OBJECTIVEIn the normal embryonic development of anorectum, apoptosis plays an important role. To explore the role of apoptosis in anorectal malformations (ARM), this study investigated cell apoptosis during the cloacal embryonic development in ARM embryos.

METHODSARM embryos were induced by intragastric administration of ethylenethiourea (125 mg/kg) for pregnant rats on embryonic day 10 (E10). The distribution of apoptotic cells in the cloaca was ascertained by hematoxylin and eosin and TUNEL staining in the normal control embryos (n=102) and ARM embryos (n=147) on E13, E13.5, E14, E15 and E16.

RESULTSOn E13, apoptotic cells were detected in the urorectal septum of rat embryos in the control group. With the development of embryos, the number of apoptotic cells in the mesenchyme of urorectal septum gradually increased and a large number of apoptotic cells were seen in the dorsal rectal mesenchyme. On E14, apoptotic cells appeared at the terminal rectum and the dorsal cloacal membrane. On E15, the urorectal septum fused with the cloacal membrane and apoptotic cells in the urorectal septum mesenchyme continuously extended down to the fusion region. Compared with the control group, apoptotic cells in the urorectal septum, the dorsal rectal mesenchyme and the cloacal membrane of the ARM rat embryos were significantly reduced during the embryonic development. The development of the urorectal septum was delayed and it did not fuse with the cloacal membrane in ARM embryos.

CONCLUSIONSDuring the embryonic development of cloaca, abnormal apoptosis in the urorectal septum, the dorsal rectal mesenchyme and the cloacal membrane may be one of the reasons for anorectal malformations. The proper regulation of cell apoptosis may be one of the key mechanisms for normal development of anorectum in the embryonic stage.