Limitation of cardiac output by a coronary α1-constrictor tone during exercise in dogs

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Abstract

This study was performed to examine whether an α1-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/dt(max)), heart rate (HR), mean aortic pressure (AoP), circumflex blood flow velocity (CFV), and CO at rest and during submaximal exercise. Either the selective α1- adrenergic antagonist prazosin (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/dt(max), CFV, stroke volume (SV), and CO, whereas systemic vascular resistance (SVR) was significantly reduced. After intracoronary α1-blockade with prazosin, CFV, dP/dt(max), 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 α1-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).

Original languageEnglish
JournalAmerican Journal of Physiology - Heart and Circulatory Physiology
Volume271
Issue number3 40-3
StatePublished - 1 Sep 1996

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Cardiac Output
Blood Flow Velocity
Dogs
Prazosin
Ventricular Pressure
Stroke Volume
Adenosine
Arterial Pressure
Heart Rate
Vasodilator Agents
Vascular Resistance
Adrenergic Antagonists
Hyperemia
Vasodilation
Arteries
Oxygen

Keywords

  • α-adrenergic receptor
  • adenosine
  • chronically instrumented dog
  • coronary blood flow
  • left ventricular function
  • prazosin

Cite this

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abstract = "This study was performed to examine whether an α1-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/dt(max)), heart rate (HR), mean aortic pressure (AoP), circumflex blood flow velocity (CFV), and CO at rest and during submaximal exercise. Either the selective α1- adrenergic antagonist prazosin (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/dt(max), CFV, stroke volume (SV), and CO, whereas systemic vascular resistance (SVR) was significantly reduced. After intracoronary α1-blockade with prazosin, CFV, dP/dt(max), 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 α1-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).",
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