Reduction of cardiac norepinephrine improves postischemic heart function in stroke-prone spontaneously hypertensive rats

Although mammalian ventricle is richly supplied with adrenergic nerves. end ogenous norepinephrine is not essential to the intrinsic contractility of t he normal heart. However, it is not clear whether acute changes in cardiac norepinephrine could alter heart function in genetically hypertensive rats. The purpose of this study was to examine the effect of cardiac norepinephr ine reduction on basal and postischemic heart function in stroke-prone spon taneously hypertensive rats (SHRSPs) using an isolated working heart prepar ation. Hypertrophied hearts of SHRSPs showed higher cardiac norepinephrine content and impaired heart function at 4 months of age as compared with nor mal Wistar-Kyoto rats. Poor postischemic recovery of heart function observe d in SHRSPs was accompanied by large amounts of coronary norepinephrine ove rflow. Cardiac norepinephrine reduction or depiction did not affect basal h eart function in SHRSPs. Considerable reduction in cardiac norepinephrine w ith acute reserpine injection (5 mg/kg) in SHRSPs significantly improved po st-ischemic recovery of cardiac output, coronary flow, and rate-pressure pr oduct. However, complete norepinephrine depletion with reserpine (10 mg/kg) was detrimental to myocardial automaticity and limited the postischemic re covery of systolic function in the hypertrophied hearts. These results sugg est that acute reduction in cardiac norepinephrine may be of potential ther apeutic importance to postischemic dysfunction in the hypertrophied hearts.