Morphology of the heart during the period of progressive growth in conditions of prolonged exposure to low temperatures

Abstract

Annotation. The aim of the research is to study the cardiac morphology during the period of growth under prolonged exposure to low temperatures. The main group consisted of outbred white rats (260 males and 190 females) undergoing active development, aged 4 weeks at the beginning of the experiment, and was kept in a room with an air temperature of +4±1 °C. The control group of animals was kept in a room with an air temperature of +20±10 °C. The experiment lasted for sixteen weeks. Research methods: macromorphometric study of the heart, histological study of paraffin sections, and ultrastructural study. Micromorphometric study was performed on semi-thin sections stained with 0.1% solution of toluidine blue at an ocular magnification of 10 and objective of 90, using a multi-purpose test system of short segments (Weibel grid) and an automatic analyzer of microscopic images “Integral-2MT”. PAS stain by A.L.Shabadash was used to detect glycogen, and the number of glycogen granules per unit area was counted on electronograms at a magnification of 20000 using a 1 cm2 area square. The stereological study of the electronograms was carried out at a magnification of 8000 using a Weibel grid. The statistical processing of the obtained results was carried out using the SPSS statistical program package, STATISTICA v. 10.0. It was found that the adaptation of the myocardium to the cold occurs according to the universal mechanism of adaptation to various extreme conditions associated with a deficit of energy metabolism. Therefore, the effect of cold can be regarded as non-specific. Based on the conducted research, the following stages of the adaptation process are defined: 1) short-term stress reaction (first 5 days); 2) myocardial hypertrophy (from 2nd to 6th weeks); 3) long-term, stable adaptation (more than 6 weeks). Morphological criteria for myocardial adaptation to long-term cold exposure have been identified: 1) physiological hypertrophy of the myocardium, mainly of the right ventricle; 2) the energy reserve of cardiomyocytes in the form of mitochondrial hyperplasia and glycogen accumulation. We plan to study the microcirculatory bed of the myocardium during the adaptation of the body to prolonged action of low temperature in the future.