The Kidney Function in Urea Loaded Sheep Fed a High Protein Diet

Abstract

BoldiÏárová K., ·. Faix, ª. Leng: The Kidney Function in Urea-loaded Sheep Fed a High Protein Diet. Acta Vet. Brno 1999, 68: 185-190.The objectives of this experiment were to investigate the effects of the increased plasma urea concentration induced by its intravenous infusion on the renal functions, especially on the glomerular filtration rate (GFR), in sheep that do not produce hypertonic urine during intake of a high protein diet. The young ewes of b.w. 22 to 25 kg were kept on a diet with the daily intake 129.3 g of crude protein and 12.03 MJ of digestible energy for at least 3 weeks before the renal function measurements. During clearance protocol, the plasma urea level was increased almost threefold in comparison to the baseline values by an infusion into the jugular vein (from 5.67 ± 0.48 mmol . l -1 to 15.70 ± 0.79 mmol . l -1 , P < 0.001). The urea load had no effects on the urine flow rate (control vs. urea infused animals, 3.07 ± 0.41 vs. 2.40 ± 0.23 ml . min -1 , NS) nor the GFR (81.43 ± 8.14 vs. 77.48 ± 5.43 ml . min -1 , NS). Obviously, both the urea concentration in urine (79.84 ± 17.16 vs. 243.22 ± 18.94 mmol . l -1 , P < 0.001) and the amount of urea excreted (198.78 ± 9.17 vs. 586.60 ± 69.69 µmol . min -1 , P < 0.001) together with the clearance of osmotically active substances (1.87 ± 0.11 vs. 3.85 ± 0.52 ml . min -1 , P < 0.01) were found to be significantly elevated in the urea-loaded group. The amount of urea reabsorbed was highly significantly larger due to urea load (245.22 ± 34.55 vs. 636.02 ± 67.17 µmol . min -1 , P < 0.001) while no changes in the fractional urea excretion (47.26 ± 4.23 vs. 47.49 ± 3.34 %, NS) nor in the urea clearance (36.20 ± 2.16 vs. 36.80 ± 3.52 ml . min -1 , NS) were observed. The presented results demonstrate that kidneys of sheep producing rather hypotonic urine during intake of a high-protein diet do not respond to the intravenous urea load with a rise in the GFR nor by a change in the urea clearance.