TUBULOGLOMERULAR FEEDBACK IN RATS WITH CHRONIC PARTIAL BILATERAL URETERAL OBSTRUCTION

Rats with chronic partial unilateral ureteral obstruction (UUO) have a paradoxical resetting of the tubuloglomerular feedback (TGF) mechanis m. During extracellular fluid volume expansion (VE) in control animals , a decrease in TGF sensitivity is normally noted. In rats with partia l UUO, however, TGF sensitivity in the obstructed kidney was increased , associated with a relative reduction in single nephron glomerular fi ltration rate. In the present study we examined the tubular and inters titial pressures, whole kidney function and the TGF system in rats wit h chronic partial bilateral ureteral obstruction. The rats were divide d into preferentially ipsilaterally and preferentially contralaterally obstructed, as judged by pelvic volume. Measurements were performed b oth during hydropenia and during VE. During hydropenia TGF characteris tics were the same in the 2 groups. During VE, however, TGF sensitivit y was unchanged in the most obstructed kidneys (ipsilateral), while if the obstruction was preferentially contralateral, TGF-sensitivity dec reased. This opposite change in TGF sensitivity resulted in higher ele ctrolyte and water excretion from the least obstructed kidney. The cha nge in TGF sensitivity was not con-elated to renal interstitial pressu re. In conclusion: rats with moderate chronic partial bilateral ureter al 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 obstruc ted kindeys, with a decreased sensitivity of TGF in the least obstruct ed kidney, while TGF sensitivity was unchanged in the most obstructed kidney.