[Nucleic acid content of normal and hypertrophic rabbit heart]

Myocardial necrosis, fibrosis, and DNA synthesis in experimental cardiac hypertrophy induced by sudden pressure overload

The development of myocardial fibrosis as a result of cardiac hypertrophy was studied in 11 cats in which the pulmonary artery was banded, six rabbits in which the ascending aorta was banded, and eight cats with various congenital cardiac anomalies. Histological examination of the myocardium revealed multifocal areas of degeneration and necrosis with healing by fibrosis in the right ventricle of cats in which the pulmonary artery was banded and in the left ventricle of rabbits in which the aorta was banded. In five of eight cats with congenital anomalies, myocardial necrosis and fibrosis were not present in spite of heart weight to body weight ratios 2-4 times greater than in the experimental models. In the other three cats, fibrosis was subendocardial or diffuse rather than multifocal as in the banded animals. This suggests that the increased connective tissue found in animals with cardiac hypertrophy induced by banding the aorta or pulmonary artery is an artifact of the preparation. Autoradiographic studies of the myocardium of pulmonary artery-banded cats indicated that all newly synthesized DNA in this model is restricted to interstitial cell and endothelial cell proliferation.

Myofibrillar ATPase, DNA and hydroxyproline content of human hypertrophied heart

70 human hearts were studied less than 36 hours after death. The apex, and in some cases other parts of the myocardium were homogenized, DNA, hydroxyproline content, myofibrillar Ca2+ and Mg2+ ATPase were measured. In normal hearts the DNA and collagen content were 372 +/- 9 mg and 36 +/- 7 mg. Ca2+ and Mg2+ ATPase of the myofibrils prepared from these hearts have shown the same specific activity (35 +/- 5 and 34 +/- 6 nmol/min./mg) as those from fresh biopsies taken during open-chest surgery. The heart weight correlates with the DNA content (r= + 0.58 -p less than 0.01) and with the myofibrillar ATPase (r= - 0.33 - p less than 0.02) but not with the DNA concentration nor with the collagen content or concentration. The main result of this study was the presence of a negative correlation between the DNA content of the heart and the Mg2+ or Ca2+ myofibrillar ATPase (r= - 0.31, p less than 0.05 - r= - 0.45, p less than 0.01). This correlation was analysed with reference to the histological and biochemical studies published by several authors in human or experimental heart hypertrophy and it was suggested that in human heart hypertrophy the decrease of the myofibrillar or myosin ATPase is a direct consequence of the high degree of polyploidy of the muscular cells observed in this condition.

Biochemical correlates of cardiac hypertrophy. 3. Changes in DNA content; the relative contributions of polyploidy and mitotic activity

DNA concentration in the left ventricle of 3-month-old rats 3 to 12 days after aortic constriction was similar to the values obtained in sham-operated litter mates (1.38 ± 0.03 µg/mg wet weight). The total DNA content of the heart was thus increased proportionally to its enlargement. In chronic hypertrophy (2 to 4 months after aortic constriction), the DNA content was increased to a significantly less extent than in short-term hypertrophy. The percentage of polyploid nuclei in 12- to 13-week-old rats increased 1 to 3 weeks after aortic constriction from a normal value of 1.8% to 4.2%. In 17- to 18-week-old rats, polyploidy was present in 3.9% of the nuclei 10 days after banding as compared with 1.6% in normal rats. Mitotic figures were localized almost exclusively outside muscle cells. Mitotic indices in hypertrophied hearts were ten times higher than in controls during the first 3 weeks after aortic constriction.