Effect of stage of lactation and dietary starch content on endocrine-metabolic status, blood amino acid concentrations, milk yield, and composition in Holstein dairy cows

Milk yield and composition are modified by level and chemical characteristics of dietary energy and protein. Those factors determine nutrient availability from a given diet, and once absorbed, they interact with the endocrine system and together determine availability of metabolites to the mammary gland. Four multiparous dairy cows in early lactation and subsequently in late lactation were fed 2 diets for 28 d in a changeover design that provided, within the same stage of lactation, similar amounts of rumen fermentable feed with either high (HS) or low starch (LS). All diets had similar dietary crude protein (15.5% dry matter) and rumen-undegradable protein (∼40% of crude protein) content. Profiles of AA were calculated to be similar to that of casein. On d 28, [1-¹³C] Leu was infused into one jugular vein with blood samples taken at 0, 2, 4, 6, and 8 h, and cows milked at 0, 2, 4, 5, 6, 7, and 8 h from start of infusion. Isotopic enrichments of plasma Leu, keto-isocaproic acid, and milk casein were determined for calculation of Leu kinetics. Data were subjected to ANOVA using the MIXED procedure of SAS (SAS Institute Inc.), with time as repeated factor and cow as the random effect. Dry matter intake within each stage of lactation was similar between groups. Feeding LS resulted in lower blood glucose and greater ratio of bovine somatotropin to insulin. This response was associated with greater blood concentrations of nonesterified fatty acids and β-hydroxybutyrate, which might have contributed to greater milk fat content in LS-fed cows. Except for His, average concentrations of all AA in blood were higher in late than early lactation. Diet did not alter average plasma concentrations of AA. However, for most of the essential AA (particularly branched-chain), the HS diet led to a marked decrease in concentrations after the forage meal, resulting in significant differences between dietary groups in early lactation. In early-lactating cows fed HS, a greater reduction in plasma concentrations at 8 h relative to pre-feeding values (time zero) was observed for Met, Lys, and His, resulting in decreases of 27.9%, 33.6%, and 38.5%, respectively. A higher bovine somatotropin/insulin ratio in early lactation and in cows fed LS could possibly have led to greater breakdown and, consequently, higher AA flux from peripheral tissues. In LS-fed cows, higher mobilization of body fat and protein was confirmed by the greater body weight loss in both stages of lactation. Higher irreversible loss of [1-¹³C] Leu in early lactation suggested lower protein retention in peripheral tissues during early compared with late lactation. Milk yield, protein output, and composition were similar between groups at both stages of lactation, whereas milk coagulation was faster (lower curd firming rate) and with higher curd firmness in response to feeding HS in late lactation. Overall, data indicated that rate of carbohydrate fermentability in the rumen can modify the availability of metabolites to the mammary gland and consequently modify milk protein coagulation.

Impacts of operating conditions on efficiency of electrokinetically enhanced filtration for de-watering of orange juice and malt extract

The effects of operational factors an on an electrokinetic-enhanced filtration (EKEF) application to dewater orange juice (OJ) and malt extract (ME) was investigated. EKEF improved dewatering of both foodstuffs and resulted in net dewatering efficiencies of 7.4% and 4.9% for OJ and 10.7% and 6.3% for ME after 5.5 h processing under 30 V and 15 V, respectively. Dry matter content was increased by 19.2% and 15.6% for OJ after 5.5 h and 14.8% and 12.8% for ME after 3.5 h under 30 V and 15 V, respectively, compared with 14.9% and 10.3% under the control conditions for OJ and ME, respectively. The EKEF process effectively improved dewatering of high moisture-content foods with positive impacts on process efficiency by increased voltage, pressure, and the pore size of filters. The initial distance between electrodes had a negative impact as the distance increased. EKEF is a useful adjunct to improve high pressure filtration of foodstuffs.

Improving the fatty acid profile of winter milk from housed cows with contrasting feeding regimes by oilseed supplementation

Many studies show concentrations of nutritionally desirable fatty acids in bovine milk are lower when cows have no access to grazing, leading to seasonal fluctuations in milk quality if cows are housed for part of the year. This study investigated the potential to improve the fatty acid profiles of bovine milk by oilseed supplementation (rolled linseed and rapeseed) during a period of indoor feeding in both organic and conventional production systems. Both linseed and rapeseed increased the concentrations of total monounsaturated fatty acids, vaccenic acid, oleic acid and rumenic acid in milk, but decreased the concentration of the total and certain individual saturated fatty acids. Linseed resulted in greater changes than rapeseed, and also significantly increased the concentrations of α-linolenic acid, total polyunsaturated fatty acids and total omega-3 fatty acids. The response to oilseed supplementation, with respect to increasing concentrations of vaccenic acid and omega-3 fatty acids, appeared more efficient for organic compared with conventional diets.

Randomized clinical trial of omega-3 fatty acid-supplemented enteral nutrition versus standard enteral nutrition in patients undergoing oesophagogastric cancer surgery

Background

Oesophagogastric cancer surgery is immunosuppressive. This may be modulated by omega-3 fatty acids (O-3FAs). The aim of this study was to assess the effect of perioperative O-3FAs on clinical outcome and immune function after oesophagogastric cancer surgery.

Methods

Patients undergoing subtotal oesophagectomy and total gastrectomy were recruited and allocated randomly to an O-3FA enteral immunoenhancing diet (IED) or standard enteral nutrition (SEN) for 7 days before and after surgery, or to postoperative supplementation alone (control group). Clinical outcome, fatty acid concentrations, and HLA-DR expression on monocytes and activated T lymphocytes were determined before and after operation.

Results

Of 221 patients recruited, 26 were excluded. Groups (IED, 66; SEN, 63; control, 66) were matched for age, malnutrition and co-morbidity. There were no differences in morbidity (P = 0·646), mortality (P = 1·000) or hospital stay (P = 0·701) between the groups. O-3FA concentrations were higher in the IED group after supplementation (P < 0·001). The ratio of omega-6 fatty acid to O-3FA was 1·9:1, 4·1:1 and 4·8:1 on the day before surgery in the IED, SEN and control groups (P < 0·001). There were no differences between the groups in HLA-DR expression in either monocytes (P = 0·538) or activated T lymphocytes (P = 0·204).

Conclusion

Despite a significant increase in plasma concentrations of O-3FA, immunonutrition with O-3FA did not affect overall HLA-DR expression on leucocytes or clinical outcome following oesophagogastric cancer surgery. Registration number: ISRCTN43730758 (http://www.controlled-trials.com). Copyright © 2012 British Journal of Surgery Society Ltd. Published by John Wiley & Sons, Ltd.

In vitro protective effects of colon-available extract of Camellia sinensis (tea) against hydrogen peroxide and beta-amyloid (Aβ((1-42))) induced cytotoxicity in differentiated PC12 cells

There is mounting evidence that the deposition and aggregation of β-amyloid peptides (Aβ) in the brain play a significant role in the development and pathogenesis of Alzheimer's disease. There is further evidence that free radical species such as hydrogen peroxide (H(2)O(2)) mediate Aβ induced toxicity. Previous studies have demonstrated that green tea polyphenols possess neuroprotective properties through their ability to ameliorate oxidative stress induced by free radical species. Green tea polyphenols have also been shown to enhance cognition in various animal models of induced cognitive impairment. Upon ingestion, green tea polyphenols are metabolised and undergo bio-transformation which affects their bioavailability and therefore efficacy. In this study, a green tea extract was subjected to a simulated gastrointestinal digestion and a 'colon-available' extract (CAGTE) prepared and assessed for its potential protective effects against H(2)O(2) and Aβ((1-42)) induced cytotoxicity using differentiated PC12 cells (dPC12) as a model for neuronal cells. CAGTE represents green tea phytochemicals potentially available after upper gastrointestinal digestion. CAGTE which was depleted in flavan-3-ols, as shown by LC-MS analysis, protected dPC12 cells at concentration ranges of 0.3-10 μg/ml and 0.03-0.125 μg/ml for H(2)O(2) and Aβ((1-42)), induced cytotoxicity, respectively. At high concentrations, CAGTE exhibited direct anti-proliferative effects, in line with the reputed anti-cancer properties of green tea polyphenols. These results demonstrate that potentially bioavailable green tea metabolites are able to ameliorate both H(2)O(2) and Aβ((1-42)) induced cytotoxicity.

In vitro protective effects of Withania somnifera (L.) dunal root extract against hydrogen peroxide and β-amyloid(1-42)-induced cytotoxicity in differentiated PC12 cells

Withania somnifera L. Dunal (Solanaceae), also known as 'ashwagandha' in Sanskrit and as 'Indian ginseng', is used widely in Ayurvedic medicine as a nerve tonic and memory enhancer, with antiaging, antistress, immunomodulatory and antioxidant properties. There is a paucity of data on the potential neuroprotective effects of W. somnifera root, as traditionally used, against H(2)O(2)- and Aβ((1-42))-induced cytotoxicity which are current targets for novel approaches to treat dementia, especially dementia of the Alzheimer's type (AD). In this study, an aqueous extract prepared from the dried roots of W. somnifera was assessed for potential protective effects against H(2)O(2)- and Aβ((1-42))-aggregated fibril cytotoxicity by an MTT assay using a differentiated rat pheochromocytoma PC12 cell line. The results suggest that pretreatments of differentiated PC12 cells with aqueous extracts of W. somnifera root significantly protect differentiated PC12 cells against both H(2)O(2)- and Aβ((1-42))-induced cytotoxicity, in a concentration dependent manner. To investigate the compounds that could explain the observed effects, the W. somnifera extract was analysed by liquid chromatography-serial mass spectrometry and numerous withanolide derivatives, including withaferin A, were detected. These results demonstrate the neuroprotective properties of an aqueous extract of W. somnifera root and may provide some explanation for the putative ethnopharmacological uses of W. somnifera for cognitive and other neurodegenerative disorders that are associated with oxidative stress.

Whole-grain intake of British young people aged 4–18 years

Inverse associations between whole-grain food consumption and risk of CVD, some cancers and type 2 diabetes have been reported. However, there are few reports of whole-grain intake, particularly among young people. The objective of the present study was to estimate whole-grain intake in a nationally representative sample of young people aged 4–18 years living in Great Britain. Whole-grain intake was estimated using 7d weighed dietary records from 1583 young people who participated in the cross-sectional National Diet and Nutrition Survey in 1997. Whole-grain intake was quantified from the consumption of all foods containing ≥10% whole-grain content. Median whole-grain intake was 7g/d (interquartile range 0–19g/d), with a corresponding mean of 13 (sd18) g/d. Intake was significantly lower among young people whose head of household had a manual occupation, but did not differ significantly by sex, age, region or season. There was no whole-grain intake for 27% of participants. The percentages for less than one and less than three 16g amounts of whole-grain intake per d were 70 and 94, respectively, while corresponding percentages based on 20g amounts were 76 and 97. Foods with <51% whole-grain content provided 28% of whole-grain intake overall, with a higher percentage in older adolescents. The main sources of whole-grain intake were breakfast cereals (56%) and bread (25%). The present study provides the first quantification of absolute whole-grain intake from all significant food sources in any representative age group in the UK. Although there is some debate regarding the quantity of whole grains required for good health, whole-grain intake among British young people is low.

Behavioural, attitudinal and dietary responses to the consumption of wholegrain foods

Whole grains are important dietary constituents as they provide a plethora of nutrients and protective chemicals that may have synergistic actions in promoting health. Regular consumption of wholegrain foods has been associated with a reduced risk of several chronic diseases such as CHD and certain cancers, although their exact role in disease prevention is not yet fully elucidated. Studies reporting levels of whole grain consumption reveal that those subjects who include higher levels of whole grain foods in their diets also have many other favourable dietary and lifestyle practices. While the actions of these practices and whole grains may not be mutually exclusive, these variables do not appear to explain the reduction in risk of disease observed for high-whole grain consumers. Actual whole grain consumption levels are extremely low and many practical barriers exist to consumer uptake of these foods. Effective communication of the whole grain health message is an important strategy to increase awareness of the importance of whole grains in the diet. Increasing the variety and availability of acceptable wholegrain foods is also important. Whole grain consumption at breakfast can have an important impact on total daily nutrient intakes. This simple dietary modification is potentially relatively easy to achieve and could greatly contribute to increased whole grain intake for many individuals.

Influence of dietary factors on the clinical course of ulcerative colitis: a prospective cohort study

BACKGROUND AND AIMS

The causes of relapses of ulcerative colitis (UC) are unknown. Dietary factors have been implicated in the pathogenesis of UC. The aim of this study was to determine which dietary factors are associated with an increased risk of relapse of UC.

METHODS

A prospective cohort study was performed with UC patients in remission, recruited from two district general hospitals, who were followed for one year to determine the effect of habitual diet on relapse. Relapse was defined using a validated disease activity index. Nutrient intake was assessed using a food frequency questionnaire and categorised into tertiles. Adjusted odds ratios for relapse were determined using multivariate logistic regression, controlling for non-dietary factors.

RESULTS

A total of 191 patients were recruited and 96% completed the study. Fifty two per cent of patients relapsed. Consumption of meat (odds ratio (OR) 3.2 (95% confidence intervals (CI) 1.3-7.8)), particularly red and processed meat (OR 5.19 (95% CI 2.1-12.9)), protein (OR 3.00 (95% CI 1.25-7.19)), and alcohol (OR 2.71 (95% CI 1.1-6.67)) in the top tertile of intake increased the likelihood of relapse compared with the bottom tertile of intake. High sulphur (OR 2.76 (95% CI 1.19-6.4)) or sulphate (OR 2.6 (95% CI 1.08-6.3)) intakes were also associated with relapse and may offer an explanation for the observed increased likelihood of relapse.

CONCLUSIONS

Potentially modifiable dietary factors, such as a high meat or alcoholic beverage intake, have been identified that are associated with an increased likelihood of relapse for UC patients. Further studies are needed to determine if it is the sulphur compounds within these foods that mediates the likelihood of relapse and if reducing their intake would reduce relapse frequency.

Defining relapse of ulcerative colitis using a symptom-based activity index

BACKGROUND

Several tools exist to assess disease activity in patients with ulcerative colitis (UC), but a definition of relapse does not exist. The aim of the study was to determine the score in the Simple Clinical Colitis Activity Index (SCCAI) that defined relapse. The reliability and validity of the SCCAI when self-administered was also examined.

METHODS

Patients with UC routinely attending hospital completed the SCCAI questionnaire, which was later administered by their clinician blinded to the scoring process. In the absence of a gold standard definition of relapse, a subjective global assessment of disease status was made by the clinician. The SCCAI was evaluated in a separate cohort of patients.

RESULTS

Seventy-one presentations were analysed; mean age 48 years, 49% male, 37% relapse rate. The mean patient score was 4.2 (range 0-14) and mean physician score 3.8 (0-14). A score of 5 or more defined relapse with 92% sensitivity, 93% specificity, 88% positive predictive value and 95% negative predictive value. The difference between the scores obtained by the patient and clinician (0.35, 95% CI 0.09-0.62) was small. Correlation with a more complex symptom and laboratory-based activity index was very high (r = 0.79, P < 0.01). The index was quick to use and comparative results for sensitivity and specificity were recorded in the second cohort of patients.

CONCLUSIONS

The SCCAI is a simple tool that can be accurately and quickly self-administered, correlates well with a more complex disease activity index, and can be used to define relapse of UC with high specificity and sensitivity.

The short inflammatory bowel disease questionnaire is reliable and responsive to clinically important change in ulcerative colitis

OBJECTIVE

The Short Inflammatory Bowel Disease Questionnaire (SIBDQ) is a health-related quality of life (HRQoL) tool measuring physical, social, and emotional status (score 10-70, poor to good HRQoL). The SIBDQ has been predominantly used in trials for Crohn's disease, and further validation of the SIBDQ is desirable in ulcerative colitis (UC) patients. The primary objective was to further validate the SIBDQ by examining discriminant ability against measures of disease activity. The secondary objectives were to examine reliability and responsiveness to change.

METHODS

UC patients attending hospital completed the SIBDQ and two activity indices. Patients' disease status (remission, mild, moderate, or severe relapse) was determined subjectively by the patients and their physician.

RESULTS

Scores were obtained for 69 events in 61 patients. mean age 47.8 yr (range 16-79). All classes of disease extent were represented. The mean SIBDQ score was 48.4 (13-70). The difference between mean score in patients in remission and relapse was -20.1 (95% CI = -25.1 to -15.1). The difference for remission and mild relapse was -14.6 (95% CI = -8.9 to -20.2). The correlation between SIBDQ and the activity indices were good, r = -0.83 and r = -0.61. Eight patients presented twice. Those with unchanged disease status showed no significant difference in the mean SIBDQ score. Patients whose disease status had deteriorated from remission to mild relapse, or from mild to moderate relapse demonstrated a mean reduction of 11.8 points (95% CI = 20.1-3.4).

CONCLUSIONS

This study contributes to the validation of the SIBDQ as a HRQoL tool in UC. It is reproducible and responsive to changes in disease activity.

Comparative gastrointestinal and plasma cholesterol responses of rats fed on cholesterol-free diets supplemented with guar gum and sodium alginate

The present study investigated the digestion and cholesterol-lowering effects of the water-soluble NSP guar gum (GG) and sodium alginate (SA) in laboratory animals. Groups of five male Wistar strain rats were fed semi-purified cholesterol-free diets containing 0, 50 or 100 g NSP source/kg for 21 d which comprised a 14-d adaptation period followed by a 7-d balance period. Weight gain over the balance period and food conversion ratio decreased linearly with increasing NSP intake ( and respectively). DM digestibility decreased with increasing NSP intake and this effect was greater for SA-containing diets compared with GG-containing diets At the lower inclusion rate, 0.9-1.0 of the additional NSP was digested, but this value fell to 0.8 for both NSP sources at the 100 g/kg inclusion rate, implying that the capacity for near complete digestion of the test NSP had been exceeded. Intestinal tissue mass was increased in response to inclusion of both NSP sources. Caecal digesta pH decreased linearly with additional GG, but increased slightly with consumption of SA. Total caecal short-chain fatty acid concentrations (micromol/g caecal contents) increased markedly with 50 g GG/kg but did not increase further with 100 g GG/kg, and were slightly lower than control values in rats consuming SA. Plasma cholesterol concentration fell linearly with increasing NSP in the diet and the effect was similar for both GG and SA. Total output of faecal bile acids rose in rats fed 50 g GG/kg and 50 g SA/kg (59 micromol/7 d v. 24 micromol/7 d for control rats) with no further increase at the higher inclusion rate. These results show that SA has a strong hypocholesterolaemic effect in rats which is similar to that of GG, and that this effect is most likely to be mediated through an interruption in the entero-hepatic circulation of bile acids and not through increased hepatic supply of propionate from fermentation of the NSP in the large bowel.

Glucose and [13C]leucine metabolism by the portal-drained viscera of sheep fed on dried grass with acute intravenous and intraduodenal infusions of glucose

The effect of exogenous glucose supply by either intrajugular (IJG) or intraduodenal (IDG) infusion at 2.0 mg glucose/kg body weight per min was investigated in four wether sheep (average weight 44 (SD 4) kg) chronically catheterized in the carotid artery and portal veins. Sheep were fed on a dried grass pellet diet hourly using continuous belt feeders. Whole-body glucose irreversible loss (IL) rate, measured with [6-3H]glucose, was increased by 0.5 and 0.8 of exogenous supply for IJG and IDG infusions respectively. Portal glucose utilization, measured by isotope dilution across the portal-drained viscera, was unaffected by additional glucose regardless of the route of glucose supply (P = 0.76 for control v. glucose infusions) and was a constant proportion of glucose IL (0.28) for all treatments. Portal plasma flow was higher during IDG infusions compared with IJG infusions (1.65 v. 1.44 litres/min, P = 0.055). Circulating total free amino acid concentrations fell during glucose infusions (2146, 1808 and 1683 mumol/l for control, IJG and IDG treatments respectively, P = 0.067 for treatment effect) but net portal absorption was not affected by increased glucose supply. Recovery in the portal vein of [1-13C]leucine infused into the duodenum averaged 0.65 and was not affected by increasing glucose supply to the gut tissues. The results show that glucose utilization by gut tissues is responsive to changes in both vascular and luminal glucose supply. The effects of changing gut tissue use of glucose and increased whole body glucose IL on metabolism of nutrients is discussed.

Effect of intraruminal propionic acid infusion on metabolism of mesenteric- and portal-drained viscera in growing steers fed a forage diet: II. Ammonia, urea, amino acids, and peptides

This experiment investigated the effect of intraruminal infusion of propionic acid on the net flux of nitrogenous compounds across the mesenteric- (MDV) and portal-(PDV) drained viscera of seven Friesian steers, average BW 127 kg (SEM 4.6), fed a grass-pellet diet. Each received by random allocation 0 (control), .5, or 1.0 mol of propionic acid/d for 7 d. Blood flow in mesenteric and portal veins was determined by downstream dilution of p-aminohippuric acid in order to determine net appearance rates across the gastrointestinal tissues. Net urea and ammonia flux was unaffected by propionic acid supply. Circulating plasma free amino acid concentrations were increased (P < .05) by propionic acid infusion (2,235, 2,428, and 2,427, error mean square [EMS] 44,370 microM, for control, .5, and 1.0 mol of propionic acid/d, respectively). Net amino acid flux rates were increased at the highest rate of propionic acid infusion across MDV and PDV (4.66, 3.69, and 6.11, EMS 2.98 mol/d for MDV [P < .05] and 2.98, 2.45, and 3.73, EMS 1.69 mol/d for PDV [P < .10] for control, .5, and 1.0 mol of propionic acid/d respectively). Positive venous-arterio concentration differences for peptide-bound amino acids (PBAA) across the MDV and PDV indicated net appearance across the gastrointestinal tissues, but this was not affected by propionic acid infusion. The data show that amino acid flux across postruminal tissues can be influenced by ruminal propionic acid supply and that this does not affect PBAA appearance.

Effect of intravenous glucose infusion on metabolism of portal-drained viscera in sheep fed a cereal/straw-based diet

This experiment investigated the effect of intrajugular infusion of glucose on whole-body glucose metabolism and the absorption of nutrients by the portal-drained viscera of four Suffolk-cross sheep, average BW 46 +/- 7 kg, fed a cereal/straw-based pelleted diet. Each sheep received by random allocation 0 (control), 1.0, or 2.0 mg of glucose.kg BW-1.min-1 for 8 h infused into the jugular vein. Glucose irreversible loss rate, measured by simultaneous infusion of 6-[3H]-glucose, increased approximately stoichiometrically during glucose infusion (.51, .75, and 1.09 error mean square [EMS] .032 mmol/min for control, 1.0, and 2.0 mg of glucose infused.kg BW-1.min-1, respectively). Utilization of glucose increased in portal tissues (P = .089) as a result of glucose infusion (.17, .18, and .33 EMS .008 mmol/min) and was a constant proportion of glucose irreversible loss (.28). Portal blood flow was not affected by glucose infusion (overall mean 1.13 L/min EMS .034). Net portal absorption of acetate increased during glucose infusion although ruminal VFA concentrations were not affected. In contrast, net free amino acid absorption by portal-drained tissues was reduced during glucose infusion (291, 115, and 4 EMS 33,816 mumol/min, P = .054). These results show that metabolism of nutrients across the gut wall is influenced by glucose availability to gastrointestinal tissues and affects the pattern of nutrients available to the liver and peripheral tissues.

Effect of intraruminal propionic acid infusion on metabolism of mesenteric- and portal-drained viscera in growing steers fed a forage diet: I. Volatile fatty acids, glucose, and lactate

This experiment investigated the effect of intraruminal infusion of propionic acid on ruminal VFA metabolism and the absorption of nutrients by the mesenteric- and portal-drained viscera of seven Friesian steers, average BW 127 kg, fed a dried grass-pellet diet. Each received by random allocation 0 (control), .5, or 1.0 mol of propionic acid/d for 7 d. Ruminal acetate and propionate irreversible loss rates and carbon exchange between VFA and CO2 were measured during continuous intraruminal infusions of 2-14C-acetic acid and 2-14C-propionic acid. Ruminal acetate irreversible loss rate was not affected by propionic acid infusion (overall mean 8.09, error mean square [EMS] 2.68 mol/d), whereas propionate irreversible loss increased incrementally with PA supply (3.22 vs 4.16, EMS .61 mol/d, for control and 1.0 mol of propionic acid/d, respectively, P = .09). Glucose irreversible loss rate was increased at the highest level of PA infusion (2.84, 2.83, and 3.22, EMS .06 mol/d, for control, .5, and 1.0 mol of propionic acid/d, respectively; P = .02 for control vs .5 + 1.0), although the proportion of glucose irreversible loss derived from propionate remained constant (.6). Net absorption into venous blood showed that propionate was extensively metabolized in the rumen wall and that the tissues of the small intestine utilized acetate. Utilization of glucose was reduced in portal tissues as a result of intraruminal infusion, and the data were used to derive a model of glucose and lactate interrelationships in gut tissues.

The effect of forage and forage-concentrate diets on rumen fermentation and metabolism of nutrients by the mesenteric- and portal-drained viscera in growing steers

Growing Friesian steers chronically catheterized in the anterior mesenteric and portal veins were used to study the influence of feeding with either a forage or forage-concentrate diet on nutrient utilization by mucosal tissue. When animals were consuming the forage-concentrate diet the molar proportion of propionate in rumen fluid was significantly increased, although production rate as measured by isotope dilution was not altered. Net rates of absorption of VFA into portal blood when compared with rumen production rates underlined the extent to which metabolism within mucosal tissue modifies the propionate supply to the liver. Net glucose utilization by splanchnic tissue was shown to be significantly lower on the forage-concentrate diet. There were no effects of diet on whole-body glucose turnover or on the proportion of glucose derived from propionate. Animals fed on the forage-concentrate diet had significantly lower concentrations of circulating essential amino acids, due mainly to a reduction in branched-chain amino acid levels. There was net absorption of all amino acids by animals on both diets except for glutamate, glutamine and taurine in forage-fed animals.

Purine metabolite concentrations in portal and peripheral blood of steers, sheep and rats

1. The concentration of purine derivatives in portal and peripheral blood of steers, sheep and rats was measured by reverse-phase high performance liquid chromatography. 2. Nucleotides, nucleosides (apart from inosine), adenine and guanine were not found in the plasma samples. Allantoin, uric acid, hypoxanthine and xanthine accounted for virtually all purine metabolites in plasma samples. 3. Non-oxidized derivatives (hypoxanthine and xanthine) were consistently detected in sheep but not in steer or rat plasma samples showing a differential availability of reutilizable purine derivatives between species.

Isolation and characterization of circulating low molecular weight peptides in steer, sheep and rat portal and peripheral blood

1. Low mol. wt peptides in plasma were isolated by reverse-phase HPLC from steer and sheep carotid arterial and rat heart blood and portal blood from all three species. 2. Elution profiles for peptide fractions were similar but the concentration of peptide-bound amino acids (PBAA) in fractions corresponding to different mol. wt peptides was not constant across species. 3. PBAA contributed between 65 and 78% to the plasma amino acid pool in steer and sheep but only 52% in the rat (P less than 0.05). 4. The percentage of many individual amino acids present in either free amino acid (FAA) or PBAA pools was different for ruminant compared with rat plasma but it was similar for steer and sheep apart from branch-chain amino acids (P less than 0.05).

Intestinal zinc transfer by everted gut sacs from rats given diets containing different amounts and types of dietary fibre

Two experiments were carried out in which rats were offered diets containing different amounts and types of dietary fibre, i.e. commercial stock diet and three semi-purified diets containing no fibre, 200 g wheat bran or 200 g pectin/kg. Dietary inclusion of fibre, and especially pectin, stimulated large bowel fermentation, as indicated by caecal hypertrophy and reduced caecal pH. After 3 weeks, mucosal:serosal zinc transfer and Zn accumulation by tissue were measured using the everted-gut-sac technique. In Expt 2, incubations were carried out in the presence and absence of 0.25 mM-ouabain to assess the importance of transfer by Na+,K+-ATPase-dependent mechanisms, and some observations on glucose transport were also made. Ouabain reduced rates of transfer of both Zn and glucose and also tissue Zn accumulation. There were no significant differences in rates of Zn transfer by everted sacs from duodenal, ileal and colonic sites, but accumulation of Zn by tissue was a more important fate than transfer across the serosal surface, and accumulation by duodenal tissue was approximately twice as great as by other tissues. Mucosal:serosal transfer of glucose by ileal tissue was much more sensitive to ouabain than was Zn transfer. Previous diet appeared to alter the capacity of the intestinal tissue to transfer Zn, with the highest rates of transfer being by colonic tissue from pectin-fed rats.

Influence of dietary picolinic acid on mineral metabolism in the rat

Male rats were fed isonitrogenous, isocaloric diets containing different amounts of dietary zinc and picolinic acid (PA) (25, 60, 120 ppm Zn, 0, 20, 40, 60 mmol PA/kg diet) and balance collections of urine and faeces made over a 4-day period. Rats fed 25 ppm Zn were in negative Zn and Cu balance during the experiment. Faecal Zn, but not urinary Zn excretion was elevated with increasing dietary Zn supply. Urinary Zn, Cu and Mg excretion increased with increasing intakes of dietary PA, regardless of Zn intake. Tissue Zn levels were unaffected by dietary Zn or PA. It is concluded that dietary PA forms soluble complexes with metal ions which are rapidly absorbed but are then re-excreted in urine and may not be available for metabolism or incorporation into tissues.

Zinc transfer among proteins in rat duodenum mucosa

Duodenums from freshly killed stock colony rats were incubated in Krebs buffer containing carrier-free 65ZnCl2 for periods of time between 5 and 60 s. Mucosa cytosol was separated and fractionated by gel filtration on Sephadex G-75. 65Zn was present in two main bands of protein with molecular weights of about 45,000 and 6,500, but the ratio between them rose progressively with time of exposure to the isotope. Addition of metabolic inhibitors greatly lowered the 45,000/6,500 ratio for 65Zn. It is concluded that when zinc enters the mucosal cytoplasm during absorption, it rapidly binds to the 6,500 protein in a passive way and is then transferred to the protein of molecular weight 45,000 by an active process.

Effect of dietary picolinic acid on the metabolism of exogenous and endogenous zinc in the rat

The excretion of 65Zn was compared by metabolic balance studies in adult male rats fed purified diets containing 0.8 mmol Zn/kg diet, with and without 40 mmol picolinic acid per kilogram diet, after single intragastric (i.g.) and intraperitoneal (i.p.) doses of the isotope. In a third experiment picolinic acid was introduced for 3 d into the diet of rats prelabeled with 65Zn. The urinary excretion of total zinc was increased by the ingestion of picolinic acid in all three experiments. The urinary and fecal outputs of 65Zn were both consistently greater in picolinic acid-fed rats than in the corresponding control animals. This was particularly marked after i.p. injection of the tracer, and the specific activities of urine and feces from the treated rats were both increased. When picolinic acid was introduced into the diet of prelabeled rats there was a delay of 24 h in the urinary response and 48 h in the fecal response. The residual 65Zn levels were reduced in several tissues from the picolinic acid-fed rats, especially after i.p. administration of the isotope. These observations indicate that dietary picolinic acid increases the turnover of endogenous zinc in addition to enhancing the absorption and excretion of ingested metal, and this has implications for its use in cases of zinc deficiency.

Chemical factors affecting the intestinal absorption of zinc in vitro and in vivo

Everted sacs of rat duodenum and ileum were used to study the effect of anions and organic ligands on the absorption of zinc. The uptake per unit weight of tissue was greater in duodenum than ileum, and it was influenced by the Zn concentration and pH of the incubation medium. The Zn uptake from inorganic salts in simple buffered medium varied in the order zinc sulphate greater than zinc chloride greater than zinc phosphate. Zinc acetate was more effective and zinc citrate less effective than ZnCl2. Addition of aspartic acid or histidine to ZnCl2 increased the uptake but galactose or lactose decreased it. 2-Picolinic acid greatly increased the Zn uptake but 4-picolinic acid reduced it. When incubated with intestinal sacs after incorporation into a synthetic rat diet, only ZnSO4 and 2-picolinic acid increased Zn uptake compared with ZnCl2, but zinc citrate and 4-picolinic acid still tended to decrease it. Metabolic balance studies showed no significant differences in the faecal excretion, total excretion or retention of Zn between rats receiving diets containing different forms of Zn. ZnSO4, zinc citrate and particularly 2-picolinic acid increased the urinary excretion of Zn. The significance of these results is discussed in relation to the suitability of methods for investigating Zn absorption and the importance of Zn-binding ligands.