This study was carried out to test the hypothesis that α-adrenergic vasoconstriction limits coronary blood flow (CBF) during exercise in the chronically pressure overloaded, hypertrophied left ventricle. Studies were performed in dogs in which left ventricular hypertrophy had been produced by banding the ascending aorta at 9 wk of age. Left circumflex coronary artery blood flow and myocardial O2 consumption (MV̇O2) were examined at rest and during treadmill exercise during control conditions, after selective α1-adrenergic blockade with prazosin, and after nonselective α-adrenergic blockade with phentolamine. All studies were performed after β-adrenergic blockade with propranolol. During control conditions CBF and MV̇O2 increased progressively during exercise, while coronary sinus O2 tension decreased. Neither prazosin nor phentolamine altered CBF at rest but, in comparison with control measurements, both agents significantly increased CBF during exercise and abolished the decrease in coronary sinus O2 tension that normally occurred during exercise. Both prazosin and phentolamine caused similar significant increases of MV̇O2 relative to the heart rate times systolic left ventricular pressure during exercise, indicating that the increased CBF produced by these agents enhanced MV̇O2. Similar findings after prazosin and phentolamine indicate that adrenergic restraint of CBF during exercise resulted principally from α1-adrenergic vasoconstrictions with little additional contribution from postjunctional α2-adrenergic mechanisms.
|Original language||English (US)|
|Journal||American Journal of Physiology - Heart and Circulatory Physiology|
|Issue number||5 29-5|
|State||Published - 1991|
- Coronary sinus oxygen pressure
- Myocardial blood flow
- β-adrenergic blockade