Myocyte morphology of free wall trabeculae in right ventricular pressure overload hypertrophy in rabbits

Right ventricular (RV) hypertrophy and changes in mechanical properties develop in response to sustained pulmonary artery construction in rabbits. We use basilar RV free wall trabeculae from rabbits for measurements of force, shortening and sarcomere length (diffraction and/or photomicrography). With enzymes we dispersed calcium tolerant myocytes from trabeculae similar to those used for the above mechanical studies. The average weight of the normal (N) rabbits ( n =16) was 2.21±0.16 1 kg and was 2.11±0.10 kg for the rabbits with RV hypertrophy (H; n =16). The ratio of RV free wall to total ventricular weight was 0.17±0.01 in the N and 0.31±0.02 in H hearts ( P 2+ tolerant myocytes from each N heart and 41±3 from each H heart. Average myocyte length increased from 102.9±0.9 in N to 109.8±1.0 μm in H (6.7% above N; P P P >0.05); consequently, the restoring forces in the myocytes were the same as N in H. The greater addition of parallel myofibrils than of series sarcomeres in H is important for tension generation in the presence of the increased pressure load of pulmonary artery constriction. The addition of sarcomeres in series may be important to sustain muscle shortening in H and is consistent with our measures of sarcomere shortening in N and H trabeculae.