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 veins, renal blood flow (RBF), glomerular filtration rate (GFR) and filtration fraction (FF) were investigated during stepwise unilateral ureteral obstruction. Elevation of the ureteral pressure in steps of 10 mm Hg to a maximum of 80 mm Hg decreased ipsilateral RBF by 45 +/- 3% from 300 +/- 25 to 168 +/- 20 ml/min (p < 0.01). Contralateral RBF did not change significantly. The mean arterial pressure ws 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 51Cr-EDTA equal to FF increased temporarily from 0.202 +/- 0.013 at start to 0.239 +/- 0.015 (p < 0.05) at 20 mm Hg in the ipsilateral kidney, whereafter it was dramatically reduced to 0.090 +/- 0.024 at maximum pressure. In addition, renal tubular handling of salt and water in the contralateral kidney were investigated using the lithium clearance technique. No significant changes were found. In conclusion, the renal hemodynamic changes during ureteral obstruction are compatible with a predominant preglomerular vasoconstriction. The inter-relationship between obstruction, high pressure and reduction in RBF and GFR is substantiated. Moreover, variation in the reactive mechanisms between species with different kidney activities is established.