NUMBER OF NUCLEI IN MAMMALIAN CARDIAC MYOCYTES

The numbers of nuclei per cardiac muscle cell were determined in adult mammalian hearts after previous enzymatic isolation of individual myocytes. A high percentage of binucleation was observed in rat (78 ± 1.8%), rabbit (78 ± 0.8%), guinea pig (81 + 1.6%), cat (76 ± 1.5%), dog (47 ± 2.4%), and beef (45 ± 1.1%), while the human myocytes were found predominantly mononucleated (90%) and only 10 ± 2.2% of them were binucleated. These findings are in agreement with our data obtained after serial sectioning of the myocardium of the above species and subsequent reconstruction of individual myocytes. We also found that in fetal and neonatal rat the cardiac myocytes are predominantly mononucleated (95% and 84%, respectively), that the binucleation develops during the early postnatal period, and that adult values are reached by 12-14 days of age. When the body growth and consequently also the heart growth were either accelerated or slowed down by nutritional intervention during the above period, the rate of appearance of binucleation correlated with the organ size rather than with the age of the rat. Early postnatal increase in binucleation was also observed in rabbit, cat, and dog during normal growth. The regional distribution of the above phenomenon was found to be uniform throughout both ventricles.