Myocardial contractile effects of nitric oxide

Area of Science:

• Cardiovascular Physiology
• Nitric Oxide Signaling
• Myocardial Contractility

Background:

• Controversies exist regarding nitric oxide's (NO) baseline contractile effects, inotropic nature, source dependency, and impact on diseased myocardium.
• Understanding NO's role is crucial for cardiovascular therapeutics.

Purpose of the Study:

• To resolve controversies surrounding the myocardial contractile effects of nitric oxide (NO).
• To investigate NO's impact on baseline contractility, inotropy, source dependency (NO-donors vs. NO synthases), and altered cardiac states (hypertrophy, failure, ischemia).

Main Methods:

• Utilized transgenic mice with cardioselective overexpression of NO synthases (NOS).
• Reviewed findings from intracoronary NO-donor infusions in isolated rodent hearts and human studies.
• Examined effects in hypertrophied, failing, and ischemic myocardium.

Main Results:

• NO induces a minor reduction in basal left ventricular (LV) pressure and hastens LV relaxation via myofilament desensitization.
• Enhanced diastolic LV distensibility and preload reserve, particularly beneficial in heart failure.
• Overall LV performance is improved due to enhanced diastolic function overriding minor reductions in developed pressure.
• NO's effects are generally consistent from NO-donors or different NOS isoforms, except when oxidative stress (e.g., NOS2 in ischemia/sepsis) leads to peroxynitrite-induced impairment.
• Altered myofilament properties in hypertrophied/failing hearts can modify NO's desensitization effects.

Conclusions:

• NO primarily exerts a lusitropic (relaxation-hastening) effect, improving diastolic function and overall cardiac performance.
• NO's contractile effects are generally consistent across sources but can be impaired by oxidative stress or altered myofilament dynamics in disease states.
• NO's beneficial effects on diastolic function are significant, especially in managing heart failure.