AJP - Heart and Circulatory Physiology, Vol 244, Issue 3 378-H386, Copyright © 1983 by American Physiological Society
Effect of calcium antagonism on contractile behavior of canine hearts
R. J. Gelpi, S. M. Mosca, G. J. Rinaldi, A. Kosoglov and H. E. Cingolani
The cardiovascular effects of prenylamine (P), verapamil (V), and
nifedipine (N) were studied in open-chest, anesthetized dogs and in
isolated, isovolumic dog hearts perfused at constant coronary blood flow
(CBF). These drugs significantly decreased left ventricular pressure (LVP)
and its maximal rates of rise (+P) and fall (-P). The tension developed by
an isometric segment of the left ventricle and its maximal rates of rise
(+T) and fall (-T) also decreased, whereas heart rate (HR) did not show
statistically significant differences. Maximal rates of fall (-P and -T)
were proportionally more depressed than maximal rates of rise (+P and +T),
producing significant increments in the ratios between both maximal
velocities (+P/-P and +T/-T). The time constant of LVP isovolumic decay tau
was significantly prolonged, either in the whole animal or in isolated
perfused hearts. The afterload reduction produced by the compounds can
account in part for the increase in +P/-P but not for the increase in +T/-T
or for the prolongation of tau. These relaxation indices remained unchanged
after comparable myocardial depressions elicited by d,l-propranolol or
pentobarbital sodium. It is concluded that calcium antagonist compounds are
characterized by an "antirelaxant" effect, not explained by changes in HR,
CBF, or loading conditions, and independent from their negative inotropic
action.
