greater under euglycemic, but not hypoglycemic conditions; 3) NHGO, but not Ra, was suppressed
more by a hyperinsulinemic euglycemic clamp, suggesting that hepatic
glucose uptake was increased; 4) a decrement in glucose
completely reversed the enhanced suppression of NHGO by insulin that
followed exercise; and 5) arterial glucagon and cortisol
were transiently higher in the presence of a decrement in glucose. In
summary, an increase in insulin action that was readily evident under
euglycemic conditions after exercise was abolished by moderate
hypoglycemia. The means by which the glucoregulatory system is able to
overcome the increase in insulin action during moderate hypoglycemia is
related not to an increase in Ra but to a reduction in
insulin-stimulated Rd. The primary site of this reduction
is the liver.
liver; metabolism; oxidation; glucose; lactate; nonesterified fatty acids
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