Excretion of purine derivatives by ruminants: effect of exogenous nucleic acid supply on purine derivative excretion by sheep

The present study examined the relationship between the supply of exogenous nucleic acid (NA) purines and their recovery as the derivatives hypoxanthine, xanthine, uric acid and allantoin in urine. Six lambs, totally nourished by intragastric infusions of volatile fatty acids (VFA) and casein (i.e. no rumen fermentation), were given by abomasal infusion a microbial NA concentrate at six levels (from zero to 24.5 mmol purines/d). The true digestibility between the abomasum and terminal ileum of the NA purines was measured in a separate experiment using three lambs. The relative proportion of urinary allantoin increased, and that of other derivatives decreased, as the amount of NA infused was increased. The relationship between total excretion of purine derivatives (Y; mmol/d) and exogenous purines absorbed (X; mmol/d) was Y = 0.84X + 0.150W0.75 e-0.25X, where W is body-weight (kg). This implies that the endogenous contribution to the total excretion of derivative decreased as the supply of exogenous purines increased, with an associated progressive replacement of de novo synthesis by exogenous purines. The model also implies that 0.16 of the purines were eliminated through routes other than derivative excretion in urine. Once excretion exceeded 0.6 mmol/kg W0.75 per d, endogenous excretion was effectively zero and thus Y = 0.84 X. In normally fed sheep, derivative excretion should therefore relate to the microbial purines and, hence, microbial protein absorbed according to these models. The changing proportions of allantoin and other derivatives in urine were probably due to changes in the relative importance of endogenous and exogenous purines as precursors.     

Effects of diet, level of intake, sodium bicarbonate and monensin on urinary allantoin excretion in sheep.

The present experiment was designed to study the effects of factors likely to alter microbial purine yield from the rumen on urinary excretion of allantoin-nitrogen (UAN). Sixteen mature Clun Forest-Welsh crossbred wethers were used in a 2 x 2 x 2 x 2 factorial design to investigate the effects of (1) level of intake, (2) wheat:nutritionally improved straw (NIS) ratio, (3) sodium bicarbonate inclusion and (4) monensin inclusion on diet digestibilities, fractional outflow rates of solids and liquids from the rumen and urinary allantoin excretion. Each treatment occurred in each of two experimental periods. The treatments were designed to influence microbial purine yield via changes in rumen outflow rate and microbial maintenance coefficient. Increasing the proportion of NIS and increasing feeding level decreased digestibility and increased the fractional outflow rate of solids. Increasing the level of intake increased the fractional outflow rate of liquids. Urinary allantoin excretion (/kg live weight0.75 per d) was significantly increased by an increased proportion of wheat in the diet and increased level of intake, and significantly reduced by NaHCO3. There was a significant interaction effect such that increasing level of intake did not increase UAN with the high-NIS diet, despite an increased fractional outflow of solids from the rumen, in contrast to the increase observed with the high-wheat diet. Taken together with other observations it is suggested that high sodium concentrations in the diet reduce the efficiency of microbial synthesis, probably by increasing the energy cost of maintaining osmolarity.(ABSTRACT TRUNCATED AT 250 WORDS)     

Nitrogen metabolism and urinary excretion of purines in goat kids

1. In Expt 1 three male goat kids of the Swedish Landrace breed were bottle-fed on isoenergetic liquid diets composed of goat's milk alone or substituted with 200, 400, 600 and 800 ml of a nitrogen-free liquid diet/l. The goat kids were 3 weeks old at the start of the experiment and weighed on average 5.3 (SD 0.22) kg. The experiment lasted for 45 d divided into nine 5 d periods. The goat kids were kept individually in metabolism cages, and faeces and urine were collected daily. 2. In Expt 1 there was a significant (P less than 0.001) relation between N intake and N retention, with an estimated (extrapolation) basal N excretion of 211 mg N/kg metabolic live weight (W0.75). While the creatinine excretion remained fairly constant (19.9 mg/W0.75), there was a tendency for both the allantoin and uric acid excretions to change with N intakes. Hypoxanthine showed no consistent excretion pattern, and xanthine could not be detected. 3. In Expt 2 three male goat kids of the Swedish Landrace breed were used to study the effect of level of intake on N and purine metabolism. The first experimental period (period 1) started at 2 weeks of age (5.5 kg live weight) and the second experimental period (period 2) at 9 weeks of age (9.8 kg live weight). The goat kids were bottle-fed on goat milk at intended intakes of 400, 600, 800 and 1000 kJ gross energy/kg W0.75. Each treatment was given for 7 d with adaptation for 3 d and collections for 4 d. 4. In Expt 2 there were significant (P less than 0.001) increases in both live weight and N retention when level of intake was increased. With increasing N intakes both total N and urea-N excretions increased significantly (P less than 0.05). The proportions of urea-N and ammonia-N were fairly constant within periods, and were on average respectively 0.81 and 0.059 in period 1 and 0.84 and 0.068 in period 2. There was no significant effect of treatment on the urinary excretion of allantoin, hypoxanthine, xanthine and creatinine. In period 2 uric acid excretion was significantly (P less than 0.01) affected by the treatments. 5. From the presented findings it is concluded that the endogenous urinary excretion of purine derivatives in a young growing ruminant was only marginally affected by large variations in protein supply, and also by the level of intake of milk.     

Differences in uricogenic effects of dietary purine bases, nucleosides and nucleotides in rats

The uricogenic effects of dietary free purines (adenine, guanine, hypoxanthine and xanthine), their nucleosides (adenosine, monophosphate, guanosine monophosphate and inosine monophosphate) were studied in rats. Casein-based diets (20% protein) supplemented with 30 mmol/kg diet of each of the free purine base, nucleoside or nucleotide were fed to male Sprague-Dawley rats (100 +/- 5 g) for 14 d. Addition of adenine resulted in less weight gain than in controls, greater kidney weight, greater urine volume and higher levels of blood urea nitrogen, serum uric acid, creatinine and allantoin but lower urinary levels of allantoin, uric acid and creatinine. The adenine diet also caused nephropathy characterized by nephromegaly and deposition of crystals. A microscopic examination of the kidneys revealed deposition of crystals mainly in the lumen of convoluted tubules of the cortex. Feeding of diets containing other purine bases, nucleosides and nucleotides had no adverse effects on kidney weight or structure, urine volume, serum uric acid or creatinine. Urinary allantoin excretion, however, was greater in rats fed hypoxanthine, xanthine, nucleoside and nucleotide diets than in control rats. Adenine produced adverse effects only when fed in the free form and not when fed as the nucleoside or nucleotide, suggesting a metabolic significance for free adenine in predicting hyperuricemic effects of foods.     

Urinary excretion of purine derivatives in Bos indicus x Bos taurus crossbred cattle

Four experiments were performed to study the kinetics of purine metabolism and urinary excretion in Zebu crossbred cattle. Fasting excretion was established in Expt 1, using eighteen male Bos indicus x Bos taurus crossbred cattle (261 (SE 9.1) kg body weight), six of each of the following genotypes: 5/8 Bos indicus, 1/2 Bos indicus and 3/8 Bos indicus. No significant differences were observed among genotypes in fasting purine derivative excretion (277.3 (SE 35.43) micromol/metabolic body weight). In a second experiment we measured the xanthine oxidase activity, which was higher in liver than in duodenal mucosa (0.64 and 0.06 (SE 0.12) units/g wet tissue per min respectively; P>0.05) being in plasma 0.60 (SE 0.36) units/l per min. The kinetics of uric acid were measured by intravenous pulse dose of [1,3-15N]uric acid (Expt 3). The cumulative recovery of the isotope in urine was 82 (SE 6.69) %, and uric acid plasma removal, pool size and mean retention time were 0.284 (SE 0.051) per h, 5.45 (SE 0.823) mmol and 3.52 (SE 0.521) h, respectively. Allantoin was removed from plasma at an estimated fractional rate of 0.273 (SE 0.081) per h and mean retention was 3.66 (SE 1.08) h. In Expt 4, the relationship between urinary purine derivative excretion (Y; mmol/d) and digestible organic matter intake (X, kg/d) was defined by the equation: Y=7.69 (SE 4.2)+5.69 (SE 1.68) X; n 16, Se 1.31, r 0.67.     

The effect of completely purine-free diet of low sodium content on purine intermediates and end-product

Intake of completely purine-free foods of low sodium content increased the plasma concentrations of both hypoxanthine and inosine and the urinary excretion of hypoxanthine, while it decreased the urinary excretion of uric acid and the fractional clearance of uric acid. However, this diet affects neither nucleotides (inosine monophosphate, adenosine monophosphate, adenosine diphosphate and adenosine triphosphate) in red blood cells, enzymes (purine nucleoside phosphorylase, adenosine deaminase and hypoxanthine guanine phosphoribosyl transferase) in red blood cells nor the fractional clearance of oxypurines. These results suggest that the salvage of purines becomes more effective by limiting the conversion of hypoxanthine to xanthine and limiting the loss of uric acid during intake of completely purine-free foods of low sodium content; also that a decrease in the fractional clearance of uric acid due to completely purine-free foods of low sodium content may be an additional mechanism associated with the conservation of purines but is more likely to be a response to the low sodium diet on the renal handling of uric acid.     

Excretion of purine derivatives by ruminants: endogenous excretion, differences between cattle and sheep

The endogenous urinary excretion of the purine derivatives allantoin, uric acid and xanthine plus hypoxanthine were measured in twenty-nine lambs, ten cattle (six steers, one cow and three preruminant calves) and four pigs. The sheep and mature cattle were nourished by intragastric infusion and the calves were given a milk-substitute. The pigs were fed on a purine-free diet. The excretion of total purine derivatives was substantially greater by the cattle, being 514 (SE 20.6) mumol/kg live weight (W)0.75 per d compared with 168 (SE 5.0) mumol/kg W0.75 per d by the sheep and 166 (SE 2.6) mumol/kg W0.75 per d by the pigs. Plasma from normally fed sheep, cows and pigs was incubated with either xanthine or uric acid. Sheep and pig plasma had no xanthine oxidase (EC 1.2.3.2) activity whereas plasma from cattle did. Uricase (EC 1.7.3.3) was not present in plasma of cattle and pigs and appeared to be present in trace amounts only in sheep plasma. It is suggested that the species differences in endogenous purine derivative excretion were probably due to the different profiles of xanthine oxidase activity in tissues and particularly in the blood. This is because a high xanthine oxidase activity would reduce the chance to recycle purines, by increasing the probability of degradation to compounds which could not be salvaged.     

Excretion of purine derivatives by ruminants: recycling of allantoin into the rumen via saliva and its fate in the gut

The saliva of sheep was shown to contain significant concentrations of uric acid (16(SD 4.5) mumol/l) and allantoin (120(SD 16.4) mumol/l), sufficient to recycle purine derivatives equivalent to about 0.10 of the normal urinary excretion. When allantoin was incubated in vitro in rumen fluid, it was degraded at a rate sufficient to ensure complete destruction of recycled allantoin. In a series of experiments in which allantoin was infused into the rumen of sheep fed normally, or into the rumen or abomasum of sheep and the rumen of cattle completely nourished by intragastric infusion of volatile fatty acids and casein, no additional allantoin was recovered in the urine. These losses were probably due to the degradation of allantoin by micro-organisms associated with the digestive tract. It is concluded that all allantion and uric acid recycled to the rumen via saliva will be similarly degraded. Therefore, the use of urinary excretion of purine derivatives as an estimator of the rumen microbial biomass available to ruminants will need to be corrected for such losses.     

Kinetics of allantoin metabolism in sheep

The kinetics of allantoin metabolism were studied in rumen-cannulated sheep by means of a single intravenous injection of [4,5-(14)C]allantoin. The decline in the specific radioactivity of allantoin in plasma following the injection of tracer was best described by a double exponential function, indicating that allantoin moves in and out of two or more kinetically distinct compartments. Sequestering of tracer in secondary or tertiary compartments in the body water appears likely to have resulted in overestimation of net flux of allantoin through the blood in the present study. In future studies, sampling of blood for several days after administration of tracer should alleviate this problem. About 80 % of the [(14)C]allantoin injected was recovered as [(14)C]allantoin in urine during the 12 h after tracer injection, increasing to 94 % after 4 d. Allantoin-C also passed through the blood bicarbonate pool, suggesting that allantoin is degraded in the gastrointestinal tract. A small amount of allantoin-C (4 % of the net flux of allantoin through the blood pool) was apparently degraded to form bicarbonate-C in the rumen and postruminally, and subsequently appeared in blood bicarbonate-C. Transfer of allantoin-C into the rumen via saliva was insignificant. In view of these findings, the net flux of allantoin through the blood should be a better predictor of rumen microbial outflow than urinary allantoin excretion, because urinary excretion of purine derivatives must be adjusted for conversion of allantoin-C to blood bicarbonate when used to predict the flow of microbial protein from the rumen.     

Urolithiasis - nutritional aspects

The progressive increase in the incidence of calcium oxalatephosphate calculi of the upper urinary tract during the 20th century in Western Europe and North America appears associated with affluence. Changes in diet over that time period have produced changes in urinary solutes which would increase the probability of calculus formation. Increased ingestion of animal protein produces a significant increase in the urinary excretion of calcium, oxalate and uric acid. Dietary calcium, oxalate and purine increase the excretion of calcium, oxalate and uric acid directly. Urine oxalate also increases with an increased ingestion of calcium but, paradoxically, also increases with severe dietary calcium restriction. Oral carbohydrate loading increases urinary calcium and magnesium excretion. Changes in urinary calcium excretion induced by dietary fiber appears related to the phytate content. A rational, though not of proven efficacy, dietary approach to urolithiasis therapy includes restriction of animal protein, avoidance of excess oxalate ingestion, a normal calcium intake, and water intake sufficient to generate 2 liters of urine per day.     

Variation between sheep in renal excretion of [14C]allantoin

The objectives of the present study were to investigate the recovery of [14C]allantoin in urine of sheep dosed intravenously and degradation of allantoin by rumen micro-organisms. The recovery of [14C]allantoin in the urine of eight sheep was measured during three periods in two experiments. Individual values of [14C]allantoin recovery varied from 66 to 95 % (mean value 83 (se 1.6) %). The recovery of [14C]allantoin showed no relation to the level of feed intake. There was some evidence that glomerular filtration rate was an important factor affecting the amount of urinary allantoin recovered in one experiment. Incomplete recovery of plasma [14C]allantoin in the urine indicated losses of plasma [14C]allantoin via non-renal routes. This is supported by the disappearance of 14C from rumen contents incubated in vitro with [14C]allantoin for 48 h (88 %) and the presence of 14C in saliva in vivo from sheep sampled after dosing with [14C]allantoin. However, the amount of 14C activity in the saliva was very low (equivalent to only 1.5 % of the total dose in sheep producing saliva at a rate of 15 litres/d). The proportion of renal and non-renal excretion of purine derivatives was found to be unpredictable both between and within individual animals. The factors responsible for this variability need to be identified, and existing models of excretion of purine derivatives may need to be modified accordingly to improve their accuracy of prediction. A single intravenous injection of [4,5-14C]allantoin provides a simple alternative to infusion methods used to measure the proportion of plasma allantoin excreted in the urine of sheep. Using this method it may be feasible to validate PD excretion models in other ruminant livestock.     

The intake, digestion and protein degradation of grazed herbage by early-weaned lambs.

Sixty-four intact lambs and twenty-four lambs fitted with a duodenal cannula were weaned at 6 weeks of age and grazed pure species swards of either lucerne (Medicago sativa), white clover ((Trifolium repens), ryegrass (Lolium perenne) or prairie grass (Bromus catharticus) for 6 weeks. Intake and duodenal digesta flow were estimated when lambs were 8 and 12 weeks of age. Lambs grazing the two legume species grew at a similar rate, as did lambs grazing the two grass species. Legumes promoted a 38% higher growth rate than grasses. The higher growth rate of lambs grazing legumes was associated with a 36% higher digestible organic matter intake (DOMI; 29.5 and 21.7 g/kg body-weight per d for legume and grass respectively) and a 33% higher duodenal non-ammonia-nitrogen (NAN) flow (1.22 and 0.92 g/kg body-weight per d respectively). There was no species difference in the site of organic matter digestion; on average 0.56 of DOMI was apparently digested in the rumen and 0.77 of DOMI was truly digested in the rumen. There was no difference in duodenal NAN flow, relative to DOMI (average, 43 g/kg) or to organic matter apparently digested in the rumen (80 g/kg). Similarly, there was no difference in microbial N flow relative to duodenal NAN (0.50 g/g) and organic matter apparently (41 g/kg) or truly (29 g/kg) digested in the rumen. It was concluded that the higher growth rates achieved by lambs grazing legumes were due to higher intakes which increased the total quantity of nutrients supplied despite more protein being lost in the rumen of lambs consuming legumes.     

Influence of purine intake on uric acid excretion in infants fed soy infant formulas

OBJECTIVE: These studies tested the hypothesis that increasing intake of purines, delivered as RNA from soy protein-based infant formula, would increase urinary uric acid excretion in infants. METHODS: Study One examined the influence of feeding on serum uric acid in a total of 178 infants from four separate trials with infants fed commercial and experimental soy-based and milk-based infant formulas or human milk. Studies Two and Three compared the effect of a standard purine soy formula (STD Purine; 180 mg purines/L from RNA) and a reduced purine soy formula (Reduced Purine; 65 mg purines/L; 26 mg/L from RNA and 39 mg/L from ribonucleotides) on urinary uric acid excretion in infants. In Study Two, 11 infants ranging in age from 16 to 128 days of age were fed both formulas in a random crossover design. Complete 72-hour urine collections were done at the end of each 11-day feeding period. Urinary uric acid excretion was expressed as mmol/day. In Study Three, 33 infants were enrolled before eight days of age and randomized to one of the formulas one week later. Spot urine samples were collected at 28 and/or 56 days of age and urinary uric acid concentration was expressed as mmol/mmol creatinine. RESULTS: In Study One, each of the feedings resulted in mean serum uric acid levels within normal reference ranges. Soy formula led to higher serum uric acid levels than human milk, and human milk to levels indistinguishable from cow milk-based formulas. In Study Two, infants excreted significantly more uric acid in the urine when fed the STD Purine formula compared to the Reduced Purine formula (0.86+/-.04 vs. 0.57+/-.04 mmol/d) (p = 0.006). In Study Three, infants fed the STD Purine formula had a significantly higher concentration of uric acid in their urine compared to those fed the Reduced Purine formula (2.1+/-0.2 vs. 1.4+/-0.1 mmol uric acid/mmol creatinine) (p = 0.0001). CONCLUSION: These data indicate that healthy infants can digest RNA and subsequently absorb the liberated purine ribonucleotides as determined by urinary uric acid concentration.     

The effect of a vegetarian and different omnivorous diets on urinary risk factors for uric acid stone formation

Summary. Background: About 10–15% of all urinary stones are composed of uric acid. A high urinary uric acid excretion, a low urine volume and an acidic urinary pH value are suggested to be the most important risk factors for uric acid stone formation. Aim of the study: The effect of a vegetarian diet and different omnivorous diets on the risk of uric acid crystallization was investigated. Methods: Ten healthy male subjects ingested a self-selected meat-containing diet (SD) for two weeks, and three different standardized diets for a period of 5 days each. The Westerntype diet (WD) was representative of the usual dietary habits,whereas the balanced omnivorous diet (OD) and the ovo-lacto-vegetarian diet (VD) were calculated according to the requirements. Results: The risk of uric acid crystallization was highest on the ingestion of diets SD and WD, due to the high urinary uric acid excretion and the acidic urinary pH. The relative supersaturation with uric acid declined significantly by 85% on the intake of diet OD, consequent to the decrease in uric acid excretion and concentration and the increase in urinary pH value. The ingestion of the vegetarian diet VD led to a further significant reduction in the risk of uric acid crystallization by 93% compared to diet WD. Conclusions: The results indicate that the intake of a balanced vegetarian diet with a moderate animal protein and purine content, an adequate fluid intake and a high alkali-load with fruits and vegetables results in the lowest risk of uric acid crystallization compared to the omnivorous diets.     

Nitrogen and purine metabolism at varying energy and protein supplies in sheep sustained on intragastric infusion

Wether sheep were fitted with rumen fistulas and polyethylene tubes to the abomasum and were given all nutrients by intragastric infusion. In Expt 1 volatile fatty acids (VFA) were given at 340, 450 and 630 kJ gross energy (GE)/kg metabolic weight (W0-75) and protein at 0, 150, 300, 600, 900 and 1500 mg nitrogen/kg W0-75. In Expt 2 VFA were infused at 450 kJ GE/kg W0-75 and protein at 0 and 300 mg N/kg W0-75. At all levels of energy intake in Expt 1 the N retention was significantly (P less than 0.01) related to N intake. The basal N requirement was estimated to be 281 mg (SE 21.8) N/kg W0-75 at 340 kJ VFA/kg W0-75, 226 (SE 21.8) mg N/kg W0-75 at 450 kJ VFA/kg W0-75 and 207 (SE 19.4) mg N/kg W0-75 at 630 kJ VFA/kg W0-75. Plasma urea concentrations varied markedly in relation to protein intake and to energy supply. On the other hand plasma ammonia, glucose, insulin and creatinine concentrations, and also urinary excretion of purine derivatives and creatinine were not significantly affected by the treatments imposed. It was concluded that the urinary excretion of purine derivatives in ruminants was largely unaffected by moderate changes in energy intake and by large changes in protein intake.     

Influence of Purine Intake on Uric Acid Excretion in Infants Fed Soy Infant Formulas

Objective: These studies tested the hypothesis that increasing intake of purines, delivered as RNA from soy protein-based infant formula, would increase urinary uric acid excretion in infants.

Methods: Study One examined the influence of feeding on serum uric acid in a total of 178 infants from four separate trials with infants fed commercial and experimental soy-based and milk-based infant formulas or human milk. Studies Two and Three compared the effect of a standard purine soy formula (STD Purine; 180 mg purines/L from RNA) and a reduced purine soy formula (Reduced Purine; 65 mg purines/L; 26 mg/L from RNA and 39 mg/L from ribonucleotides) on urinary uric acid excretion in infants. In Study Two, 11 infants ranging in age from 16 to 128 days of age were fed both formulas in a random crossover design. Complete 72-hour urine collections were done at the end of each 11-day feeding period. Urinary uric acid excretion was expressed as mmol/day. In Study Three, 33 infants were enrolled before eight days of age and randomized to one of the formulas one week later. Spot urine samples were collected at 28 and/or 56 days of age and urinary uric acid concentration was expressed as mmol/mmol creatinine.

Results: In Study One, each of the feedings resulted in mean serum uric acid levels within normal reference ranges. Soy formula led to higher serum uric acid levels than human milk, and human milk to levels indistinguishable from cow milk-based formulas. In Study Two, infants excreted significantly more uric acid in the urine when fed the STD Purine formula compared to the Reduced Purine formula (0.86±.04 vs. 0.57±.04 mmol/d) (p=0.006). In Study Three, infants fed the STD Purine formula had a significantly higher concentration of uric acid in their urine compared to those fed the Reduced Purine formula (2.1±0.2 vs. 1.4±0.1 mmol uric acid/mmol creatinine) (p=0.0001).

Conclusion: These data indicate that healthy infants can digest RNA and subsequently absorb the liberated purine ribonucleotides as determined by urinary uric acid concentration.     

Uricogenic potential of selected cooked foods in rats

Samples of beefsteak, beef liver, haddock, and mushrooms were cooked by two methods: boiling and broiling. Growth and purine metabolism in rats fed diets containing 20% protein (N x 6.25) were studied for a period of 26 days. The cooked meats and fish were used as the sole source of dietary protein, while cooked mushrooms provided 5% protein in mushroom-casein diets. Body weight, and food and water intakes were recorded weekly while total urine was collected during the last 6 days of the feeding period. Levels of purine metabolites (uric acid and allantoin) in blood and urine were determined by enzymatic methods and reverse-phase HPLC techniques. Dietary treatments had no significant effects on weight gain and food consumption. Compared with animals fed the casein control diet, rats fed the broiled liver, broiled haddock, and boiled mushroom diets had significantly (p less than 0.05) higher concentrations of serum allantoin, suggesting that uricogenicity of these foods was influenced by the method of cooking. The renal excretion of purine metabolites was significantly correlated with purine intake, the renal excretion of allantoin and uric acid being the highest in rats fed the liver diets.     

Uricogenic potential of selected cooked foods in rats.

Samples of beefsteak, beef liver, haddock, and mushrooms were cooked by two methods: boiling and broiling. Growth and purine metabolism in rats fed diets containing 20% protein (N × 6.25) were studied for a period of 26 days. The cooked meats and fish were used as the sole source of dietary protein, while cooked mushrooms provided 5% protein in mushroom-casein diets. Body weight, and food and water intakes were recorded weekly while total urine was collected during the last 6 days of the feeding period. Levels of purine metabolites (uric acid and allantoin) in blood and urine were determined by enzymatic methods and reverse-phase HPLC techniques. Dietary treatments had no significant effects on weight gain and food consumption. Compared with animals fed the casein control diet, rats fed the broiled liver, broiled haddock, and boiled mushroom diets had significantly (p less than 0.05) higher concentrations of serum allantoin, suggesting that uricogenicity of these foods was influenced by the method of cooking. The renal excretion of purine metabolites was significantly correlated with purine intake, the renal excretion of allantoin and uric acid being the highest in rats fed the liver diets.     

Ammonia production and its contribution to urinary nitrogenous compounds in chickens fed low or high protein diet

The rates of total ammonia production and of ammonia retention and contribution of endogenous ammonia to urinary nitrogenous compounds were assessed using a constant intravenous infusion method with [15N]ammonia for 6 h in adult cockerels fed 7.00 or 1.75 g of protein per kilogram body weight per day for 5 d. At the 7.00-g protein intake level the mean total body ammonia production rate was 47.1 mumol/kg per min, with total excretion and retention rates being 10.1 mumol/kg per min and 37.0 mumol/kg per min, respectively. In birds with 1.75 g protein intake the mean total body ammonia production rate was 27.9 mumol/kg per min, with total excretion and retention rates being 3.1 mumol/kg per min and 24.8 mumol/kg per min, respectively. These values were significantly different between the two dietary groups (P less than 0.05-0.01). Ammonia N produced at low and high levels of dietary protein intake, contributed 33% and 84% of urinary uric acid N and 27% and 58% of urinary total N, respectively. With the above protein intake levels, 88% of urinary ammonia N and 6-9% of urinary nitrogenous compounds other than ammonia and uric acid were donated by ammonia N produced in the body. It is concluded that ammonia N produced in the body is the main source of uric acid N, which entirely explains the increase in urinary total N caused by feeding a high protein diet.     

A study of the effectiveness of calcined magnesite as a neutralizing agent for hydrochloric acid in the diet of sheep.

1. Five experimental diets were offered ad lib. for 21 d to five sheep in a 5 x 5 Latin-square design experiment as follows: pelleted grass meal alone (control); pelleted grass meal plus hydrochloric acid (470 mmol/kg dry matter (OM); pelleted grass meal plus 470 mmol HCl/kg DM and either an equivalent amount of calcined magnesite (MgO) (235 mmol/kg DM) or twice the amount (470 mmol MgO/kg DM); pelleted grass meal plus 470 mmol MgO/kg DM. 2. MgO supplementation partly prevented the reduction in food intake caused by HCl, being more effective at the low than at the high level. When fed alone, the high level of MgO had a slight adverse effect on food intake. 3. There was no significant treatment effect on either the pH or volatile fatty acid concentrations of rumen fluid. MgO supplementation was only slightly effective in preventing the metabolic acidosis caused by HCl supplementation, as indicated by blood and urine acid-base measurements. 4. With the MgO-supplemented diets, values for the faecal and urinary excretion of magnesium were approximately 70 and 10% respectively of Mg intake and were not significantly affected by HCl supplementation. For rumen fluid, the water-soluble Mg concentration as a percentage of the total Mg concentration was similar for each treatment, approximately 90%. For faeces, the corresponding value was also similar for each treatment, approximately 30%. 5. MgO supplementation altered the effect of dietary HCl on faecal calcium excretion and on the balance of Ca, but did not alter its effect on urinary Ca excretion. 6. It is concluded that the beneficial effect of MgO supplementation on the intake of the HCl-treated diet was related more to its influence on dietary pH than on conditions in the rumen or the acid-base balance of the sheep.