1. Rats were mated and at weekly intervals during pregnancy and lactation, and after weaning, the dipeptidase activity in the supernatant fraction from small intestinal mucosa extracts was determined for two dipeptides: glycyl–L-leucine dipeptidase (EC 3.4.3.2) and L-alanyl–L-glutamic acid dipeptidase.

2. Dipeptidase activity is found mainly in the soluble (supernantant) fraction of the mucosa homogenate.

3. Compared with those values obtained for unmated controls, the food consumption of the animals and the nitrogen content, total and specific activities of the dipeptidases (per unit quantity of N) in the soluble fraction of the small intestinal mucosa extracts increased slightly during pregnancy and markedly during lactation. After the pups were weaned, values for all these measurements fell rapidly.

4. Whether the increases found in enzyme activity were simply a response to increased food intake or were the result of hormonal stimulus is discussed.

1. An immunohistochemical method was used to study the effect of a low-protein diet on growth hormone (GH) cells in the pituitaries of developing rats. The deficient diet (80 g protein/kg) was administered during gestation and lactation, or during the time after weaning until 90 d of age, or during both periods.

2. GH-cell changes were much more striking in males than in females.

3. In males, GH-producing cells were usually reduced in size and number in all treatments. The effect was most intense when protein deprivation occurred throughout gestation and sucking, and continued until 90 d of age, but it was also evident in animals given the low protein diet only after weaning. Recuperation appeared to be almost complete when offspring of deprived dams were fed on a normal diet after weaning.

4. It is concluded that a low-protein diet reduces the amount of GH in the rat pituitary in a way similar to that with a protein-free diet.

1. Food consumption, live weight, anatomical measurements on the gut organs and the absorptive capacity of the small intestine for L-leucine and D(+)-glucose were made on virgin (control), pregnant and lactating albino rats.

2. Food intake increased by approximately 60% during pregnancy and a further 250% during lactation.

3. Pregnancy did not markedly influence the gross anatomy of the gastrointestinal tract. There was evidence for increased villus height and percentage water in the small intestine and for increased length of the colon during pregnancy.

4. During lactation, the alimentary canal progressively increased in weight and size. It partially regressed following weaning.

5. All anatomical measurements, except the length of the small intestine, completely regressed to control values within 20 d of weaning. The increased intestinal length had not completely regressed by day 30 post-weaning.

6. No significant change was observed in absolute absorption of glucose or leucine during pregnancy.

7. Absolute absorption of leucine and of glucose was increased during lactation. Greatest absorption occurred on the 10th day of lactation.

8. Results for absorption of leucine and glucose per unit length indicated that the ability of the mucosal cells to absorb or the number of absorptive cells/mm had changed during lactation and the post-lactation periods.

1. To determine the effect of diet and level of energy intake on glucose metabolism in sheep, four dietary treatments consisting of feeding a low-roughage (LR) and a high-roughage (HR) diet at each of two intake levels estimated to provide 586 and 1172 kJ (140 and 280 kcal) digestible energy (DE)/kg body-weight0·75 per d were given to each of eight yearling rams in four different time periods each of 4 weeks duration. Both diets contained 140 g crude protein/ kg using ground maize, mixed hay and soya-bean meal and were given in two meals/d. Estimated DE values of food were verified during the study and actual intakes of DE were within 9·5% of the estimated values.

2. To study glucose metabolism, a single intravenous injection of [2-3H]glucose and subsequent withdrawal of nine venous blood samples within 3 h were made in each experiment. Two experiments were conducted on consecutive days for each sheep on each dietary treatment.

3. Coefficients of determination (r2) for linear regressions to measure the effect of time after a single injection of [2-3H]glucose on log specific radioactivity of plasma glucose were calculated for fifty-eight experiments. In fifty-six of the experiments, r2 values exceeding 0·95 were obtained.

4. Compared to the HR diet, the LR diet increased (P < 0·05) the pool size and decreased (P < 0·05) the half-life of glucose. At both intake levels, the LR diet increased (P < 0·05) the plasma concentration and the entry rate of glucose compared to the HR diet but interaction (P < 0·05) between diet and intake level was attributed to a greater difference obtained between diets at the higher compared to the lower level of food intake. Increasing the level of intake caused a greater (P < 0·05) pool size and space, and a shorter (P < 0·05) half-life of glucose.

5. It was concluded that substitution of roughage by concentrate in a ruminant's diet may increase the rate of glucose entry during a short time period after eating.

1. [75Se]selenomethionine was administered to four rabbits and after 4 d their kidneys were removed and homogenized. The long-term fate in rats of an oral dose of this kidney homogenate (RK-75Se) was compared with that of an oral dose of [75Se]selenomethionine mixed with unlabelled rabbit kidney homogenate.

2. Urinary and faecal radioactivities were measured during the 1st week and whole-body radioactivity was determined for 10 weeks. Rats were killed at weekly intervals for 4 weeks for analysis of tissue distribution of 75Se.

3. Intestinal absorption of RK-75Se was 87%; that of [75Se]selenomethionine was 91%. Urinary excretion of absorbed RK-75Se was 13·3% and that of [75Se]selenomethionine was 7·6%, in the 1st week.

4. Whole-body retention of 75Se was greater for [75Se]selenomethione than for RK-75Se but after the 1st week decreased at a similar rate in both groups. Tissue distribution of retained 75Se was also similar in both groups.

5. The initial utilization of 75Se in rabbit kidney is different from that of [75Se]selenomethionine. However, after the 1st week 75Se from these sources appears to be metabolized similarly, suggesting that Se from both is ultimately incorporated into the same metabolic pool.

1. The serum immunoreactive insulin (IRI) concentrations, and glucose disappearance rate-constants after intravenous glucose administration were measured on admission and during recovery in children suffering from protein-energy malnutrition (PEM).

2. A high potassium intake resulted in a considerable increase in the serum IRI levels early in the treatment period. There was a definite relationship between potassium depletion and many measurements of insulin secretion.

3. The results are consistent with the hypothesis that impaired insulin release in children suffering from PEM is partly the result of potassium depletion.

1. The effects of seasonal conditions and nutrition on serum proteins and serum urea concentrations were studied in female reindeer and reindeer calves in Finland. With the exception of one group in winter, the reindeer were roaming wild in the forests. This one group was kept in captivity, out of doors, on a comparatively high nutritional plane. One group lived wild during the winter in very poor nutritional conditions.

2. A very clear seasonal variation in the serum protein and urea concentration was found. The serum protein concentration was low in late winter and increased rapidly during the summer, being high in the autumn. The serum urea concentration was also low in the winter and high in the summer. In the autumn, however, the serum urea concentration was again low.

3. Changes in the serum protein concentration were normally associated with the serum globulins. Only in the very poor-nutrition group did the albumin content decrease significantly. As a result of the large changes in the concentration of serum globulins, there were also considerable changes in the albumin: globulin ratio.

4. The serum protein concentration was much lower in the reindeer calves than in the adult reindeer. The concentration of globulins in particular was much lower than in the adults.

1. The effects of retinol and retinoic acid supplementation of retinol-deficient rats were studied for a variety of metabolic processes shown to be affected by retinol deficiency.

2. Retinol-deficient rats were found to have decreased body-weight, liver and testes weights, a degeneration of testicular germinal cells, an increased incorporation of labelled choline into liver and testes phospholipids, an increased protein synthetic activity (in vitro) of liver ribosomes, an increased transfer-RNA methyltransferase activity in liver and a decreased activity in testes, an increased DNA content of testicular nuclei, and a decreased uptake of [3H]thymidine by testicular nuclear DNA.

3. In retinol-deficient rats supplemented for 8 weeks with retinol these changes were reversed, measurements returning to control levels.

4. In retinol-deficient rats supplemented for 8 weeks with retinoic acid all changes were reversed except those in the testes.

5. Testicular signs of retinol deficiency appeared to be delayed when retinoic acid was added to the retinol-deficient diet of weanling rats. This suggests a sparing action of retinoic acid on the rat's utilization of retinol.

6. Suggestions are offered as to why retinoic acid will support growth and development but not spermatogenesis in the rat.

1. The changes in the solubility of calcium, magnesium and phosphorus in digesta flowing along the intestinal tract and the net movement across the intestinal wall of these elements were determined in six rams, each equipped with three T-shaped cannulas; cannulas were placed in a total of six different sites of the small intestine. Cr2O3 was used as a marker substance to measure the rate of flow of the digesta.

2. The concentrations of soluble Ca, Mg and P decreased as digesta moved along the intestine. The greatest fall in soluble Ca occurred after the first 3 m of the intestine, while a significant decrease in soluble Mg was found only at 15 and 25 m from the pylorus. The concentration of soluble P in digesta decreased until the 7 m site and then remained stable. In the faeces, the level of soluble Mg was approximately 4 times higher than, and that of Ca equal to, the levels of Mg and Ca found in digesta flowing through the upper intestine. Unlike Ca and Mg, a very low concentration of soluble P was found in the faeces.

3. In the duodenum, 84, 78 and 62% of the total Ca, Mg and P respectively were soluble, whereas in the digesta flowing through the terminal ileum the corresponding values were 3·2, 7·2 and 19% for Ca, Mg and P respectively.

4. The forestomachs and the colon were found to be the main sites of Mg net absorption; 1·12 mmol/h was apparently absorbed from the stomach and 1·05 mmol/h from the colon. The upper small intestine (1–3 m from the pylorus) appeared to be the major site of Ca and P absorption.

5. In the last 10 m of the small intestine, considerable amounts of minerals were secreted; 4·70, 0·96 and 1·85 mmol Ca, Mg and P/h respectively were added to the digesta flowing between 15 and 25 m from the pylorus. The effect of the increase in the pH of digesta along the small intestine on the solubility of these minerals is discussed.

1. An intestinal perfusion technique was used in six normal human subjects to study absorption of sixteen individual amino acids from an amino acid mixture simulating casein and from an enzymic hydrolysate of casein, prepared for oral administration to these subjects, which consisted of a mixture of oligopeptides and free amino acids.

2. Total absorption of α-amino nitrogen was greater from the casein hydrolysate than from the amino acid mixture, and the considerable variation in percentage absorption of individual amino acids from the amino acid mixture was much reduced when the enzymic hydrolysate solution was perfused, as a number of amino acids which were poorly absorbed from the amino acid mixture were absorbed to a greater extent from the casein hydrolysate.

3. These findings indicate that after extensive intestinal resections or in malabsorption there might be significant nutritional advantages in the administration of protein hydrolysates rather than amino acid mixtures.

1. A study has been made of pure proteins heated either alone or in contact with sugars, so as to cause a severe fall in their reactive lysine contents, and also of commercial protein concentrates.

2. For unheated materials, and for bovine plasma albumin and fat-extracted, dried chicken muscle severely heated in the absence of sugar, Acid Orange 12 binding values (mmol bound dye/kg crude protein (nitrogen × 6·25)) were close to the sum of total histidine, total arginine and reactive lysine contents (mmol/kg crude protein (N × 6·25)), which we have termed HARL values. The dye-binding values and the HARL values were reduced similarly by heat treatment.

3. For materials in which protein and glucose had reacted under mild conditions (37°), the dye-binding capacity with Acid Orange 12 was unchanged even though the HARL value of these materials was considerably reduced. When protein and glucose or sucrose were heated more severely, the dye-binding capacity was slightly lowered but not to the same extent as the reduction in the basic amino acids.

4. Animal feeding-stuffs, whether unheated, industrially processed or deliberately heated, appeared to react with Acid Orange 12 in the same way as the model systems (selected to represent three types of heat damage: ‘advanced’ and ‘early’ Maillard and protein–protein damage).

5. Remazol blue binding values and fluorodinitrobenzene (FDNB)-reactive lysine values were similarly reduced in materials that had been severely heated, either with or without added sugars; however, when protein and glucose had reacted under mild conditions the fall in Remazol blue binding was less than that in FDNB-reactive lysine.

6. For the model materials, binding with cresol red was, in general, higher for heated samples but the results showed no correlation with FDNB-reactive lysine values. For meat and groundnut meals, changes in values after heat treatment were smaller than those that have been reported for soya-bean meals.