Ultrastructure and stereology of cardiomyocytes in the development of regenerative and plastic myocardial insufficiency during ontogeny.

The age-related features of ultrastructural reorganization of cardiomyocytes were studied in rats with anthracycline-induced injury. The development of regenerative and plastic insufficiency of cardiomyocytes in animals of various age groups was accompanied by stereotypic ultrastructural reorganization. The major changes concerned the nucleus, myofibrillar compartment, and rough sarcoplasmic reticulum. Intracellular reorganization of cardiomyocytes in young animals was observed in the same period, but included a greater decrease in the volume density of myofibrils as compared to that in old rats. The recovery of cardiomyocyte ultrastructure in young animals occurred in the earlier period. Cardiomyocytes of old rats were characterized by greater structural modification of mitochondria and considerable area of lytic changes in myofibrillar bundles. Cardiotoxicity of doxorubicin in young animals was manifested in severe destruction of the capillary endothelium, which occurred in the early period after treatment.