An autoradiographic study of the excretion of labeled Biligrafin, Hypaque and Urografin during urography, with and without ureteral stasis, is reported. The examination was performed in a series of 16 rabbits. The stasis was produced either by simple ligation of the left ureter for one half to one hour before contrast medium injection or by catheterization of the proximal end of the ureter with a polythene catheter and elevation of its external end. When the urine level in the tube had stabilized, the intravenous injection was given. At fixed times ranging from 30 sec to 30 min after the beginning of the contrast medium injection the kidneys were removed. Suitable pieces were chryostatsectioned and prepared for autoradiographic analysis. Initially there was no difference in the autoradiographs of the kidney with and the one without impaired urinary flow in the same animal. This indicates that ureteral obstruction of a duration of about one hour or application of a hydrostatic counterpressure, to balance with the secretory pressure, did not stop excretion of the contrast medium, irrespective of whether the excretion was predominantly cellular (Biligrafin) or glomerular (Hypaque and Urografin). When the nephrographic effect occurred, the kidneys with obstruction were enlarged and the dilated tubular system was intensely filled with highly concentrated contrast medium. Following ureteral ligature the contrast medium accumulated retrograde from the papilla and was assumed to be accentuated by the final water resorption from the collecting tubules. The magnitude of the intra-cellular component seemed to be dependent upon the character of the contrast medium used.
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