We correlated levels of circulating norepinephrine (NE) and epinephrine (Epi) induced by 1) infusions, 2) treadmill exercise, and 3) hemorrhage with left ventricular (LV) function in conscious dogs instrumented for the measurement of LV and arterial pressures, LV diameter, and calculations of indexes of myocardial contractility. With infusions of NE, significant hemodynamic changes were observed only when plasma levels of NE exceeded 1,000 pg/ml. While statistically significant, the increase in rate of rise of LV pressure (LV dP/dt) at these levels was relatively slight, i.e., 8 ± 2.3%. With further increases in catecholamines (> 1,000 pg/ml) good correlations were observed with increases in arterial pressure and myocardial contractility. Similar results occurred with infusions of Epi. Moderate treadmill exercise doubled LV dP/dt, while NE and Epi rose by only 563 ± 128 and 292 ± 50 pg/ml, respectively. Hemorrhage (30 ml/kg) decreased all indexes of contractility but increased plasma NE by 1,108 ± 206 pg/ml and Epi by 1,475 ± 266 pg/ml. Despite arterial NE and Epi levels 10-20 times those during exercise, infusions were unable to reproduce the peak changes in contractility seen with exercise. Infusions of NE or Epi to equal the plasma levels during exercise increased contractility by only 5-10%. In view of the marked disparity between levels of circulating catecholamines and LV function during exercise, hemorrhage, and catecholamine infusion, we conclude that circulating catecholamines do not adequately reflect the degree of inotropic stimulation to the myocardium. Specifically, increases in plasma catecholamines to levels under 1,000 pg/ml do not necessarily presage a positive inotropic effect.
|Original language||English (US)|
|Journal||American Journal of Physiology - Heart and Circulatory Physiology|
|State||Published - 1985|
All Science Journal Classification (ASJC) codes
- Cardiology and Cardiovascular Medicine
- Physiology (medical)