Changes in the urine composition during its passage through the ureter. A concept of urothelial function.

Studies in our and other laboratories have negated the general assumption that the urothelium functions as a simple conduit and support the concept of a dynamic urothelium. Based on this concept, we investigated the hypothesis that urine undergoes changes during its passage in the ureter. Urine samples were separately collected from the renal pelvis and ureters of 23 volunteers (15 men, eight women, mean age 37.6 years) through cutaneous ureterostomy performed as a treatment for bladder cancer. The pH was determined using a pH electrode, osmolality by means of micro-osmometry and Na and K by flame photometry. The pH and osmolality of ureteric urine showed no significant differences from renal pelvic urine, whereas the Na and K levels of the ureteric urine were significantly increased (both P<0.05). Gender and age differences were not significant. Renal pelvic urine undergoes changes in Na and K concentrations during its passage through the ureter. These findings presumably indicate that the ureteral urothelium is a functioning epithelium and that the renal pelvic and ureteric urine are not identical.