Proliferation of the rat myocardium after early postnatal injury

Abstract

A small quantity of 96% ethanol was injected into the left ventricle of noninbred albino rats aged 7, 14, and 30 days, causing focal necrosis of the myocardium. The animals were killed 2–30 days after the operation. The mitotic index (MI) of the muscle nuclei was determined in different parts of the heart: in the left and right atria and their auricles, the trabecular and compact myocardium and the subepicardial zones of both ventricles, and also in the zone around the focus. Proliferation of myocytes in the compact myocardium was found to be inhibited and was not resumed after injury to the left ventricle. In all other zones, in which mitoses were present in the control animals, MI of the myocytes increased after trauma to the heart. The later the injury was inflicted, the less marked the rise in MI. In animals aged 7 days, MI on the 4th day after the operation reached 320–500% of the control, and on the 7th day it reached 120–380%. MI in the group of animals undergoing the operation at the ages of 14 and 30 days was increased only in some “high-mitosis” rats and not in all parts of the heart. The ability of connective tissue to replace the defect increases with growth of the heart.