AJP - Heart and Circulatory Physiology, Vol 249, Issue 2 207-H211, Copyright © 1985 by American Physiological Society
Responses of the atrial myocardium to cardiac sympathetic nerve stimulation
Y. Masuda and M. N. Levy
The cardiac responses to sympathetic nerve stimulation were measured in
open-chest, anesthetized dogs before and after infusions of cocaine, which
were given to inhibit the neuronal uptake of norepinephrine. Cocaine did
not augment the inotropic or chronotropic responses, but it did retard
their decay after cessation of sympathetic stimulation. Before cocaine, the
half-times for decay of the chronotropic, atrial inotropic, and ventricular
inotropic responses were 28.4 +/- 2.2, 29.8 +/- 2.7, and 22.1 +/- 1.9 (+/-
SE) s, respectively. After cocaine, however, the half-times were
significantly greater (147 +/- 12.0, 51.4 +/- 3.9, and 32.9 +/- 2.5 s,
respectively). The cocaine-induced prolongation of the decay time in a
given cardiac tissue is a measure of the relative efficacy of neuronal
uptake as a mechanism for dissipating the neurally released norepinephrine.
Our data indicate, therefore, that among the various cardiac tissues that
we studied, the neuronal uptake mechanism is least effective in the
ventricular myocardium, somewhat more effective in the atrial myocardium,
and most effective in the sinoatrial nodal region.
