Norepinephrine release is increased in the hibernating heart, studied in achronic canine model of myocardial hibernation

We examined the change in cardiac sympathetic function in the hibernating h eart. To induce hibernating hearts in dogs, we placed a nylon tube via the carotid artery in the left circumflex artery (LCx) and obstructed the LCx f low. The plasma norepinephrine (NE) and epinephrine (E) concentrations in t he coronary sinus and the aorta were measured before and 1 week after the t ube placement to evaluate the catecholamine release from the heart. The wal l motion was followed by echocardiography and, 1 week after the tube placem ent, regional myocardial blood flow (RBF) was measured using colored micros pheres. Also, the restorability of myocardial dysfunction was examined in o ther dogs by extracting the LCx tube I week after the placement. Finally, t he heart was removed for pathological observation and dogs showing myocardi al infarction were excluded. One week after placing the tube, wall thickeni ng was reduced in the LCx area, but was not in the left anterior descending (LAD) area. Compared with the LAD area, RBF in the LCx area was decreased in the endocardium (p < 0.05), but was not in the epicardium. In other dogs , the reduced wall thickening in the LCx area was restored to normal levels 1 or 2 weeks after the tube extraction. Thereby, our dogs with the tube pl aced were considered to be models of myocardial hibernation. The plasma NE and E concentrations were not significantly changed by placing the tube, bu t NE release from the heart was increased after the tube placement (p < 0.0 5). E uptake from the heart did not differ. Therefore, it is suggested that NE release is increased in the hibernating heart and may contribute to its mechanism.