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1 Dalton Cardiovascular Research Center and 2 Departments of Physiology and 3 Veterinary Biomedical Sciences, University of Missouri, Columbia, Missouri 65211; and 4 Department of Medical Physiology, Texas A&M University, College Station, Texas 77843
We previously
reported that canine collateral-dependent coronary arteries exhibit
impaired relaxation to adenosine but not sodium nitroprusside. In
contrast, exercise training enhances adenosine sensitivity of normal
porcine coronary arteries. These results stimulated the hypothesis that
chronic coronary occlusion and exercise training produce differential
effects on cAMP- versus cGMP-mediated relaxation. To test this
hypothesis, Ameroid occluders were surgically placed around the
proximal left circumflex coronary artery (LCx) of female Yucatan
miniature swine 8 wk before initiating sedentary or exercise training
(treadmill run, 16 wk) protocols. Relaxation to the cAMP-dependent
vasodilators adenosine (10
7 to
10
3 M) and isoproterenol (3 × 10
8 to 3 × 10
5 M) were impaired in
collateral-dependent LCx versus nonoccluded left anterior descending
(LAD) arterial rings isolated from sedentary but not exercise-trained
pigs. Furthermore, adenosine-mediated reductions in simultaneous
tension and myoplasmic free Ca2+ were impaired in LCx
versus LAD arteries isolated from sedentary but not exercise-trained
pigs. In contrast, relaxation in response to the cAMP-dependent
vasodilator forskolin (10
9 to
10
5 M) and the cGMP-dependent
vasodilator sodium nitroprusside (10
9 to
10
4 M) was not different in LCx versus
LAD arteries of sedentary or exercise-trained animals. These data
suggest that chronic occlusion impairs receptor-dependent,
cAMP-mediated relaxation; receptor-independent cAMP- and cGMP-mediated
relaxation were unimpaired. Importantly, exercise training restores
cAMP-mediated relaxation of collateral-dependent coronary arteries.
vascular smooth muscle; myoplasmic free calcium; collateral dependent; adenosine 3',5'-cyclic monophosphate; guanosine 3',5'-cyclic monophosphate
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