Effects of exercise training on smooth muscle relaxation and myoplasmic free Ca 2+ (Ca m) responses of coronary arteries distal to chronic occlusion
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We evaluated combined effects of chronic coronary occlusion and exercise training on vasodilator responsiveness of coronary artery rings (1.0-2.5 mm OD) isolated from sedentary (SED; pen-confined) or exercise-trained (EX; treadmill run, 5 days/wk for 16-20 wk) Yucatan miniature swine. Ameroid occluders were surgically placed on the proximal left circumflex coronary artery (LCX) 8 weeks prior to SED or EX protocols. In SED animals (n=10), relaxation responses to adenosine (ADO;10 -8 to 10 -3 M), but not nitroprusside (NP;10 -10 to 10 -4 M), were significantly (P<0.05) impaired in LCX arteries distal to occlusion, as compared to size-matched unoccluded LAD arteries. In contrast, in EX animals (n=11), neither ADO nor NP-induced relaxation was different in LCX vs LAD arteries. ADO-mediated reductions in simultaneous tension and Ca m measures were impaired in LCX vs LAD arteries isolated from SED, but not EX animals. Preliminary studies (n=5) suggest that relaxation to the -adrenergic agonist, isoproterenol, (ISO; 10 -9 to 10 -6 M) was impaired in LCX vs. LAD arteries, but unlike ADO, ISO-induced relaxation remained impaired in EX animals. Our data suggest exercise corrects impaired ADO-mediated relaxation and Ca m responses associated with chronic coronary occlusion; mechanisms may involve receptor-specific and/or second-messenger (cAMP vs cGMP) pathways.