Correlation between cardiac performance and plasma catecholamine levels in conscious dogs.

Area of Science:

• Cardiovascular Physiology
• Autonomic Nervous System
• Myocardial Contractility

Background:

• Circulating catecholamines, including norepinephrine (NE) and epinephrine (Epi), are key regulators of cardiovascular function.
• Their role in modulating left ventricular (LV) function during physiological stress is complex and not fully understood.
• Assessing myocardial contractility often relies on measuring catecholamine levels, but the direct correlation requires investigation.

Purpose of the Study:

• To correlate circulating levels of norepinephrine (NE) and epinephrine (Epi) with left ventricular (LV) function.
• To investigate the relationship between catecholamine levels and myocardial contractility under various conditions: infusions, exercise, and hemorrhage.
• To determine if circulating catecholamine levels adequately reflect the degree of inotropic stimulation to the myocardium.

Main Methods:

• Conscious dogs were instrumented to measure LV and arterial pressures, LV diameter, and myocardial contractility indexes.
• NE and Epi levels were measured during infusions, moderate treadmill exercise, and hemorrhage (30 ml/kg).
• LV function parameters, including the rate of rise of LV pressure (LV dP/dt), were analyzed in conjunction with catecholamine concentrations.

Main Results:

• Infusions of NE and Epi showed significant hemodynamic changes and increased myocardial contractility only at plasma levels exceeding 1,000 pg/ml.
• Moderate treadmill exercise significantly increased LV dP/dt, with only moderate elevations in NE and Epi levels.
• Hemorrhage decreased LV contractility while significantly increasing NE and Epi; however, infusions could not replicate exercise-induced contractility changes even at higher catecholamine levels.

Conclusions:

• Circulating catecholamine levels, specifically NE and Epi, do not consistently correlate with the degree of inotropic stimulation to the myocardium.
• Physiological stressors like exercise and hemorrhage induce greater changes in LV function than predicted by circulating catecholamine concentrations alone.
• The study suggests that factors beyond circulating catecholamines significantly influence myocardial contractility during stress.