[Changes in the protein mass and ploidy level of the myocytes in the mouse heart].

Neonatal mice were grown until 3 weeks of age at a rate of four or sixteen per litter (groups I and II, respectively). The group I animals were characterized by accelerated growth. At day 21 of postnatal development their body and heart weights were three times greater than those of the group II animals. The mean protein content in cardiomyocytes of the group I animals increased faster, correlating with the increase of the heart weight. The fast-growing mice showed an increase in the number of polyploid cardiomyocytes (polynucleate cells mainly), amounting to 15-16% as compared with 2-4% seen in normal and slow-growing animals.