Correlation of the mechanical responses of the heart with the norepinephrine overflow during cardiac sympathetic neural stimulation in the dog.

The changes in heart rate and right ventricular contractile force were measured in anaesthetised dogs during stimulation of each ansa subclavia, and the responses were correlated with the overflow or norepinephrine (NE) into the coronary sinus blood. The increase in heart rate was considerably greater during stimulation of the right than of the left ansa subclavia. Conversely, left ansa stimulation had a slightly greater effect on right ventricular contractile force than did right-sided stimulation. The changes in norepinephrine overflow into the coronary sinus blood paralleled the alterations in contractile force; during stimulation at 2 and 4 Hz, the rates of norepinephrine overflow were 50 and 34% greater, respectively, with left-sided than with right-sided stimulation. On both the right and left sides, stimulation of the anterior limb of the ansa subclavia produced greater increments in heart rate and contractile force than did stimulation of the posterior limb. Similarly, the rates of norepinephrine overflow during anterior ansal stimulation were 100 and 75% greater than during posterior ansal stimulation for the right and left sides, respectively. Thus, both limbs of the two ansae subclaviae innervate the myocardial regions drained by the coronary sinus, but the greatest innervation arises from the anterior limb on the left side.