Although obstruction of urinary drainage is the current pathogenetic mechanism believed responsible for renal dysplasia, the results of experimental studies have not uniformly substantiated this impression. To help resolve this issue, we evaluated the effect of obstruction of the urinary drainage of the embryonic kidney upon the later development of the kidney. We developed a model which allowed us to ligate the ureter surgically of the chick embryo before and after the appearance of nephrones. 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 chorioallantoic membrane (CAM) grafts. Then, 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 non-ligated rudiments cultivated as CAM grafts resembled that which appeared in situ. Renal differentiation of 87 per cent of nonligated rudiments which survived grafting displayed normal renal development and 13 per cent displayed mild hydronephrosis. Renal differentiation of 67 per cent of the ligated rudiments which survived grafting displayed hydronephrosis and 33 per cent 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. It appears that renal dysplasia is not solely caused by simple mechanical obstruction to urinary drainage, even when the obstruction is imposed at early stages of renal development.
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