Effects of high and low protein diets on sheep renal function and metabolism

Rabinowitz, L.; Gunther, Robert A.; Shoji, Ellen S.; Freedland, R. A.; Avery, E. H.

doi:10.1038/ki.1973.101

Cited by 53 publications

(33 citation statements)

References 77 publications

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“…As in previous results [8,22], the kidneys of sheep adapted to restricted protein intake by reducing the amounts of urea eliminated in the urine. This decrease was larger than what we expected from the simple fall of the urea blood produced by the reduction of the N intake.…”

Section: Discussionsupporting

confidence: 74%

Microbial protein production determined by urinary allantoin and renal urea sparing in normal and low protein fed Corriedale sheep

et al. 2002

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-The aim of the present study was to compare the amount of microbial N entering the duodenum and the efficiency of N utilisation for microbial protein synthesis in normal (NP, 17.4 g N/d) and low protein (LP, 7.5 g N/d) fed Corriedale sheep. Renal functional tests for urea handling studies, and determination of urinary allantoin as an indirect method to estimate the microbial protein production were used. Although the N intake was 57% lower in LP sheep, the microbial N production was not very different between both diets (NP: 3.99 ± 0.01 vs. LP: 3.79 ± 0.02 g/d, P < 0.05). The efficiency of the microbial protein synthesis in the rumen, expressed as grams of microbial N per kg of digestible organic matter apparently digested in the rumen, was not statistically different for both diets. The urinary elimination of urea was reduced by 84% in LP sheep, essentially due to an important decrease in both renal plasma flow (-63%) and glomerular filtration rate (-71%). These haemodynamic changes would also reduce the filtered load and the urinary elimination of allantoin, thereby leading to an underestimation of the amount of microbial protein entering in the duodenum. Since the renal urea spared by the kidneys remains in the blood, it limits the drop of the available urea for ruminal recycling consecutive to a low nitrogen diet. (NP,17,4 g N/j) ou hypoprotéique (LP, 7,5 g N/j). Des tests de fonctionnement rénal pour étudier les transferts d'urée, et le dosage de l'allantoïne pour estimer la production de protéine microbienne ont été utilisés. Malgré une ingestion d'azote réduite de 57% chez les moutons LP, la production d'azote microbien n'a pas été très différente entre les deux régimes (NP: 3,99 ± 0,01 vs. LP: 3,79 ± 0,02 g/j, P < 0,05). L'efficacité de la synthèse protéique microbienne dans le rumen, exprimée en grammes d'azote microbien par kg de matière organique apparemment digérée dans le rumen, n'a pas été statistiquement différente dans les deux régimes. L'élimination urinaire d'urée a été réduite de 84% chez les moutons LP, grâce essentiellement à une importante diminution du débit plasmatique rénal (-63%) et de la filtration glomérulaire (-71%). Ces modifications hémodynamiques réduisant également la charge filtrée et la quantité d'allantoïne éliminée, peuvent être responsables d'une sous estimation de la quantité de protéine microbienne entrant dans le duodénum. L'urée épargnée au niveau rénal restant dans le sang, limite la baisse de l'urée disponible pour le recyclage dans le rumen, observée lors des régimes pauvres en azote.protéine microbienne / allantoïne / urée / mouton

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Section: Discussionsupporting

confidence: 74%

Microbial protein production determined by urinary allantoin and renal urea sparing in normal and low protein fed Corriedale sheep

et al. 2002

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“…Intravenous infusion of urea for 19-46 h had no effect on the high protein diet but on the low protein diet GFR and FF were increased to values approaching those observed on the high protein diet. On the low protein diet GFR was unaffected by infusion of urea for 4 h or of saline alone for 30 h. It is suggested that the observed changes in GFR are associated with changes in the quantity of protein passing to the abomasum and small intestine.In the previous paper Ergene and Pickering [1978] confirmed the reports of Gans and Mercer [1962] and Rabinowitz, Gunther, Shoji, Freedland and Avery [1973] that a fall in glomerular filtration rate (GFR) of sheep occurred when nitrogen intake was reduced. The fall in GFR resulted mainly from reduction in filtration fraction (FF), was associated with an approximately six-fold reduction in plasma urea concentration, and was unaffected by increasing the intake of sodium chloride.…”

supporting

confidence: 75%

The Effects of Urea Infusion on Glomerular Filtration Rate and Renal Plasma Flow in Sheep Fed Low and High Protein Diets

Ergene¹,

Pickering²

1978

Exp Physiol

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Reducing the dietary N intake of sheep resulted in a significant fall in GFR with no change in RPF. Intravenous infusion of urea for 19-46 h had no effect on the high protein diet but on the low protein diet GFR and FF were increased to values approaching those observed on the high protein diet. On the low protein diet GFR was unaffected by infusion of urea for 4 h or of saline alone for 30 h. It is suggested that the observed changes in GFR are associated with changes in the quantity of protein passing to the abomasum and small intestine.In the previous paper Ergene and Pickering [1978] confirmed the reports of Gans and Mercer [1962] and Rabinowitz, Gunther, Shoji, Freedland and Avery [1973] that a fall in glomerular filtration rate (GFR) of sheep occurred when nitrogen intake was reduced. The fall in GFR resulted mainly from reduction in filtration fraction (FF), was associated with an approximately six-fold reduction in plasma urea concentration, and was unaffected by increasing the intake of sodium chloride.O 'Connor and Summerill [1976a, b] showed that the increase in GFR which occurred in dogs after a meal of meat was accompanied by increases in plasma urea concentration but that no increase in GFR occurred when similar increases in plasma urea concentration were produced by urea given by stomach tube. The present experiments were designed to investigate the possible association between plasma urea concentration and the changes in GFR of sheep induced by changes in nitrogen intake. Some of the results have been communicated to the Physiological Society [Ergene and Pickering, 1976]. METHODSSix Clun Forest ewes aged 3-5 yr and weighing 51-69 kg were housed in individual pens, allowed free access to water and to salt blocks (KNZ mineral salt licks: Pan Britannica Industries Ltd.) and fed once daily. Clearance studies were carried out in metabolism crates of the design described by Harrison [1974]. The high protein (HP) and low protein (LP) diets used were as described by Ergene and Pickering [1978] and provided respectively 18 5-20*5 gN and 8-3 gN per day. An acclimatization period of 10 days was allowed following change of diet before carrying out clearance procedures.The effects of short term infusion of urea were studied in four sheep on the LP diet in which urea was infused intravenously at 0X83 mmol. min-1 in sterile saline (9 g.1-1 NaCI) for 4 h with clearances measured during successive 20 min collection periods. The effects of more prolonged infusion were studied in three sheep on both LP and HP diets (see Table I). Intravenous infusion of urea at 0 33 mmol .min-1 in sterile saline (1 0 cm3. minm 1) was begun 77

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“…The reduction in the quantity of urea filtered resulted from not only the fall in plasma urea concentration but also from reduction in the GFR. Since a fall in GFR when animals are fed low protein diets has also been noted in sheep by Gans and Mercer [1962] and by Rabinowitz et al [1973], and in cattle by Bailey [1970] and by Phillips, Pickering and Wilkinson [1974], this may be regarded as a renal response to low protein feeding which, in conjunction with an increase in the fraction of filtered urea reabsorbed, restricts urinary losses of urea and so contributes to nitrogen economy.…”

Section: Resultsmentioning

confidence: 99%

“…A fall in GFR associated with reduction in dietary protein has been reported in sheep by Gans and Mercer [1962] and by Rabinowitz, Gunther, Shoji, Freedland and Avery [1973] but was not observed by Schmidt-Nielsen et al [1958]. Changes in GFR of sheep have also been noted in connection with alterations in salt intake [Potter, 1961] and the interdependence of urea and electrolytes in the production of a concentrated urine discussed by SchmidtNielsen, O'Dell and Osaki [1961] suggested that alteration in salt intake may exert a post-glomerular influence on urea excretion and reabsorption.…”

mentioning

confidence: 99%

The Effects of Reducing Dietary Nitrogen and of Increasing Sodium Chloride Intake on Urea Excretion and Reabsorption and on Urine Osmolality in Sheep

Ergene¹,

Pickering²

1978

Exp Physiol

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Renal responses to reducing dietary nitrogen were studied in four ewes during intravenous infusion of arginine vasopressin. The fall in urea excretion and in plasma urea concentration was accompanied by significant reduction in GFR and in urine osmolality. The fraction of filtered urea reabsorbed increased despite reduction in the urea U/P concentration ratio and this increase was sustained when the urea U/P ratio was further reduced at higher urine flows observed when the drinking water was replaced with saline. This procedure also sustained the RPF which in the absence of additional salt was significantly reduced on the low protein diet. It is suggested that the fall in GFR and the increase in the fraction of filtered urea reabsorbed may contribute to nitrogen economy and that the increase in fractional reabsorption and the reduction in urine osmolality on the low protein diet provided evidence of active reabsorption of urea by renal tubules.

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Effects of high and low protein diets on sheep renal function and metabolism

Cited by 53 publications

References 77 publications

Microbial protein production determined by urinary allantoin and renal urea sparing in normal and low protein fed Corriedale sheep

Microbial protein production determined by urinary allantoin and renal urea sparing in normal and low protein fed Corriedale sheep

The Effects of Urea Infusion on Glomerular Filtration Rate and Renal Plasma Flow in Sheep Fed Low and High Protein Diets

The Effects of Reducing Dietary Nitrogen and of Increasing Sodium Chloride Intake on Urea Excretion and Reabsorption and on Urine Osmolality in Sheep

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