SPONTANEOUS AND INDUCED ALTERATIONS IN THE CARDIAC MEMBRANOUS VENTRICULAR SEPTUM OF FETAL, WEANLING, AND ADULT-RAT

Alterations of the cardiac membranous ventricular septum were studied using macrodissection, scanning electron and light microscopy of fetal , weanling, and adult Sprague-Dawley rats. Membranous Ventricular sept al defects (VSDs) were observed in 2.0% of fetuses on day 21 postcoitu s (pc) but not in weanling or adult rats. The most common observation was a nonpatent depression in the membranous septum with an incidence of 38.1, 10.5, 4.3% for fetuses on days 17, 19, or 21 pc, respectively , 11.8% for weanlings, and 9.1% for adults. VSDs were characterized by a split in the endocardial cushion cells in the interventricular comp onent of the membranous septum. Nonpatent depressions were characteriz ed by a split in the endocardial cushion cells in the atrioventricular component of the septum, and they persisted postnatally as a blind-en ded diverticulum directed above the tricuspid valve. The cardiovascula r teratogens, trimethadione and trypan blue, produced in fetuses nonpa tent depressions and VSDs morphologically similar to untreated fetuses . Maternal diet restriction (25% of controls) lowered fetal (day 21 pc ) body weight by 47% but did not affect the incidence of ventricular s eptal alterations, suggesting that intrauterine growth retardation is not necessarily associated with alterations in the development of the ventricular septum. We conclude that neither VSDs nor nonpatent depres sions in Sprague-Dawley rats affect postnatal survival and that VSDs c lose spontaneously during neonatal life. (C) 1997 Wiley-liss, Inc.