AJP - Heart and Circulatory Physiology, Vol 253, Issue 6 1581-H1585, Copyright © 1987 by American Physiological Society
Increased heart rate accelerates norepinephrine washout from normal myocardium
R. J. Henning, J. Cheng, A. M. Bhat and M. N. Levy
Division of Investigative Medicine, Mt. Sinai Medical Center, Cleveland, Ohio.
We determined whether a change in heart rate affected the decay of the
ventricular inotropic response to sympathetic stimulation in an
experimental group and in a control group of anesthetized dogs. We induced
complete heart block in each animal and paced the ventricles at rates of
90, 120, and 150 min-1 during two observation periods. In the experimental
group, desipramine hydrochloride was given during the second period to
block the neuronal uptake mechanism. The control animals did not receive
desipramine during either period. The time required for the ventricular
inotropic response to decay by 50% after cessation of a 2-min train of
sympathetic stimulation was used as an index of the rate of norepinephrine
washout from the myocardial interstitium. As we increased the pacing rate
over the range of 90-150 min-1 in the experimental group, the mean decay
half times (+/- SE) decreased by 36 +/- 4% (P less than 0.001) before
desipramine and by 26 +/- 6% (P less than 0.001) in the presence of
desipramine. These decrements in the decay half times were not
significantly different from each other. The mean decay half times
decreased by 36 +/- 4% (P less than 0.001) in the control dogs; the effects
did not change appreciably from the first to the second observation period.
We conclude that an increase in pacing frequency facilitates the washout of
norepinephrine from the ventricular myocardium; this facilitation is
equally pronounced regardless of whether the neuronal uptake mechanism is
intact or suppressed.
