Endogenous nitrogen excretion and utilization of dietary protein By Nicol B. M., and the late Philips P. G. Vol. 35 (1976), no. 2 p. 188

1. Net amino acid uptake, and incorporation into protein have been measured in vitro in the presence and absence of porcine growth hormone (GH) in muscle from intact rabbits fed for 5 d on low-protein (LP), protein-free (PF) or control diets.

2. In muscle from control and LP animals GH had no effect on the net amino acid uptake but stimulated amino acid incorporation into protein, although this response was less in LP animals than in control animals.

3. In muscle from PF animals, GH stimulated both amino acid incorporation into protein and the net amino acid uptake, a type of response which also occurs in hypophysectomized animals. The magnitude of the effect of GH on the incorporation of amino acids into protein was reduced in muscle from PF animals.

4. The effect of GH on the net amino acid uptake in PF animals was completely blocked by cycloheximide; the uptake effect of GH in these animals was dependent therefore on de novo protein synthesis.

5. It is proposed that in the adult the role of growth hormone in protein metabolism is to sustain cellular protein synthesis when there is a decrease in the level of substrate amino acids, similar to that which occurs during a short-term fast or when the dietary protein intake is inadequate.

1. The endogenous nitrogen losses of men of different ethnic, ecological and socio-economic backgrounds are similar when calculated per unit body-weight or per unit basal energy consumption. The hypothesis that endogenous N losses, adjusted upwards by a factor of 0.30 to equate them with N equilibrium, can be used to derive man's physiological requirements for proteins of high quality, e.g. those of egg and milk, was studied..

2. Men living in Nigeria, accustomed to eat diets which provided mixtures of protein only slightly higher than the ‘safe level of intake’ proposed by the Joint FAO/WHO ad hoc Expert Committee on Energy and Protein Requirements (FAO/WHO, 1973), were found to use absorbed N more efficiently than University of California students who habitually consume diets which supply a great excess of protein over that ‘safe level’..

3. The greater protein-sparing effect of carbohydrates than of fats and oils may play a part in this more efficient use of protein by men living in developing countries. Also, man possesses mechanisms in intermediary metabolism which allow him to adjust to low levels of protein intake..

4. Thus it appears that all apparently healthy men cannot be considered equal in regard to their requirements for protein.

1. A 21 d slaughter trial was done using weanling male rats offered sodium chloride added at 10, 20 and 30 g/kg to a nutritionally adequate, control diet containing 13 g NaCl/kg, or added to the drinking-water at 5, 10, or 15 g NaCl/l. Food and drinking-water with or without NaCl were offered ad lib. and their intakes were measured..

2. NaCl in the food reduced food intake by 10–15%; NaCl in solution reduced food intake only when added at the 15 g/l level; the reduction was 25%..

3. NaCl increased the fluid intake of the rats; for NaCl in the food the increments ranged from 23 to 44%; for NaCl in the drinking-water they ranged from 44 to 229%..

4. Body fat was significantly reduced by 20 and 30 g NaCl/kg added to the control diet, indicating a reduction in the efficiency of fat synthesis. Comparable amounts of NaCl taken in the drinking-water had a negligible effect on fat deposition..

5. It is suggested that NaCl in the food produces hypodipsia, i.e. a failure to drink an optimal amount of water, causing changes in the electrolyte balance which reduce food intake and progressively reduce the efficiency of fat synthesis.

1. [35S]sulphate was used to measure the apparent turnover of sulphate, sulphide and microbial-protein-S in the rumen contents of four sheep that were intraruminally infused with 10 g sodium sulphate/d alone, or together with 126 mg sodium molybdate (50 mg molybdenum/d).

2. Infusion of molybdate increased the concentration of sulphate in rumen fluid from 2.2 to 7.2 μg S/ml and decreased the rate of reduction of sulphate to sulphide by 50%. Although the rate of sulphide production was slower, the concentration of sulphide in rumen contents was increased. A dual role for molybdate in the metabolism of sulphide in the rumen is suggested to explain these changes.

3. In animals that were not infused with molybdate, only one-third of the S (3.0 g/d) that passed through the sulphate pool in rumen fluid was converted to sulphide, decreasing to one-sixth when molybdate was infused.

4. The turnover of S amino acids in microbial protein was not significantly affected by molybdate. Only 52–57% of the S amino acid content of microbial protein was synthesized de novo by way of the sulphide pool.

1. L-histidine (20 g/kg) added to vitamin B12-deficient and cyanocobalamin-supplemented diets based on soya-bean flour reduced the growth of rats given the vitamin B12-deficient diet but stimulated growth of rats given the cyanocobalamin-supplemented diet. Liver weight (g/kg body-weight) increased, but the protein content of the livers decreased, in rats given histidine supplements. The histidine was associated with significantly higher folate concentrations in the livers of cyanocobalamin-supplemented rats.

2. Vitamin B12-deficient and cyanocobalamin-supplemented rats were given diets based on a mixture of amino acids that was balanced apart from methionine, which was added in various amounts, and with the addition of homocystine. The only vitamin B12-deficient rats which had reasonable gains in weight were those receiving a diet containing 8 g L-methionine/kg. The remainder, particularly those given diets containing only homocystine, had little or no increase in weight. All the cyanocobalamin-supplemented rats gained weight; those given diets containing 2 and 8 g L-methionine/kg, or 8 g homocystine/kg, had the highest gains.

3. There was a tendency for a higher concentration of either methionine or homocystine in the diet to be associated with higher concentrations of both folate and vitamin B12 in the livers.

4. In vitamin B12 deficiency methionine appeared to increase the accumulation of folate in the liver, affecting mainly the amounts of polyglutamate derivatives.

1. Two diets, an all-roughage diet and a high-concentrate diet, were fed at two levels, a low level of estimated 1.5 times maintenance energy requirement and a higher level of estimated two times maintenance energy requirement, to South African Mutton Merino castrated male sheep, aged 13 months and in fairly lean condition at the start of the 93 d experimental period..

2. Body composition and energy retention were determined using the comparative slaughter technique and two series of digestibility and balance studies were done during the course of the experiment. Metabolizability of each diet was estimated and corrected for fermentation heat using the fermentation balance approach..

3. Although there were significantly different rates of energy gain on different diets and feeding levels, fat energy gained (% total energy gained) was similar for the four groups, i.e. 78–80..

4. Regression of energy gain v. corrected metabolizable energy (ME) intake indicated that the maintenance energy requirements of sheep used in this experiment were 310.2 and 302.3 kJ ME/kg body-weight0.75 per d and the values for net utilization of ME for body energy gain were 0.411 and 0.479 with the roughage and concentrate diets respectively..

5. It was concluded that the estimated maintenance energy requirements of sheep obtained in this study are realistic values and that the efficiency of utilization of surplus ME for the two diets did not differ significantly.

1. Monosodium glutamate (MSG) was administered by various methods to mice and rats of various ages and the incidence of obesity was later measured.

2. Newborn mice were injected subcutaneously with 3 mg MSG/g body-weight at 1, 2, 3, 6, 7 and 8 d of age; 16% died before weaning. Of the survivors, 90% or more became markedly obese. Mean carcass lipid content was increased by about 120% in both sexes at 20–30 weeks of age. In male mice, MSG treatment increased body-weight and epididymal fat pad weight, and greatly decreased adrenaline-stimulated lipolysis in isolated fat cells. Body-weight of females was not increased significantly. Food intake was not increased in either sex from weeks 13 to 15. Blood glucose level was not generally increased by MSG but some of the male mice had abnormally high values.

3. Obesity was not detected in the offspring of female mice that had received 100 g MSG/kg diet, either from 3 weeks before mating until weaning, or from the 14th day of pregnancy until weaning.

4. Intraperitoneal injection of 10 mg MSG/g body-weight (in two doses) at weaning increased carcass lipid content in female mice by 34% by 23 weeks of age, but female rats were not affected.

5. The addition of 20 g MSG/l to the drinking-water from weaning onwards did not increase carcass lipid content in female rats or mice.

6. The addition of 20 g MSG/kg diet from weaning onwards did not alter body-weight or carcass lipid content in male and female rats by 14 weeks of age.

7. The obesity induced in mice by MSG was not associated with hyperphagia, unlike genetic obesity and obesity induced by gold thioglucose (GTG).

8. All types of mouse studied, obese and lean, had essentially the same linear relationship between carcass water content and carcass lipid content.

9. Although MSG-obese mice could not readily be differentiated from normal mice by the increase in body-weight, which was only about 10% compared to 50–120% for genetic and GTG-induced obesity, the proposed schedule of injections in the newborn was almost 100% reliable in inducing a high extent of adiposity.

1. Copper deficiency was induced in five Friesian cattle offered a semi-synthetic diet containing < 1 mg Cu/kg. Changes in blood and liver Cu contents and in the Cu-containing enzymes, ferroxidase I (caeruloplasmin; EC 1.16.3.1) and monoamine oxidase (EC 1.4.3.4) of plasma and cytochrome oxidase (EC 1.9.3.1) of liver and skeletal muscle were monitored during Cu depletion.

2. Rapid decreases in blood and liver Cu and plasma ferroxidase I activity were found at least 80 d before the first appearance of overt clinical signs of deficiency. Plasma monoamine oxidase and liver cytochrome oxidase activities decreased less rapidly and thus may provide useful indices of chronic Cu depletion.

3. Although results of these assays indicated that Cu depletion was occurring and metabolic defects supervening, none facilitated the early recognition of individuals that subsequently showed marked overt clinical signs of Cu deficiency compared with those less severely affected.

4. Irrespective of their clinical appearance at slaughter, Cu-depleted cattle showed gross or microscopic lesions of the skeleton and cardiovascular system and, in some instances, lesions of the ligamentum nuchae and small intestine. The aetiology of these lesions is considered with particular respect to changes in the activities of the Cu-dependent enzymes studied and to the interpretation of field surveys based solely upon determination of blood or liver Cu content.

5. A second group of five cattle was offered the same diet supplemented with Cu to provide 8 mg Cu/kg and, later, 15 mg Cu/kg. Although no pathological lesions attributable to Cu deficiency were detected at slaughter a marked reduction in liver Cu content, a decrease in plasma ferroxidase I activity and, in four animals, the development of a diarrhoea controlled by oral administration of Cu, suggested that 8 mg Cu/kg diet did not meet their requirement for Cu.

1. A study was made of the assay of available lysine and available methionine using Tetrahymena pyriformis W, as applied to a variety of protein-rich feedstuffs.

2. Results were strongly influenced by the conditions under which the analyses were done. With most of the test samples predigestion with papain caused a large increase in the values obtained.

3. An improved assay procedure was developed which included enzymic predigestion of the test samples, ‘all-in’ sterilization of the medium constituents, and measurement of growth from extinction values. It gave results for available lysine that were broadly similar to those obtained in growth tests with rats, and in chemical tests by the method of Carpenter (1960). Values for available methionine agreed closely with those obtained in microbiological tests with Streptococcus zymogenes.

1. Sixty-four male rats were fed on a nutritionally complete diet containing 30% of the dietary energy as fat. For thirty-two rats (control) the fat source was maize oil; for the remaining thirty-two rats (experimental) the fat source was triundecanoin–maize oil (7:3, w/w).

2. After 6 weeks, groups of control and experimental rats were fasted and killed on days 0, 1, 2 and 4 of the fasting period. In the experimental group, adipose-tissue fatty acids contained, on average, 246 mmol undecanoic acid/mol total fatty acids. In contrast, the adipose tissue of the control group did not contain odd-carbon-number fatty acids.

3. Plasma glucose levels were significantly higher for all fasted experimental groups and blood ketone levels were significantly lower for these groups.

4. Thus, during prolonged starvation, animals which accumulated odd-C-number fatty acids resisted the development of ketosis. It appeared that odd-C-number fatty acids mobilized from fat depots during fasting may provide their terminal three-C residues for gluconeogenesis rather than for acetyl-CoA production, thereby allowing for better maintenance of blood glucose and insulin levels than in control animals.

5. It is concluded that the lower acetyl-CoA production and higher blood insulin levels reduce ketogenesis.

1. The nutritional status of children showing no clinical signs of malnutrition, from the University School of Khon Kaen, Khon Kaen province, north-east Thailand and from two villages nearby, was tested. The children were grouped according to their body-weight expressed as a percentage of expected weight-for-height (Harvard standards (Stuart & Stevenson, 1959), as given by Jelliffe (1966))..

2. The differing prealbumin concentrations indicated that nutritional status differed between the groups..

3. The urinary urea: creatinine ratio was significantly lower in the village children compared with the children from Khon Kaen, indicative of the higher dietary protein intake of the latter..

4. α1-Acid glycoprotein and the first ‘post-albumin peak’ (obtained by polyacrylamide gel electrophoresis of serum and containing mainly Gc-globulin, α1-antichymotrypsin and α1-B-glycoprotein) were found to be significantly higher in the village children compared with children from Khon Kaen..

5. The three main proteins of the first ‘post-albumin peak’ from polyacrylamide gel electrophoresis of serum were tested separately using the electroimmunoassay method. There was no significant difference in Gc-globulin between the children from Khon Kaen and the village children. The concentration of α1-B-glycoprotein from those Khon Kaen children whose body-weight was more than 95% expected weight-for-height was significantly lower compared with that of village children. α1-Antichymotrypsin concentration was significantly higher in serum from Khon Kaen children than in serum from village children.

1. In the first experiment sheep taken from pasture were given a low-protein diet for 6 weeks in individual pens. Then, for 1 week, groups were given a supplement of lucerne chaff, safflower meal or lucerne chaff plus safflower meal. In the second experiment eighteen sheep maintained on lucerne chaff rather than pasture were then depleted of protein to a greater extent by feeding on a restricted low-protein diet. Six of the sheep received a supplement of molasses throughout the period of protein depletion while six of the sheep on the basal ration received a supplement of safflower meal after 6 weeks on the low-protein diet.

2. The urea tolerance of the sheep, as indicated by blood ammonia levels after oral dosing with aqueous solutions of urea, was determined after the period of supplementation. ‘Arginine synthetase’ activity (combined activities of argininosuccinate synthetase (EC 6.3.4.5) and argininosuccinate lyase (EC 4.3.2.1)) was determined in liver samples obtained by biopsy at various intervals during the experiment.

3. Supplementation for 7 d with 73 g crude protein (nitrogen × 6.25)/d increased the tolerance to urea, as indicated by reduced blood NH3 levels, and also increased ‘arginine synthetase’ activity.

4. Giving supplements of molasses delayed the onset of urea toxicity but not the extent of toxicity.

5. It is suggested that short-term feeding of protein concentrates to sheep before giving urea supplements can increase their tolerance to urea.

1. In a comparative slaughter experiment, growing lambs were given concentrate diets in which 14 or 19% metabolizable energy (ME) provided by barley was replaced by sodium, calcium and potassium salts of acetic acid. As the proportion of ME as acetate was increased, energy retention decreased. ME intake was 9271, 9430 and 9217 ± 67 kJ/d and energy retention was 2698, 2422 and 2280 ± 71 kJ/d for the diets containing 0, 14 or 19% ME as acetate respectively. There were no differences in protein deposition. The efficiency of utilization of acetate for energy retention (kf) was calculated by difference to be 3 and 10 ± 13% respectively for the diets containing 14 and 19% ME as acetate.

2. In a second experiment, growing lambs were given concentrate diets in which 4 or 16% ME provided by barley was replaced by salts of acetic acid, and utilization was measured by indirect calorimetry. There were no significant differences in the utilization of the diets for maintenance (km) or energy retention (kf). The km values were 82.4 ± 2.3 and 81.2 ± 0.7%, and kf values were 67.4 ± 4.5 and 65.8 ± 2.7% respectively for the diets providing 4 and 16% ME as acetate. The kf of the additional acetate in the diet providing 16% ME as acetate was calculated by difference to be 54%.

3. The acetate and Ca concentrations of the rumen digesta were increased by including acetate salts in the diet, but Na and K concentrations were not affected.

4. It is concluded that the best explanation for the poor utilization of acetate in the comparative slaughter experiment is that acetate was poorly utilized for lipogenesis. The calorimetry experiment contained relatively large errors, but the results suggest that acetate may be utilized efficiently in some circumstances. It is suggested that these results and apparently conflicting results in the literature may be explained by the concept that the efficient utilization of acetate is dependent upon the supply of glucose or glucose precursor.

1. The results obtained for 236 Viennese schoolchildren between 11 and 12 years of age indicated that 38% of children had an increased concentration of cholesterol in their serum and 3% had an increased serum triglyceride concentration..

2. The results of the preliminary study suggested that, by extending the dimensions of the screening, further problems, for example the correlation between different ‘risk’ factors and the significance of nutritional habits, might be studied.

1. A method of obtaining dialysed samples from the caecum of the conscious rabbit is described.

2. Values for total volatile fatty acid content and for molar proportions of individual volatile fatty acids in dialysate samples were in good agreement with those obtained from caecal material.

3. The volatile fatty acid level in the caecum throughout the day was determined using two groups of animals, one group fed ad lib. and the other group on a restricted food intake. These results indicated a marked diurnal fluctuation in volatile fatty acid level in the caecum of rabbits fed once/d which was not evident in those fed ad lib.

1. When nineteen ‘free-living’ male students, who normally ate 231 (SEM 14) g white bread/d changed to wholemeal bread for a 19-week period, there was no significant change in body-weight, plasma cholesterol or plasma triglyceride levels. These values, as well as plasma concentrations of calcium, phosphate, urate and haemoglobin, remained essentially the same as those for a control group.

2. Increasing the wheat-fibre intake by eating wholemeal bread is not an effective method for reducing blood lipid levels, at least in healthy young men with a moderate bread intake.