Anorectal atresia. An experimental model in the rat

Aiming to assess the development of the anorectal sphincteric apparatus and whether it is influenced by the presence of an intestinal conduit through the muscular complex, we seek to develop an experimental model of anorectal atresia in foetuses of female pregnant rats, given orally the herbicide ethylenethiourea (ETU). Six 3-months-old, 300 g female Wistar rats were included in the study group (SG). The foetuses of another unexposed rat formed the control group (CG). In the SG 54, foetuses were alive, all had hypoplasia of the tail and 47 (87%) had no visible anal orifice. The 18 foetuses of the CG were normal. The histological study was performed at the level of the pubic symphysis. Type I anorectal atresia was defined when this section demonstrated an intestinal conduit and Type II when only a muscular cord was found, without any intestinal tube. This study was completed in 15 (32%) of the SG, 9 (60%) with anorectal atresia Type II and 6 (40%) with atresia Type I, and in 11 animals (61%) of the CG. The thickness of the sphincter muscle was larger in the CG (260.47+/-35.32 micro) than in the SG (208.98+/-55.01 micro), p<0.05, but this difference was due to the animals showing atresia Type II. To conclude: ETU had a teratogenic effect. The foetuses with atresia, particularly Type II, had a decreased development of the muscular complex. The presence of an intestinal conduit does not significantly influence the development of the muscular complex.