Ultrastructural Characterization of the Inner Sheath of the Wall of the Ascending Part of the Aorta of Prematurely Born Rats

The aim of the study was to describe the peculiarities of the ultrastructural organization of the inner sheath of the wall of the ascending part of the aorta of rats born prematurely at 24 h and to compare them with similar structures of rats born at term. Material and methods. The study was performed on male and female Wistar rats, which were divided into 2 groups: control group (premature rats, gestational age 22 days, n=32)  and experimental group  (rats born 24 hours prematurely, gestational age 21 days, n=22). Premature birth Wistar rats one day before the planned time of labor. Animals of control and experimental groups were bred at 1, 2, 4, 8 and 24 weeks of postnatal development by carbon dioxide asphyxia. Fragments of the wall of the ascending part of the aorta of preterm and premature animals were analyzed using a transmission electron microscope (transmission electron microscopy). Results. In prematurely born immature animals degenerative processes in the form of swelling of organelles of synthetic and energetic apparatuses are determined in endotheliocytes of the inner sheath of the aortic wall.  In the later postnatal period of ontogenesis (4-8 weeks) in sexually mature prematurely born rats, Weibel-Pallade's corpuscles, absent in prematurely born rats, are detected. In the late postnatal period of ontogenesis, vacuolization of endotheliocyte cytoplasm and thickening of the subendothelial layer, in which cells with fibroblast-like morphology are detected in prematurely born rats. Thinning and ruptures of the internal elastic membrane of the wall of the ascending part of the aorta of prematurely born rats are detected from the 4th week of the experiment. Conclusion. Premature birth leads to the development of endothelial dysfunction characterized by degenerative processes of endotheliocytes, thickening of the subendothelial layer, and thinning of the internal elastic membrane.

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