Coordinated changes in contractility, energetics, and isomyosins after aortic stenosis

To investigate possible alterations of myocardial performance in young rats, cardiac hypertrophy was induced by stenosis of the ascending aorta (AS) in three groups of 25-day-old rats that were compared with three groups of sham-operated controls (C). The cardiac overload duration was 8-10 days, 1 mo, and 2 mo in groups 1, 2, and 3, respectively. Mechanics and energetics were studied in left ventricular papillary muscles, and determination of the V1 and V3 isomyosin pattern was achieved in the same papillary muscle. The majority of quantitative changes concerning the cardiac growth process, contractility, and isomyosin shifts occurred within 8-10 days of stenosis. At this point, the degree of left ventricular hypertrophy relative to C was 53 +/- 6%, whereas maximum unloaded shortening velocity (Vmax) decreased significantly (2.8 +/- 0.1 in C vs. 1.9 +/- 0.1 Lmax/s in AS), peak power output (Emax) decreased (1.8 +/- 0.3 in C vs. 0.6 +/- 0.1 in AS), and the curvature of Hill's hyperbola increased (1.3 +/- 0.4 in C vs. 2.0 +/- 0.7 in AS); moreover, the percent V1 isomyosin decreased significantly (98 +/- 1 in C vs. 51 +/- 3% in AS) and the percent V3 isomyosin increased significantly (2 +/- 1 in C vs. 26 +/- 2% in AS). Beyond 8-10 days of AS, additional changes in cardiac hypertrophy and in mechanical and biochemical parameters were less marked.(ABSTRACT TRUNCATED AT 250 WORDS)