Regional differences of myocyte hypertrophy and three-dimensional deformation of the heart

Cross-sectional area was compared between the latitudinally and longitudinally oriented muscle fibers of the hypertrophied left ventricle of the rat heart under aortic banding and isoproterenol infusion. In addition, end-diastolic three-dimensional deformation of the left ventricle as expressed by cavity volume and eccentricity was examined in the early and chronic stages of these treatments. Under aortic banding, myocyte hypertrophy occurred to a greater extent in the latitudinally oriented fibers of the midwall layer than in the longitudinal fibers of the inner and outer layers. Such a regional difference of hypertrophy was not seen under isoproterenol infusion. At the early stage of aortic banding, the left ventricle at end diastole was more dilated and spherical, whereas at the acute stage of isoproterenol infusion, it was more decreased in size and prolate than that of the controls. The deformation of the left ventricle at the early stage of aortic banding is considered to cause, during diastole, axial stretching and increase in tensile stress more on the latitudinal fibers, leading them to the predominant hypertrophy.