Teratogenic effects of bis-diamine on early embryonic rat heart: an in vitro study

BACKGROUND: Bis-diamine induces cardiac defects, including conotruncal anomalies in rat embryos when the agent is administered to the mother. To evaluate the teratogenic effects and mechanism of bis-diamine, we performed morphological and immunohistochemical analyses of early rat embryos cultured in medium containing bis-diamine. METHODS: The embryos were removed from mother rats on gestational day 10.5 and cultured in medium containing 1 mg of bis-diamine for 6 hr. The embryos were then cultured in medium only for another 6, 12, 18, and 42 hr, corresponding to embryonic day (ED) 11.0, 11.25, 11.5, and 12.5, respectively. Some embryos from the same mothers were used as controls and were cultured in medium only for the corresponding periods to the embryos exposed to bis-diamine. Some mother rats were given a single oral dose of 200 mg of bis-diamine on gestational day 10.5. Embryos from these pregnant rats were removed 6 hr after the oral administration of bis-diamine, and were also cultured in medium only for 6, 12, 18, and 42 hr. RESULTS: No cardiac abnormalities were detected in the controls at any stage of development. Thirty-three of 51 (65%) embryos exposed to bis-diamine and 15 of 20 (75%) embryos removed from bis-diamine-administered mothers showed abnormal cardiac development, including dilated ventricle, elongation of outflow tract, and pericardial defect on ED 11.5. Four of six (67%) embryos exposed to bis-diamine, and five of seven (71%) removed from bis-diamine-administered mothers also presented almost the same cardiac abnormalities on ED 12.5. No cardiac abnormalities were detected in bis-diamine-treated embryos before ED 11.5. In addition, the expression of neural cell adhesion molecule (N-CAM) was examined using immunohistochemical methods. Fewer N-CAM immunoreactive cells were detected in the third and fourth aortic arches in the bis-diamine-treated embryos than in controls on ED 11.5. However, more N-CAM immunoreactive cells were detected in the bis-diamine-treated embryos than in controls on ED 12.5. CONCLUSIONS: These results suggest that bis-diamine induces cardiac anomalies by delaying the migration of neural crest cells into the heart and by disturbing the proliferation of pericardial precursor during early cardiac development.