Micropuncture study on urea movements in the kidney cortical tubules of low protein fed sheep.

Micropuncture studies of late proximal, early and late distal cortical tubules were carried out on kidneys of normal (NP) and low (LP) protein fed sheep in order to investigate the participation of these segments in the urea sparing induced by protein restriction in the diet. A low protein diet induced significant reductions in the fractional (-54%) and total (-84%) urea excretion, revealing an enhanced capacity for urea conservation. Micropuncture data did not show any difference in the proximal tubule functions between both groups of sheep. In distal cortical tubules the fractional delivery of urea (early distal, 0.61 +/- 0.06 for NP and 0.77 +/- 0.06 for LP sheep, not significant (NS); late distal, 0.45 +/- 0.07 for NP and 0.71 +/- 0.09 for LP sheep, P < 0.05) showed a relatively larger amount of urea present in the late distal tubule of protein restricted sheep. The tubular fluid-to-plasma inulin ratio in the late distal tubule was found to be lower in LP sheep (4.33 +/- 0.23 versus 8.58 +/- 0.9 in NP sheep, P < 0.01). The tubular flow rate, reduced in the early distal tubules of LP sheep (10.87 +/- 0.99 versus 18.92 +/- 2.58 nL.min-1 in NP sheep, P < 0.05), was not different in the late distal tubules from values in normally fed animals (6.65 +/- 0.90 versus 7.73 +/- 0.94 nL.min-1 in NP sheep, NS). These findings suggest a decreased distal water reabsorption coincident with the relatively larger amounts of intraluminal urea in LP sheep. This relatively larger urea delivery to the initial collecting duct could increase the subsequent urea reabsorption in protein restricted sheep.

[The effect of a low-protein diet on the epithelium of nephron segments in sheep]. / Vplyv nízkobielkovinovej diéty na epitel segmentov nefrónu oviec.

Changes in the epithelium thickness of proximal and distal convoluted tubule of cortex, thin descending limb of Henle loop from inner stripe of outer medulla, thick ascending limb from outer stripe of outer medulla and of collecting duct from inner medulla were investigated in young growing sheep fed a low protein diet (LP). Sheep on LP-diet were given a daily ration with 5.73 g of nitrogen and 6.13 MJ of digestible energy (DE) while the daily intake of control group was 19.51 g of N and 12.29 MJ of DE. Both groups of animals were fed these diets at least 6 weeks before collection of kidneys. Morphometric analysis with digitizing tablet showed that intake of LP-diet resulted in significant reduction of epithelium thickness in both distal convoluted tubule and thick ascending limb while the epithelium of collecting duct was found to be thicker. No changes of the epithelium dimensions were determined in proximal tubule and in thin descending limb of Henle loop. Presented results point to the morphological expression of the adaptation of sheep kidneys to a low dietary protein intake which is associated with the increased renal reabsorption of urea.

Urine concentrations in the spaces of the sheep renal pelvis.

Urine concentrations were measured in samples from the ureter, the pelvic cavity, close to the tip of the papilla, and from the most proximal part of the fornices of sheep kidneys. It was found that the concentration of urea, the osmolality, and the urine-to-plasma ratios of inulin, urea and the osmolality were higher in the ureter than in the pelvic cavity. The same parameters were found to be higher in the pelvic cavity than in the fornices except for the urea concentration which was unchanged. The results of this study revealed the various concentrations of urine in the ureter, the pelvic cavity and the proximal part of fornices of sheep kidney.

Partition of nitrogenous substances in the urine of sheep on different dietary protein intakes.

The distribution of nitrogenous substances in urine was studied in sheep fed high (28.71 g N daily) and low (9.32 g N daily) protein diets for 6-8 weeks. The concentrations of total nitrogen and urea, allantoin, free amino acids, uric acid, hippuric acid, creatinine, creatine and ammonia were measured in urine. The nitrogen content of these measured substances was calculated. The results showed that the concentrations of total urinary nitrogen and nitrogen of individual nitrogenous substances were lower in sheep on a low protein diet, except for uric acid nitrogen which was unchanged. Urea nitrogen was responsible for up to 74% of the total urinary nitrogen of both groups of animals without any significant difference. The individual nitrogen portions of nitrogenous substances other than urea in total urinary-N did not exceed 7% during the intake of both diets. The intake of a low protein diet resulted in a significant increase in the proportion of nitrogen from uric acid, hippuric acid, creatinine and free amino acids, while the fraction of ammonia nitrogen in the total urinary N was significantly reduced. It is concluded that different protein or nitrogen intake in the diet do not have any significant effect on the urea nitrogen fraction in the total urinary nitrogen of sheep.

Renal response of sheep fed a low protein diet to intraportal infusion of arginine and glycine.

The renal effects of infusions of arginine and glycine into the portal vein were studied in the anaesthetized sheep with a reduced glomerular filtration rate (GFR) after 6 weeks of low dietary protein intake. Arginine significantly elevated urine flow (V), whole kidney GFR and the amount of urea excreted (UureaV) concomitantly with plasma urea level (P(urea)) without changes in fractional urea excretion (FEurea). Sheep infused with glycine showed significantly increased urinary flow only. Free-flow micropuncture of the late proximal tubule revealed that both the fluid flow and single nephron GFR were increased by arginine without any significant changes in tubular fluid to plasma inulin ratio. There was no effect of glycine on the micropuncture parameters of the sheep kidney. These results suggest that the synthesis of urea from arginine in the liver and its subsequent delivery to the kidney may be involved in the regulation of dietary induced changes of the glomerular filtration rate in sheep.

Effect of 2 inhibitors of oxidative phosphorylation on urea excretion in rats.

The effects of phloretin and carbonyl-cyanide-m-chlorophenylhydrazone (CCCP), both inhibitors of oxidative phosphorylation, on renal urea excretion in Wistar rats were investigated. Phloretin and CCCP infusions did not influence plasma urea concentration (P(urea)), compared with controls (0.15 M NaCl and Tris solution in 0.15 M NaCl-a solvent for phloretin and CCCP). The fractional urea excretion (FEurea) was not altered by phloretin infusion. It decreased significantly only when compared with 0.15 M NaCl infusion (P < 0.05). CCCP infusion had no effect on FEurea. The total amount of urea excreted by urine (UureaV) was not altered by phloretin compared with controls. CCCP significantly enhanced Uurea V only when compared with 0.15 M NaCl (P < 0.001), not when compared with Tris. Glomerular Filtration rate (GFR) increased significantly during phloretin infusion (P < 0.001), CCCP (P < 0.001) and also after Tris in 0.15 M NaCl (P < 0.001), in comparison with 0.15 M NaCl alone. Our results showed that phloretin and CCCP had no effect on urea excretion in rats. The increase in GFR is attributed to Tris, not to phloretin or CCCP. It is concluded that inhibition of oxidative phosphorylation in kidney has no effect on urea excretion.

Micropuncture study of the kidney in sheep: effects of iodoacetate on renal urea handling.

1. The effects of intrarenal infusion of iodoacetate, an inhibitor of anaerobic glycolysis, on urea transport in kidney of sheep was studied by micropuncture free-flow technique. 2. Iodoacetate decreased the tubular fluid to plasma urea ratio in late distal tubules only; no changes were found in both the late proximal and early distal tubules. Fractional delivery of urea to the same superficial segments of nephron and the urea excretion by whole kidney were not significantly influenced. 3. Our results do not support the concept of active urea transport in the kidney of sheep which would be dependent on energy derived from anaerobic metabolism.

Effect of dietary energy intake on tubular reabsorption of urea in sheep.

The aim of the experiment was to determine the effect of dietary energy intake on renal urea excretion in sheep with different nitrogen intakes. The control sheep, with a high nitrogen and energy intake, were given a daily feed dose of 21.18 g N and 15.2 MJ digestible energy (DE). The two experimental groups, with an equal, low nitrogen intake, were given diets with a different energy content. The high energy diet contained 3.63 g N and 14.18 MJ DE, the low energy diet 3.4 g N and 6.44 MJ DE. After nine weeks' adaptation to the diets, renal functions were measured by a standard clearance technique. It was found that, under stable urine flow conditions, both groups given the low nitrogen diet had a significantly lower glomerular filtration rate, fractional urea excretion and total urea excretion. A reciprocal comparison of these two groups showed that fractional urea excretion by the sheep with a high energy intake was significantly lower than in the group with a low energy intake. There were no differences in the glomerular filtration rate. A raised dietary energy intake in the presence of a low nitrogen intake caused marked natriuresis and kaliuresis. The results indicate that a raised dietary energy intake can be a significant factor in potentiating the renal effect of urea retention in sheep with a low nitrogen intake.

Creatinine and inulin clearance at the different nitrogen and energy intake in sheep.

1. Renal creatinine and inulin clearances were compared between sheep fed (a) high nitrogen and high energy diet; (b) low nitrogen and high energy diet and (c) low nitrogen and low energy diet. 2. Inulin clearance was significantly lower in sheep on both low nitrogen diets vs the group with high nitrogen intake. Differences were not ascertained between the groups on low nitrogen diets. 3. No significant differences were found in the creatinine clearance. The creatinine inulin clearance ratio was higher when animals were fed low nitrogen diets, vs the group on a high nitrogen diet. 4. Results suggest that the endogenous creatinine is not suitable for the GFR measurement in sheep under the different conditions of nutrition.

[The effect of water depletion on renal excretion of urea and electrolytes in sheep]. / Vplyv vodnej deplécie na renálnu exkréciu mocoviny a elektrolytov u oviec.

Experiments were conducted with the sheep of Merino breed given water only at a rate corresponding to 0.5% of their live weight for three days. The animals were given feed ad libitum and during the control measurements water was also available to them ad lib. The fourth day the sheep were given no water and no feed and their renal functions were measured by the standard clearance technique. In the water-depleted sheep the diuresis was naturally reduced and the glomerular filtration rate (GFR) was also observed to have decreased from 77.6 +/- 5.3 to 62.2 +/- 4.2 ml X min-1, P less than 0.05. A small, though significant, decrease was also recorded in plasma urea concentration as a result of the reduced intake of food. The amount of excreted urea decreased by 41% (from 354.0 +/- 41.6 to 208.5 +/- 25.5 mumol X min-1, P less than 0.01) without significant changes in fractional excretion and tubular reabsorption of urea. After three days of water depletion the sheep exhibited a tendency of slight natriuresis whereas the excretion of potassium was reduced. Water depletion was also accompanied by a significant increase in the osmolality of plasma (from 298.0 +/- 1.3 to 317.0 +/- 1.8 mosmol X kg-1 H2O, P less than 0.001) and urine from 789.0 +/- 95.0 to 1547.0 +/- 53.0 mosmol X kg-1 H2O, P less than 0.001), without changes in the clearance of free water. On the other hand, the osmotic clearance was reduced as a result of suppressed excretion of urea and potassium (from 2.33 +/- 0.21 to 1.61 +/- 0.17 ml X min-1, P less than 0.02).(ABSTRACT TRUNCATED AT 250 WORDS)

[Renal retention of urea in sheep]. / Renálna retencia mocoviny u oviec.

The urea-retaining ability of kidneys of ruminants and returning it back to the blood circulation are important features of the mechanism of nitrogen conservation in the organism. Applying the model of a low-nitrogen diet to sheep we found out the low fractional excretion of urea (FE urea) as a result of increased urea transport capacity in renal tubules. The decrease in the amount of excreted urea by 85% was also accompanied by a reduced glomerular filtration rate (GFR). We tried to verify our hypothesis by the cross-perfusion method that the renal excretion of urea in sheep is regulated by a factor circulating in the blood. We found out that FE urea decreased significantly in the cross-perfused kidney (in sheep on a high-nitrogen diet, connected to sheep on a low-nitrogen diet), without any changes in GFR. Our hypothesis is well-supported by the above result. The kidneys of sheep on low nitrogen diet retain urea through a decrease in the GFR and increased tubular urea transport.

Simple fluorometric ultramicroassay for urea in tubular fluid of the kidney.

Sensitive fluorometric method for the determination of picomole amount of urea in tubular fluid of the kidney is presented. It is a modification and simplification of the macromethod by McCleskey (6) for the urea determination in blood. Assay is based on the reaction of urea with diacetylmonoxime and sulphuric acid in boiling water within 20 minutes. The reaction is highly specific for urea. The simple procedure requires only one micropipetting step. The fluorometric determination of urea can be made in 20 nanoliters of proximal and in 5 nanoliters of distal tubular fluid with the reproducibility of +/- 4.44% and of +/- 5.38%, respectively. The minimum detection limit is 20 picomoles of urea.

[Renal excretion of urea in the Merino and Steppe fat-tailed breeds of sheep after a short period of fasting]. / Renálna exkrécia mocoviny u oviec plemena merino a u stepných tucnochvostých oviec po krátkodobom hladovaní.

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.

The renal response of sheep to a low dietary nitrogen intake.

Renal functions were tested in sheep fed on a low nitrogen diet (LN sheep), with a daily N intake of 4.7 g (gross energy 17.76 . 10(6) J). Sheep given a high nitrogen diet (HN sheep) with 21.2 g N (24.12 . 10(6) J) acted as the control. The functions of the left kidney were measured in anaesthetized animals by the standard clearance technique. A comparison of HN and LN sheep showed that a low nitrogen intake led to a drop in the plasma urea level (from 5.91 +/- 0.35 to 2.87 +/- 0.36 mmol.1-1, (P less than 0.001), the glomerular filtration rate (GFR, from 36.6 +/- 3.6 to 20.7 +/- 2.4 ml.min-1, P less than 0.005), amount of urea excreted (from 106.7 +/- 18.1 to 15.7 +/- 3.3 mumol.min-1, P less than 0.001), fractional urea excretion (from 51.0 +/- 3.0 to 24.6 +/- 3.1 %, P less than 0.001) and the absolute tubular reabsorption of urea (Reaburea/GFR (from 3.06 +/- 0.27 to 2.12 +/- 0.28 mumol.ml-1, P less than 0.05), without a significant change in the effective renal plasma flow (182.6 +/- 20.0 and 138.5 +/- 21.0 ml.min-1, non-significant - N.S.) and in sodium and potassium excretory function. Free water clearance rose in LN sheep (from -0.53 +/- 0.11 to -0.19 +/- 0.06 ml.min-1, P less than 0.05) owing to inhibited urea excretion. A regression analysis of the relationship of the tubular reabsorption of urea to the amount of filtered urea (both normalized to the GFR) showed that the urea transport capacity of the tubules of LN sheep was significantly higher.(ABSTRACT TRUNCATED AT 250 WORDS)

[Amino acid production in the isolated and perfused rumen wall of sheep]. / Produkcia aminokyselín izolovanou perfundovanou stenou bachora oviec.

The metabolism of amino acids and urea in an isolated perfused wall of sheep rumen was studied by the method of organ perfusion, using 3 kinds of perfusate. In experiments with semisynthetic perfusate containing urea (SPurea) the levels of lysine, valine, glutamic acid and alanine increased at a simultaneous decrease of levels of leucine, arginine, aspartic acid, threonine and methionine. In perfusions with the semisynthetic medium without urea (SP) the levels of lysine, valine, phenylalanine, isoleucine, glutamic acid, glycine and alanine increased, the level of threonine dropped. In perfusions with whole autologous blood (KP) the levels of valine, glutamic acid and alanine increased, the level of arginine decreased. The level of urea decreased sharply at using SPurea and KP, however, the equal cumulation of ammonia (200-400 mumol x 1(-1)) was found in all three types of perfusate after 2-hr perfusion. Moreover, in experiments with SP a low level of urea was found already after 5-min. of perfusion. The results of the experiments suggest that the rumen wall is capable of producing amino acids also without the contents of rumen, and that independently on the presence or absence of urea as a nitrogen source.

[Renal excretion of urea and electrolytes in sheep after extracellular fluid expansion with an isotonic solution of sodium chloride]. / Renálna exkrécia mocoviny a elektrolytov u oviec po expanzii extracelulárnych tekutín izotonickým roztokom chloridu sodného.

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.

[The effect of the antidiuretic hormone on the renal excretion of urea and electrolytes in fed and fasting sheep]. / Vplyv antidiuretického hormónu na renálnu exkréciu mocoviny a elektrolytov u kremených a hladujúcich oviec.

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.