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. 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. 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. 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. 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. The long-term fate of an oral dose of [75Se]selenomethionine was studied in four women.

2. Urinary and faecal excretion, respiratory losses and whole-body retention of 75Se were measured, and also 75Se turnover in whole body, plasma and erythrocytes during a period of 33–44 weeks.

3. Intestinal absorption of [75Se]selenomethionine by the four subjects was 95.5–97.3% of the administered dose.

4. Urinary excretion accounted for 6–9% of absorbed 75Se in the first 2 weeks. No radioactivity was detected in expired air.

5. After the initial 8 weeks during which radioactivity decreased more rapidly, whole-body retention of 75Se decreased exponentially with a half-time of 207–290 d.

6. Plasma 75Se concentration reached a maximum level 3–4 h after the dose. Transient initial uptake of 75Se in erythrocytes during the first hour was followed by a gradual increase to a maximum concentration at 8–12 weeks.

7. These results are compared with the results of an earlier study of the metabolism of [75Se]selenite in two of the same women. 75Se from [75Se]selenomethionine was found to be more completely absorbed, had a greater retention and smaller endogenous urinary and faecal losses than 75Se from [75Se]selenite, and these differences persisted throughout the experimental period. These findings differed from those obtained in rats in which, after an initial period, 75Se from selenite was metabolized similarly to that from selenomethionine.

1. Studies have been made with solvent-extracted chicken muscle, bovine plasma albumin (BPA) and other proteins, all severely heated in the absence of carbohydrates so as to cause a large decrease in their fluorodinitrobenzene (FDNB)-reactive lysine contents.

2. ɛ-N-(β-L-aspartyl)-L-lysine and ɛ-N-(γ-L-glutamyl)-L-lysine isopeptides were determined after enzymic digestion of heated chicken muscle, and their content was found to increase as the material was subjected to more heat treatment. Heated chicken muscle was not found to contain lanthionine. Heated BPA, on the other hand, was found to contain lanthionine but not the isopeptides. Both lanthionine and isopeptide cross-linkages were detected in most of the other heated proteins. There was some difficulty in quantifying the amounts of isopeptides formed on heat treatment, because the enzymic digestion procedure used in their isolation appeared to be incomplete. Neither lysinoalanine nor ornithinoalanine was detected in any of the test materials.

3. The severely heated chicken muscle was fed to rats, and ileal and faecal digestibilities were studied. Protein digestibility was found to be greatly reduced after heat treatment, although the isopeptides themselves appeared to be at least as digestible as the total N component, total lysine, or FDNB-reactive lysine. However, the reduction in ileal N digestibility only partly accounted for the much larger reduction in nutritive value, as measured by net protein ratio ((weight loss of N-free animals + weight gain of test animals) ÷ weight of crude protein (N × 6.25) consumed by test animals). Possible reasons for this are discussed.

1. Electromyographical studies were made on the motility of the stomach and small intestine of five pigs when given a standard diet either ad lib., or as one or two meals/d. Recordings were made from electrodes placed chronically on the antrum, the duodenum and the jejuno-ileum, and a continuous 24 h recording was made every 2 d for a period of 4 weeks. A simple ‘T’-shaped cannula was positioned in the proximal duodenum in two of the pigs.

2. The basic pattern of activity of the small intestine was grouped in phases of irregular and regular activity characteristic of the myoelectric complex. This pattern recurred about eighteen times/d in fasting pigs, or in animals fed ad lib. and so eating frequent but small meals. When a myoelectric complex on the duodenum reached its regular ‘spiking’ phase, antral activity and passage of digesta ceased completely for a period (5–15 min) which varied according to the time elasped since the last meal.

3. In animals receiving one meal/d a postprandial pattern of activity lasted about 6 h. The proximal part of the intestine showed continuous activity with vigorous isolated or peristaltic spike bursts. The average number of myoelectric complexes was thirteen/d. When receiving two meals/d the postprandial pattern lasted for only 2–3 h, and approximately sixteen myoelectric complexes/d were recorded.

4. It is concluded that the extent of disruption of the basic intestinal motility pattern depends on the amount of food consumed per meal and subsequent release of nutrients.

1. Feeding sheep a concentrate diet compared with grass diets increased the hepatic specific activities of the three glycolytic enzymes studied, and that of glucose-6-phosphate dehydrogenase (EC 1.1.1.49), and reduced the specific activity of D-fructose-1,6-diphosphate 1-phosphohydrolase (EC 3.1.3.11). The specific activities of phosphogluconate dehydrogenase (EC 1.1.1.43) and malate dehydrogenase (decarboxylating) (NADP) (EC 1.1.1.40) were unaffected by diet.