[Ultrastructural changes of myocardium in rats with hypoxic pulmonary hypertension]

Ultrastructural changes of the myocardia of rats with chronic hypoxia for 40 and 60 days are reported. The rats were caged in a hypobaric chamber simulating an altitude of 5000 meters above sea level. The heart functions were examined before myocardial specimens were taken from both ventricles for electron microscopy study. The results indicated that the myofibril structure of the right ventricle remained normal in the 40 days hypoxic group, except for the occasional appearance of obscure or disappearing Z lines. The mitochondria were slightly increased in number, with a disarrangement of the mitochondria and structural changes in the cristae. The myofibrils of the 60 days hypoxic group showed more obvious structural changes, with disruption of myofilaments. Structural changes in the right ventricle were consistent with apparent decompensation of the right ventricle. The changes of myocardium and mitochondria in the left ventricle were similar to but less sever than those in the right ventricle, and this observation corresponds with a less severe decompensation of the left ventricle. The data suggest that during chronic hypoxic exposure, a decline occurring after the peak increase of cardiac compensation might signal the onset of structural changes of the myocardium.