Pelvic pressure and tubuloglomerular feedback in hydronephrosis

From previous studies on hydronephrotic rats in our laboratory, an increased sensitivity of the tubuloglomerular feedback (TGF) mechanism was found during extracellular volume expansion (VE). In contrast, the mechanism resets to a lower sensitivity during VE in control animals. The resetting in hydronephrotic rats was reversed by blocking the thromboxane (Tx) system. The present study was performed to measure changes in pelvic pressure (Pp) in hydronephrotic kidneys during VE, and the effect of Tx inhibition on those changes. In addition, TGF was characterized during VE of hydronephrotic rats while Pp was kept at the pre-VE level. On VE, Pp increased moderately from a control value of 2.9 mm Hg to a plateau with a mean value of 6.0 mm Hg (control, 0.7 vs. 2.1 mm Hg). After Tx inhibition, Pp was increased by more than 100%, with a plateau value of 13.6 mm Hg. When Pp was normalized and fixed, the direction of resetting of TGF was normal. The results from this study indicate that the resetting of TGF is of importance to keep glomerular filtration rate low and reduce Pp in the hydronephrotic kidney. Tx and Pp are involved in the resetting of TGF.