Objectives. To investigate the effects of ischemic preconditioning in hearts from adult and both sedentary and trained senescent rats. Background. Ischemic preconditioning does not prevent postischemic dysfunction in the aging heart, probably because of reduction of cardiac norepinephrine release. Exercise training can reverse the age-related decrease of norepinephrine production. Methods. We investigated the effects on mechanical parameters of ischemic preconditioning against 20 min of global ischemia followed by 40 min of reperfusion in isolated perfused hearts from adult (six months) and sedentary or trained (six weeks of graduated swim training) senescent (24 months) rats. Norepinephrine release in coronary effluent was determined by high-performance liquid cromatography. Results. Final recovery of percent-developed pressure was significantly improved after preconditioning in adult hearts (91.6 ± 9.6%) versus unconditioned controls (54.2 ± 5.1%, p <0.01). The effect of preconditioning on developed pressure recovery was absent in sedentary but present in trained senescent hearts (39.6 ± 4.1% vs. 64.3 ± 7.1%, p <0.05). Norepinephrine release significantly increased after preconditioning in adult and in trained but not in sedentary senescent hearts. The depletion of myocardial norepinephrine stores by reserpine abolished preconditioning effects in adult and trained senescent hearts. Conclusions. In adult and trained but not in sedentary senescent hearts, preconditioning reduces postischemic dysfunction and is associated with an increase in norepinephrine release. Preconditioning was blocked by reserpine in both adult and trained senescent hearts. Thus, exercise training may restore preconditioning in the senescent heart through an increase of norepinephrine release. (C) 2000 by the American College of Cardiology.
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