The renal response of sheep fed a high protein diet to treatment with vasopressin analogue

This experiment was designed to test whether the long-term formation of hig hly concentrated urine rises the glomerular filtration rate in sheep like i n simple stomach animals. Experiments were carried out on young sheep fed a high protein diet for 3 weeks. In order to produce animals with highly con centrating kidneys, the experimental group was treated with 1-desamino-8-D- arginine vasopressin (dDAVP, Adiuretin-SD, Ferring, Prague). Subcutaneous i njections of 12.5 mu g dDAVP given twice daily started one week before the measurements of renal function. The clearance protocol showed a decreased u rine flow rate (from 3.19 +/- 0.50 to 0.33 +/- 0.03 ml.min(-1), P < 0.001) without changes in glomerular filtration rate (80.18 +/- 6.36 vs. 77.86 +/- 6.26 ml.min(-1), NS) due to dDAVP. The plasma level of urea was significan tly increased (from 5.76 +/- 0.39 to 7.28 +/- 0.25 mmol.l(-1), P < 0.01) co ncomitantly with the larger renal urea reabsorption (from 239.72 +/- 26.16 to 390.53 +/- 33.25 mu mol.min(-1), P < 0.01) in dDAVP treated group. Both fractional urea excretion (48.44 +/- 3.12 vs. 30.33 +/- 1.94%, P < 0.001) a nd the amount of urea excreted were significantly reduced (206.22 +/- 9.04 vs. 170.41 +/- 10.76 mu mol.min(-1), P < 0.05). One week-lasting treatment with a vasopressin analogue resulted in the decreased urea clearance (from 36.95 +/- 2.07 to 23.76 +/- 1.97 ml.min(-1) P < 0.001) but it did not influ ence the osmotic clearance (1.77 +/- 0.10 vs. 1.62 +/- 0.08 ml.min(-1), NS) . In conclusion, the kidneys of sheep do not respond to a long-term formati on of highly concentrated urine per se with a rise in the glomerular filtra tion rate. A possible explanation is that urea recycling through digestive tract of ruminants is of an order of magnitude larger than that in simple s tomach animals.