335 CARDIAC DEVELOPMENT IN THE PERINATAL PERIOD

Abstract

In early extrauterine life the heart undergoes rapid anatomic development. The underlying biochemical events responsible for this change are poorly understood. We investigated the mechanism of myocardial growth in fetal and neonatal animals. Piglet hearts from 0.9 gestation(0.9G), one day(l DPP), 5 day(5 DPP) and 10 day(10 DPP) old animals were divided into left ventricular free wall(LVFW), right ventricular free wall(RVFW) and intraventricular septum(IVS). Between 0.9G and 10 DPP total heart weight increased from 3.63 ± 0.23 to 13.63 ± 0.47g. During this period, LVFW weight increased 5-fold (1.34 ± 0.11: 6.70 ± .18g) and IVS increased almost 4-fold (0.93 ± 0.06: 3.71 ± 0.16g). RVFW demonstrated an approximate 2.5-fold increment in growth (1.31 ± 0.08: 3.22 ± .17g). Total protein content parallels total RNA content of each myocardial structure at every age studied. Nuclear hyperplasia was greater in the LVFW and IVS than in the RV (DNA levels (μg): RVFW 313 ± 34 VS 554 ± 44; LVFW 342 1± 25 VS 1036 ± 53; IVS 255 ± 11 VS 630 ± 26). Cellular hypertrophy was likewise greater in LV and IVS than in RV as indicated by changes in protein/DNA content (LV .46 ± .02 VS .93 ± .05 IVS: .45 ± .01 VS .86 ± .04: RV .51 ± .03 VS 0.80 ± .06) however hypertrophy did not occur in RV beyond 1 DPP. These data indicate the importance of hypertrophy as well as hyperplasia in early neonatal cardiac development and that changes in protein synthesis of each myocardial structure are due to changes in RNA levels at this age.