The Influence of Preterm Birth on the Development of Rat Myocardium in the Early Postnatal Period of Ontogenesis

The development of neonatology makes it possible to overcome increasingly severe degrees of prematurity. It has been established that the preterm birth in human beings is associated with a predisposition to the development of pathologies of the cardiovascular system in adulthood, but the pathogenetic mechanisms of this relationship have not been studied. In this work, we studied the effect of preterm birth on the development of the left ventricular myocardium in rats during 14 days of the postnatal period of ontogenesis. The myocardium of the left ventricle of male Wistar rats born after 21 and 21.5 days of gestation was analyzed by histology, immunohistochemistry, and morphometry (the full gestational age is 22 days). The relative heart mass of prematurely born rats exceeds that of control animals on the 14th day of the postnatal period. The diameter of the contractile cardiomyocytes of rats born on the 21st day of gestation exceeds that of full-term animals on the first day of the postnatal period of ontogenesis. Preterm birth in rats causes an increase in the number of Ki67-positive cardiomyocytes (a marker of proliferation) of the left ventricle in the early postnatal period of ontogenesis compared to full-term animals. The morphofunctional changes in the rat myocardium are more pronounced with a shorter gestational age. Preterm birth in rats is the reason for the intensification of myocardial growth in the early postnatal period of ontogenesis.