Activity of cytochrome c oxidase and citrate synthase in rat heart homogenates was determined in 5-, 15-, 28- and 60-day-old rats. The activity of both enzymes increased during postnatal development but their changes followed different kinetics. The membrane-bound cytochrome c oxidase reached its adult values during the early postnatal period, i.e. between days 5 and 15, whereas soluble matrix-localized citrate synthase also continued to increase between days 15 and 60. Our data indicate a relative excess of cytochrome c oxidase in neonatal cardiocytes.
Samples of myocardial tissue were obtained during surgical intervention from children operated for different types of congenital heart disease (tetralogy of Fallot, ventricular and atrial septal defect). Sarcoplasmic, contractile and collagenous proteins were isolated by stepwise extraction from the both right ventricular and atrial musculature. It has been found that: a) the concentration of contractile proteins is significantly higher in the ventricles, b) the concentration of collagenous proteins is significantly higher in the atrium, c) the concentration of sarcoplasmic proteins was not different, d) in children with chronic hypoxia the above atrio-ventricular differences persisted. Moreover, the proportion of the soluble collagenous fraction in the atria was significantly increased.
Aortic banding induced in 2-day-old (A2) and 6-day-old (A6) male rats increased the left ventricular (LV) weight after 60 days; right ventricular (RV) enlargement occurred in the A2 group only. The concentration of collagenous proteins in the LV was elevated in both experimental groups (more in the A2 rats) at the expenses of sarcoplasmic proteins. Aortic banding also affected the proportion of collagen types (lower collagen I, higher collagen 111, V) and myosin light chains (higher LC1/LC2) in the LV. Similar changes of proteins in the RV were less pronounced.