The alimentary tract malformations in the rabbit thalidomide embryopathy.

Among 906 thalidomide exposed young from 6 different rabbit strains, 141 major malformations involving the alimentary tract were found. All but 4 of the defects can confidently be regarded as a drug effect. The lesions occurred in the derivatives of the foregut, hindgut and umbilicus. Foregut anomalies (68 specimens) comprised hiatus hernia, megaoesophagus, prepyloric notching of the greater curvature of the stomach and deficient septum formation between oesophagus and trachea. In many rabbits all 4 lesions were present together. Hindgut malformations (61 specimens) were made up of rectal atresia and a small number of diverticula and/or saccular dilatations of the terminal colon, some in company with atresia. The 32 examples of atresia which were examined in detail had a coexistent fistula extending to the urethra or the anus. Omphalocoele (6 specimens in one strain) was the umbilical defect. It is suggested that some of the lesions result from impeded septum formation in the laryngotracheal grouve and the cloaca.