Subcellular alterations of cardiac fibers in rats subjected to hypothyroidism.

Subcellular changes of the atrial cardiomyocytes of rats submitted to hypothyroidism caused by administration of 1 mg/100 g of body weight of propylthiouracil showed a) swollen mitochondria and lysis of their cristae; b) myofibrils with marked heterogeneity of patterns, some exhibiting rupture and loss of continuity of their myofilaments; c) lesser concentration of atrial granules in the perinuclear area; d) abundant granular interstitial tissue and collagen separating the myofibrils.