VARIABILITY OF CARDIOMYOCYTE DNA CONTENT, PLOIDY LEVEL AND NUCLEAR NUMBER IN MAMMALIAN HEARTS

DNA content, ploidy level, cell size and nuclear number were investiga ted in 54 mammalian hearts from nine species. DNA content was determin ed biochemically and ploidy level of cells was studied by the means of Feulgen cytophotometry. Nuclear number was calculated by a new method , while cell size was determined by using ocular micrometry. In most m ammals diploid cell nuclei predominate. Higher ploidy levels were foun d in the human and the pig hearts. The total amount of DNA correlated with the myocardial weight, Eight million heart muscle cell nuclei wer e found in mice (myocardial weight 160 mg), and 2600 million heart mus cle cell nuclei in the human heart (myocardial weight 210 g), but in t he hearts of horses up to 35 000 million heart muscle cell nuclei (myo cardial weight 3.4 kg) were found. The number of heart muscle and conn ective tissue cell nuclei was correlated with myocardial weight, The r atio of connective tissue cell nuclei to heart muscle cell nuclei was between 2:1 and 3:1. In cardiac growth this ratio shifted towards conn ective tissue cell nuclei. Increased heart weight corresponds to an in crease in cell size, Diameter between 11 mu m and 18 mu m may be an op timum for heart muscle cells of mammals.