Abstract
We studied morphological changes in the left and right ventricles of fetal rats in late-gestation using rapid whole-body freezing technique. Pregnant Wistar rats (term, 21.5 day) were immediately frozen in liquid nitrogen on 17-, 18-, 19-, 20-, and 21-day of gestation. The frozen fetal hearts were serially sectioned with a sliding microtome and photographed. The ventricular volume, mass, wall thickness, and area of valvular orifice were measured on the photographs. During the study period, the left and right ventricular volumes increased very rapidly (9.9-fold and 7.6-fold, respectively) compared with the increase in the body weight (4.0-fold); the volumes divided by body weight increased linearly. Left and right ventricular masses also rapidly increased (5.9-fold and 5.0-fold, respectively). Mass/volume ratios for the two ventricles rapidly decreased. The wall thicknesses divided by body weights rapidly decreased with the progression of the gestational age. The left and right ventricles at 17 day of gestation have relative hypertrophy and relatively large valvular orifices as compared with those in terminal gestation. The improvement of the relative hypertrophy of the ventricles may indicate the morphological and functional maturation of the fetal heart.
