1. Twenty-five northern Thai mothers, breast-feeding their infants on demand, were studied in their homes for 24 h. All breast-feeds were test-weighed and pre- and post-feed expressed breast-milk samples (0·5 ml) taken at each feed.

2. The fat concentration of milk taken during a feed showed significant circadian variation, with maximum values between 16.00 and 20.00 hours and minimum values between 04.00 and 08.00 hours. Fat concentration at the start and at the end of a feed also varied significantly over 24 h.

3. Multiple regression analysis showed that the most important predictor of fat concentration at a feed was the length of time elapsed since the previous feed – the longer this interval, the lower the subsequent fat concentration. Other significant predictors were the fat concentration at the end of the previous feed, and the milk intake at the previous and at the current feed.

4. Fat concentration declined between feeds in proportion to the length of time between feeds, but the decline was less between sleep feeds than between waking feeds. This would appear to be a reflection of the lower post-feed fat concentration and higher pre-feed fat concentration of sleep feeds compared with waking feeds, when other variables relating to feeding pattern are taken into account.

5. The larger the milk intake at a feed, the greater was the increase in fat concentration from the start to the end of the feed. The change in fat concentration was less in feeds taking place during the sleep period than in daytime feeds.

1. The present study assesses the accuracy with which mean 24 h breast-milk composition can be estimated if milk samples can only be collected during the daytime.

2. Twenty-five northern Thai mothers, feeding their infants on demand, were studied in their homes for 24 h. All feeds were test-weighed and 0·5 ml pre- and post-feed expressed milk samples taken at each feed.

3. If daytime sampling was restricted to two breast-feeds, it was found that the best estimate of 24 h fat concentration was given by two randomly chosen daytime feeds, predicting 24 h fat concentration with 95% confidence limits of ±7·0 g/l (equivalent to 21% of mean 24 h fat concentration).

4. Alternative sampling methods using the mean fat concentration of the feed after 08·00 hours and after 18·00 hours, or the first two feeds after 12·00 hours, predicted fat concentration with 95% confidence limits of ±9·7 g/l and ±8·9 g/l (28 and 26% of mean 24 h fat concentration) respectively.

5. If well-tolerated by mothers, it would be preferable to sample all daytime feeds, since this reduces the 95% confidence limits to ±3·3 g/l, equivalent to 10% of the mean 24 h fat concentration.

1. Five healthy volunteers (usual fat intake 103) (SE 9) g/d and energy intake 9855 (SE 937) kJ/d were given on two separate occasions (a) 100 g oral glucose and (b) sufficient intravenous (IV) glucose to obtain similar arterialized plasma glucose levels to those after oral glucose.

2. Subjects increased their fat intake by 68 (SE 9·6) % for 28 d by supplementing their diet with 146 ml double cream/d (fat intake on high-fat diet (HFD) 170 (SE 8) g/d; energy intake 12347 (SE 770)).

3. The 100 g oral glucose load was repeated and IV glucose again given in quantities sufficient to obtain similar arterialized blood glucose levels. Immunoreactive plasma insulin, C-peptide and gastric inhibitory polypeptide (GIP) were measured.

4. Plasma GIP levels were higher following oral glucose after the HFD (area under plasma GIP curve 0–180 min 1660 (SE 592) v. 2642 (SE 750) ng/l.h for control and HFD respectively; P < 0·05). Both insulin and C-peptide levels were significantly higher after oral than after IV glucose (P < 0·01) but neither were affected by the HFD. Glucose levels were lower following the HFD after both oral and IV glucose (area under plasma glucose curve 0–180 min, following oral glucose 6·7 (SE 0·3) mmol/l.h for control and 4·2 (SE 0·6) mmol/l.h for HFD; P < 0·01).

5. Glucose-stimulated GIP secretion was thus enhanced by the HFD. Insulin secretion in response to oral glucose was unchanged, in spite of an improvement in glucose tolerance.

6. The improvement in glucose tolerance post-HFD could possibly be due to a GIP-mediated inhibition of hepatic glycogenolysis, or a decreased rate of glucose uptake from the small intestine.

1. Riboflavin may play a part in the transport of iron across the gastrointestinal mucosa. Fe absorption was measured in the rat by monitoring whole-body retention of a dose of 59Fe using a small-animal γ-counter.

2. Female Norwegian Hooded rats were fed on a diet deficient in riboflavin (B2−) from 5 weeks of age. Control animals, fed on a complete diet (B2+), were weight-matched to rats fed on the B2− diet. After 7 weeks all rats were fed on a test meal extrinsically labelled with 59Fe and whole-body radioactivity measured for 15 d.

3. Riboflavin deficiency was associated with a reduction in the percentage of the dose absorbed and an increase in the rate of loss of Fe post absorption.

4. A smaller percentage of the absorbed dose was present in the livers of the riboflavin-deficient animals.

1. Iron and zinc retentions in young male rats, given 3 g starch–sucrose paste containing 120 μg Fe as FeSO4 or 139 μg Zn as ZnC12 (extrinsically labelled with 59Fe or 65Zn) and increasing amounts of Gypsophila saponins, were measured by whole-body counting. The results were compared with whole-body Fe and Zn retention from a meal containing crude or purified saponin fractions. In a separate experiment Fe retention from a meal containing Gypsophila saponins, soyasaponin I, or saponins extracted from lucerne (Medicago sativa) plant tops, was measured in older rats.

2. Results indicated that Fe absorption decreased with increasing concentration of Gypsophila saponins. This was significant at a saponin: Fe molar value of approximately 1, with maximum effect occurring at molar ratios of 4 and above, when Fe absorption was reduced by approximately 17%. Gypsophila saponins had no effect on Zn absorption from a test meal.

3. Fe absorption was similar in groups given purified or crude Gypsophila saponins at the same saponin: mineral molar value of 8, demonstrating that the ‘non-saponin’ fraction of the commercial preparation does not affect the absorption of this mineral.

4. Saponins extracted from lucerne plant tops, fed at a saponin:Fe value of approximately 8, also reduced Fe absorption from a single meal. Fe absorption from a meal containing a similar amount of soyasaponin I was not significantly different from controls.

5. These results indicate that some dietary saponins may reduce Fe absorption and hence have an adverse effect on Fe status in man and simple-stomached animals.

1. We have investigated the relations between changes in plasma insulin and 3,5,3'-triiodothyronine (T3), and muscle growth and protein turnover in the rat in response to diets of varying protein concentrations.

2. Young rats were fed ad lib. on a control (180 g casein/kg) diet or low-protein diets containing 80, 45 and 0 g casein/kg in four separate experiments. Measurements were made of food intakes, muscle and body-weight growth rates, muscle protein turnover in vivo, plasma insulin, and plasma free and total T3.

3. The food intakes of the 80 and 45 g casein/kg diet groups were variable, with the 80 g casein/kg diet group consuming either the same or more than the controls, and the 45 g casein/kg diet group consuming less or more than the controls. Body-weight and skeletal-muscle growth rates varied with the protein but not energy intakes, which in turn reflected both dietary composition and the food intake, with the hyperphagic 80 g casein/kg diet group of rats growing almost normally and the 0 g casein/kg diet group losing body-weight and muscle mass.

4. Changes in rates of muscle growth were accompanied by parallel changes in rates of protein synthesis and degradation, as well as parallel changes in concentrations of plasma insulin and free T3, to the extent that all these variables were highly correlated with each other.

5. Partial correlation analysis was used to separate interactions between variables. This indicated that dietary energy had no identifiable influence on muscle growth. In contrast dietary protein appeared to stimulate muscle growth directly by increasing muscle RNA content and inhibiting proteolysis, as well as increasing insulin and free T3 levels. Insulin and free T3 stimulated each other as well as muscle protein turnover; insulin stimulating the RNA activity particularly at low insulin levels, free T3 stimulating the RNA content and both hormones stimulating proteolysis.

6. These apparent relations are shown to be consistent in the main part with previous studies of the mechanism of action of insulin and T3 but the possibility cannot be discounted that other anabolic hormones not measured in these studies are involved, particularly in the apparent direct influence of dietary protein on muscle.

1. The regulatory role of prostaglandins (PGs) E2 and F2a on the zinc transport rate across the jejunal segments of rats was examined by employing the Ussing chamber technique. The Zn flux rate from mucosa to serosa across jejunal segments (Jms) was 5·24 (SE 1·54) nmol/h per cm2 (n 48) and that from serosa to mucosa (Jsm) was 15·16 (SE 2·38) nmol/h per cm2 (n 48) when both sides of the segment were bathed with Ringer's bicarbonate solution containing 0·5 mM-zinc chloride and 3 mM-L-histidine.

2. When 5·0 or 50 μM of either PGE2 or PGF2α were added to the serosal side of the tissue, Jsm generally decreased and Jms generally increased, compared with controls. On the other hand, when PGE2 or PGF2α was added to the mucosal side of the tissue, Jms either did not change or increased while Jsm had a tendency to decrease.

3. The Zn uptake capacity of tissue increased significantly when PG was added to the serosal side of the tissuebathing medium, but not when PG was added to the mucosal side. The uptake capacity of mucosal Zn by jejunal segments was approximately twice that of serosal Zn.

4. When PG was included in the tissue-bathing medium, the short-circuit current, potential difference and conductance between the mucosa- and serosa-bathing media generally decreased.

5. These results suggest that (a) PGs influence Zn flux rate not by chelating Zn and carrying it across the mucosal cell membrane but by interacting with the cytosolic components, (b) it is the serosal PGs which control the Zn flux rate and (c) PGs play a part in triggering a transduction mechanism in the intestinal Zn transport process.

1. The dynamics of protozoa were studied in two groups of rumen-fistulated cattle fed on a basal diet of molasses ad lib., with oaten chaff given at 6 or 18 g/kg live weight. This diet resulted in different mixtures of protozoal species in the populations in the rumen.

2. The rumen protozoa were studied by intrarumen injections of protozoa labelled in vitro with [14CH3]choline. An indication of protozoal death and fermentation of protozoal cell residues was obtained by measuring 14C loss via the methane pool.

3. After a single injection of labelled protozoa, the decline in the specific radioactivity (μCi/g nitrogen) of the protozoal pool in the rumen indicated that first-order kinetic processes applied. Conversely the specific radioactivity of protozoa, incubated in rumen fluid, remained constant indicating no growth in vitro, presumably owing to a rapid exhaustion of essential nutrients.

4. The protozoal populations in the rumen of cattle fed on the diet with the low level of oaten chaff were mainly small ciliates; but on the higher level of chaff in the diet, the large ciliates were a higher proportion of the total protozoal population present.

5. The mean pool size of protozoa in the rumen was significantly larger and the protozoal half-life tended to be longer for cattle fed on the higher level of chaff in the diet. The apparent production rate of protozoa in cattle fed on each diet was not significantly different and there were no differences in the production rate of methane. The percentage losses of label from protozoa in the rumen via the methane pool were not significantly different on the two diets and indicated that 74% of the protozoa that were apparently irreversibly lost from the rumen could be accounted for by death and lysis in the rumen and therefore only 26% of protozoa apparently entered the lower digestive tract.

1. The possibility of an effect of zinc on the rate of tumour cell division, mediated through a regulation of cellular cAMP concentration, was investigated in the present study in rats.

2. Dietary Zn deficiency (< 1·5 mg Zn/kg) but not Zn excess (500 mg Zn/kg) resulted in an increased cAMP concentration in transplanted hepatoma cells. Neither treatment had any effect on the cAMP concentration in regenerating liver or normal resting liver. Both the deficient and excess Zn diets resulted in a small reduction in tumour growth (not statistically significant).

3. The results seem to indicate that the relation investigated in the present study does not apply in the cell line used.

1. Dunaliella bardawil, a β-carotene-accumulating alga, has been tested as a source of retinol and β-carotene in a diet given to rats. The β-carotene in this alga is composed of about equal amounts of the 9-cis and all-trans isomers. Male weanling rats were fed on a retinol-deficient diet for 60 d. Thereafter, the rats were divided into groups and fed on a diet deficient in retinol or supplemented with retinol, synthetic β-carotene, dry alga or an algal oil-extract. Following further growth for 7 d, samples were taken for liver analyses of retinol, retinol isomers and β-carotene.

2. Liver analyses revealed a comparable content of retinol and normal conversion rates in the rats grown on the diets supplemented with synthetic or natural β-carotene. Rats fed on the alga and the algal-oil-supplemented diets accumulated 9-cis retinol in addition to the all-trans isomer. Rats fed on synthetic β-carotene, alga and algal oil had a liver retinol: β-carotene value of about 3:1.

3. These studies demonstrate the possibility of using dried D. bardawil or an oil extract of the alga as a dietary natural β-carotene supplement which satisfies the total requirement of retinol in rats.

4. Rats fed on alga or on algal oil, accumulated in the liver 9-cis β-carotene and all-trans β-carotene in a ratio similar to that present in the alga.

1. For a period of 24 d, young rats received a diet containing 120 g casein/kg or the same basic diet supplemented with 1·93 g cysteine/kg.

2. The thyroxine (T4) turnover was decreased in rats receiving the cysteine-deficient diet compared with that of rats on the supplemented diet. Moreover, the extrathyroidal T4 pool and T4 disposal rate decreased.

3. Cysteine deprivation also decreased the peripheral metabolism of 3,5,3'-triiodothyronine (T3). The T3 distribution space, extrathyroidal pool of T3 and T3 disposal rate were diminished.

4. In vitro, deiodination of T4 in liver homogenate assayed with endogenous glutathione (GSH) demonstrated decreased T3 production rates in the case of cysteine deficiency. This difference was minimized by the addition of GSH in amounts sufficient to saturate the reaction kinetics. In the light of this finding, GSH is probably involved in the promotion of certain thyroidal problems induced by a cysteine-deficient diet.

1. Five Greyface wethers (42–45 kg) fed on various fixed amounts of dried grass pellets (either approximately 1·3 times maintenance or 2 times maintenance) by means of belt-type continuous feeders were housed in opencircuit respiration chambers for periods of 45 d. Between days 15 and 35 they received daily oral doses of 1·5 mg of the β-adrenergic agonist clenbuterol (adsorbed on to the feed). Continuous energy and nitrogen balance measurements each of 5 d duration were conducted throughout the chamber confinement.

2. On six occasions (twice during the 15 d pre-clenbuterol period, on days +4, +11 and +18 of clenbuterol administration and once during the post-treatment period) animals were infused with [l-14C]leucine to determine the rates of leucine oxidation and the amounts of leucine available for protein synthesis.

3. Clenbuterol administration caused a marked increase in N retention (2–3 g N/d; P < 0·001) throughout the 20 d treatment period. It also increased (P < 0·001) the energy expenditure of the animals (on average by 1·1 MJ/d over the first 5 d, compared with immediate pretreatment values, and 0·6 MJ/d over the 20 d period, compared with the mean of pre- and post-treatment control values). The effect of treatment was calculated to result, on average, in the daily retention of 19 (SE 1·5) g more protein and 30 (SE 5·5) g less fat.

4. During clenbuterol treatment leucine oxidation was reduced (P < 0·01). However, values for the amounts of leucine available for protein synthesis were equivocal, with an increase (P < 0·001) on day 11 of treatment, but no change on days 4 and 18.

5. Withdrawal of the clenbuterol resulted in rapid alterations of N and energy metabolism towards those expected of control animals of that weight.

1. The present study concerns the question whether the hypercholesterolaemic effect of casein, a phosphorylated protein, is modified in species differing both in glycine-taurine conjugation of bile acids and in intestinal alkaline phosphatase (EC 3.1.3.1).

2. Since these two variables are entirely different in rabbits and rats, identical (cholesterol-free) semi-purified diets containing either casein or soya-bean protein were given to both species.

3. In rabbits casein, as compared with soya-bean protein, did not affect calcium absorption but immediately increased phosphate absorption and decreased faecal excretion of bile acids. These effects preceded the accumulation of apo B-cholesterol in serum, which indicates a cause-and-effect relation.

4. In contrast, none of these casein-specific effects were observed in rats.

5. These results suggest that the hypercholesterolaemic potential of casein is expressed mainly in species (like the rabbit) with a low activity of intestinal phosphatase and with a high glycine conjugation of bile acids. This might explain why species (like rat and man) are rather insensitive to dietary casein.

1. Branched-chain amino acid aminotransferase (EC 2.6.1.42; BCAAT) and branched-chain α-keto acid dehydrogenase (EC 1.2.4.4; BCKDH) activities were measured in preruminant lamb liver, longissimus dorsi muscle, kidney, jejunum and adipose tissue, 2 h after a meal with or without an excess of leucine.

2. Skeletal muscle contained about 70% of the total basal BCAAT activities of the tissues studied whereas liver contained about 60% of the total BCKDH activities of these tissues.

3. BCAAT activities were very low in preruminant lamb tissues. BCKDH was more phosphorylated in tissues of preruminant lambs than in rats, especially in liver. These low catalytic potentialities might contribute to a low rate of branched-chain amino acid catabolism in sheep.

4. Ingestion of an excess of leucine led to an increase in liver and jejunum BCAAT activities and activation of BCKDH in jejunum.

1. The uptake of 5-methyltetrahydrofolate (MTHF) and folic acid (pteroylmonoglutamate) by enterocytes and brush-border-membrane vesicles prepared from the small intestine of the 6-d-old male goat was determined using a rapid-filtration assay.

2. Both MTHF and folic acid were taken up by membrane vesicles at 25° and enterocytes at 37° by a pH-dependent mechanism with maximum uptake when the pH of the incubation medium was 5·0.

3. Experiments in which the osmotic pressure of the medium was raised in successive increments with the non-absorbable sugar cellobiose indicated that transport rather than membrane binding was the main component of uptake.

4. Experiments at pH 5·0 showed that uptake of MTHF and folic acid was saturable and that the characteristics of folate transport were similar in both tissue preparations: (a) transport rates of both MTHF and folic acid were constant during the first 1-2 min for a given folate concentration, then declined to reach a steady-state in 10-30 min; (b) initial velocities of transport of MTHF and folic acid increased in proportion to their concentrations up to 7-10 μM, but the rate of increase slowed thereafter until saturation was reached at 20-25 μM (Km for brushborder-membrane vesicles 40·8 and 62·9 μM, Km for enterocytes 50·9 and 55·2 μM for MTHF and folic acid respectively). Values of Vmax for membrane vesicles (pmol/mg protein per min) were 46·5 MTHF or 40·3 folic acid; enterocytes Vmax (pmol/107 cells per min) 15·9 MTHF or 30·6 folic acid; (c) uptake of MTHF and folic acid by brush-border-membrane vesicles and enterocytes measured under steady-state conditions approached saturation at 50 μM for each analogue (Km for membrane vesicles 58·1 and 55·2 μM, Km for enterocytes 43·1 and 49·4 μM for MTHF and folic acid respectively; Vmax for membrane vesicles 49·7 and 77·8 pmol/mg protein, for enterocytes 52·8 and 54·7 pmol/107 cells for MTHF and folic acid respectively).

5. It was concluded that transport of MTHF and folic acid was by a similar pH-dependent mechanism both in brush-border-membrane vesicles and in intact enterocytes. At pH 5·0, transport involved a saturable carrier-mediated process located in the brush-border membrane.

1. The influence of goat's-milk folate-binding protein (FBP) on the uptake of 5-methyltetrahydrofolate (MTHF) by brush-border-membrane vesicles prepared from the small intestine of the 6-d-old goat was investigated using a rapid-filtration assay.

2. Uptake of MTHF by the membrane vesicles was strongly enhanced by FBP within the pH range 4·5-6·5, with an optimum at pH 5-5·5.

3. Both the initial rate of MTHF uptake and uptake of MTHF at equilibrium were markedly increased in the presence of FBP.

4. Uptake of MTHF by brush-border-membrane vesicles was maximal when the molar ratio FBP: MTHF was 1·0-2·5.

5. The relation between pH and 125I-labelled FBP binding to the membranes was similar to that for uptake of MTHF, with an optimum at pH 5.

6. In experiments in which the osmotic pressure of the incubation medium was progressively increased with cellobiose, 125I-labelled FBP was found to be taken up primarily by binding to the brush-border-membrane surface.

7. Uptake of 125I-labelled FBP was time-dependent and saturable, with a Km of 0·39 (SE 0·07) μM and Vmax of 6·73 (SE 0·92) μg/mg protein.

8. Experiments in which various milk proteins (cow FBP, goat FBP, α-lactalbumin, β-lactoglobulin, bovine serum albumin and lactoferrin) were allowed to compete in turn with 125I-labelled FBP for uptake by brush-border-membrane vesicles indicated that high-affinity binding was probably specific to FBP, although lactoferrin reduced uptake possibly by non-specific coating of the mucosal surface.

9. It was concluded that a folate transport mechanism mediated by the FBP in milk exists at the intestinal brush border of neonatal goats. It is suggested that this may reinforce the developing endogenous transport system.

1. Increases in plasma tocopherol concentrations were compared in sheep after a single oral administration of (per kg body-weight): 67 mg D- and 91 mg DL-epimers of α-tocopherol, and 74 mg D- and 100 mg DL-epimers of α-tocopheryl acetate, or intravenous administration of DL-α-tocopherol and DL-epimers of DL-α-tocopheryl acetate.

2. The results showed that biological availability was higher after D-α-tocopherol dosing than after the other forms. Intravenous administration of D-α-tocopherol acetate was a more effective way of dosing in sheep than equivalent intravenous amounts of DL-α-tocopheryl acetate or DL-α-tocopherol.

1. Over- or undernutrition of newborn mice was caused by suckling in litters consisting initially of four or eighteen pups. After weaning mice were fed ad lib. At 13 weeks of age some mice from large litters received gold thioglucose (GTG: 600 mg/kg intraperitoneally) to induce hyperphagia, and mice were killed at 13, 19·5, 26, 39 and 52 weeks.

2. Total carcass lipid and the size and number of adipocytes in the inguinal subcutaneous, genital, perirenal and mesenteric depots were determined.

3. Mice, both male and female, raised in small litters were heavier and had more carcass fat at all ages than mice raised in large litters. After GTG-treatment mice from large litters were heavier and fatter than mice raised in small litters.

4. Fat distribution between the depots was related to carcass lipid content and not to treatment. The order of depot development was subcutaneous, parametrial, perirenal and mesenteric in females and epididymal, subcutaneous, perirenal and mesenteric in males. At 13 weeks the depots in males were more developed than those in females.

5. Litter size had no effect on adipocyte volume in female mice at 13 weeks but by 52 weeks small-litter mice had larger cells in all depots and more cells in the parametrial and perirenal depots.

6. Male mice from small litters had bigger cells at 13 weeks in all depots compared with males from large litters but by 52 weeks no significant differences remained. Greater numbers of cells were present only in the perirenal and mesenteric depots of small-litter males at some ages.

7. Depots of GTG-treated large-litter female mice had larger cells than those of small-litter females, while a similar number of cells was found by 52 weeks in all but the perirenal depot, which had significantly more cells.

8. GTG treatment of male mice from large litters also caused bigger cells than in small-litter mice, and an increased depot cell number at earlier ages in all but the epididymal depot. By 52 weeks cell numbers were similar in depots from small-litter and GTG-treated large-litter mice, except for the epididymal depot from the latter which had fewer cells.

9. Increases in cell numbers with age in different depots occurred independently of existing cell mean volume and even of tissue growth, suggesting the presence of an in-built chronology, at least in older mice.

10. We suppose that the differences in response to the level of preweaning nutrition in males and females result from a greater effect on the hypothalamic appetite centre in the latter. Whereas the cellular changes in large-litter males occur in the late-developing depots and are reversed naturally with time, those in the large-litter females are more extensive and require induction of hyperphagia for reversal.