Myocardial mechanics at various stages of the cardiac hypertrophy induced by a transitory work load in the rat.

Cardiac hypertrophy was induced in rats by abdominal aortic constriction lasting 5-28 days. In other rats, release of aortic constriction after 5 or 15 days led to hypertrophy regression, which was completed within 15 days. Left ventricular papillary muscle study during cardiac hypertrophy demonstrated an early but transitory decrease of tension development and shortening velocity, a prolonged contraction duration, a slowed relaxation, and a reduced response to changes in the stimulation rate. After hypertrophy regression, the prolongation of contraction persisted; mechanical performance was similar to control, except for increased peak isometric tension in early released animals. These findings indicated that anomalous excitation-contraction coupling may be related to the hypertrophy process itself and that prolonged contraction could act as a compensatory mechanism.