Ultrastructural and cytochemical changes in the heart of iron-deficient rats.

Male Sprague-Dawley rats aged 3 weeks that were maintained on an iron-deficient diet for 4-5 weeks developed severe anemia with markedly reduced hemoglobin levels (3.94 +/- 0.14 Hb g% versus controls 12.9 +/- 0.11 Hb g%). Iron-deficiency resulted in marked cardiac hypertrophy (cardiomegaly). On sacrifice, the hearts were processed for light and transmission electron microscopy. The major ultrastructural changes were found in the hypertrophied left ventricle and left papillary muscles. Iron-deficiency caused marked edema in myocytes, sarcomeres were out of register, and degeneration and discontinuities in myofilaments were common. Iron-deficiency resulted in the enlargement of the interfibrillar mitochondria, changes in the matrix and the formation of electron-dense amorphous bodies. The ultrastructural changes in myocytes in response to experimental iron-deficiency were similar to those described by others in cases of experimental ischemia or hypoxia. Mitochondrial changes were also found in the atria of iron-deficient rats. Quantitative cytochemical measurement of succinate dehydrogenase activity was determined and was shown to be substantially reduced in the iron-deficient heart. In severely iron-deficient rats restored to a normal iron-sufficient diet for two weeks, hemoglobin levels recovered, however the myocytes of the hypertrophied left ventricles and papillary muscles continued to show severe degenerative changes.