The Role of Urinary Obstruction in the Genesis of Renal Dysplasia—A Model in the Chick Embryo

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Abstract
Although obstruction of urinary drainage is the current pathogenetic mechanism believed responsible for [human] renal dysplasia, the results of experimental studies have not uniformly substantitated this impression. To help resolve this issue, the effect of obstruction of the urinary drainage of the embryonic kidney on the later development of the kidney was evaluated. A model was developed which allowed the ureter in the chick embryo to be surgically ligated before and after the appearance of nephrons. Initially, the normal morphologic features of renal development were studied in 22 embryos at various stages of incubation and in 94 metanephric rudiments cultivated as chorio-allantoic membrane (CAM) grafts. The morphologic features of renal development were studied in 151 metanephric rudiments subjected to surgical ligation of the primitive ureter and then cultivated as CAM grafts. The ligations were performed with 9-0 silk suture, aided by the operating microscope, and induced before and after the appearance of nephrons. Renal differentiation of the nonligated rudiments cultivated as CAM grafts resembled that which appeared in situ. Renal differentiation of 87% of nonligated rudiments which survived grafting displayed normal renal development and 13% displayed mild hydronephrosis. Renal differentiation of 67% of the ligated rudiments which survived grafting displayed hydronephrosis and 33% displayed normal development. Dysplasia was never seen in any specimen. Obstruction of the ureter of the developing kidney caused only hydronephrosis in the chick model. Apparently, renal dysplasia is not solely caused by simply mechanical obstruction to urinary drainage, even when the obstruction is imposed at early stages of renal development.