Sympathetic mechanisms in poststenotic myocardial ischemia

Area of Science:

• Cardiovascular Physiology
• Autonomic Nervous System Research
• Myocardial Ischemia Studies

Background:

• Coronary stenosis can be compensated by poststenotic vasodilation.
• Cardiac sympathetic nerve activation can disrupt this compensatory mechanism.

Purpose of the Study:

• To investigate the impact of cardiac sympathetic nerve activation on coronary blood flow and myocardial oxygen balance in the presence of stenosis.
• To elucidate the mechanisms underlying sympathetic-induced poststenotic vasoconstriction and ischemia.

Main Methods:

• Experiments were conducted in anesthetized, vagotomized dogs.
• Stimulation of cardiac sympathetic nerves and reflex sympathetic activation (bilateral carotid occlusion) were employed.
• Poststenotic vasoconstriction was assessed, and its mediation by alpha 2-adrenoceptors was investigated.
• Myocardial ischemia was evidenced by contractile dysfunction, lactate production, and histological changes.

Main Results:

• Sympathetic activation induced vasoconstriction distal to severe coronary stenoses.
• This vasoconstriction is mediated by alpha 2-adrenoceptors and exacerbates myocardial ischemia.
• Alpha-antagonists (phentolamine, rauwolscine), calcium antagonists (nifedipine), and epidural anesthesia prevented poststenotic vasoconstriction and ischemia.
• Beta-blockers (propranolol) enhanced vasoconstriction but prevented ischemia.

Conclusions:

• Cardiac sympathetic nerves play a critical role in the genesis and aggravation of poststenotic myocardial ischemia.
• Alpha 2-adrenoceptor-mediated vasoconstriction is a key mechanism in this process.
• Targeting alpha 2-adrenoceptors or central sympathetic outflow offers potential therapeutic strategies.