Morphological maturation of left ventricle in fetal rats: changes in left ventricular volume, mass, wall thickness, and mitral valvular size.

Morphological changes in the left ventricles of fetal rats from 17 to 21 days of gestation were studied using the rapid whole-body freezing technique. Wistar rats (pregnant period, 21.5 days) were used. Left ventricular volume, mass, wall thickness, and area of mitral valvular orifice increased rapidly and linearly during the observation period. The ratio of the mass to volume of the left ventricle gradually decreased as the fetuses grew older, and by 21st day of gestation it was 52% that of 17 days of gestation. The ratio of the area of mitral valvular orifice to left ventricular volume also decreased by 29% during the same period. Thus we see that the left ventricle of fetal rat was in the condition of physiological hypertrophy and had the large mitral valvular orifice in early gestational age. We suggest that the decrease of the ratio of mass to volume of the left ventricle with the progression of gestational age indicates the morphological maturation of the left ventricle to adapt to the rapid increase of volume overload during the perinatal period.