THE CONTRIBUTION OF ULTRAFILTRATION PRESSURE FOR GLOMERULAR HYPERFILTRATION IN YOUNG NEPHRECTOMIZED RATS

Ablation of renal tissue in infancy is followed by increased ultrafiltration pressure, enlarged filtering area and decreased hydraulic conductivity of the glomerular capillaries. This study examines the effect of a calcium channel blocker, felodipine, on ultrafiltration pressure and renal function in rats uni-nephrectomized at 5 days of age. The rats were treated with felodipine from 24 to 60 days of age or left untreated. Sham-operated untreated rats were used as controls. Arterial blood pressure levels were similar in the three groups of rats. Glomerular filtration rate and renal plasma flow in the left kidney were significantly higher in treated and untreated rats than in sham-operated untreated rats; significantly higher values were also found in treated than in untreated rats. Single nephron glomerular filtration rate was significantly higher in treated and in untreated than in sham-operated untreated rats, but was not different in treated and untreated rats. Ultrafiltration pressure was significantly higher in untreated rats than in treated and in sham-operated untreated rats; no difference was found between treated and sham-operated untreated rats. Ultrafiltration coefficient (K(f)) was significantly higher in treated rats than in untreated and sham-operated untreated rats. Hydrolic conductivity of the glomerular capillaries was significantly lower in untreated than in treated and in sham-operated rats, but was not different in treated and sham-operated rats. Glomerular volume was higher in treated and untreated rats than in sham-operated rats. Conclusion: high ultrafiltration pressure is not an absolute requirement for the hyperfiltration that follows infant nephrectomy.