Interaction of exercise, insulin and hypoglycemia studied using
hyperinsulinemic euglycemic and hypoglycemic clamp techniques.
Zinker, Bradley A., Robert G. Allison, D. Brooks Lacy, and David H.
Wasserman.
Department of Molecular Physiology and Biophysics, Vanderbilt
University, School of Medicine, Nashville, TN 37232
APStracts 3:0258E, 1996.
Hyperinsulinemic euglycemic and hypoglycemic clamps were used to study
the interaction of exercise, insulin and hypoglycemia at rest and
during exercise in the dog. Sampling (artery and portal, hepatic, and
iliac veins) and infusion (vena cava) catheters and a flow probe
(external iliac artery) were implanted surgically >17 days
prior to study. Following an 18 h fast and an 80 min tracer
equilibration period, dogs were studied in the basal state (t=-40 to
0 min) and during a moderate treadmill exercise (t=0 to 150 min)
period or an equivalent duration sedentary period. Insulin was
infused at 1 mU/kg x min from t=0 to 150 min. In one group of
sedentary (n=7) and one group of exercised (n=6) dogs, glucose was
clamped at basal during the insulin infusion. In another group of
sedentary (n=6) and another group of exercised (n=6) dogs, arterial
glucose was clamped at hypoglycemic levels (65 mg/dl) during the
insulin infusion. Arteriovenous difference and isotopic (3-3H
-glucose, U-14C-glucose) techniques were used to assess glucose
metabolism. Insulin levels were 40 [mu]U/ml in all groups. Data show
that, (a) counterregulatory hormone (glucagon, catecholamines and
cortisol) responses to exercise and hypoglycemia combined are
synergistically higher than the response to either stimulus alone;
(b) exercise-induced increases in insulin action are negated during
hypoglycemia by the counterregulatory response; (c) decreased need
for exogenous glucose during hypoglycemic compared to euglycemic
exercise is due to stimulation of endogenous glucose production,
which accounts for 30% of the decrease, and reduction of glucose
utilization which accounts for 70%; and (d) insulin-stimulated non
-oxidative glucose metabolism is unaffected by exercise or
hypoglycemia, while insulin-stimulated oxidative glucose metabolism
is selectively increased by exercise and decreased by hypoglycemia.
In conclusion, the marked rise in insulin action during exercise is
matched, under insulin-induced hypoglycemic conditions, by an equally
profound increase in counterregulation. The effectiveness of the
potent insulin counterregulatory response may be important in
decreasing the magnitude and frequency of exercise- induced
hypoglycemia.
Received 20 September 1996; accepted in final form 5 December
1996.
APS Manuscript Number E475-6.
Article publication pending Am. J. Physiol. (Endocrinol. Metab.).
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 31 December 1996