Tubuloglomerular feedback response in the contralateral kidney after 24-hour unilateral ureteral obstruction.

Reduction of the functioning renal mass by unilateral nephrectomy or unilateral ureteral occlusion (UUO) leads to increased function of the remaining nephrons, an important factor being the glomerular filtration rate (GFR). GFR can be modified via the tubuloglomerular feedback control (TGF), which senses the distal delivery of fluid and alters the tonus of the glomerular arterioles. The aim of the present study was to investigate the TGF sensitivity in the intact left kidney of rats after 24 hours of right ureteral occlusion. Using a micropuncture technique, proximal tubular stop-flow pressure (Psf), as a relative index of glomerular capillary pressure, was measured upstream to the block, while late proximal segments were perfused with Ringer solution (rates 0-40 nl/min). The maximal drop in Psf and the tubular flow rate at which 50% of this response was achieved, the turning point (TP), were determined. Considerable decrease in the sensitivity of the TGF system in the contralateral kidney during UUO was indicated by a significantly higher TP as compared with control rats (sham operation), viz. 29 v. 19 nl/min. Maximal Psf drop after UUO was significantly less than in the controls (6 v. 12 mm Hg). Reduced TGF sensitivity in the contralateral kidney after protracted UUO is a prerequisite for that kidney's increased excretion of salt and water to compensate for the loss of functioning renal mass.