Postnatal closure of membranous ventricular septal defects in Sprague-Dawley rat pups after maternal exposure with trimethadione.

BACKGROUND: Congenital membranous ventricular septal defects (VSD) have been shown to close during postnatal development in rats [Solomon et al., Teratology 55:185-194, 1997]. Although they may differ in size, spontaneous and treatment-related VSD are histologically similar; however, the postnatal fate of treatment-induced VSD is not known. The objective of this study was to determine if treatment-induced VSD persist throughout postnatal development. METHODS: Groups of 40 female rats were given oral doses of trimethadione (TMD) at 400 mg/kg/day (200 b.i.d.) or 600 mg/kg/day (300 b.i.d.) on Gestation Days (GD) 9 and 10. Twenty dams in each group were designated for Cesarean section and 20 were allowed to deliver and rear their offspring to Postnatal Day (PND) 21. The integrity of the ventricular septum was evaluated in fetuses (GD 21) and pups (PND 21). RESULTS: The incidence of membranous VSD was 0.6, 7.6, and 49.8% per litter in the Control, 400, and 600 mg/kg groups, respectively, on GD 21. Both the incidence and severity of VSD increased with dose. The VSD at 400 mg/kg were small in size and initially detected by the presence of blood flowing through the defect from the closed right ventricle. In the 600 mg/kg dose group, the VSD, although still membranous, were larger and more readily detected without the need to examine the blood flow. At 600 mg/kg, not only were the VSD larger than those in the Control or the 400 mg/kg group, 10.1% per litter of the affected fetuses had other vessel anomalies associated with the VSD, which were incompatible with pup survival. On PND 21, VSD was noted in 0.3, 0, and 6.4% per litter evaluated in the Control, 400, and 600 mg/kg groups, respectively. This demonstrates that the small, isolated treatment-related VSD can resolve postnatally; however, the closure of the larger or more severe VSD may be prolonged or may not occur at all. Although TMD exposure reduced group mean fetal weights at both dose levels, there was no difference between the mean weight of fetuses with VSD and those fetuses without VSD in the same group. CONCLUSION: Treatment-induced VSD close postnatally, and appears to be a delay in cardiac development not associated with fetal weight. The timing of closure and survivability during closure is dependent on the severity of the VSD. Further characterization of the two sizes of VSD may provide diagnostic clarity; however, the current data support the smaller VSD as a variation with no significant impact on viability and growth, and the more severe VSD to be a malformation.

Embryo/fetal development studies with hydroxypropyl methylcellulose acetate succinate (HPMCAS) in rats and rabbits.

BACKGROUND: Hoshi et al. [Hoshi et al. J Toxicol Sci 10(Suppl):187-255, 1985a,b,c,d] evaluated the potential for hydroxypropyl methylcellulose acetate succinate (HPMCAS) to produce developmental and reproductive toxicity in a series of studies that included rat and rabbit teratology studies, a rat fertility study, and a rat peri- and postnatal study. The authors concluded that there were no compound-related findings. In the cesarean-section phase of the rat teratology study, however, clubfoot was reported for 0.8, 2.1, 5.5, and 4.1% of fetuses in the control, 625, 1250, and 2500 mg/kg groups, respectively. There were no significant increases in external anomalies, but the apparent dose-related increase in clubfoot was not specifically addressed. In the rabbit teratology study, the number of litters evaluated (12-13 per group) was not consistent with current regulatory guidelines. Therefore, to definitively establish the potential of HPMCAS to produce developmental toxicity, embryo/fetal development studies were carried out in rats and rabbits. METHODS: Groups of 20 pregnant Sprague-Dawley rats and New Zealand White rabbits were dosed with 0, 50, 150, 625, or 2500 mg/kg HPMCAS from gestational day (GD) 6-17 or GD 7-19 for rats and rabbits, respectively. Fetuses were collected by cesarean section and examined for external, visceral and skeletal development. RESULTS: No developmental toxicity was observed as a result of HPMCAS exposure demonstrating that maternal HPMCAS exposure during gestation does not induce developmental anomalies. There were no findings of clubfoot or other limb anomalies in these studies at dose levels equivalent to those that were previously associated with a possible increase in clubfoot. CONCLUSIONS: The conclusion of the earlier study indicating that treatment with HPMCAS at doses up to and including 2500 mg/kg did not produce developmental toxicity was confirmed with these studies. It is likely that the clubfoot noted in the earlier rat teratology study was a misdiagnosis or artifact.