[Mitotic activity of cardiomyocytes during myocardial growth and injury in one-day-old rats].

Significant differences were noted in the mitotic index in various parts of the heart of 3, 5, 8 and 15-day-old rats. In the atria and auricles, in the subepicardial layer of both ventricles and trabecular myocardium, mitoses of cardiomyocytes were detected more often with their number decreasing more slowly as compared to the compact myocardium. The mitotic index in all parts of the heart abruptly decreased by the 5th postnatal day. Ethanol injection into the compact left ventricular myocardium of 1-day-old ratlings caused local necrosis. The mitotic activity of cardiomyocytes surrounding the necrotic area never increased (days 2, 4, 7 and 14 after injury) while on the 4th postoperative day the mitotic index fluctuated from 120 to 250% of the control level in both atria and auricles as well as in the subepicardial layer of both ventricles. The mitotic activity of cardiomyocytes increased during the following two weeks.