Pyelorenal backflow in normal and ischemic rabbit kidneys.

Pyelorenal backflow during retrograde pyelography was studied in 68 kidneys of anesthetized rabbits. Thirty-three of the experiments were performed during or shortly after temporary renal arterial clamping. Pyelosinous backflow was observed in 67 and pyelovenous backflow in 65 of the 68 kidneys, occurring at an average intrapelvic pressure of 70 mmHg. This was true in intact kidneys and during arterial occlusion. Intrarenal backflow--intrusion of contrast material into the renal parenchyma--could be produced in only one of 35 experiments on intact kidneys, and occurred at an intrapelvic pressure of 119 mmHg. During arterial clamping, intrarenal backflow was observed in eight of nine experiments, occurring at intrapelvic pressures of about 70 mmHg. After removal of the clamp, intrarenal backflow was less frequent with shorter periods of arterial clamping and longer time between restoration of arterial flow before pyelography. Subcapsular extravasation of the medium with total blurring of the kidneys shadow and a prompt fall in intrapelvic pressure was the ultimate result of prolonged and extreme overdistension of the renal pelvis. It occurred at an average intrapelvic pressure of 80 mmHg. Histologic examination revealed tears in the fornix of the pelvic cavity in cases with pyelosinous backflow. If intrarenal backflow was present, there were tears leading from the pelvic cavity into the renal parenchyma. Supplementary experiments using a contrast material that could be demonstrated histologically (barium sulfate with gelatin) showed that the contrast filled the intertubular capillaries and venules. There was no evidence of backflow through the canalicular route.