Basic Res Cardio190:73 - 83 (1995) 9 Steinkopff Verlag 1995 D. J. Duncker J. Zhang M. J. Crampton R. J. Bache 1-Adrenergic tone does not influence the transmural distribution of myocardial blood flow during exercise in dogs with pressure overload left ventricular hypertrophy Received: 8 June 1994 Accepted: 31 October 1994 This study was supported by U.S. Public Health Servicegrants HL21872 and HL20598 from the National Heart, Lung and Blood Institute. Dr. Duncker was in part supported by a NATO Science Fellowship awarded by the Netherlands Organization for Scientific Research (NWO) and a grant from the Min- nesota Affiliate of the Minnesota Heart Association. R. J. Bache (N~. D. J. Duncker 1 J. Zhang 9 M. J. Crampton Cardiovascular Division Department of Medicine University of Minnesota Medical School Box 508 UMHC 420 Delaware Street SE Minneapolis, Minnesota 55455, USA JPresent address: Laboratory for Experimental Cardiology, Thoraxcenter Erasmus University Rotterdam RO. Box 1738 3000 DR Rotterdam The Netherlands Abstract This study was carried out to test the hypothesis that oq-adrener- gic activation during exercise causes preferential vasoconstriction of sub- epicardial coronary resistance ves- sels, thereby augmenting blood flow to the subendocardium. Studies were performed in 7 dogs in which left ventricular hypertrophy was pro- duced by banding the ascending aorta at 6-9 weeks of age. Animals were studied at approximately 1 year of age when the left ventricular/body weight ratio was 7.7 + 0.3 g/kg (mean+SE). Left anterior descend- ing (LAD) coronary artery flow was measured with a Doppler velocity flow probe at rest and during a three- stage graded treadmill exercise pro- tocol. The transmural distribution of myocardial blood flow was assessed with radioactive microspheres. Coro- nary blood flow increased progres- sively as a function of heart rate and rate-pressure product in response to exercise. In contrast to normal dogs which maintain preferential blood flow to the subendocardium (ENDO) relative to the subepicardium (EPI) during exercise, the ENDO/EPI flow ratio in the hypertrophied left ventri- cles was 0.88 _+ 0.10 during exercise. Selective ofl-adrenergic blockade by infusion of prazosin (10 ~g/kg) into the LAD decreased mean aortic pressure during exercise from 86 + 6 to 76 + 4 mmHg (p < 0.05), but did not change coronary pressure, heart rate, left ventricular systolic or end- diastolic pressures, or LVdP/dtm~x. Coronary blood flow was not signific- antly altered by prazosin at rest, but was progressively increased during increasing levels of exercise levels. During the heaviest level of exercise prazosin caused a 22 _+ 3 % increase in mean myocardial blood flow which was similar in all transmural layers, with no change in the transmural distribution of perfusion (ENDO/ EPI = 0.85 + 0.09). These findings demonstrate that o~radrenergic vaso- constrictor tone limits blood flow during exercise in the hypertrophied left ventricle, but do not support the concept that oq-adrenergic activation augments perfusion of the subendo- cardium during exercise. Key words Coronary vasodilation- coronary vasoconstriction - prazosin - supravalvular aortic stenosis