Renal blood flow increase during volume expansion in hydronephrotic rats

Purpose: We assessed the renal blood flow pattern in experimental hydronephrosis during normal hydration and extracellular volume expansion. Materials and Methods: Partial obstruction of the left ureter was created in 3-week-old Sprague-Dawley rats by embedding the ureter in a psoas muscle groove. Moderate hydronephrosis without kidney weight reduction developed in all cases. The effects on renal hemodynamics were studied with real-time ultrasound flowmetry 3 weeks later during normal hydration and then during volume expansion. The degree of hydronephrosis was classified as mild, moderate or severe. Results: Under baseline conditions renal blood flow was normal in mild and moderate hydronephrosis but low in severe hydronephrosis, During volume expansion renal blood flow increased significantly in all experimental animals (mean 14%) compared to that in controls, which remained unaffected or decreased (mean -3%). The flow increase was related to the degree of dilatation, which was 2% in mild, 13% in moderate and 44% in severe hydronephrosis when the groups were considered separately. Conclusions: A significant increase in renal blood flow proportional to the degree of hydronephrosis occurred as a result of volume expansion. This finding may be explained by a st-ate of vasodilatation combined with a reduction in the filtration coefficient.