CHANGES IN NUCLEAR SIZE OF CARDIAC MYOCYTES DURING THE DEVELOPMENT AND PROGRESSION OF HYPERTROPHY IN RATS

It is generally believed that nuclear enlargement indicates polyploidy . The purpose of this study was to establish whether nuclear enlargeme nt is also a marker for cellular hypertrophy. Using isolated myocytes, we examined the growth of cardiac myocyte nuclei during cellular hype rtrophy in rats with aortocaval fistulas or left ventricular myocardia l infarction. A Coulter Channelyzer was used to measure the volume of the myocytes. Isolated myocytes were stained with the DNA-specific flu orochrome 4'-6-di-amidino-2 phenylindole-HCl for measurements of nucle ar length and width, and calculation of nuclear volume, one week 1 mon th and 5 months after aortocaval fistula surgery, the nuclear volume o f right ventricular myocytes increased by 24, 55 and 56% respectively. Increased length, rather than width, accounted for most of the nuclea r growth. Nuclear hypertrophy was associated with a progressive increa se in cell volume at each time point (34, 88 and 118%). Adaptive growt h of left ventricular myocytes followed the same trend, though the ext ent of cellular and nuclear hypertrophy was reduced. One month after p roducing a myocardial infarction, there was an increase in nuclear vol ume (18%) and nuclear length (11%) in right ventricular myocytes, but no changes in the surviving left ventricular myocytes. The cell volume increased in both right and left ventricles (72 and 18%, respectively . Thus, nuclear size increased as myocytes enlarged though at a slower rate. Since nuclear DNA content does not increase in rats with aortoc aval fistulas or myocardial infarction, the increase in nuclear volume was associated with cellular enlargement rather than increased polypl oidy.