[Endogenous catecholamines and heart function in stimulation of the accelerator nerve]

Area of Science:

• Cardiology
• Neuropharmacology
• Cardiac Physiology

Background:

• The augmenting cardiac nerve influences heart function.
• Catecholamines, like noradrenaline and adrenaline, are key mediators in cardiovascular regulation.
• Understanding the specific roles of these catecholamines during nerve stimulation is crucial for cardiac research.

Purpose of the Study:

• To investigate the role of catecholamines in mediating the effects of augmenting cardiac nerve stimulation.
• To quantify the release and myocardial accumulation of noradrenaline and adrenaline during nerve stimulation.
• To determine the relative contribution of noradrenaline and adrenaline to the positive inotropic effects observed.

Main Methods:

• Acute experiments were conducted on dogs anesthetized with hexenal.
• Augmenting cardiac nerves were stimulated.
• Noradrenaline and adrenaline concentrations in coronary sinus blood were measured.
• Myocardial contractility and pump function were assessed.

Main Results:

• Nerve stimulation led to increased noradrenaline concentration in coronary sinus blood, correlating with enhanced pump function and myocardial contractility.
• Adrenaline synthesis kept pace with its consumption, and myocardial adrenaline accumulated during stimulation.
• Accumulated myocardial adrenaline contributed less significantly to the positive inotropic effect compared to noradrenaline.
• Adrenaline did not exert adverse effects on cardiac function.

Conclusions:

• Noradrenaline is the primary catecholamine responsible for the positive inotropic effects of augmenting cardiac nerve stimulation.
• While adrenaline accumulates in the myocardium, its role in mediating the immediate positive inotropic response is limited.
• The findings clarify the distinct roles of noradrenaline and adrenaline in cardiac neuro-modulation.