Ultrastructural analysis of the structure and distribution of the adherens junctions in the rats’ ventricular myocardium during postnatal stages of ontogeny after the infl uence of chronic prenatal hypoxia

Abstract

Background.

Antenatal and prenatal hypoxia causes changes in all the organs of fetuses and newborns and in the heart, particularly. Hypoxic damage of the cardiovascular system occurs in 40-70% of newborns. Currently we observe the increase of meaning of the morphological studies for the prenatal diagnosis of human’s heart diseases. It’s known that in adaptive remodeling of cardiomyocytes in the postnatal cardiogenesis of rat redistribution of diffusely located intercellular junctions from the periphery to the terminal areas of the cell occurs. The formation of a definitive pattern of intercellular junctions is completed at the puberty. But how chronic prenatal hypoxia influences the specialized adherens junctions in the rats’ ventricular myocardium is completely unknown and this requires further study.

Objective. To provide complex qualitative and quantitative comparative ultrastructural analysis of the intercellular connection changes in rat ventricular myocardium on the stages of postnatal ontogenesis in the norm and under the chronic fetal hypoxia.

Materials and methods. We have conducted ultrastructural analysis and distribution of the adherens junctions in the rats’ ventricles on the 1^st, 3^rd, 7^th, 14^th, 30^th days during postnatal ontogeny and among mature animals in the normal development and under the chronic fetal hypoxia. Experimental chronic hypoxia was modeled by intraperitoneal injection of 1% aqueous solution of the NaNO₂ in a daily dose of 50 mg/kg of body weight in the term from 10^th to 21^st days of pregnancy. Transmission electron microscopy, morphometric and statistical methods were applied. Pairwise comparisons between means of different groups were performed using a Student t-test where, for each couple of normally distributed populations, the null hypothesis that the means are equal was verified.

Results. Pronounced increase (80,6%; p <0,05) of the content of desmosomes in the intercalated disk in the period from 7^th to 14^th day was found in the experimental rats’ group. Growth level of the fascia adherens at the ends of cardiomyocytes also was observed from 14^th to 30^th day of postnatal life and was 50,9% (p <0,05). There is a significant dilatation of the intermembrane space area of the fascia adherens in experimental group of rats, that in the mature myocardium is 303,9% (p <0,05) greater than norm in the left and 37,3% (p <0,05) in the right ventricle, and the degree of junction’s ectasia in the left ventricle is 216,5% (p <0,05) greater than in the right one.

Conclusion. We found that there is retention of redistribution of the adherens junctions from the lateral surface of the cell to the area of the intercalated disks. The qualitative changes of the desmosomes are characterized by their dystopic location and also at the level of the myofilaments line and there is the appearance of the heteromorphy of the profile length. Morphology of the fascia adherens is characterized by a significant degree of variation: from the direct oblique oriented to the convoluted profiles of junctions. Adaptive adjustment of the contact apparatus, which was described, occurred against the background of the intercellular fibrosis in the rats’ myocardium of the experimental group, which may be one of the other causes of deterioration of the cardiomyocytes mechanical cooperation.