The effect of the antidiuretic hormone on the renal excretion of urea and electrolytes in fed and fasting sheep]

The effects of the antidiuretic hormone (ADH) on the renal excretion of urea and electrolytes were studied in sheep, subjected to water stress, before and after 36-hour fasting. The intravenous administration of synthetic lysine-vasopressin (L-VP) at the dose of 100 microgram per kg induced only a temporary, statistically insignificant, drop of the urinary urea outputs by the fed as well as fasting sheep. L-VP did not influence the excretion of sodium and potassium electrolytes either. It follows from the results that there are no differences in the renal response to ADH between the fed sheep and sheep that have fasted for 36 hours.     

Renal excretion of urea and electrolytes in sheep after extracellular fluid expansion with an isotonic solution of sodium chloride

Sheep of the Merino breed, given 10.11 g nitrogen daily (after Czechoslovak Standard CSN 46 7007) were studied for the effect of the expansion of the extracellular fluid (ECF) by an infusion of an isotonic solution of NaCl (at a rate of 5% of live weight), as exerted on the renal excretion of urea and on the sodium and potassium electrolytes. The high natriuresis, induced by the expansion of ECF, resulted in a statistically significant increase in the clearance of urea, free water, and solutions, and in higher diuresis. An increase was observed in the excretion of urea with urine (UureaV; P < 0.005) and in the excretion of the studied electrolytes of sodium (UNaV; P < 0.001) and potassium (UKV; P < 0.005) by the same route. No variation was recorded in the clearance of inulin as a measure of the glomerular filtration rate (GFR). The fractional excretion of urea, sodium, and potassium also showed a significant increase. The results imply that the fractional excretion of urea increases under the conditions of artificially induced natriuresis.     

Renal excretion of creatinine, electrolytes, protein, and enzymes in healthy sheep

Urinary indices of renal function and damage were measured in 6 healthy, mature ewes over a 48-hour period. Endogenous creatinine clearance, total and fractional electrolyte excretion rates, protein excretion, urine volume, and urine gamma-glutamyltransferase and beta-glucuronidase activities were measured. Significant variations in the excretion rates of creatinine, electrolytes, and protein were not found between intervals within the 48-hour urine collection period. Total urinary electrolyte excretion rates were significantly (P less than 0.001) correlated with fractional electrolyte excretion rates normalized for creatinine concentration; however, coefficient of determination was low.     

Changes in the renal handling of urea in sheep on a low protein diet exposed to saline drinking water

Previous trials have demonstrated that sheep on a low protein diet and free access to water, and sheep dosed with boluses of NaCl intraruminally also with free access to water, showed decreases in urea loss via the urine compared to control animals. We monitored urea excretion in sheep on a relatively poor protein diet when they were exposed to saline drinking water, i.e. they were unable to vary their intake of NaCl:water. Sheep on isotonic saline drinking water (phase 3) excreted significantly more urea via the urine (284 mM/day) compared to phase 1 when they were on non-saline drinking water (urea excretion = 230 mM/day) and phase 2 when they were on half isotonic saline drinking water (urea excretion = 244 mM/day). This finding was explained by the high glomerular filtration rate (GFR) 91.9 l/day, compared to 82.4 l/day (phase 1) and 77.9 l/day (phase 2), together with a significantly raised fractional excretion of urea (FEurea) (51.1 %) during this phase, and was in spite of the significantly lower plasma concentrations of urea in phase 3 compared to phase 1. The FEurea probably results from the osmotic diuresis caused by the salt. There were indications of a raised plasma antidiuretic hormone (ADH) concentration and this would have opposed urea loss, as ADH promotes urea reabsorption. However, this ADH effect was probably counteracted to some extent by a low plasma angiotensin II concentration, for which again there were indications, inhibiting urea reabsorption during the phases of salt loading. As atrial natriuretic peptide both increases GFR and decrease sodium reabsorption from the tubule, it was probably instrumental in causing the increase in GFR and the increase in the fractional excretion of sodium (FE(Na)).     

尿素在养羊业中的应用

羊作为反刍家畜，具有特殊的消化特点，其瘤胃中的微生物能利用非蛋白氮合成机体需要的高品质菌体蛋白。当前作为羊氮营养来源，工业合成含氮物种类很多，但尿素是应用最广的一种。尿素含氮量达42％～45％，蛋白质当量2.62～2.81，1千克尿素相当于5.6～6.0千克大豆饼。况且尿素来源广泛，价格低廉。若能在养羊业中得以合理利用，不仅能降低饲养成本，改善增重效果，还能节约有限的蛋白质饲料，是缓解蛋白饲料紧缺、人畜争粮矛盾的有效途径。1 尿素在羊体内的利用机理尿素在羊瘤胃内被一部分微生物产生的脲酶分解成氨和二氧化碳，可作为瘤胃…     

The effect of mercuric chloride intoxication on urinary psi-glutamyl transpeptidase excretion in the sheep.

The activity of the enzyme psi-glutamyl transpeptidase (psi-GT) was measured in the urine of sheep. In clinically normal animals the mean value was 6-3+/-0-6 mU/ml. In sheep with kidney damage induced by the administration of mercuric chloride there were marked increases in urinary concentrations of psi-GT, in some cases values in excess of 1000 mU/ml were recorded. This enzyme may be of value in the diagnosis of certain forms of renal disease.     

Enhancement of tetrathiomolybdate-induced biliary copper excretion in sheep by general anaesthesia and the effect on copper excretion in urine and bile

To determine whether copper removed from the liver by tetrathiomolybdate (TTM) but not excreted in bile, is excreted in saliva or urine, the effect of an intravenous injection of 100 mg of TTM, as ammonium tetrathiomolybdate, on copper excretion by these routes was measured in conscious sheep and sheep maintained under general anaesthesia. During 4.5 hours the total amount of copper excreted in bile in the untreated, conscious animal was 0.52 +/- 0.04 mumols (mean +/- SE). A dose of 100 mg TTM increased excretion by an average of 11.7-fold to 6.06 +/- 0.29 mumols. Under halothane or barbiturate general anaesthesia copper excretion was increased 3.4-fold to 1.78 +/- 0.30 mumols. In anaesthetised sheep 100 mg TTM produced a 40.7-fold increase to 21.18 +/- 0.95 mumols. Neither anaesthesia nor TTM caused any increase in copper excretion in saliva or urine.     

The effect of feed intake and body weight on purine derivative excretion and microbial protein supply in sheep.

Urinary excretion of purine derivatives (PD) was used to estimate the microbial N (MN) supply to sheep in three experiments designed to examine the effects of DMI and BW on the efficiency of microbial N supply (EMNS) to the host animal. In Exp. 1, four sheep of about 45 kg BW were given 328, 656, 984, and 1313 g of DM/d of a hay/concentrate diet in a Latin square design. Excretion of PD per kilogram of digestible organic matter intake (DOMI) increased with intake, and EMNS increased from 12.0 to 28.3 g of MN/kg of OM digested in the rumen (DOMR). In Exp. 2, 19 sheep ranging from 22 to 73 kg BW were all offered 820 g of DM/d of the same diet as that fed in Exp. 1. Although DM digestibility was relatively constant, PD excretion varied from 4.5 to 13.5 mmol/d and EMNS from 8 to 36 g of MN/kg of DOMR, both inversely related to animal BW. In Exp. 3, five sheep of 48 to 57 kg BW were given a different diet at 702, 966, or 1,237 g of DM/d. Purine derivative excretion per kilogram of DOMI increased with the DMI:BW ratio. Calculated EMNS ranged from 23 to 35 g of MN/kg of DOMR. Pooled data from all experiments showed EMNS to be related to the DMI:BW ratio. It is suggested that the DMI:BW ratio defines the ruminal digesta passage rate and hence outflow of microbial protein. The results imply that the EMNS for a given diet is not constant, but changes with intake.     

Evaluation of renal gentamicin depletion kinetic properties in sheep, using serial percutaneous biopsies

Tissue drug residue research often involves the killing of an animal every time tissue concentrations are determined. To decrease the number of animals required to perform tissue depletion studies and to circumvent the statistical problems associated with determining tissue depletion kinetic properties, using multiple animals, the renal depletion profile of gentamicin from individual sheep was studied, using a bilateral renal translocation technique. Seven ewes were surgically altered, allowed to stabilize, and then allocated into 2 groups; group-1 sheep (n = 4) were given 3 mg of gentamicin/kg, IM, q 12 h for 10 days, and group-2 sheep (n = 3) were not given gentamicin. The kidneys from all ewes were biopsied 9 times over 74 days after the termination of gentamicin treatment. The renal concentrations of gentamicin were measured by use of a validated tissue digestion procedure coupled with a liquid-phase fluorescence polarization immunoassay. On days 75 and 77 after the end of gentamicin treatment, all ewes were euthanatized and necropsied. The concentrations of gentamicin in the biopsy specimens ranged from 71.9 to 183 micrograms/g on days 1 and 2 after dosing, and decreased to concentrations ranging from 3.99 to 7.35 micrograms/g on days 73 and 74 after the end of dosing. The decrease in renal gentamicin concentrations was best described by a biexponential equation. The early phase half-life was 2.8 days, whereas the terminal phase half-life was 59 days (harmonic means). There was no difference in the appearance or histologic features of the kidneys from groups 1 and 2. The only lesions noticed were linear fibroses that were attributed to the biopsy procedure.     

The effect of an angiotensin-converting enzyme inhibitor on water and electrolyte balance in water-restricted sheep

The importance of angiotensin II in the regulation of water and electrolyte balance in sheep is questionable. In this trial the effects of an angiotensin-converting enzyme (ACE) inhibitor were quantified in sheep on restricted water intake. Comparing the phase of water restriction only with that of water restriction plus ACE inhibition, significant increases were observed during the latter phase in urine volume, sodium and potassium excretion via the urine, sodium concentration in the plasma and osmolar clearance. Urine osmolarity decreased with inhibition of angiotensin II formation while variables such as water, sodium and potassium loss via the faeces were unaffected. Most of the renal effects of ACE inhibition, except the increase in urinary potassium excretion, were explicable in terms of the established functions of angiotensin II. Furthermore, results of this trial indicate that angiotensin II has no significant effect on the intestine in regulating water and electrolyte excretion via the faeces.     

Renal excretion of urea in the Merino and Steppe fat-tailed breeds of sheep after a short period of fasting

Urea excretion was studied in an experiment with two sheep breeds (steppe fat-tailed and merino) on the second day of fasting when the urea concentration in blood increases in fasting animals. The control group in the two breeds was given free-choice feed and water while fasting sheep were given ad libitum only water. Diuresis in both breeds was steady during the experiment. Glomerular filtration rate was not found to vary, in comparison with the control, although the plasma urea concentration rose in fat-tailed sheep (P less than 0.01) as well as in the sheep of merino breed (P less than 0.001). Fractional excretion of urea decreased in fat-tailed sheep (P less than 0.05) and also in the sheep of merino breed (P less than 0.02) while total output of urea remained steady in fat-tailed sheep but it increased in merino sheep (P less than 0.02). Tubular reabsorption of urea on the second day of fasting was observed to be higher by 65% in merino sheep (P less than 0.001), but in steppe fat-tailed sheep the increase was much higher--by up to 180% (P less than 0.001), in comparison with the control. It was demonstrated by the results that the increased tubular reabsorption of urea contributes to the rise of plasma urea concentration in sheep on the second day of fasting.