Tubuloglomerular feedback in rats with chronic partial bilateral ureteral obstruction.
UNLABELLED: Rats with chronic partial unilateral ureteral obstruction (UUO) have a paradoxical resetting of the tubuloglomerular feedback (TGF) mechanism. During extracellular fluid volume expansion (VE) in control animals, a decrease in TGF sensitivity is normally noted. In rats with partial UUO, however, TGF sensitivity in the obstructed kidney was increased, associated with a relative reduction in single nephron glomerular filtration rate. In the present study, we examined the tubular and interstitial pressures, whole kidney function and the TGF system in rats with chronic partial bilateral ureteral obstruction. The rats were divided into preferentially ipsilaterally and preferentially contralaterally obstructed, as judged by pelvic volume. Measurements were performed both during hydropenia and during VE. During hydropenia TGF characteristics were the same in the 2 groups. During VE, however, TGF sensitivity was unchanged in the most obstructed kidneys (ipsilateral), while if the obstruction was preferentially contralateral, TGF-sensitivity decreased. This opposite change in TGF sensitivity resulted in higher electrolyte and water excretion from the least obstructed kidney. The change in TGF sensitivity was not correlated to renal interstitial pressure. IN CONCLUSION: rats with moderate chronic partial bilateral ureteral obstruction have an almost preserved function with regard to renal hemodynamics and excretion during hydropenia. During volume expansion, however, different responses were found in the least and most obstructed kidneys, with a decreased sensitivity of TGF in the least obstructed kidney, while TGF sensitivity was unchanged in the most obstructed kidney.