Relation of nephron recruitment to detectable filtration and recovery of function after release of ureteral obstruction.

In this study, the role of nephron recruitment to measurable filtration in the recovery of whole kidney GFR following release of ureteral obstruction of 18 hr duration was characterized in the young rat with a modification of Hanssen's technique. Following release of bilateral (BUO) or unilateral (UUO) ureteral obstruction, the expected increases in fractional sodium and water excretion were observed and remained constant throughout the interval of the study (approximately 3 hr). However, the GFR of the postrelease kidney of rats subjected to BUO and UUO increased significantly within this time frame. Surprisingly, the percent increase in GFR was greater in the the UUO group. In both groups, there was a positive correlation between the number of filtering nephrons and time after release. The increase in the number of filtering juxtamedullary and superficial nephrons detectable with this technique was symmetrical after release of UUO and BUO. However, at all intervals of study, there were significantly fewer filtering nephrons in the postrelease kidney of the UUO and the BUO group. These studies indicate that the mechanism of recovery of GFR in the postrelease kidney in the two settings of ureteral obstruction is quite different.