Journal of Applied Physiology, Vol 70, Issue 2 907-913, Copyright © 1991 by American Physiological Society
Myocardial biochemical and hemodynamic adaptations to chronic tachycardia
C. D. Ianuzzo, S. Brotherton, P. O'Brien, T. Salerno and M. H. Laughlin
Department of Physical Education, York University, Toronto, Ontario, Canada.
The purpose was to determine the biochemical and hemodynamic adaptations of
the myocardium to chronic tachycardia. Cardiac pacemakers were implanted in
Yorkshire pigs and set at a rate of 180 beats/min for a period of 35-42
days. Animals were then anesthetized with pentobarbital sodium. Myocardial
blood flow and hemodynamics were determined at three different heart rates
(i.e., 120, 180, and 220 beats/min). Tissue samples were then taken for
microsphere and biochemical analyses. Chronically paced hearts maintained
better cardiac function and had consistently higher left ventricular blood
flow with a higher endocardial-to-epicardial ratio. The activities of
citrate synthase and 3-hydroxyacyl-CoA dehydrogenase were 23 and 45%
greater in the paced hearts, respectively. The sarcoplasmic reticulum
adenosinetriphosphatase activity was 55% greater in the paced hearts,
whereas the myosin adenosinetriphosphatase was the same as in the control
hearts. Polyacrylamide gels of the ventricular myosin isoforms showed only
the V3 type to be present in both the control and paced hearts. These
findings show that the heart of a large mammal adapts to chronic
tachycardia (i.e., 180 beats/min) by elevating the aerobic and
calcium-sequestering capacities without altering its myosin type.
