doi: 10.1161/hc3601.094274
(Circulation. 2001;104:1393.)
© 2001 American Heart Association, Inc.
Basic Science Reports |
Endothelium-Mediated Relaxation of Porcine Collateral-Dependent Arterioles Is Improved by Exercise Training
From Dalton Cardiovascular Research Center (K.L.G., C.W., E.P., M.H.L., J.L.P.) and the Departments of Physiology (K.L.G., M.H.L., J.L.P.) and Veterinary Biomedical Sciences (C.W., E.P., M.H.L.), University of Missouri, Columbia, and the Department of Medical Physiology, Texas A&M University System Health Science Center, College Station (J.L.P.).
Correspondence to Janet L. Parker, PhD, Department of Medical Physiology, 336 Reynolds Medical Bldg, College Station, TX 77843-1114. E-mail jlp{at}tamu.edu
Background—— Endothelium-dependent modulation of coronary tone is impaired in the collateral-dependent coronary microcirculation. We used a porcine model of chronic coronary occlusion and collateral development to evaluate the hypothesis that exercise training enhances endothelium-mediated relaxation and increases endothelial nitric oxide synthase (ecNOS) mRNA levels of collateral-dependent microvasculature.
Methods and Results—— Adult female miniature swine were subjected to chronic, progressive ameroid occlusion of the proximal left circumflex coronary artery (LCx); after 2 months, animals were randomly exposed to 16-week exercise-training (EX group; treadmill running) or sedentary (SED group; cage confinement) protocols. After completion of EX or SED programs, coronary arterioles (
100 µm in diameter) were isolated from collateral-dependent LCx (distal to occlusion) and nonoccluded left anterior descending coronary artery (LAD) regions of each heart. Arterioles were studied by in vitro videomicroscopy or frozen for ecNOS mRNA analysis (RT-PCR techniques). Relaxation to the endothelium-dependent vasodilator bradykinin was decreased (P<0.05) in arterioles isolated from collateral-dependent LCx versus nonoccluded LAD regions of SED animals. Bradykinin-mediated relaxation, however, was not different in LCx versus LAD arterioles isolated from EX animals. Nitroprusside-induced relaxation was unaffected by either chronic occlusion or exercise. Importantly, ecNOS mRNA expression was significantly decreased in arterioles isolated from LCx versus LAD regions of SED animals. After training, ecNOS mRNA expression was not different between LAD and LCx arterioles.
Conclusions—— These data indicate that exercise training enhances bradykinin-mediated relaxation of collateral-dependent LCx arterioles isolated after chronic coronary occlusion, most likely because of effects on ecNOS mRNA expression and increased production of NO.
Key Words: bradykinin • collateral circulation • occlusion • nitric oxide • microcirculation
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