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.