1. Feeding rats on a low-tryptophan, niacin-free, high-leucine diet resulted in impaired synthesis from tryptophan of the nicotinamide nucleotide coenzymes, NAD and NADP, and N1-methyl nicotinamide in isolated hepatocytes, compared with cells from animals fed on a low-tryptophan, niacin-free control diet providing an appropriate amount of leucine. This was accompanied by reduced accumulation of the tryptophan metabolites kynurenine, 3-hydroxykynurenine and xanthurenic acid.

2. With hepatocytes from animals fed on the low-tryptophan, niacin-free control diet, the addition of leucine to the incubation medium resulted in reduced synthesis of niacin from tryptophan, and a small increase in the accumulation of 3-hydroxykynurenine.

3. With hepatocytes from animals fed on the low-tryptophan, niacin-free control diet, the addition of 2-oxo-isocaproate to the incubation medium resulted in increased synthesis of NAD(P) and niacin, and increased accumulation of 3-hydroxykynurenine.

4. The results suggest that a dietary excess of leucine alters the activity of the enzymes of tryptophan→niacin metabolism, or the uptake of tryptophan into the liver, in a different manner from the simple inhibition and activation seen in experiments in vitro.

5. Differences between studies in isolated hepatocytes and intact animals suggest that extra-hepatic metabolism of tryptophan, catalysed by indoleamine dioxygenase, is more important than has been believed hitherto.

1. Eight women maintained on a constant diet throughout a single menstrual cycle were studied for cyclical changes in body-weight, carbohydrate, fat and protein metabolism.

2. A cyclical variation in weight occurred with two phases corresponding to the time of ovulation and menstruation.

3. Creatinine and nitrogen excretion in the urine also tended to be higher in the luteal phase.

4. Analysis of gas exchange in a respiratory chamber for 24 h periods at intervals during the cycle suggested that carbohydrate utilization tended to be less in the early follicular phase.

5. Feeding with a mixed diet produced marked increases in carbohydrate utilization during the day with little change in fat utilization from the fasting state. Carbohydrate utilization was less when fasting at night and tended to be less when fed during the day in the early follicular phase of the menstrual cycle.

6. Weight changes were not readily ascribed to changes in colonic function, or in glycogen or body protein storage.

1. Fifteen normal premenopausal women followed a low-fat diet for a period of 2 months.

2. Daily fat intake was reduced from 81 g on their customary diet to 36 g on the low-fat diet. A significant reduction in total energy intake and an increase in the dietary polyunsaturated fat: saturated fat ratio was also observed. There was a significant decline in body-weight, percentage body fat and total serum cholesterol, but no significant change in high-density-lipoprotein-cholesterol.

3. Luteal-phase prolactin concentrations were not altered, but there was a significant decline in oestradiol concentrations on the low-fat diet. The proportion of erythrocyte inositol-phospholipid was increased on the low-fat diet and there was a significant increase in the 20:4ω6 (arachidonate) content of inositol-phospholipids. No significant changes in the content or fatty acid compositions of other phospholipid fractions were observed.

4. Further investigation of the effect of level and type of dietary fat on the content and fatty acid composition of membrane inositol-phospholipids are required. Long-term studies investigating the response of both prolactin and oestradiol to dietary fat reduction are also warranted.

1. Metabolic changes associated with Ramadan fasting were studied in eleven Asian pregnant mothers. This was compared with a group of control mothers undergoing a normal physiological fast.

2. At the end of the Ramadan fast day there was a significant fall in glucose, insulin, lactate and carnitine, and a rise in triglyceride, non-esterified fatty acid and 3-hydroxybutyrate. When compared with the control group, none of the Ramadan mothers had a completely normal set of biochemical values at the end of the fast day.

3. Pregnancy outcome in the two groups was comparable.

4. We are wary of the metabolic departures from normal observed in the Ramadan fasting mothers. If asked we advise mothers to take up the dispensation from fasting during pregnancy which is allowed.

1. An in vitro method, using duodenal and ileal digesta and faeces from pigs as inocula for the preparation of three incubation media for simulating the digestive processes in the pig, was proposed. The kinetics of degradation in these three media of three feed samples (pig-grower diet, sugar-beet pulp and wheat bran) with crude protein (nitrogen × 6.25) contents varying from 111 to 196 g/kg, starch contents from 10 to 446 g/kg and dietary fibre contents from 168 to 686 g/kg, were studied.

2. The method was investigated by incubating the feeds in the three media for up to 96 h, and determining the rate and extent of disappearance of feed components.

3. For each feed the 96 h dry matter disappearance was almost equal for all media, although the rate of disappearance varied considerably, with ileal digesta the most potent, particularly for the high-fibre feeds, and duodenal digesta the least. The patterns of disappearance of individual components were similar in all media, with the exception of crude protein which was apparently less degraded in ileal and especially faecal media.

4. Results suggest that a combination of a short (6–12 h) and a long (48–72 h) in vitro incubation could be employed to simulate digestion in the small and large intestine respectively of the pig.

1. An in vitro method involving incubation of feed samples with buffered duodenal digesta for 12 h or with buffered ileal and faecal inocula for 48 h was compared with in vivo ileal or faecal apparent digestibilities in pigs.

2. The five diets investigated had crude protein (nitrogen × 6.25) contents from 164 to 185 g/kg, starch contents from 296 to 463 g/kg and dietary fibre contents from 176 to 347 g/kg.

3. In vitro disappearances with duodenal inocula were correlated (P < 0.05) with in vivo ileal apparent digestibilities for crude protein, ash, starch, energy and dry matter, but not for dietary fibre.

4. In vitro disappearances with the ileal and faecal inocula were generally correlated (P < 0.1) with in vivo faecal apparent digestibilities for dietary fibre, energy and dry matter, but not for ash or crude protein. The patterns of degradability of fibre polysaccharide residues in vitro and in vivo were also similar.

5. Results indicate that this in vitro method could be used to predict the availability of starch and crude protein for digestion in the small intestine, and the degradability of dietary fibre, and thus for comparing the nutritive value of pig feeds.

1. The relations between food intake, reticulo-ruminal motility and abomasal digesta outflow were investigated in ewes receiving lucerne (Medicago sativa) v. orchard grass (Dactylis glomerata) hay. Abomasal digesta outflow was recorded continuously by means of an electromagnetic flowmeter probe inserted into a duodenal T-shape cannula and the motility using strain-gauge force transducers. Volumes and turnover rates of both rumen and abomasal liquid phases were measured by CrEDTA dilution.

2. The voluntary intake of lucerne was higher (60%) than that of orchard grass hay, and paralleled by an increased abomasal outflow (65%) corresponding to an increased number of gushes of digesta through the flowmeter probe: 129/h instead of 78/h on orchard grass hay. Abomasal motor activity was enhanced (35%), and periods of regular spiking activity were seen passing along the duodenum at a higher velocity for the lucerne diet than for the orchard grass diet. The increased abomasal outflow with lucerne hay was associated with a higher reticulo-ruminal turnover rate, but not abomasal turnover rate. Abomasal, but not reticulo-ruminal volume, was increased (30%) when lucerne hay was fed ad lib.

3. The total number of reticulo-ruminal contractions was increased by 6.6% when the dry matter entering the duodenum was increased by 70.6%, suggesting the level of voluntary intake, rather than reticulo-ruminal motility, as a major factor governing abomasal outflow in sheep.

4. More frequent passages of digesta, unrelated to duodenal contractions, were recorded in ewes receiving lucerne compared with orchard grass. Both a higher viscosity of the contents due to the addition of guar gum and the impairment of antroduodenal motility by 5-hydroxytryptophan were able to reduce the flow rate of orchard grass digesta, but did not affect the higher flow rate of lucerne digesta. The findings suggest that the high abomasal outflow in sheep fed on lucerne ad lib. is related to a low viscosity of the contents that are propelled, even in the case of antral contractions of low magnitude.

1. The absorption rates of calcium, inorganic phosphate (P1) and magnesium were determined from buffered solutions placed in the temporarily isolated and washed reticulo-rumen of conscious sheep. The basic composition of these solutions was similar to that found in supernatant fractions of ultracentrifuged rumen contents.

2. The Pi concentrations studied in these solutions were 2, 8·7, 14, 17·3 and 38 mmol/l. The initial concentration of Ca was 2·0 mmol/l and that of Mg was 2.5 mmol/l in all experiments.

3. Increasing the Pi concentration in the rumen solution from 2 to 38 mmol/l resulted in increases in the net absorption rates of both Ca and Pi, and a decrease in the potential difference across the wall of the rumen.

4. Similarly, increasing the Pi concentration from 2 to 17·3 mmol/l resulted in an increase in the net absorption rate of Mg from the rumen.

5. Mineral analysis of strained rumen fluid or a 30000 g centrifugate of strained rumen fluid revealed a reduced Pi concentration in sheep fed on frozen spring grass as opposed to the pellet + hay diet. The values obtained were within the range studied.

1. Liquid-associated bacteria (LAB) were harvested from the liquid phase (LAB1) and from the solid phase of rumen contents after washing and manual shaking (LAB2). Solid-adherent bacteria (SAB) were recovered after washing and pummelling the total particles (SAB1). The distribution and the chemical composition of these three bacterial compartments were investigated in four dairy cows fitted with rumen fistulas. The animals received successively a diet consisting of one part hay and one part barley-based concentrate (diet C) and the same diet containing free soya-bean oil (79 g/kg dry matter (DM); diet So).

2. The efficiency of removal of SABI from total particles of rumen digesta collected I h after feeding, was calculated from the diaminopimelic acid content in particles and of the corresponding detached bacteria. It was 24% on diet C and 18% on diet So (P < 0.05), using a combination of homogenizing and ‘stomaching’ treatments in saline (9 g sodium chloride/1) (reference treatment). For diets C and So respectively it was lowered by Tween in saline solution (1 g/l; 22.7 and 17.8 %, not significant), but was increased when using a previous chilling (6 h at 4°) of homogenized particles before stomaching in saline (28.8 and 24.7%, P < 0.05) and in Tween 80 in saline (1 g/l; 26.6 and 20.8%, P < 0.05).

3. The extent of removal of SABI from the solid fraction of rumen digesta by the reference treatment decreased with decreasing particle size; it was at the highest for particles retained on 4 and 2 mm sieves (62.1–82.1 %) and still elevated for particles retained on 0.8, 0.4 and 0.1 mm sieves (41.3–57.9%). It was very much reduced for particles smaller than 0.1 mm (11.7–14.5 %), suggesting the occurrence of favourable conditions for the adhesion of SAB firmly resistant to removal (SAB2).

4. The concentration of total SAB (SABI +SAB2) in particles collected l h after feeding was lower (P < 0.05) in diet C (190 g/kg DM) than in diet So (234 g/kg DM). Values averaged 595–645 g/kg DM for particles smaller than 0.1 mm, but only 61 and 81–98 g/kg DM for particles retained on 4 and 0.4 mm sieves, and on a 0.1 mm sieve respectively. No significant differences were noted between diets but the effect of particle size was highly significant (< 0.1 mm v. others).

5. Postprandial variations of concentrations of total SAB on total particles exhibited a large increase I h after feeding in diet So (P < 0.05). Similar but amplified variations were observed for LAB in both diets (P < 0.05).

6. Total bacterial mass amounted to 213 and 231 g DM/kg whole-rumen contents DM in diets C and So respectively 6 h after feeding. Mean percentages of total SAB (69.8), LAB1 (7.3) and LAB2 (22.9) in total rumen contents were not significantly modified by the lipid level of the diet.

1. The inhibitory effects of inorganic and organic sulphur-containing compounds, copper and tungsten on nitrate reduction by mixed rumen micro-organisms were investigated in two in vitro studies.

2. Coarsely strained rumen fluid from nitrate-adapted (Expt 1) or non-adapted (Expt 2) Suffolk Down wethers maintained on lucerne (Medicago sativa) cubes was used as an inoculum. In Expt 1, anaerobic incubation was carried out for 24 h for each medium supplemented with 10 mM-sodium nitrate and the following chemicals: 0, 1, 2, 3, 5, 8 and 10 mM-sodium sulphide, 1 and 10 mM-sodium sulphite, 1 and 10 mM-sodium sulphate, 1 and 10 mM-L-cysteine, 1 and 10 mM-DL-methionine, 1 mM-sodium tungstate and I mM-copper sulphate. In Expt 2, 1 and 10 mM-Na2S, 1 and 10 mM-L-cysteine, 1 mM-Na2WO4, and 1 mM-CuSO4 were added to incubation media to test for chemical inhibition of microbial reduction of nitrate.

3. In Expt 1, the amount of nitrite formed decreased with increasing concentration of sulphide-S added. The additions of L-cysteine, W and Cu suppressed nitrite formation in media from both nitrate-adapted and non-adapted sheep.

4. In contrast to the effects of sulphide, L-cysteine and W counteracted, to some degree, nitrate-induced reduction of volatile fatty acid (VFA) production. Addition of Cu to the media resulted in a further depression of VFA production.