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1 School of Physical and Health Education, University of Wyoming, Laramie, Wyoming 82071; and 2 Department of Physiology, University of Birmingham Medical School, Birmingham B15 2TT, United Kingdom
The purpose of
this study was to assess whether electrical stimulation-induced
increases in muscular activity could improve capillary supply and
correct previously documented abnormal vasodilator and vasoconstrictor
responses of arterioles in limb skeletal muscle post-myocardial
infarction (MI). Extensor digitorum longus (EDL) muscle from rats with
surgically induced MI (~30% of the left ventricle) was chronically
stimulated (Stim) 8 h/day for 6 ± 1 days, at 11 wk
post-MI. Third- (3A) and fourth-order (4A) arterioles in
EDL from nine MI rats and four MI+Stim rats were compared with those of
11 controls (Con). Compared with Con rats, MI alone caused a reduction
in the resting diameter of 3A and 4A arterioles, which was completely
reversed by MI+Stim. However, Stim did not correct the attenuated
vasodilator response to 10
4
M adenosine seen in 4A arterioles from MI rats compared with Con. The
constrictor response of both 3A and 4A vessels in MI rats to low doses
of acetylcholine (10
9 M,
10
8 M) and norepinephrine
(10
9 M) was accentuated in
MI+Stim. The proportion of oxidative fibers in EDL was unaffected by MI
or MI+Stim combination. However, Stim significantly increased
(P < 0.05) the capillary-to-fiber
ratio in this muscle compared with Con. Thus, although the increase in
muscle activity induced by chronic electrical stimulation normalized the reduction in resting vessel diameter seen after MI, it failed to
correct the abnormalities in vasoreactivity of these same vessels.
endothelium; skeletal muscle activity; nitric oxide; heart failure
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