TRANSPLANTATION-INDUCED ATROPHY OF NORMAL AND HYPERTROPHIC RAT HEARTS- EFFECT ON CARDIAC MYOCYTES AND CAPILLARIES

Changes in tissue structure of hearts undergoing atrophy following het erotopic isotransplantation were studied. Both normal and hypertrophic hearts were used, originating from male and female rats. Aortic const riction produced in newborn rats. resulted in an 86 and 155% increase of left ventricular mass in male and female rats, respectively. On day 50, control and experimental animals were killed, half of their heart s were analysed morphometrically, while remaining hearts were transpla nted into the abdominal cavity of recipient rats. Transplantation resu lted in significantly decreased cardiac mass in control hearts (approx imately 50% decrease compared to values at transplantation), and an ev en more pronounced decrease in hypertrophic hearts. Cardiac hypertroph y was characterized by significant decreases in capillary and myocyte densities. While myocyte density simply reflected changes in cell size , evidence for additional capillary growth was found (the aggregate le ngth of capillaries per left ventricle increased by 57-88%). Cardiac a trophy resulted in increased capillary density, despite evidence of so me capillary involution in transplanted hearts (aggregate length of ca pillaries decreased by 30-35% and 52-64% for transplants of normal and of hypertrophic hearts, respectively). Myocyte density increased due to a proportional decrease in the size of cardiac myocytes. In transpl anted hearts, an increasing number of myocytes containing nuclei locat ed close to the nearest capillary, suggests that changes in myocyte si ze are not symmetrical. The present study demonstrated the remarkable plasticity of the heart in neonatal animals; they were capable of larg e increases and decreases in cardiac mass within a felv weeks, with mo re pronounced changes in female rats. These changes were accompanied b y changes in myocardial structure, indicating some capillary growth in cardiac hypertrophy, and involution of coronary capillaries in cardia c atrophy. (C) 1997 Academic Press Limited.