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1 Departments of Veterinary Biomedical Sciences and Physiology and Dalton Cardiovascular Research Center, University of Missouri, Columbia, Missouri 65211; and 2 Department of Kinesiology, University of Waterloo, Waterloo, Ontario, Canada N2L 3G1
Our objective was to test the
hypothesis that short-term exercise training (STR) of pigs increases
endothelium-dependent dilation (EDD) of coronary arteries but not
coronary arterioles. Female Yucatan miniature swine ran on a
treadmill for 1 h, at 3.5 mph, twice daily for 7 days (STR;
n = 28). Skeletal muscle citrate synthase activity was
increased in STR compared with sedentary controls (Sed;
n = 26). Vasoreactivity was evaluated in isolated segments of conduit arteries (1-2 mm ID, 3-4 mm length)
mounted on myographs and in arterioles (50-100 µm ID) isolated
and cannulated with micropipettes with intraluminal pressure set at 60 cmH2O. EDD was assessed by examining responses to
increasing concentrations of bradykinin (BK) (conduit arteries
10
12-10
6 M and arterioles
10
13-10
6 M). There were no differences
in maximal EDD or BK sensitivity of coronary arterioles from Sed and
STR hearts. In contrast, sensitivity of conduit arteries (precontracted
with PGF2
) to BK was increased significantly
(P < 0.05) in STR (EC50, 2.33 ± 0.62 nM, n = 12) compared with Sed animals
(EC50, 3.88 ± 0.62 nM, n = 13).
Immunoblot analysis revealed that coronary arteries from STR and Sed
animals had similar levels of endothelial nitric oxide synthase (eNOS). In contrast, eNOS protein was increased in STR aortic endothelial cells. Neither protein nor mRNA levels of eNOS were different in
coronary arterioles from STR compared with Sed animals. STR did not
alter expression of superoxide dismutase (SOD-1) protein in any artery
examined. We conclude that pigs exhibit increases in EDD of conduit
arteries, but not in coronary arterioles, at the onset of exercise
training. These adaptations in pigs do not appear to be mediated by
alterations in eNOS or SOD-1 expression.
nitric oxide; endothelial nitric oxide synthase; superoxide dismutase; bradykinin
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