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Surgical Placement of Catheters for Long-term Cardiovascular Exercise Testing in Swine
Published on: February 9, 2016
Acute adaptations of the coronary circulation to exercise
Dirk J Duncker1, Daphne Merkus
1Experimental Cardiology, Thoraxcenter, Erasmus MC, University Medical Center Rotterdam, Box 1738, 3000 DR Rotterdam, The Netherlands. d.duncker@erasmusmc.nl
Insights
During exercise, swine coronary blood flow relies on beta-adrenergic control and parasympathetic withdrawal, not metabolic factors. Endothelin withdrawal also aids vasodilation, with pathways acting additively.
Area of Science:
- Cardiovascular Physiology
- Exercise Physiology
- Coronary Circulation Regulation
Background:
- Coronary blood flow (CBF) is tightly coupled to myocardial oxygen consumption, relying on high oxygen extraction.
- Regulation involves oxygen tension, cardiomyocyte signals (adenosine), endothelium (prostanoids, nitric oxide, endothelin), and autonomic influences (catecholamines).
- Previous studies primarily used dogs; swine models offer new insights into coronary vasomotor tone regulation.
Purpose of the Study:
- To investigate the regulatory pathways of coronary vasomotor tone during exercise in swine.
- To elucidate the roles of adrenergic, parasympathetic, endothelin, and endothelial/metabolic pathways in exercise-induced vasodilation.
Main Methods:
- Studies conducted on chronically instrumented exercising swine.
- Analysis of coronary resistance vessel vasomotor tone regulation.
- Assessment of adrenergic, parasympathetic, and endothelin influences during exercise.
Main Results:
- Swine coronary resistance vessels exhibit beta-adrenergic feed-forward control during exercise, augmented by parasympathetic withdrawal.
- Withdrawal of endothelin-mediated vasoconstriction contributes to exercise-induced coronary vasodilation.
- Endothelial and metabolic vasodilator pathways regulate resting tone but not exercise-induced vasodilation; pathways act additively, not synergistically.
Conclusions:
- Exercise-induced coronary vasodilation in swine is primarily mediated by beta-adrenergic control, parasympathetic withdrawal, and endothelin withdrawal.
- Metabolic and endothelial vasodilator pathways do not contribute significantly to exercise-induced vasodilation.
- Coronary vasomotor control mechanisms operate in a linear additive fashion, not through synergistic interactions.
Abstract:
Coronary blood flow is tightly coupled to myocardial oxygen consumption to maintain a consistently high level of myocardial oxygen extraction. This tight coupling has been proposed to depend on periarteriolar oxygen tension, signals released from cardiomyocytes (adenosine acting on K+(ATP) channels), and/or the endothelium (prostanoids, nitric oxide, endothelin [ET]) and autonomic influences (catecholamines), but the contribution of each of these regulatory pathways and their interactions are still incompletely understood. Until recently, experimental studies into the regulation of coronary blood flow during exercise were principally performed in the dog. We have performed several studies on the regulation of vasomotor tone in coronary resistance vessels in chronically instrumented exercising swine. These studies have shown that the coronary resistance vessels in swine lack significant alpha-adrenergic control, but that these vessels are subject to beta-adrenergic feed-forward control during exercise, which is aided by a parasympathetic withdrawal. In addition, withdrawal of an ET-mediated vasoconstrictor influence also contributes to exercise-induced coronary vasodilation. Coronary blood flow regulation by endothelial and metabolic vasodilator pathways contributes to resting vasomotor tone regulation but does not appear to contribute to the exercise-induced coronary vasodilation. Furthermore, blockade of one vasodilator pathway is not compensated by an increased contribution of the other vasodilator mechanisms, suggesting that porcine coronary vasomotor control by endothelial and metabolic factors occurs in a linear additive rather than a nonlinear synergistic fashion.
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