MORPHOMETRIC CHARACTERIZATION OF LEFT-VENTRICULAR MYOCARDIAL-CELLS OF MALE-RATS DURING POSTNATAL-DEVELOPMENT

Morphometric investigations of the left ventricular myocardial cells of male Wistar rats aged 0, 1, 2, 3, 4, 5, 6, 7, 14, 21 days and 1, 2, 3, 4, 5, 6 months were carried out. The volume density of the sarcoplasm decreased from 0.33 (at birth) to 0.018 (6th month). The volume density of the myofibrils diminished during the first 7 days of life, whereas after the 6th month (0.57) it was nearly the same again as at birth (0.52). The volume density of the mitochondria increased from 0.16 at birth to 0.33 in the 6th month. The surface density of the outer mitochondrial membrane increased at different rates. The number of mitochondria per unit area grew from 0.51 (at birth) to 0.88 (6th month). The distance between the mitochondria decreased from 4.33 μm (at birth) to 1.67 μm (6th month). The mitochondrial/myofibrillar ratio doubled in the course of the period covered by the study (0.32 at birth; 0.64 in the 6th month). The postnatal development of heart muscle cells can be characterized by data obtained on the heart at birth, at the ages of 3, 4, 5, 7, and 14 days and in the 1st, 3rd and 6th month. © 1979.