title: Limitation of cardiac output by a coronary alpha 1-constrictor tone during exercise in dogs.
abstract: This study was performed to examine whether an alpha 1-constrictor tone, which limits coronary functional hyperemia during exercise, imposes a significant limitation on global cardiac performance as determined by cardiac output (CO). Seven dogs were chronically instrumented to measure left ventricular pressure (LVP), maximum rate of rise of LVP (dP/dtmax), heart rate (HR), mean aortic pressure (AoP), circumflex blood flow velocity (CFV), and CO at rest and during submaximal exercise. Either the selective alpha 1-adrenergic antagonist prazo (0.5 mg) or the vasodilator adenosine was administered into the circumflex artery during exercise at 6.4 kilometers per hour (kph)/16% treadmill incline. Exercise caused significant increase in mean AoP, HR, LVP, dP/dtmax, CFV, stroke volume (SV), and CO, whereas systemic vascular resistance (SVR) was significantly reduced. After intracoronary alpha 1-blockade with prazosin, CFV, dP/dtmax, SV, and CO increased further (17 +/- 2, 19 +/- 3, 16 +/- 2, and 17 +/- 2%, respectively) without changing mean AoP, HR, or SVR. Comparable increases were observed when CFV was increased by a similar degree using the direct vasodilator adenosine. These results indicate that increasing coronary flow by removing a coronary alpha 1-constrictor tone with prazosin or by direct vasodilation with adenosine during submaximal exercise leads to an increase in myocardial oxygen supply and, as a result, cardiac pump performance (SV and CO).
authors.affiliation: Department of Physiology, University of North Texas Health Science Center, Fort Worth 76107-2699, USA.
authors.forename: S J
authors.initials: SJ
authors.lastname: Kim
authors.forename: G
authors.initials: G
authors.lastname: Kline
authors.forename: P A
authors.initials: PA
authors.lastname: Gwirtz
mesh_terms: D000241:Adenosine / Q000494:pharmacology; D000317:Adrenergic alpha-Antagonists / Q000494:pharmacology; D000818:Animals; D001011:Aorta / Q000502:physiology; D001783:Blood Flow Velocity / Q000187:drug effects; D002302:Cardiac Output / Q000502:physiology*; D003331:Coronary Vessels / Q000187:drug effects / Q000502:physiology*; D004285:Dogs; D005260:Female; D006321:Heart / Q000187:drug effects / Q000502:physiology; D006439:Hemodynamics / Q000187:drug effects; D008297:Male; D009043:Motor Activity / Q000502:physiology*; D011224:Prazosin / Q000494:pharmacology; D011942:Receptors, Adrenergic, alpha / Q000502:physiology*; D014661:Vasoconstriction / Q000502:physiology*; D014665:Vasodilator Agents / Q000494:pharmacology; D016277:Ventricular Function, Left / Q000187:drug effects
chemical_list: D000317:Adrenergic alpha-Antagonists; D011942:Receptors, Adrenergic, alpha; D014665:Vasodilator Agents; D000241:Adenosine; D011224:Prazosin