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Adrenergic vasoconstriction limits coronary blood flow during exercise in hypertrophied left ventricle

R J Bache1, D C Homans, X Z Dai

  • 1Department of Medicine, University of Minnesota, Minneapolis 55455.

The American Journal of Physiology
|May 1, 1991
PubMed

Insights

Alpha-adrenergic vasoconstriction limits coronary blood flow during exercise in hypertrophied hearts. Blocking these receptors, particularly alpha 1-adrenergic, increases blood flow and oxygen supply to the heart muscle.

Area of Science:

  • Cardiovascular Physiology
  • Exercise Physiology
  • Adrenergic Signaling

Background:

  • Chronic pressure overload leads to left ventricular hypertrophy, altering cardiac function.
  • The role of alpha-adrenergic vasoconstriction in regulating coronary blood flow during exercise in hypertrophied ventricles is not fully understood.

Purpose of the Study:

  • To test the hypothesis that alpha-adrenergic vasoconstriction limits coronary blood flow (CBF) during exercise in chronically pressure-overloaded, hypertrophied left ventricles.
  • To investigate the specific contribution of alpha-1 and alpha-2 adrenergic mechanisms to this limitation.

Main Methods:

  • Studies were conducted in dogs with experimentally induced left ventricular hypertrophy.
  • Coronary artery blood flow and myocardial oxygen consumption were measured at rest and during exercise.
  • Pharmacological blockade of alpha-adrenergic receptors (selective with prazosin, nonselective with phentolamine) was performed after beta-adrenergic blockade with propranolol.

Main Results:

  • Neither prazosin nor phentolamine affected resting coronary blood flow.
  • Both alpha-adrenergic blockers significantly increased coronary blood flow during exercise compared to control conditions.
  • The decrease in coronary sinus oxygen tension during exercise was abolished by alpha-adrenergic blockade, indicating improved oxygen supply.

Conclusions:

  • Alpha-adrenergic vasoconstriction, primarily mediated by alpha-1 receptors, significantly limits coronary blood flow during exercise in the hypertrophied left ventricle.
  • Pharmacological blockade of alpha-adrenergic receptors enhances coronary blood flow and myocardial oxygen consumption during exercise in this condition.

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