AJP - Heart and Circulatory Physiology, Vol 242, Issue 5 855-H861, Copyright © 1982 by American Physiological Society
Load dependence of mammalian heart relaxation during cardiac hypertrophy and heart failure
Y. Lecarpentier, J. L. Martin, P. Gastineau and P. Y. Hatt
Mechanical properties of relaxation were studied in left ventricular rat
papillary muscle during cardiac hypertrophy induced by chronic pressure
and/or volume overload. Maximum velocity of isotonic lengthening was
linearly related to total extent of isotonic shortening and to maximum
velocity of isotonic contraction and depended on the type of chronic
overloading without correlation with the degree of cardiac hypertrophy.
Time to peak shortening was significantly increased in each group of
hypertrophied heart muscles as compared to controls. The sensitivity of
cardiac relaxation to the loading conditions was determined by the time
course of relaxation. To quantify the degree of load sensitivity, we
measured the ratio of isotonic area to isometric area, which was the area
limited by the afterloaded force vs. time at 50% of the isometric peak
tension divided by the area of the force vs. time trace in the isometric
twitch below the same level of load. The value of this ratio was about 0.81
in normal rat and did not show any significant differences in hypertrophied
heart muscles even at the terminal stage of congestive heart failure.
During acute hypoxia the load sensitivity of relaxation disappeared both in
normal and in hypertrophied hearts. Thus inadequacy in oxygen supply has
more drastic effects, as compared with those induced by chronic overload,
probably by affecting the sarcoplasmic reticulum uptake of activating
calcium.
