AJP - Heart and Circulatory Physiology, Vol 249, Issue 4 820-H826, Copyright © 1985 by American Physiological Society
Decreased auxotonic sarcomere shortening in hypertrophied rabbit myocardium
P. B. Hultgren and B. B. Hamrell
Auxotonic sarcomere length change occurs during isometric twitches of
isolated cardiac muscle preparations. To assess the amount of internal work
in hypertrophied myocardium, we measured auxotonic sarcomere length change
during isometric tension development over a range of initial muscle and
sarcomere lengths. Hypertrophy was produced by banding the pulmonary
artery, which resulted in an increase in the ratio of right ventricular
free wall weight to total ventricular weight (normal 0.19 +/- 0.004;
hypertrophy 0.35 +/- 0.008; P less than 0.001). Right ventricular free wall
trabeculae and papillary muscles were studied with optical and mechanical
instrumentation, including a helium-neon laser, to measure sarcomere length
and isometric twitch parameters. The resting sarcomere length-resting
tension relationship was shifted to the left of normal in the hypertrophied
preparations (P less than 0.001). The relationship of sarcomere length at
the peak of the twitch with total tension at the same instant was shifted
downward and to the right of normal in hypertrophy (P less than 0.01). For
the same amount of total tension development there was less than normal
sarcomere shortening in the hypertrophied preparations (P less than 0.001).
Consequently, there is less than normal work per sarcomere during auxotonic
sarcomere shortening in hypertrophied heart muscle. Less sarcomere work for
a particular functional state is important to consider in the assessment of
the basis of myocardial function in compensated pressure overload
hypertrophy.
