Urea kinetics were measured in normal women aged 22-34 years at weeks 16, 24 and 32 on either their habitual protein intake (HABIT.) or a controlled intake of 60 g protein/d (CONTROL), using primed-intermittent oral doses of [15N15N]urea and measurement of plateau enrichment in urinary urea over 18 h (ID) or a single oral dose of [15N15N]urea and measurement of enrichment of urea in urine over the following 48 h (SD). The intake of protein during HABIT-ID (80 g/d) was greater than that on HABIT-SD (71 g/d); urea production as a percentage of intake was significantly greater at week 16 for HABIT-ID than HABIT-SD, whereas urea hydrolysis at week 16 was greater for HABIT-SD than HABIT-ID and urea excretion at week 32 was greater for HABIT-ID than HABIT SD. The combined results for HABIT-ID and HABIT-SD showed a significant reduction in urea production at week 32 compared with week 24. Urea excretion decreased significantly from week 16 to week 24 with no further decrease to week 32 and urea hydrolysis was significantly greater at week 24 than either week 16 or week 32. Compared with HABIT, on CONTROL there was a decrease in urea production at week 16, and urea excretion was significantly reduced at week 16. For all time periods urea production was closely related to the sum of intake plus hydrolysis. Hydrolysis was greatest at week 24 and closely related to urea production. There was a significant inverse linear relationship overall for hydrolysis as a proportion of production and excretion as a proportion of intake. The results show that on HABIT N is more effectively conserved in mid-pregnancy through an increase in urea hydrolysis and salvage, and during late pregnancy through a reduction in urea formation. Lowering protein intake at any stage of pregnancy increased the hydrolysis and salvage of urea. The staging of these changes was later than that in pregnancy in Jamaica.

Urinary 5-L-oxoproline was measured during normal pregnancies in Southampton, England and Kingston, Jamaica. The CV of 5-L-oxoproline excretion in urine, determined over 7 d in a non-pregnant woman and three pregnant women, was 10–36%. Compared with non-pregnant women, urinary 5-L-oxoproline increased three to four times from early pregnancy in women in Southampton, a highly significant difference, and remained elevated at similar levels during mid and late pregnancy. For women in Kingston, the excretion of 5-L-oxoproline was similar to that of Southampton women in the non-pregnant group and during early pregnancy. However, there was a progressive increase in the excretion of 5-L-oxoproline as pregnancy advanced and by late pregnancy excretion was from three to ten times greater than the average for the non-pregnant women. There was a significant difference between the women in Southampton and the women in Kingston during mid and late pregnancy, with women in Kingston excreting twice as much 5-L-oxoproline during late pregnancy. If the excretion of 5-L-oxoproline is a measure of glycine insdciency, the results would indicate that in some pregnancies the ability of the mother to provide glycine for herself and the developing fetus is marginal or inadequate and the constraint appears more marked in Jamaica than in England.

Patients with cirrhosis of the liver require an increased amount of protein to achieve N balance. However, the utilization of protein with increased protein intake, i.e. the slope from regression analysis of N balance v. intake, is highly efficient (Nielsen et al. 1995). In the present study, protein requirement and protein utilization were investigated further by measuring protein synthesis and degradation. In two separate studies, five or six patients with cirrhosis of the liver were refed on a balanced diet for an average of 2 or 4 weeks. Protein and energy intakes were doubled in both studies. Initial and final whole-body protein metabolism was measured in the fed state by primed continous [15N]glycine infusion. Refeeding caused a statistically significant increase of about 30% in protein synthesis in both studies while protein degradation was only slightly affected. The increase in protein synthesis was associated with significant increases in plasma concentrations of total amino acids (25%), leucine (58%), isoleucine (82%), valine (72%), proline (48%) and triiodothyronine (27%) while insulin, growth hormone, insulin-like growth factor (IGF)-I and IGF-binding protein-3 were not changed significantly. The results indicate that the efficient protein utilization is due to increased protein synthesis, rather than decreased protein degradation, and suggest that increases in plasma amino acids may be responsible for the increased protein synthesis. A comparison of the patients who had a normal protein requirement with the patients who had an increased protein requirement suggests that the increased protein requirement is due to a primary increase in protein degradation. It is speculated that this is due to low levels of IGF-I secondary to impaired liver function, since initial plasma concentration of IGF-I was about 25% of control values and remained low during refeeding.

Apolipoprotein (apo) A-IV is primarily associated with HDL or with the lipoprotein-free fraction of plasma, and in small amounts with chylomicrons and VLDL. The aim of the present study was to assess the effect of a fatty meal on the postprandial variation in plasma apo A-IV and on its distribution among lipoprotein fractions following absorption of fat. Twenty healthy male subjects participated in the study. After an overnight fast, subjects were given a fatty breakfast containing 1 g fat/kg body weight (% energy: fat 65, carbohydrate 20, protein 15). Blood samples were taken every hour during the next 10 h. Apo A-IV was measured by ELISA. Postprandial lipaemia was associated with a moderate, although significant, increase in the plasma levels of apo A-IV. Apo A- IV increased from the median baseline value of 0·15 g/1 to 0·165 g/l (median + 17 %; P < 0·01) 5 h after fat ingestion. The postprandial peak of apo A-IV occurred 1 h after the triacylglycerol peak. There were no statistically significant correlations between baseline lipids, baseline apo A-IV and postprandial changes in apo A-IV levels, or between postprandial changes in lipids and apo A-IV at any time. To assess apo A-IV distribution among lipoproteins, plasma was fractionated by fast performance liquid chromatography at baseline and 3, 6 and 10 h postprandially. There was a substantial heterogeneity in the apo A-IV distribution among lipoproteins following the fatty meal. At 3 h after fat ingestion, apo A-IV levels increased in the triacylglycerol-rich lipoprotein (TRL) fraction and decreased in the denser plasma fraction. At 6 h after the fatty meal, apo A-IV was still present in the TRL but was decreased in the HDL fractions. The findings of the present study support the concept that apo A-IV particles transfer from the denser plasma fraction to TRL during postprandial lipaemia

Nutritional assessments are frequently based on amounts of nutrients consumed. In the present paper the usefulness of nutrient intake data for assessing nutrient adequacy is examined in an elderly British population. Subjects were ‘free-living’ elderly aged 68-90 years (sixty men, eighty-five women) in Norwich. Forty-two of forty-nine surviving males and sixty-seven of seventy-nine surviving females were reassessed after 2 years. With few exceptions, estimated micronutrient intake was not statistically predictive of biochemical measures of nutrient adequacy. Initial biochemical measures of nutritional adequacy were compared with those found 2 years later in an attempt to assess whether initial biochemical assessment was predictive of the ‘longer term’situation. Biochemical measurements at the start of the study were correlated to the same measurements made 2 years later for: serum ferritin, haemoglobin and erythrocyte count, whole-blood Se-glutathione peroxidase (EC 1.11.1.9; males only), plasma Cu, alkaline phosphatase (EC 3.1.3.1), ascorbic acid, vitamin B6 (pyridoxal-5-phosphate), folate and vitamin B12, total erythrocyte thiamin (males only), riboflavin (erythrocyte glutathione reductase (EC 1.6.4.1) activation coefficient): but not for: erythrocyte Cu-superoxide dismutase (EC 1.15.1.1) or plasma Zn. Either only small changes, or no changes, in mean values were seen over the 2 years for most of the biochemical measures. One exception was a large increase in plasma folate. The only important ‘negative’ features seen at 2-year follow up were a large fall in serum ferritin concentration and a large increase in the activity of two antioxidant defence enzymes, superoxide dismutase and glutathione peroxidase. As judged by currently accepted biochemical deficiency threshold values, asmall proportion of subjects were possibly at risk of Fe (3% men; 1% women), folate (7%, 3%), thiamin (12%;3%) and vitamin C (15%; 17%) deficiency. Many more appeared to be at risk of vitamin B6 (42%; 47%) and riboflavin (77%; 79%) deficiency. It was concluded that the requirements of the elderly for vitamins B1, B2 and C, and the biochemical deficiency threshold vahes used to indicate vitamin B6 deficiency, need review

An experiment was designed to investigate whether the degree of synchrony between the rates of digestion of carbohydrates and N of foods offered as a choice would have an effect, through their consequences, on the short- and long-term diet selection of sheep. Four foods (RL, RH, SL and SH) with the same high metabolizable energy, and similar high metabolizable protein contents were made into pellets. Foods RL and RH were based on a rapidly fermentable carbohydrate source and foods SL and SH on a slowly fermentable carbohydrate source; within each source one food (RL or SL) had a low, and the other (RH or SH) a high, men-degradable protein (RDP) content. The foods within a carbohydrate source were offered either singly or as a choice (RI/RH or SI/SH) to eleven rumen-fistulated mature sheep. The design was two 3 x 3 Latin squares (replicated once) with 5- week periods; squares consisted of two single foods and their respective choice. Weeks 1, 3 and 5 were considered to be controls, and weeks 2 and 4 used for remen infusions of either urea or fructose infused over 4h (10·00-14·00 hours). Food intake (FI) and diet selections (DS) were recorded daily and every 2 h (08·00-16·00 hours) on days 2-5 of each week; m e n pH and NH3 concentrations were also measured during these time intervals of day 5. As expected, feeding treatment affected significantly the rumen measurements: m e n NH3 concentrations were higher on foods RH and SH, and men pH lowest on RL. Daily FI was lowest on treatments SL and choice SI/ The mean daily proportion of the low-RDP food in the selected diet was lower when the carbohydrate source was rapidly (choice RI/RH) rather than slowly fermentable (choice SI/SH); this was consistent with the experimental hypothesis. Short-term infusions affected further rumen variables (in the expected directions), irrespective of feeding treatment. However, DS over the 4 h infusion period were unaffected; these short-term DS were consistent with the ones selected over the longer term (daily). The results suggest that the long-term (daily) diet selection of sheep may be affected by the degree of synchrony of energy and protein to the men. The fact that diet selections were not altered further by short-term manipulations of these supplies might reflect inadequacies of the methodology (infusions) adopted here.

Rates of protein synthesis for the liver, plasma albumin and total plasma protein were quantified in sheep either offered a supra-maintenance intake or fasted for 3 d. The technique of continuous infusion over a 12 h period was employed with the simultaneous infusion of [1-13C]glycine, [1-13C]leucine and [2H5]phenylalanine. Blood and plasma samples were removed at timed intervals from the hepatic portal and hepatic veins plus the aorta. Enrichments of the free amino acids (AA) were determined in all blood and plasma samples as was the protein-bound AA in an apolipoprotein B100 extract. Protein-bound phenylalanine enrichments were also measured in albumin and total protein from plasma plus samples from liver biopsies. The apolipoprotein B100 enrichments agreed well with those of the free AA in hepatic (and hepatic portal) plasma but were lower than for arterial free AA and greater than liver homogenate free AA. This adds support to the concept that export proteins may preferentially use AA directly from extracellular sources. Intake had no significant effect on constitutive liver protein synthesis and the values agreed well with those obtained by other isotopic approaches. There were, however, signicant declines, based on hepatic venous free phenylalanine enrichment, at the lower intake in both the fractional (3·4v. 4·7 % per d; P=0·024) and absolute (2·4 v. 4·2 g/d; P=0·011) synthesis rates of albumin, which matched the estimated decrease in total plasma albumin content (52 v. 67 g, P <0·01). In contrast, there was a smaller reduction in total plasma protein mass (145 v. 151 g, P=0·035) with no observed significant difference in kinetic parameters. Albumin synthesis was calculated to account for a maximum of 17 % of total liver protein synthesis in the fed condition and this may fall to 8 % during moderate fasts.

Sheep fitted with a PVC cannula in the dorsal rumen, a silastic infusion tube in the abomasum, and single ‘T’-shape PVC cannulas in the proximal duodenum (D1), distal duodenum (D2), mid-jejunum (J), and terminal ileum (I), were fed on diets varying in crude protein (Nx6·25) and fibre contents. 15N was administered to the sheep as a 15N-labelled grass meal-beer yeast suspension which was continuously infused into the abomasum over a period of 1 week. Subsequently, over a period of 4 d, 15N excess in the D1, D2, J and I digesta and faeces was measured and related to 15N excess in blood plasma TCA-soluble N. Average daily intakes of DM and N were 1·12 kg and 26·3 g respectively. Average daily endogenous N (g) amounted to 3·1 at D1, 10·2 at D2, 6·1 at J, 5·0 at I, and 5·1 in the faeces (F). Corresponding percentage values for total N were: D1 12·4, D2 32·9, J 46-4, I 48.4 and F 50.7. The secretion, particularly of pancreatic juice and/or bile, varied. The apparent re-absorption of endogenous protein varied among experimental diets, on average by 50·4% between D2 and I. Along the small intestine the percentage of 15N in the TCA-precipitable fraction gradually changed, on average by 66·0, 63·0, 46·3 and 55·7 at D1, D2, J and I respectively. Because of differential rates of enrichment and turnover among protein pools which contribute towards endogenous secretion, care should be taken in interpreting these data as absolute values.

We hypothesized that feed preference depends on the interplay between flavour and postingestive effects, and we tested two predictions based on this hypothesis: (1) lambs acquire preferences for poorly nutritious feeds paired with starch; and (2) preferences persist when starch is no longer administered. Twenty lambs were randomly allocated to two groups and conditioned as follows: on odd-numbered days, lambs in group 1 received onion-flavoured wheat straw and lambs in group 2 received oregano-flavoured wheat straw. On even-numbered days, the flavours were switched and starch (2-5-9.4% of the digestible energy received/d) was infused into the rumen of aU animals during straw consumption. Four periods of 8 d of conditioning were performed and on the 9th day of each period all animals were offered a choice between onion- and oregano-flavoured straw. After conditioning, starch administration was suspended and lambs were offered onion- and oregano- flavoured straw at weekly intervals for 8 weeks (extinction). Lambs strongly preferred the flavoured straw paired with starch, and this preference persisted during extinction. Thus, these results suggest that the postingestive effects of energy play an important role in the development of feed preferences of ruminants

The purpose of the present experiments was to extend previous data on the strategy used by adult rats to select feed appropriately when faced with diets devoid of protein or an essential amino acid (EAA), and to compare this strategy with that used when facing vitamin (thiamin) deficiency. Rats fed on either balanced or deficient (EAA or protein) diets were offered a choice between a novel deficient and a familiar (deficient or corrected) diet and their choice was monitored. It was shown that protein- and EAA-deficient rats acquired an aversion for their corresponding familiar devoid diet, which by itself promoted a neophilia for the novel diet. This neophilia was not non-specific because protein-deficient rats facing a choice between a protein-devoid and an EAA-devoid diet did exhibit neophilia but only in the short term (less than 5h), and then switched to a preference for the familiar protein-devoid diet. These results show that, in contrast to the case of vitamin deficiency, the protein- or EAA-devoid diet-induced neophilia can be rapidly reversed if the novel feed happens to be more deleterious than the familiar, inappropriate one. This behaviour suggests the existence of sensitive mechanisms able to reveal within a short time the EAA inadequacy of the ingested feed and to adapt the choice for the most appropriate feeds more promptly than in the face of thiamin deficiency. Thus it appears that balancing EAA is more urgent than balancing thiamin.

The purpose of this study was, first to explore metabolic interactions between Cu and ascorbic acid in guinea-pigs, particularly with respect to any possible disadvantages of high ascorbatein the presence of low Cu intakes, and second, to test the hypothesis that variations in ascorbate and/or Cu status might inhence collagen cross-linking, either by inducing a change in thecross-links: hydroxyproline ratio, or by inducing a change in the pyridinoline: deoxypyridinoline cross-linls ratio. Four matched groups, each of eight male weanliig Dunkin-Hartley guinea-pigs, were maintained on purified diets containing either no added Cu, or 150 mg Cu/kg diet, and either 0·1 g or 30 g ascorbic acid/kg diet. They were then killed 8 weeks later, and the following indices were measured body and organ weights; blood haemoglobin; adrenal ascorbate concentrations; Cu concentrations in plasma, liver and femur; superoxide dismutase (EC 1.15.1.1) activity in whole blood and liver; hydroxyproline, pyridinoline and deoxypyridinoline in femur and in urine. The principal observations were: Cu intake significantly affected blood and tissue Cu concentrations and superoxide dismutase activity; and ascorbic acid intake significantlyaffected adrenal ascorbate levels and the deoxypyridinoline: pyridinoline cross-links ratio, especially in bone (femur). There was evidence of a significant interaction between ascorbateand Cu with respect to adrenal and plasma Cu concentrations, blood superoxide dismutase activityand body weights. We conclude that interactions between ascorbate and Cu at the functional level were present but modest, and that a new and potentially powerful functional index of ascorbate status may exist within the deoxypyridinoline: pyridinoliie collagen cross-link ratio.

Vitamin E is the major lipid-soluble antioxidant in human subjects and is crucial in protecting polyunsaturated fatty acids (PUFA) against lipid peroxidation. Dietary PUFA have been suggested to inhibit the absorption of vitamin E. The present study in young male rats was designed to investigate the effect of increasing concentrations of dietary linoleic acid on the faecal excretion of vitamin E. The rats were fed on semi-synthetic diets containing two concentrations of fat (59 g/kg diet, 15 energy % (en%) or 131 g/kg, 30 en%) for 3 weeks. Triacylglycerol rich in linoleic acid was added at the expense of triacylglycerol rich in saturated fatty acids to obtain dietary concentrations of 13,39 or 66 g linoleic acid/kg diet for the high-fat diet (131 g fat/kg) and 12, 24 or 36 g linoleic acid/kg diet for the reduced-fat diet (59 g fat/kg). The results from the present study demonstrate that the faecal excretion of vitamin E was significantly lower in rats fed on diets with high levels of linoleic acid compared with rats fed on lower levels of linoleic acid irrespective of the dietary fat content. The concentration of vitamin E in liver and plasma was significantly lower in animals fed on the highest concentration of linoleic acid compared with those fed on the lowest level. Results from the present study also demonstrate that at the same concentration of linoleic acid, the faecal excretion of vitamin E in rats fed on reduced-fat diets was significantly lower than in rats fed on high-fat diets. Our findings indicate that the apparent absorption of vitamin E is not inhibited by dietary PUFA. Results from the present study also demonstrate that a reduction of dietary fat content from 30 en% to 15 en% does not lower the apparent absorption of vitamin E