Abstract
The local changes in the left ventricle (LV) of spontaneously hypertensive rats (SHR) were compared with those of Wister rats (WR) in reference to the onset of hypertension and the duration maintaining hypertensive state. Two strains of rats, SHR from Zichi Medical College colony and age-matched normotensive WR were examined at 6, 16, 30, 40 weeks of age. After measuring arterial systolic blood presser (BP), the hearts were fixed at diastolic phase and then isolated. Histological preparations at three transverse levels of LV (Apex, Middle, Base) were made, in all of which wall thicknesses, ratio of external to internal circumflex areas of transverse sections of LV and numbers of myocardial cells per unit area were studied. It was investigated, furthermore, whether or not degenerative changes of myocardium were observed in every specimen. As the results, BP in SHR was significantly higher than that in WR except 6 weeks of it. Both ventricular septum and left ventricular free wall in SHR were significantly thicker than those of WR, and the form of LV in SHR was symmetrical and concetric from 16 to 40 weeks of SHR. Cell numbers per unit area in SHR decreased, and the areas of left ventricular cavity in SHR were smaller than those of WR from 6 through 40 weeks of rats. These indicate that LV of SHR is pathologically different from that of WR already before the onset of hypertension. The fibrosis and fatty degeneration were recognized at 30, 40 weeks of SHR, and the same slight degenerations in 40 weeks of WR. Consequently chronic hypertensive state influences on the advance in cardiac hypertrophy and tissue degenerations, and also local hypertrophy of LV as seen in human's were not observed in SHR. The pathological differences in 6 weeks of SHR from WR are not due to hypertensive state, but may be related to congenital and other unknown factors.
