Cardiomyocyte proliferation and hypertrophy in the human fetus: quantitative study of the myocyte nuclei.

Quantitative analyses about the cardiac growth are important today because non invasive methods of diagnosis allow in vivo study of the fetal heart. Eight human fetuses of single pregnancy were studied. The ages of the fetuses were determined according to the foot length. Four fetuses were aged in the 2nd trimester and four fetuses were aged in the 3rd trimester of gestation. We used the dissector method to obtain the volume and numerical densities of the cardiac myocytes. We studied fifteen random dissector pairs for each specimen. For reasons of efficiency, one nucleus was considered one myocyte. We counted the number of the myocyte nuclei in the test-area appearing in an unbiased counting frame of 1600 microns 2 on the one-slice plane. We determined the numerical density of myocyte nuclei (Nv[nu] 1/mm3), the volume density of the myocyte nuclei (Vv[nu]%) and the average volume of the myocyte nuclei (V[nu]micron 3). Both Vv[nu] and Nv[nu] decreased from the second to the third trimesters of gestation and these differences are significant (p = 0.03 a reduction of more than 40%). However, the V[nu] remains practically unchangeable during the last two trimesters of gestation (p > 0.05). During this period the cardiac weight increases almost 800% and, of course, we can expect that the absolute number of the myocyte nuclei increase so much. So, the increasing number of myocytes with the simultaneous decreasing of the Nv[nu] might explained by the overall growth of the myocardium. This fact explains why the unitary volume of the myocyte nuclei remains practically unchangeable during this period.