Epinephrine translocates glut-4 but inhibits insulin-stimulated
glucose transport in rat muscle.
Han, Xiao-Xia, and Arend Bonen.
Department of Kinesiology, University of Waterloo, Waterloo,
Ontario, N2L, 3G1, Canada.
APStracts 4:0287E, 1997.
We examined the effects of epinephrine (25, 50 150 nM) on 1) basal and
insulin-stimulated 3-O-methyl glucose (3-MG) transport in perfused
rat muscles and 2) on GLUT-4 in skeletal muscle plasma membranes.
Insulin increased glucose transport 330-600% in three types of
skeletal muscle (white (WG) and red gastrocnemius (RG), soleus
(SOL)). Glucose transport was also increased by epinephrine (22-48%)
in these muscles (P<0.05). In contrast, the insulin-stimulated 3-MG
transport was reduced by epinephrine in all three types of muscles;
maximal reductions were observed at 25 nM epinephrine in WG (- 25%)
and RG (-32.5%). A dose-dependent decrease occurred in SOL (-27% at
25 nM; -55% at 150 nM P<0.05). Insulin (20 mU/ml) and epinephrine
(150 nM) each translocated GLUT-4 to the plasma membrane, and no
differences in translocation were observed between insulin and
epinephrine (P>0.05). In addition, epinephrine did not inhibit
insulin-stimulated GLUT-4 translocation, and the combined epinephrine
and insulin effects on GLUT-4 translocation were not additive. The
increase in surface GLUT-4 was associated with an increases in muscle
cAMP concentrations, but only when epinephrine alone was present. No
relationship was evident between muscle cAMP concentrations and
surface GLUT-4 in the combined epinephrine and insulin-stimulated
muscles. These studies indicate that epinephrine can translocate
GLUT-4 while at the same time increasing glucose transport when
insulin is absent, or inhibiting glucose transport when insulin is
present.
Received 20 June 1997; accepted in final form 18 December 1997.
APS Manuscript Number E290-7.
Article publication pending Am. J. Physiol. (Endocrinol. Metab.).
ISSN 1080-4757 Copyright 1997 The American Physiological Society.
Published in APStracts on 7 January 1998