RENAL HEMODYNAMIC-RESPONSE TO GRADATED URETER OBSTRUCTION IN THE PIG

In anesthetized pigs with ultrasonic flow probes mounted on each renal artery and catheters placed in the abdominal aorta and both renal vei ns, renal blood flow (RBF), glomerular filtration rate (GFR) and filtr ation fraction (FF) were investigated during stepwise unilateral urete ral obstruction. Elevation of the ureteral pressure in steps of IO mm Hg to a maximum of 80 mm Hg decreased ipsilateral RBF by 45 +/- 3% fro m 300 +/- 25 to 168 +/- 20 ml/min (p < 0.01). Contralateral RBF did no t change significantly. The mean arterial pressure was constant during the experimental procedures, suggesting that the decrease of RBF was due to a significant increase in ipsilateral renal vascular resistance . Concomitantly with these changes ipsilateral GFR was reduced by 75% from 40 +/- 2 to 10 +/- 3 ml/min. In the contralateral kidney, GFR was unchanged during the experiment. The renal extraction of Cr-51-EDTA e qual to FF increased temporarily from 0.202 +/- 0.013 at start to 0.23 9 +/- 0.015 (p < 0.05) at 20 mm Hg in the ipsilateral kidney, whereaft er it was dramatically reduced to 0.090 +/- 0.024 at maximum pressure. In addition, renal tubular handling of salt and water in the contrala teral kidney were investigated using the lithium clearance technique. No significant changes were found. In conclusion, the renal hemodynami c changes during ureteral obstruction are compatible with a predominan t preglomerular vasoconstriction. The interrelationship between obstru ction, high pressure and reduction in RBF and GFR is substantiated. Mo reover, variation in the reactive mechanisms between species with diff erent kidney activities is established.