Teratogenic effects of bis-diamine on the developing cardiac conduction system.

Background: Congenital heart defects, including conotruncal anomalies, are often associated with arrhythmias. Bis-diamine induces conotruncal anomalies in embryos when administered to pregnant female rats. To investigate the mechanism of arrhythmia in conotruncal anomalies, we histologically examined the development of the cardiac conduction system in this animal model.

Methods: A single dose of 200 mg of bis-diamine was administered to pregnant Wistar rats on ED 10.5 of pregnancy. The embryos were removed on each day from ED 11.5 to 15.5. Immunoexpression of HNK-1, connexin40, and connexin43 were examined in serial sections. The distribution pattern of TUNEL-positive cells around the conduction system was also examined.

Results: HNK-1 immunoreactivity was evident in interventricular septum, in both the control and the bis-diamine-treated embryos from ED 12.5. Although a chain of connexin40-immunoreactive cells from interventricular septum to trabeculae, corresponding to the His bundle and its branches, was demonstrated at ED 13.5 in the control embryos, this chain was first detected at ED 14.5 in the bis-diamine-treated embryos. Immunoexpression of connexin43 in the working myocardium was also less in the bis-diamine-treated embryos than in the control at ED 13.5. The number of TUNEL-positive cells in the interventricular septum was highest at ED 12.5 in the control and at ED 13.5 in the bis-diamine-treated embryos. Furthermore, these TUNEL-positive cells were HNK-1 negative, vimentin-positive, and alpha smooth muscle actin-positive.

Conclusions: Bis-diamine disturbed the normal development of gap junctions and apoptosis of myofibroblasts around the HNK-1-positive conduction tissue through overall poor myocardial proliferation and growth.