[Ultrastructural changes in the myocardium of rats with experimental hypothyroidism]

The dynamics of ultrastructural changes in the heart were studied in the setting of experimental hypothyroidism following surgical removal of the thyroid gland. The studies examined the capillary bed, the connective tissue and the muscle fibers. The initial changes were observed in the per vascular spaces which were distended and filled with a substance of low electron density. These changes were followed by alterations in the endothelium and in the muscle fibers whereby the dynamics of this sequence were related to the degree of mitochondrial injury. Damage to the cardiac musculature parallels the changes observed by other investigators in skeletal muscle. The issue of basophilic degeneration of muscle fibers in hypothyroidism is also discussed.