Inner medullary plasma flow in the kidney with ureteral obstruction

To test the thesis that ureteral obstruction causes medullary ischemia, the authors determined inner medullary plasma flow (IMPF) in rats with bilateral or unilateral ureteral obstruction, and after relief of obstruction, by the intravenous ¹²⁵I albumin infusion technique. A progressive decline in IMPF was observed during obstruction of 18 h duration, greater in bilateral obstruction (7% of normal at 5 h) than in unilateral obstruction (28% of normal at 5 h). The elevation in ureteral pressure was greater and more sustained in bilateral obstruction. After relief of obstruction, IMPF rose to 69-78% of normal in both groups within 2 h. Histologic studies showed tubular necrosis in portions of the inner and outer medulla immedately beneath the renal pelvic epithelium after bilateral or unilateral obstruction of 18 h duration, and India ink perfusion studies showed very poor filling of vasa recta in these areas. The concentrating defect in the postobstructive kidney may be related, at least in part, to damage inflicted by medullary ischemia during obstruction.