The Renal Response of Sheep Fed a High Protein Diet to Treatment with Vasopressin Analogue

Abstract

This experiment was designed to test whether the long-term formation of highly concentrated urine rises the glomerular filtration rate in sheep like in 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 concentrating kidneys, the experimental group was treated with 1-desamino-8-D-arginine vasopressin (dDAVP, Adiuretin-SD, Ferring, Prague). Subcutaneous injections of 12.5 µg dDAVP given twice daily started one week before the measurements of renal function. The clearance protocol showed a decreased urine 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 significantly increased (from 5.76 ± 0.39 to 7.28 ± 0.25 mmol . l -1 , P < 0.01) concomitantly with the larger renal urea reabsorption (from 239.72 ± 26.16 to 390.53 ± 33.25 µmol . 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) and the amount of urea excreted were significantly reduced (206.22 ± 9.04 vs. 170.41 ± 10.76 µmol . 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 influence 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 formation of highly concentrated urine per se with a rise in the glomerular filtration rate. A possible explanation is that urea recycling through digestive tract of ruminants is of an order of magnitude larger than that in simple stomach animals.

Short-term vasopressin analogue treatment does not influence the nitrogen balance in sheep

“…No differences were found in nitrogen intake, faecal and urine nitrogen excretion between the control and experimental groups. The higher concentration of nitrogen in urine of animals treated with dDAVP was related to a lower urine flow rate, which was described earlier (Boldižárová et al, 1999). 1.9 ± 0.5 1.9 ± 0.3 NS Total N excretion, % N intake 94 ± 3 97 ± 3 NS On the other hand, long-term treatment (5 months) with the same vasopressin analogue in growing lambs resulted in the relative enlargement of the kidney medulla and reduction in the size of the cortex.…”

“…Our recent results with sheep injected with a vasopressin analogue (dDAVP) resulted in a 26% increase in the plasma urea, while renal urea reabsorption was concomitantly elevated by 63% (Boldižárová et al, 1999). This difference has been explained by extensive urea recycling into the digestive tract.…”

The urinary excretion of purine derivatives in sheep is not influenced by long term treatment with vasopressin

“…Plasma urea concentration (P urea ) and renal urea reabsorption (Reab urea ) showed higher values in the dDAVP group in comparison with the control group, but without significant differences compared with our previous paper, where these differences were significantly higher (Boldižárová et al, 1999). The explanation lies in the number of sheep which were used for statistical analysis, when in our previous experiments we used 11 sheep for each group and now 6 sheep for each group.…”

“…During a low protein diet, renal excretion of urea is reduced by a decreased filtered load of urea and an enhanced capacity for urea reabsorption from tubules and the renal pelvis (Cirio and Boivin, 1990). The effect of highly-concentrated urine induced by vasopressin administration in sheep which are fed a high protein diet does not result in a rise of glomerular filtration rate, but this is a possible response to recycling of urea nitrogen through the digestive tract (Boldižárová et al, 1999).…”