1. Six 45 kg pigs with re-entrant ileal cannulas were used in two 3 × 3 Latin-square design experiments to study the site of absorption of protein and amino acids. Semi-purified diets containing soya-bean meal (SBM), rapeseed meal (RSM) or no protein source (protein-free) were offered at the rate of 1 kg dry matter/d.

2. Flow-rates of ileal contents for 24 h collection periods, corrected for recovery of marker, were 3135, 3127 and 1243 ml (SE 390) for SBM, RSM and protein-free diets respectively.

3. Amounts of dry matter digested in the small intestine were 730, 669 and 809 g/d for SBM, RSM and protein-free diets respectively, all values being significantly different (P < 0·001).

4. Nitrogen intakes were 32·6, 29·9 and 5·9 g/d, and amounts digested in the small intestine were 25·7, 20·2 and 1·6 g/d for SBM, RSM and protein-free diets respectively, all values being significantly different (P < 0·001). Amounts digested in the large intestine were 2·6, 3·7 and 0·7 g/d.

5. Total amino acid intakes and amounts collected at the ileum and in the faeces were (g/d): SBM, 177, 24 and 18; RSM, 149, 28 and 22; protein-free 3, 9 and 12. Digestibility in the small intestine was higher for SBM than RSM for seventeen of the eighteen amino acids estimated. Greater quantities of arginine, methionine, cystine and tyrosine were voided in the faeces than passed through the ileal cannulas for pigs receiving the SBM and RSM diets. For those receiving the protein-free diet this was true for each amino acid except proline.

6. Significant differences were found between all diets in the concentration of some amino acids in ileal and faecal amino-N, and endogenous protein secretions did not mask the differences between diets.

7. Differences in digestibility between SBM and RSM were greater at the ileum than in the faeces. Amino acid fermentation in the large intestine obscured or reduced differences between SBM and RSM.

1. The response to cyanocobalamin and folic acid therapy was studied in forty-seven subjects with severe nutritional megaloblastic anaemia; twenty-five were vitamin B12 deficient and, of these, ten were also folic acid deficient.

2. In twenty-four of the subjects, absorption of orally administered cyanocobalamin was normal, and there was a haematological response to small doses of orally administered cyanocobalamin, indicating adequate absorption. In one subject there was impaired cyanocobalamin absorption although free gastric hydrochloric acid was present.

3. The findings indicate that the absorptive function of the small intestine was unimpaired, with one exception, although there was a possible defect in nucleoprotein synthesis associated with a lack of vitamin B12 and folic acid. Addisonian pernicious anaemia was not found in any of the subjects.

1. Absorption rates of glucose (from a 200 mM solution), glycine (from a 100 mM solution), and glycylglycine (from a 50 mM solution) have been estimated in six Zambian African adults with clinical evidence of malnutrition. A double-lumen tube technique was used to determine absorption rates from a 300 mm section of jejunum in vivo.

2. Two of the subjects had ileal tuberculosis and Kaposi's sarcoma respectively. A third probably had abdominal tuberculosis. Three of them had pellagra. Mean serum albumin concentration was 24 (14–43) g/l. Absorption rates have been compared with those in Zambian Africans (control subjects), previously studied, who had no clinical evidence of malnutrition, systemic infection or of gastrointestinal disease.

3. Mean glucose, glycine and glycylglycine absorption rates in the malnourished subjects were not significantly different from those in the control subjects. Mean net water absorption rate from the glucose solution was similar in the malnourished subjects and controls; during the glycine and glycylglycine perfusions the mean net absorption rate was, however, significantly lower in the malnourished subjects (P < 0.01 and P < 0.05 respectively); mean net water transfer during the glycine perfusions was towards the jejunal lumen in the malnourished subjects. One subject with pellagra had an abnormal excretion of D-xylose after a 25 g oral load; all other tests were normal.

4. It seems probable that malnutrition must be very severe, with jejunal mucosal abnormalities, before absorption rates of glucose, glycine and glycylglycine are significantly altered. The present study does not support the view that subclinical malnutrition is important in producing malabsorption of dietary components in Zambian African subjects. Systemic bacterial infections, and raised serum γ-globulin and immunoglobulin IgG concentrations have previously been associated with an impairment of glucose absorption rate in Zambian African subjects; those factors seem much more likely than subclinical malnutrition to be relevant, in the context of absorption, in the pathogenesis of overt malnutrition.

1. A study of the effects of four dietary treatments on body-weight and the water, protein, fat and energy content of the empty bodies of forty-three Suffolk ewes is reported. The treatments were as follows: T1, ad lib. food intake from a full-body-weight (FBW) of 40 kg to 71 kg; T2, partial fasting with a resulting weight loss from 71 kg to 50 kg FBW; T3, realimentation and regrowth from 50 kg to 71 kg FBW; T4, a slight food restriction producing a reduced growth rate from 40 kg to 50 kg FBW followed by ad lib. food intake from 50 kg to 71 kg FBW. On all treatments sheep were slaughtered in groups of three at 7 kg intervals between 50 kg and 71 kg FBW.

2. The whole body, with the exception of several body organs and glands, wool and the contents of the gastrointestinal tract, was minced and analysed for water, protein, fat and energy. Adipose tissue samples were removed at slaughter from subcutaneous and internal fat depots for histological examination. Regression analysis was used in comparing treatment effects on body composition.

3. No significant differences were observed between the results of T1 and T4. In consequence these results were pooled and are referred to as T1. At 40 kg FBW the empty (ingesta-free) bodies of the lambs contained approximately 52% water, 14 % protein and 29% fat. Through normal growth to 71 kg FBW on T1 these values had changed to 40, 11.5 and 45 %, respectively. Following weight loss to 50 kg FBW on T2 the water, protein and fat contents of the empty bodies were 47, 13.5 and 35 %, respectively. Regrowth on T3 to 71 kg FBW resulted in little change in these components, the respective values being 46, 13 and 36 %. The sheep which had undergone weight loss and regrowth retained significantly more water and less energy than normally grown controls and tended to deposit less fat and more protein.

4. Gastrointestinal tract contents accounted for 11 % of FBW at 71 kg in T3 animals. In T1, the value was 7.1 % at a similar FBW. Thus there was an average increase of over 56 % in contents in the realimented animals.

5. Mean adipocyte diameter at 50 kg FBW on T1 was 134 ± 3 μm. At 71 kg FBW the mean diameter had increased to 152 ± 9 μm. Weight reduction (T2) and regrowth (T3) resulted in mean diameters of 122 ± 4 μm and 143 ± 4 μm at 50 kg and 71 kg FBW, respectively.

1. Escherichia coli and mixed cultures of rumen bacteria were grown with [8-14C]adenine to label their nucleic acids specifically.

2. The labelled bacteria were injected into the rumen of sheep and the radioactivity incorporated into tissue nucleic acids and that excreted in the urine and faeces was determined.

3. The radioactivity was present in the cold trichloroacetic acid-soluble fraction and the RNA and DNA fractions of all tissues examined. Liver, kidney, spleen, and blood had the highest levels of radioactivity.

4. The radioactivity of the RNA was present only in adenosine monophosphate and guanosine monophosphate.

1. The purine nucleotide cycle has been proposed (Lowenstein, 1972) as an alternative scheme for amino acid deamination in tissues, such as skeletal muscle, having low concentrations of glutamate dehydrogenase (EC 1.4.1.2).

2. Activities of AMP deaminase (EC 3.5.4.6), one of the enzymes of the cycle, have been measured in soleus, plantaris and extensor digitorum longus muscles of rats maintained for 18 d on diets providing 0, 0·035 or 0·10 net dietary protein energy (energy supplied by utilizable protein: total metabolizable energy, NDp:E), and in rats given the 0·10 NDp:E diet for 3 d after the 0 or 0·035 NDp:E regimens.

3. Concentration of AMP deaminase in the different muscles from the control (0·10 NDp:E diet) rats appeared to bear an inverse relationship to the proportion of mitochondria-rich fibres (i.e. rich in glutamate dehydrogenase) in each muscle.

4. Dietary protein deprivation (0 or 0·035 NDp:E) led to adaptive reductions in AMP-deaminase activity in the soleus and plantaris muscles, but in the extensor muscle the 0·035 NDp:E diet produced no change, while the 0 NDp:E diet caused an increase in activity.

5. Refeeding the 0·10 NDp:E diet to the protein-deprived rats caused reductions of AMP-deaminase activity to lower levels in all three muscles, except in the instance of soleus in rats refed after the 0·035 NPp:E diet.

6. In view of the different responses shown by the three muscles to the dietary treatments, the importance of specifying the particular muscles used in future nutritional studies is emphasized.

7. The adaptive changes in AMP deaminase are discussed in terms of operation of the purine nucleotide cycle for amino acid deamination responding to the changes in amino acid catabolism known to be caused in muscle by these protein-deficient diets.

1. The plasma concentration of retinol-binding holoprotein (holo-RBP) in rats given retinol-sufficient diets containing 50 g soya-bean protein/kg was 90 % of the concentration found in controls given 200 g soya-bean protein/kg, whereas in rats given 50 g rice protein/kg it was only 68 % of the control value. Plasma albumin concentrations in the low-protein groups were lower by 20–25 %.

2. The rats given retinol-deficient diets, whose plasma levels of holo-RBP were reduced almost to zero after 5–8 weeks, were given 1·5 mg retinol/kg body-weight. Changes in plasma holo-RBP were measured for 7 d. The rapid rise in the latter to a peak above normal control levels within 1·5–2 h indicated that a pool of the apoprotein had accumulated in the liver during the period of deficiency and that retinol was necessary for its release.

3. The maximum value reached in the groups of rats given the rice-protein diet was smaller than the values for the groups given the soya-bean-protein diets, reflecting a reduced rate of synthesis of the carrier protein in the livers of those groups.

4. The administration of 100 g casein/kg diet to the rats receiving only 50 g rice-protein/kg immediately stimulated the synthesis of the carrier protein which was released into plasma, reaching a peak after 24 h before settling down after 3–4 d to the steady-state level expected for normal well-nourished controls.

5. The half-life for excess holo-RBP released into plasma of rats receiving a normal level of good-quality protein was 7 h, where it was 14 h for the groups of low-protein diets.

1. The effects of dietary sulphur on the availability of dietary copper were estimated by means of a repletion technique. The responses of initially hypocupraemic ewes to repletion with Cu-supplemented diets containing supplements of organic S, as methionine, and of inorganic S, as Na2SO4, were compared with those obtained with a diet low in S.

2. The two forms of S had similar effects. Responses in plasma Cu were reduced by 39–56 % when S was increased from 1.0 to 3.0 or 4.0 g/kg diet and the availability of dietary Cu was estimated to have decreased from 0.062 to 0.041. Both S supplements produced marked increases in rumen sulphide concentrations.

3. Dietary S had no effect on plasma Cu when added to the low-Cu diet of hypocupraemic ewes being repleted by a continuous intravenous infusion of Cu.

4. The addition of CuS, providing 5 mg Cu/kg, to the diet of hypocupraemic ewes produced no response in plasma Cu or haemoglobin. The same amount of Cu, given as CuSO4, increased plasma Cu by 0.46±0.15 mg/l and haemoglobin by 33±3.8 g/l after 36 d: the subsequent replacement of CuSO4 by CuS induced hypocupraemia again but had no effect on haemoglobin.

5. It was concluded that variations in dietary S within the normal range for herbage exert an independent effect on Cu metabolism, possibly through the formation of insoluble CuS at sites beyond the rumen.

1. Intestinal and renal vitamin D-dependent calcium-binding protein (CaBP) activity and cholecalciferol metabolism were investigated in the protein-deficient rat (40 g casein/kg diet) and in control animals (200 g casein/kg diet). Compared to control animals, 3 weeks of protein deprivation resulted in consistently reduced intestinal CaBP activity, while renal CaBP activity was not significantly altered.

2. Intestinal CaBP activity was greatly reduced in rats fed on diets deficient in both protein and vitamin D. CaBP activity was doubled by cholecalciferol administration, but did not reach control values. The rate of conversion of intravenously injected [3H]cholecalciferol to 25-hydroxycholecalciferol (25-HCC) and the disappearance rates of plasma 25-HCC were similar in the two groups of animals.

3. It is concluded that in the protein-deficient rat: (a) intestinal CaBP activity is reduced; (b) coexistent vitamin D deficiency reduces intestinal CaBP activity still further, but the intestinal mucosa retains the potential to respond to administered cholecalciferol: (c) hepatic and probably renal metabolism of cholecalciferol appear to be normal; (d) reduced CaBP is likely to be the result of reduced CaBP synthesis as a consequence of deficient amino acid substrate.

1. Folate deficiency was produced in baboons by feeding them on a diet which was deficient in folic acid.

2. Loss of body-weight, anorexia, asthenia, gingivitis and diarrhoea were common features of the deficiency.

3. Haematologically, the deficiency was characterized by leucopenia with a greater proportional decrease in the polymorphonuclear neutrophils, thrombocytopenia and in some baboons macrocytic anaemia.

4. Deficient baboons had low serum, erythrocyte and liver folate levels and excreted increased amounts of formiminoglutamic acid. The fall in the serum folate level was more rapid than that of the erythrocytes, occurring mainly during the 1st month of deficiency, while erythrocyte levels decreased gradually over a 5-month period.

5. Serum and liver vitamin B12 levels and methylmalonic acid excretion were normal in deficient baboons.

1. Analyses have been made of materials in which proteins were caused to react with sugars so as to cause a severe fall in their nutritionally available lysine content as assayed with both rats and chicks.

2. With materials in which the reactions had proceeded under mild conditions (37°), the direct use of either fluorodinitrobenzene (FDNB), o-methylisourea or sodium borohydride to measure selectively those lysine units which had not engaged in Maillard reactions gave similar values which, in turn, appeared to reflect the full extent of the nutritional damage.

3. Analysis by a procedure using trinitrobenzenesulphonic acid (TNBS), or the use of FDNB indirectly to measure ‘bound lysine’ failed to indicate the full extent of the Maillard reaction in mildly heated materials, although the same procedures did appear to do so when applied to materials in which sugar and proteins had been allowed to react at a higher temperature.

4. With a pure protein and with fat-extracted, dried muscle that had been severely heated, all the procedures for measuring reactive lysine gave similar results, with the exception of the procedure using sodium borohydride which proved ineffective in measuring the type of damage that had occurred in these materials.

5. The findings are discussed in relation to the nature of the reactions believed to take place in different types of heat damage.

6. Suggestions are made of the types of materials with which different procedures can be satisfactorily used. The direct FDNB procedure and that using o-methylisourea appeared to be applicable to all our samples.

1. Drinks of milk, lactose and casein were given to children who, though suspected of having malabsorption, were subsequently found to have normal gastrointestinal tracts. The plasma concentrations of glucose, amino acids, urea and insulin following these drinks were measured. The results can probably be taken to represent control values when investigating children with gastrointestinal or metabolic disorders.

2. The rise in plasma amino acids after giving casein and the rise in plasma glucose after giving lactose were greater than those after giving equivalent amounts of milk.

3. The absorption of an individual food constituent and its uptake by the tissues are influenced by the presence of other food constituents so that ‘tolerance tests’ with individual nutrients may not be truly physiological.

1. The capacity of animals to conserve branched-chain amino acids was assessed during 3 weeks on a protein-free (PF) diet in groups of female rats at three stages of development, i.e. at weaning (35 g), in a period of rapid growth (85 g) and at maturity (200 g).

2. Leucine and valine oxidation was assessed by monitoring the evolution of 14CO2 from a tracer dose of the [1-14C]-labelled L-amino acid given intragastrically. Activities of the L-leucine:2-ketoglutarate aminotransferase (EC 2.6.1.6) and α-keto acid dehydrogenase enzymes in leucine and valine metabolism were also determined in muscle and liver at weekly intervals.

3. All three groups of rats given a normal protein intake excreted the same proportion of the dose of labelled leucine and valine. In rats given PF diet there was a consistent reduction in 14CO2 output from both L-[1-14C]leucine and L-[1-14C]valine, but valine was not conserved as efficiently as leucine.

4. Muscle dehydrogenase responded to a PF diet in all three groups of rats, but the most marked changes occurred in the youngest group. In addition, there was a decrease in hepatic dehydrogenase activities for leucine and valine catabolism in the weanling group; in older animals there was little change in the α-keto-isovalerate, but a consistent decrease in the activity of the α-keto-isocaproic acid dehydrogenase. The difference in the responsiveness of the dehydrogenases, therefore, matched the difference between leucine and valine oxidation rates in vivo.

5. Weanling animals responded rather more efficiently than the older animals to the need to conserve amino acids and there was no evidence of a poorly developed system for adapting to PF intake at this early stage of development.

6. Despite reduced catabolism of the amino acids, aminotransferase activities in liver and muscle rose in the first 1–2 weeks on a PF regimen. Aminotransferase activity as such is unlikely to control acid oxidation.

1. To assess the part played by the microflora in the digestion of proteins, the amino acid composition of the excreta and the apparent and true digestibilities of individual amino acids were measured in germ-free (GF) and conventional (CV) chicks.

2. Three diets were used: diet 1, nitrogen-free; diet 2,280 g protein/kg as (g/kg): casein 80, gelatin 100 and freeze-dried egg albumen 100 and diet 3,280 g protein/kg as diet 2 but with heat-damaged instead of freeze-dried egg albumen. Half of the GF and half of the CV chicks received the N-free diet in the first 7 d of test and the other half of each group received either diet 2 or diet 3. In the second 7 d test period those chicks which had been given the N-free diet received either diet 2 or diet 3 while those which had been given protein diets received the N-free diet. Total amino acids were measured in hydrolysates of the soluble and insoluble fractions of the excreta collected in the last 3 d of each test period.

3. The amino acid composition of the soluble fraction of the excreta of chicks given either diet 2 or diet 3 differed markedly from that of chicks given the N-free diet. The amino acid composition of the insoluble fraction of the excreta of chicks given diet 2 was similar to that of chicks given the N-free diet, whereas that of chicks given diet 3 was markedly different and resembled egg albumen in composition.

4. In the soluble fraction of excreta from CV chicks given diets 1 and 2 the proportions of threonine, serine and glucosamine were lower and those of methionine, leucine, isoleucine and phenylalanine were higher than in those from GF chicks, particularly on diet 1. In the insoluble fraction of excreta from CV chicks given these two diets, compared with GF chicks, there were lower proportions of serine and proline and higher proportions of cysteic acid and lysine, the latter particularly with diet 1.

5. Lower proportions of threonine, serine and glucosamine were also observed in the soluble fractions of excreta from the CV chicks given diets 1 and 3, compared with GF chicks, whereas the proportion of glutamic acid was higher. With these two diets the insoluble fraction from CV chicks contained a higher proportion of alanine. In each instance the environmental effect was greater with diet 1.

6. No effect of environment on either apparent or true digestibility of individual dietary protein amino acids was demonstrated, with the exception of threonine in diet 2, the true digestibility of which was higher in GF than in CV chicks.

7. It was concluded that the gut microflora of the chick had little influence on the digestion of the proteins in the diets tested, but may serve an important role in the degradation of endogenous proteins and the recycling of N.

1. Pigs were fitted with re-entrant duodenal cannulas anterior to the pancreatic duct, and total collections of digesta were made for 12 h periods.

2. Maize–soya-bean diets were made from maize which had been harvested with a dry-matter content of 770 g/kg and either dried, preserved with acetic or propionic acid or ensiled naturally. The pigs received two meals of these diets/d at 12 h intervals, and the amount of digesta flowing through their cannulas was measured.

3. Between 4.5 and 5.25 l of digesta flowed through the cannulas in the 12 h collection period, 0.9 of the total 12 h flow passed through the cannulas in the first 9 h with the dry-maize diet and 0.8 with the acid-treated-maize diets.

4. The mean total dry matter intake was 358 g/meal, and 304 g dry matter passed through the duodenal cannulas in the 12 h collection period. The corresponding intake and flow of nitrogen (g/12 h) was 11.1 and 9.6, and for chromic oxide 1.13 and 0.94.

5. The pigs consumed 205 g starch (total α-linked glucose polymers)/meal, and 1.5 g free glucose/meal. Only 110 g starch and 4.1 g free glucose reached the duodenal cannulas, suggesting that digestion and absorption of up to 92 g glucose had taken place anterior to the pancreatic ducts.

1. Twelve commercial samples of high-protein feeding-stuffs, six of them fish meals, were used for a study of the reproducibility of chemical, microbiological and biological assay values for individual amino acids. Comparisons were also made of results obtained by different methods for the same amino acid.

2. For lysine there was quite good agreement between the results from the different laboratory tests for ‘available’ lysine. The values for ‘total’ lysine were, on average, 10 % higher than those for ‘available’ lysine.

3. For methionine the correlations between the chick assay and each of the laboratory tests were similar.

4. The results from the ‘total protein efficiency’ test of over-all protein quality, using chicks, showed a close correlation with the results of lysine or methionine assays according to which of the two amino acids was most deficient.

5. The results with tryptophan were difficult to interpret and no recommendations could be made as to procedures suitable for general use.

6. Although most of the present samples proved to be of good quality, only screening of a much larger number of samples will reveal to what extent commercial protein concentrates of low availability are still liable to come onto the market.