Regression of cardiomegaly induced in newborn rats.

Pressure overload was induced by banding the abdominal aorta in newborn male rats on day 5. Half of the animals were killed on day 30 while in the remaining animals the aortic band was removed and the rats were killed four weeks later. The banded rats had 2.5 x greater left ventricular mass than their sham-operated controls. This was due to both increased number of myocytes (hyperplasia) and of their increased size (hypertrophy). In the hearts of banded rats, significantly higher concentrations of RNA and hydroxyproline were found together with decreased concentrations of DNA. However, the total DNA content increased as well as the amount of DNA contributed by muscle cell nuclei. In the debanded rats, the mass of the left ventricle remained moderately elevated and contained more myocytes as compared to their age-controls. Similarly, myocardial RNA concentration, total DNA, and the amount of DNA contributed by muscle nuclei remained elevated in contrast to the concentrations of DNA and hydroxyproline which returned to control values. In addition, the percentage of polynucleated myocytes was higher in the hearts from experimental animals.